Patrick Welche <prlw1@cam.ac.uk>

[netbsd-mini2440.git] / external / bsd / ntp / dist / ntpd / ntp_proto.c

/*      $NetBSD$        */

/*
 * ntp_proto.c - NTP version 4 protocol machinery
 *
 * ATTENTION: Get approval from Dave Mills on all changes to this file!
 *
 */
#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include "ntpd.h"
#include "ntp_stdlib.h"
#include "ntp_unixtime.h"
#include "ntp_control.h"
#include "ntp_string.h"

#include <stdio.h>
#ifdef HAVE_LIBSCF_H
#include <libscf.h>
#include <unistd.h>
#endif /* HAVE_LIBSCF_H */


#if defined(VMS) && defined(VMS_LOCALUNIT)      /*wjm*/
#include "ntp_refclock.h"
#endif

/*
 * This macro defines the authentication state. If x is 1 authentication
 * is required; othewise it is optional.
 */
#define AUTH(x, y)      ((x) ? (y) == AUTH_OK : (y) == AUTH_OK || \
                            (y) == AUTH_NONE)

#define AUTH_NONE       0       /* authentication not required */
#define AUTH_OK         1       /* authentication OK */
#define AUTH_ERROR      2       /* authentication error */
#define AUTH_CRYPTO     3       /* crypto_NAK */

/*
 * traffic shaping parameters
 */
#define NTP_IBURST      6       /* packets in iburst */
#define RESP_DELAY      1       /* refclock burst delay (s) */

/*
 * System variables are declared here. Unless specified otherwise, all
 * times are in seconds.
 */
u_char  sys_leap;               /* system leap indicator */
u_char  sys_stratum;            /* system stratum */
s_char  sys_precision;          /* local clock precision (log2 s) */
double  sys_rootdelay;          /* roundtrip delay to primary source */
double  sys_rootdisp;           /* dispersion to primary source */
u_int32 sys_refid;              /* reference id (network byte order) */
l_fp    sys_reftime;            /* last update time */
struct  peer *sys_peer;         /* current peer */

/*
 * Rate controls. Leaky buckets are used to throttle the packet
 * transmission rates in order to protect busy servers such as at NIST
 * and USNO. There is a counter for each association and another for KoD
 * packets. The association counter decrements each second, but not
 * below zero. Each time a packet is sent the counter is incremented by
 * a configurable value representing the average interval between
 * packets. A packet is delayed as long as the counter is greater than
 * zero. Note this does not affect the time value computations.
 */
/*
 * Nonspecified system state variables
 */
int     sys_bclient;            /* broadcast client enable */
double  sys_bdelay;             /* broadcast client default delay */
int     sys_authenticate;       /* requre authentication for config */
l_fp    sys_authdelay;          /* authentication delay */
double  sys_offset;     /* current local clock offset */
double  sys_mindisp = MINDISPERSE; /* minimum distance (s) */
double  sys_maxdist = MAXDISTANCE; /* selection threshold */
double  sys_jitter;             /* system jitter */
u_long  sys_epoch;              /* last clock update time */
static  double sys_clockhop;    /* clockhop threshold */
int     leap_tai;               /* TAI at next next leap */
u_long  leap_sec;               /* next scheduled leap from file */
u_long  leap_peers;             /* next scheduled leap from peers */
u_long  leap_expire;            /* leap information expiration */
static int leap_vote;           /* leap consensus */
keyid_t sys_private;            /* private value for session seed */
int     sys_manycastserver;     /* respond to manycast client pkts */
int     peer_ntpdate;           /* active peers in ntpdate mode */
int     sys_survivors;          /* truest of the truechimers */

/*
 * TOS and multicast mapping stuff
 */
int     sys_floor = 0;          /* cluster stratum floor */
int     sys_ceiling = STRATUM_UNSPEC; /* cluster stratum ceiling */
int     sys_minsane = 1;        /* minimum candidates */
int     sys_minclock = NTP_MINCLOCK; /* minimum candidates */
int     sys_maxclock = NTP_MAXCLOCK; /* maximum candidates */
int     sys_cohort = 0;         /* cohort switch */
int     sys_orphan = STRATUM_UNSPEC + 1; /* orphan stratum */
int     sys_beacon = BEACON;    /* manycast beacon interval */
int     sys_ttlmax;             /* max ttl mapping vector index */
u_char  sys_ttl[MAX_TTL];       /* ttl mapping vector */

/*
 * Statistics counters - first the good, then the bad
 */
u_long  sys_stattime;           /* elapsed time */
u_long  sys_received;           /* packets received */
u_long  sys_processed;          /* packets for this host */
u_long  sys_newversion;         /* current version */
u_long  sys_oldversion;         /* old version */
u_long  sys_restricted;         /* access denied */
u_long  sys_badlength;          /* bad length or format */
u_long  sys_badauth;            /* bad authentication */
u_long  sys_declined;           /* declined */
u_long  sys_limitrejected;      /* rate exceeded */
u_long  sys_kodsent;            /* KoD sent */

static  double  root_distance   (struct peer *);
static  void    clock_combine   (struct peer **, int);
static  void    peer_xmit       (struct peer *);
static  void    fast_xmit       (struct recvbuf *, int, keyid_t,
                                    int);
static  void    clock_update    (struct peer *);
static  int     default_get_precision (void);
static  int     peer_unfit      (struct peer *);


/*
 * transmit - transmit procedure called by poll timeout
 */
void
transmit(
        struct peer *peer       /* peer structure pointer */
        )
{
        int     hpoll;

        /*
         * The polling state machine. There are two kinds of machines,
         * those that never expect a reply (broadcast and manycast
         * server modes) and those that do (all other modes). The dance
         * is intricate...
         */
        hpoll = peer->hpoll;

        /*
         * In broadcast mode the poll interval is never changed from
         * minpoll.
         */
        if (peer->cast_flags & (MDF_BCAST | MDF_MCAST)) {
                peer->outdate = current_time;
                if (sys_leap != LEAP_NOTINSYNC)
                        peer_xmit(peer);
                poll_update(peer, hpoll);
                return;
        }

        /*
         * In manycast mode we start with unity ttl. The ttl is
         * increased by one for each poll until either sys_maxclock
         * servers have been found or the maximum ttl is reached. When
         * sys_maxclock servers are found we stop polling until one or
         * more servers have timed out or until less than minpoll
         * associations turn up. In this case additional better servers
         * are dragged in and preempt the existing ones.
         */
        if (peer->cast_flags & MDF_ACAST) {
                peer->outdate = current_time;
                if (peer->unreach > sys_beacon) {
                        peer->unreach = 0;
                        peer->ttl = 0;
                        peer_xmit(peer);
                } else if (sys_survivors < sys_minclock ||
                    peer_associations < sys_maxclock) {
                        if (peer->ttl < sys_ttlmax)
                                peer->ttl++;
                        peer_xmit(peer);
                }
                peer->unreach++;
                poll_update(peer, hpoll);
                return;
        }

        /*
         * In unicast modes the dance is much more intricate. It is
         * desigmed to back off whenever possible to minimize network
         * traffic.
         */
        if (peer->burst == 0) {
                u_char oreach;

                /*
                 * Update the reachability status. If not heard for
                 * three consecutive polls, stuff infinity in the clock
                 * filter. 
                 */
                oreach = peer->reach;
                peer->outdate = current_time;
                peer->unreach++;
                peer->reach <<= 1;
                if (!(peer->reach & 0x0f))
                        clock_filter(peer, 0., 0., MAXDISPERSE);
                if (!peer->reach) {

                        /*
                         * Here the peer is unreachable. If it was
                         * previously reachable raise a trap. Send a
                         * burst if enabled.
                         */
                        if (oreach)
                                report_event(PEVNT_UNREACH, peer, NULL);
                        if ((peer->flags & FLAG_IBURST) &&
                            peer->retry == 0)
                                peer->retry = NTP_RETRY;
                } else {

                        /*
                         * Here the peer is reachable. Send a burst if
                         * enabled and the peer is fit.
                         */
                        hpoll = sys_poll;
                        if (!(peer->flags & FLAG_PREEMPT &&
                            peer->hmode == MODE_CLIENT))
                                peer->unreach = 0;
                        if ((peer->flags & FLAG_BURST) && peer->retry ==
                            0 && !peer_unfit(peer))
                                peer->retry = NTP_RETRY;
                }

                /*
                 * Watch for timeout. If preemptable, toss the rascal;
                 * otherwise, bump the poll interval. Note the
                 * poll_update() routine will clamp it to maxpoll.
                 */ 
                if (peer->unreach >= NTP_UNREACH) {
                        hpoll++;
                        if (peer->flags & FLAG_PREEMPT) {
                                report_event(PEVNT_RESTART, peer,
                                    "timeout");
                                if (peer->hmode != MODE_CLIENT) {
                                        peer_clear(peer, "TIME");
                                        unpeer(peer);
                                        return;
                                }
                                if (peer_associations > sys_maxclock &&
                                    score_all(peer)) {
                                        peer_clear(peer, "TIME");
                                        unpeer(peer);
                                        return;
                                }
                        }
                }
        } else {
                peer->burst--;
                if (peer->burst == 0) {

                        /*
                         * If ntpdate mode and the clock has not been
                         * set and all peers have completed the burst,
                         * we declare a successful failure.
                         */
                        if (mode_ntpdate) {
                                peer_ntpdate--;
                                if (peer_ntpdate == 0) {
                                        msyslog(LOG_NOTICE,
                                            "ntpd: no servers found");
                                        printf(
                                            "ntpd: no servers found\n");
                                        exit (0);
                                }
                        }
                }
        }
        if (peer->retry > 0)
                peer->retry--;

        /*
         * Do not transmit if in broadcast client mode. 
         */
        if (peer->hmode != MODE_BCLIENT)
                peer_xmit(peer);
        poll_update(peer, hpoll);
}


/*
 * receive - receive procedure called for each packet received
 */
void
receive(
        struct recvbuf *rbufp
        )
{
        register struct peer *peer;     /* peer structure pointer */
        register struct pkt *pkt;       /* receive packet pointer */
        int     hisversion;             /* packet version */
        int     hisleap;                /* packet leap indicator */
        int     hismode;                /* packet mode */
        int     hisstratum;             /* packet stratum */
        int     restrict_mask;          /* restrict bits */
        int     has_mac;                /* length of MAC field */
        int     authlen;                /* offset of MAC field */
        int     is_authentic = 0;       /* cryptosum ok */
        int     retcode = AM_NOMATCH;   /* match code */
        keyid_t skeyid = 0;             /* key IDs */
        u_int32 opcode = 0;             /* extension field opcode */
        sockaddr_u *dstadr_sin;         /* active runway */
        struct peer *peer2;             /* aux peer structure pointer */
        l_fp    p_org;                  /* origin timestamp */
        l_fp    p_rec;                  /* receive timestamp */
        l_fp    p_xmt;                  /* transmit timestamp */
#ifdef OPENSSL
        struct autokey *ap;             /* autokey structure pointer */
        int     rval;                   /* cookie snatcher */
        keyid_t pkeyid = 0, tkeyid = 0; /* key IDs */
#endif /* OPENSSL */
#ifdef HAVE_NTP_SIGND
        static unsigned char zero_key[16];
#endif /* HAVE_NTP_SIGND */

        /*
         * Monitor the packet and get restrictions. Note that the packet
         * length for control and private mode packets must be checked
         * by the service routines. Some restrictions have to be handled
         * later in order to generate a kiss-o'-death packet.
         */
        /*
         * Bogus port check is before anything, since it probably
         * reveals a clogging attack.
         */
        sys_received++;
        if (SRCPORT(&rbufp->recv_srcadr) < NTP_PORT) {
                sys_badlength++;
                return;                         /* bogus port */
        }
        restrict_mask = restrictions(&rbufp->recv_srcadr);
#ifdef DEBUG
        if (debug > 1)
                printf("receive: at %ld %s<-%s flags %x restrict %03x\n",
                    current_time, stoa(&rbufp->dstadr->sin),
                    stoa(&rbufp->recv_srcadr),
                    rbufp->dstadr->flags, restrict_mask);
#endif
        pkt = &rbufp->recv_pkt;
        hisversion = PKT_VERSION(pkt->li_vn_mode);
        hisleap = PKT_LEAP(pkt->li_vn_mode);
        hismode = (int)PKT_MODE(pkt->li_vn_mode);
        hisstratum = PKT_TO_STRATUM(pkt->stratum);
        if (restrict_mask & RES_IGNORE) {
                sys_restricted++;
                return;                         /* ignore everything */
        }
        if (hismode == MODE_PRIVATE) {
                if (restrict_mask & RES_NOQUERY) {
                        sys_restricted++;
                        return;                 /* no query private */
                }
                process_private(rbufp, ((restrict_mask &
                    RES_NOMODIFY) == 0));
                return;
        }
        if (hismode == MODE_CONTROL) {
                if (restrict_mask & RES_NOQUERY) {
                        sys_restricted++;
                        return;                 /* no query control */
                }
                process_control(rbufp, restrict_mask);
                return;
        }
        if (restrict_mask & RES_DONTSERVE) {
                sys_restricted++;
                return;                         /* no time serve */
        }

        /*
         * This is for testing. If restricted drop ten percent of
         * surviving packets.
         */
        if (restrict_mask & RES_TIMEOUT) {
                if ((double)ntp_random() / 0x7fffffff < .1) {
                        sys_restricted++;
                        return;                 /* no flakeway */
                }
        }
        
        /*
         * Version check must be after the query packets, since they
         * intentionally use an early version.
         */
        if (hisversion == NTP_VERSION) {
                sys_newversion++;               /* new version */
        } else if (!(restrict_mask & RES_VERSION) && hisversion >=
            NTP_OLDVERSION) {
                sys_oldversion++;               /* previous version */
        } else {
                sys_badlength++;
                return;                         /* old version */
        }

        /*
         * Figure out his mode and validate the packet. This has some
         * legacy raunch that probably should be removed. In very early
         * NTP versions mode 0 was equivalent to what later versions
         * would interpret as client mode.
         */
        if (hismode == MODE_UNSPEC) {
                if (hisversion == NTP_OLDVERSION) {
                        hismode = MODE_CLIENT;
                } else {
                        sys_badlength++;
                        return;                 /* invalid mode */
                }
        }

        /*
         * Parse the extension field if present. We figure out whether
         * an extension field is present by measuring the MAC size. If
         * the number of words following the packet header is 0, no MAC
         * is present and the packet is not authenticated. If 1, the
         * packet is a crypto-NAK; if 3, the packet is authenticated
         * with DES; if 5, the packet is authenticated with MD5; if 6,
         * the packet is authenticated with SHA. If 2 or * 4, the packet
         * is a runt and discarded forthwith. If greater than 6, an
         * extension field is present, so we subtract the length of the
         * field and go around again.
         */
        authlen = LEN_PKT_NOMAC;
        has_mac = rbufp->recv_length - authlen;
        while (has_mac != 0) {
                u_int32 len;

                if (has_mac % 4 != 0 || has_mac < MIN_MAC_LEN) {
                        sys_badlength++;
                        return;                 /* bad length */
                }
                if (has_mac <= MAX_MAC_LEN) {
                        skeyid = ntohl(((u_int32 *)pkt)[authlen / 4]);
                        break;

                } else {
                        opcode = ntohl(((u_int32 *)pkt)[authlen / 4]);
                        len = opcode & 0xffff;
                        if (len % 4 != 0 || len < 4 || len + authlen >
                            rbufp->recv_length) {
                                sys_badlength++;
                                return;         /* bad length */
                        }
                        authlen += len;
                        has_mac -= len;
                }
        }

        /*
         * If authentication required, a MAC must be present.
         */
        if (restrict_mask & RES_DONTTRUST && has_mac == 0) {
                sys_restricted++;
                return;                         /* access denied */
        }

        /*
         * Update the MRU list and finger the cloggers. It can be a
         * little expensive, so turn it off for production use.
         */
        restrict_mask = ntp_monitor(rbufp, restrict_mask);
        if (restrict_mask & RES_LIMITED) {
                sys_limitrejected++;
                if (!(restrict_mask & RES_KOD) || hismode ==
                    MODE_BROADCAST)
                        return;                 /* rate exceeded */

                if (hismode == MODE_CLIENT)
                        fast_xmit(rbufp, MODE_SERVER, skeyid,
                            restrict_mask);
                else
                        fast_xmit(rbufp, MODE_ACTIVE, skeyid,
                            restrict_mask);
                return;                         /* rate exceeded */
        }
        restrict_mask &= ~RES_KOD;

        /*
         * We have tossed out as many buggy packets as possible early in
         * the game to reduce the exposure to a clogging attack. now we
         * have to burn some cycles to find the association and
         * authenticate the packet if required. Note that we burn only
         * MD5 cycles, again to reduce exposure. There may be no
         * matching association and that's okay.
         *
         * More on the autokey mambo. Normally the local interface is
         * found when the association was mobilized with respect to a
         * designated remote address. We assume packets arriving from
         * the remote address arrive via this interface and the local
         * address used to construct the autokey is the unicast address
         * of the interface. However, if the sender is a broadcaster,
         * the interface broadcast address is used instead.
         * Notwithstanding this technobabble, if the sender is a
         * multicaster, the broadcast address is null, so we use the
         * unicast address anyway. Don't ask.
         */
        peer = findpeer(&rbufp->recv_srcadr, rbufp->dstadr,  hismode,
            &retcode);
        dstadr_sin = &rbufp->dstadr->sin;
        NTOHL_FP(&pkt->org, &p_org);
        NTOHL_FP(&pkt->rec, &p_rec);
        NTOHL_FP(&pkt->xmt, &p_xmt);

        /*
         * Authentication is conditioned by three switches:
         *
         * NOPEER  (RES_NOPEER) do not mobilize an association unless
         *         authenticated
         * NOTRUST (RES_DONTTRUST) do not allow access unless
         *         authenticated (implies NOPEER)
         * enable  (sys_authenticate) master NOPEER switch, by default
         *         on
         *
         * The NOPEER and NOTRUST can be specified on a per-client basis
         * using the restrict command. The enable switch if on implies
         * NOPEER for all clients. There are four outcomes:
         *
         * NONE    The packet has no MAC.
         * OK      the packet has a MAC and authentication succeeds
         * ERROR   the packet has a MAC and authentication fails
         * CRYPTO  crypto-NAK. The MAC has four octets only.
         *
         * Note: The AUTH(x, y) macro is used to filter outcomes. If x
         * is zero, acceptable outcomes of y are NONE and OK. If x is
         * one, the only acceptable outcome of y is OK.
         */

        if (has_mac == 0) {
                restrict_mask &= ~RES_MSSNTP;
                is_authentic = AUTH_NONE; /* not required */
#ifdef DEBUG
                if (debug)
                        printf(
                            "receive: at %ld %s<-%s mode %d len %d\n",
                            current_time, stoa(dstadr_sin),
                            stoa(&rbufp->recv_srcadr), hismode,
                            authlen);
#endif
        } else if (has_mac == 4) {
                restrict_mask &= ~RES_MSSNTP;
                is_authentic = AUTH_CRYPTO; /* crypto-NAK */
#ifdef DEBUG
                if (debug)
                        printf(
                            "receive: at %ld %s<-%s mode %d keyid %08x len %d auth %d\n",
                            current_time, stoa(dstadr_sin),
                            stoa(&rbufp->recv_srcadr), hismode, skeyid,
                            authlen + has_mac, is_authentic);
#endif

#ifdef HAVE_NTP_SIGND
                /*
                 * If the signature is 20 bytes long, the last 16 of
                 * which are zero, then this is a Microsoft client
                 * wanting AD-style authentication of the server's
                 * reply.  
                 *
                 * This is described in Microsoft's WSPP docs, in MS-SNTP:
                 * http://msdn.microsoft.com/en-us/library/cc212930.aspx
                 */
        } else if (has_mac == MAX_MD5_LEN && (restrict_mask & RES_MSSNTP) &&
           (retcode == AM_FXMIT || retcode == AM_NEWPASS) &&
           (memcmp(zero_key, (char *)pkt + authlen + 4, MAX_MD5_LEN - 4) ==
           0)) {
                is_authentic = AUTH_NONE;
#endif /* HAVE_NTP_SIGND */

        } else {
                restrict_mask &= ~RES_MSSNTP;
#ifdef OPENSSL
                /*
                 * For autokey modes, generate the session key
                 * and install in the key cache. Use the socket
                 * broadcast or unicast address as appropriate.
                 */
                if (crypto_flags && skeyid > NTP_MAXKEY) {
                
                        /*
                         * More on the autokey dance (AKD). A cookie is
                         * constructed from public and private values.
                         * For broadcast packets, the cookie is public
                         * (zero). For packets that match no
                         * association, the cookie is hashed from the
                         * addresses and private value. For server
                         * packets, the cookie was previously obtained
                         * from the server. For symmetric modes, the
                         * cookie was previously constructed using an
                         * agreement protocol; however, should PKI be
                         * unavailable, we construct a fake agreement as
                         * the EXOR of the peer and host cookies.
                         *
                         * hismode      ephemeral       persistent
                         * =======================================
                         * active       0               cookie#
                         * passive      0%              cookie#
                         * client       sys cookie      0%
                         * server       0%              sys cookie
                         * broadcast    0               0
                         *
                         * # if unsync, 0
                         * % can't happen
                         */
                        if (has_mac < MAX_MD5_LEN) {
                                sys_badauth++;
                                return;
                        }
                        if (hismode == MODE_BROADCAST) {

                                /*
                                 * For broadcaster, use the interface
                                 * broadcast address when available;
                                 * otherwise, use the unicast address
                                 * found when the association was
                                 * mobilized. However, if this is from
                                 * the wildcard interface, game over.
                                 */
                                if (crypto_flags && rbufp->dstadr ==
                                    any_interface) {
                                        sys_restricted++;
                                        return;      /* no wildcard */
                                }
                                pkeyid = 0;
                                if (!SOCK_UNSPEC(&rbufp->dstadr->bcast))
                                        dstadr_sin =
                                            &rbufp->dstadr->bcast;
                        } else if (peer == NULL) {
                                pkeyid = session_key(
                                    &rbufp->recv_srcadr, dstadr_sin, 0,
                                    sys_private, 0);
                        } else {
                                pkeyid = peer->pcookie;
                        }

                        /*
                         * The session key includes both the public
                         * values and cookie. In case of an extension
                         * field, the cookie used for authentication
                         * purposes is zero. Note the hash is saved for
                         * use later in the autokey mambo.
                         */
                        if (authlen > LEN_PKT_NOMAC && pkeyid != 0) {
                                session_key(&rbufp->recv_srcadr,
                                    dstadr_sin, skeyid, 0, 2);
                                tkeyid = session_key(
                                    &rbufp->recv_srcadr, dstadr_sin,
                                    skeyid, pkeyid, 0);
                        } else {
                                tkeyid = session_key(
                                    &rbufp->recv_srcadr, dstadr_sin,
                                    skeyid, pkeyid, 2);
                        }

                }
#endif /* OPENSSL */

                /*
                 * Compute the cryptosum. Note a clogging attack may
                 * succeed in bloating the key cache. If an autokey,
                 * purge it immediately, since we won't be needing it
                 * again. If the packet is authentic, it can mobilize an
                 * association. Note that there is no key zero.
                 */
                if (!authdecrypt(skeyid, (u_int32 *)pkt, authlen,
                    has_mac))
                        is_authentic = AUTH_ERROR;
                else
                        is_authentic = AUTH_OK;
#ifdef OPENSSL
                if (crypto_flags && skeyid > NTP_MAXKEY)
                        authtrust(skeyid, 0);
#endif /* OPENSSL */
#ifdef DEBUG
                if (debug)
                        printf(
                            "receive: at %ld %s<-%s mode %d keyid %08x len %d auth %d\n",
                            current_time, stoa(dstadr_sin),
                            stoa(&rbufp->recv_srcadr), hismode, skeyid,
                            authlen + has_mac, is_authentic);
#endif
        }

        /*
         * The association matching rules are implemented by a set of
         * routines and an association table. A packet matching an
         * association is processed by the peer process for that
         * association. If there are no errors, an ephemeral association
         * is mobilized: a broadcast packet mobilizes a broadcast client
         * aassociation; a manycast server packet mobilizes a manycast
         * client association; a symmetric active packet mobilizes a
         * symmetric passive association.
         */
        switch (retcode) {

        /*
         * This is a client mode packet not matching any association. If
         * an ordinary client, simply toss a server mode packet back
         * over the fence. If a manycast client, we have to work a
         * little harder.
         */
        case AM_FXMIT:

                /*
                 * If authentication OK, send a server reply; otherwise,
                 * send a crypto-NAK.
                 */
                if (!(rbufp->dstadr->flags & INT_MCASTOPEN)) {
                        if (AUTH(restrict_mask & RES_DONTTRUST,
                           is_authentic)) {
                                fast_xmit(rbufp, MODE_SERVER, skeyid,
                                    restrict_mask);
                        } else if (is_authentic == AUTH_ERROR) {
                                fast_xmit(rbufp, MODE_SERVER, 0,
                                    restrict_mask);
                                sys_badauth++;
                        } else {
                                sys_restricted++;
                        }
                        return;                 /* hooray */
                }

                /*
                 * This must be manycast. Do not respond if not
                 * configured as a manycast server.
                 */
                if (!sys_manycastserver) {
                        sys_restricted++;
                        return;                 /* not enabled */
                }

                /*
                 * Do not respond if we are not synchronized or our
                 * stratum is greater than the manycaster or the
                 * manycaster has already synchronized to us.
                 */
                if (sys_leap == LEAP_NOTINSYNC || sys_stratum >=
                    hisstratum || (!sys_cohort && sys_stratum ==
                    hisstratum + 1) || rbufp->dstadr->addr_refid ==
                    pkt->refid) {
                        sys_declined++;
                        return;                 /* no help */
                }

                /*
                 * Respond only if authentication succeeds. Don't do a
                 * crypto-NAK, as that would not be useful.
                 */
                if (AUTH(restrict_mask & RES_DONTTRUST, is_authentic))
                        fast_xmit(rbufp, MODE_SERVER, skeyid,
                            restrict_mask);
                return;                         /* hooray */

        /*
         * This is a server mode packet returned in response to a client
         * mode packet sent to a multicast group address. The origin
         * timestamp is a good nonce to reliably associate the reply
         * with what was sent. If there is no match, that's curious and
         * could be an intruder attempting to clog, so we just ignore
         * it.
         *
         * If the packet is authentic and the manycast association is
         * found, we mobilize a client association and copy pertinent
         * variables from the manycast association to the new client
         * association. If not, just ignore the packet.
         *
         * There is an implosion hazard at the manycast client, since
         * the manycast servers send the server packet immediately. If
         * the guy is already here, don't fire up a duplicate.
         */
        case AM_MANYCAST:
                if (!AUTH(sys_authenticate | (restrict_mask &
                    (RES_NOPEER | RES_DONTTRUST)), is_authentic)) {
                        sys_restricted++;
                        return;                 /* access denied */
                }

                /*
                 * Do not respond if unsynchronized or stratum is below
                 * the floor or at or above the ceiling.
                 */
                if (hisleap == LEAP_NOTINSYNC || hisstratum <
                    sys_floor || hisstratum >= sys_ceiling) {
                        sys_declined++;
                        return;                 /* no help */
                }
                if ((peer2 = findmanycastpeer(rbufp)) == NULL) {
                        sys_restricted++;
                        return;                 /* not enabled */
                }
                if ((peer = newpeer(&rbufp->recv_srcadr, rbufp->dstadr,
                    MODE_CLIENT, hisversion, NTP_MINDPOLL, NTP_MAXDPOLL,
                    FLAG_PREEMPT, MDF_UCAST | MDF_ACLNT, 0, skeyid)) ==
                    NULL) {
                        sys_declined++;
                        return;                 /* ignore duplicate  */
                }

                /*
                 * We don't need these, but it warms the billboards.
                 */
                if (peer2->flags & FLAG_IBURST)
                        peer->flags |= FLAG_IBURST;
                peer->minpoll = peer2->minpoll;
                peer->maxpoll = peer2->maxpoll;
                break;

        /*
         * This is the first packet received from a broadcast server. If
         * the packet is authentic and we are enabled as broadcast
         * client, mobilize a broadcast client association. We don't
         * kiss any frogs here.
         */
        case AM_NEWBCL:
                if (sys_bclient == 0) {
                        sys_restricted++;
                        return;                 /* not enabled */
                }
                if (!AUTH(sys_authenticate | (restrict_mask &
                    (RES_NOPEER | RES_DONTTRUST)), is_authentic)) {
                        sys_restricted++;
                        return;                 /* access denied */
                }

                /*
                 * Do not respond if unsynchronized or stratum is below
                 * the floor or at or above the ceiling.
                 */
                if (hisleap == LEAP_NOTINSYNC || hisstratum <
                    sys_floor || hisstratum >= sys_ceiling) {
                        sys_declined++;
                        return;                 /* no help */
                }

#ifdef OPENSSL
                /*
                 * Do not respond if Autokey and the opcode is not a
                 * CRYPTO_ASSOC response with associationn ID.
                 */
                if (crypto_flags && skeyid > NTP_MAXKEY && (opcode &
                    0xffff0000) != (CRYPTO_ASSOC | CRYPTO_RESP)) {
                        sys_declined++;
                        return;                 /* protocol error */
                }
#endif /* OPENSSL */

                /*
                 * Determine whether to execute the initial volley.
                 */
                if (sys_bdelay != 0) {
#ifdef OPENSSL
                        /*
                         * If a two-way exchange is not possible,
                         * neither is Autokey.
                         */
                        if (crypto_flags && skeyid > NTP_MAXKEY) {
                                sys_restricted++;
                                return;         /* no autokey */
                        }
#endif /* OPENSSL */

                        /*
                         * Do not execute the volley. Start out in
                         * broadcast client mode.
                         */
                        if ((peer = newpeer(&rbufp->recv_srcadr,
                            rbufp->dstadr, MODE_BCLIENT, hisversion,
                            pkt->ppoll, pkt->ppoll, 0, 0, 0,
                            skeyid)) == NULL) {
                                sys_restricted++;
                                return;         /* ignore duplicate */

                        } else {
                                peer->delay = sys_bdelay;
                                peer->bias = -sys_bdelay / 2.;
                        }
                        break;
                }

                /*
                 * Execute the initial volley in order to calibrate the
                 * propagation delay and run the Autokey protocol.
                 *
                 * Note that the minpoll is taken from the broadcast
                 * packet, normally 6 (64 s) and that the poll interval
                 * is fixed at this value.
                 */
                if ((peer = newpeer(&rbufp->recv_srcadr, rbufp->dstadr,
                    MODE_CLIENT, hisversion, pkt->ppoll, pkt->ppoll,
                    FLAG_IBURST | FLAG_PREEMPT, MDF_BCLNT, 0,
                    skeyid)) == NULL) {
                        sys_restricted++;
                        return;                 /* ignore duplicate */
                }
#ifdef OPENSSL
                if (skeyid > NTP_MAXKEY)
                        crypto_recv(peer, rbufp);
#endif /* OPENSSL */

                return;                         /* hooray */

        /*
         * This is the first packet received from a symmetric active
         * peer. If the packet is authentic and the first he sent,
         * mobilize a passive association. If not, kiss the frog.
         */
        case AM_NEWPASS:
                if (!AUTH(sys_authenticate | (restrict_mask &
                    (RES_NOPEER | RES_DONTTRUST)), is_authentic)) {

                        /*
                         * If authenticated but cannot mobilize an
                         * association, send a symmetric passive
                         * response without mobilizing an association.
                         * This is for drat broken Windows clients. See
                         * Microsoft KB 875424 for preferred workaround.
                         */
                        if (AUTH(restrict_mask & RES_DONTTRUST,
                            is_authentic)) {
                                fast_xmit(rbufp, MODE_PASSIVE, skeyid,
                                    restrict_mask);
                                return;                 /* hooray */
                        }
                        if (is_authentic == AUTH_ERROR) {
                                fast_xmit(rbufp, MODE_ACTIVE, 0,
                                    restrict_mask);
                                sys_restricted++;
                        }
                }

                /*
                 * Do not respond if synchronized and stratum is either
                 * below the floor or at or above the ceiling. Note,
                 * this allows an unsynchronized peer to synchronize to
                 * us. It would be very strange if he did and then was
                 * nipped, but that could only happen if we were
                 * operating at the top end of the range.
                 */
                if (hisleap != LEAP_NOTINSYNC && (hisstratum <
                    sys_floor || hisstratum >= sys_ceiling)) {
                        sys_declined++;
                        return;                 /* no help */
                }

                /*
                 * The message is correctly authenticated and
                 * allowed. Mobiliae a symmetric passive association.
                 */
                if ((peer = newpeer(&rbufp->recv_srcadr,
                    rbufp->dstadr, MODE_PASSIVE, hisversion, pkt->ppoll,
                    NTP_MAXDPOLL, FLAG_PREEMPT, MDF_UCAST, 0,
                    skeyid)) == NULL) {
                        sys_declined++;
                        return;                 /* ignore duplicate */
                }
                break;


        /*
         * Process regular packet. Nothing special.
         */
        case AM_PROCPKT:
                break;

        /*
         * A passive packet matches a passive association. This is
         * usually the result of reconfiguring a client on the fly. As
         * this association might be legitamate and this packet an
         * attempt to deny service, just ignore it.
         */
        case AM_ERR:
                sys_declined++;
                return;

        /*
         * For everything else there is the bit bucket.
         */
        default:
                sys_declined++;
                return;
        }

#ifdef OPENSSL
        /*
         * If the association is configured for Autokey, the packet must
         * have a public key ID; if not, the packet must have a
         * symmetric key ID.
         */
        if (is_authentic != AUTH_CRYPTO && (((peer->flags &
            FLAG_SKEY) && skeyid <= NTP_MAXKEY) || (!(peer->flags &
            FLAG_SKEY) && skeyid > NTP_MAXKEY))) {
                sys_badauth++;
                return;
        }
#endif /* OPENSSL */
        peer->received++;
        peer->flash &= ~PKT_TEST_MASK;
        if (peer->flags & FLAG_XBOGUS) {
                peer->flags &= ~FLAG_XBOGUS;
                peer->flash |= TEST3;
        }

        /*
         * Next comes a rigorous schedule of timestamp checking. If the
         * transmit timestamp is zero, the server has not initialized in
         * interleaved modes or is horribly broken.
         */
        if (L_ISZERO(&p_xmt)) {
                peer->flash |= TEST3;                   /* unsynch */

        /*
         * If the transmit timestamp duplicates a previous one, the
         * packet is a replay. This prevents the bad guys from replaying
         * the most recent packet, authenticated or not.
         */
        } else if (L_ISEQU(&peer->xmt, &p_xmt)) {
                peer->flash |= TEST1;                   /* duplicate */
                peer->oldpkt++;
                return;

        /*
         * If this is a broadcast mode packet, skip further checking. If
         * an intial volley, bail out now and let the client do its
         * stuff. If the origin timestamp is nonzero, this is an
         * interleaved broadcast. so restart the protocol.
         */
        } else if (hismode == MODE_BROADCAST) {
                if (!L_ISZERO(&p_org) && !(peer->flags & FLAG_XB)) {
                        peer->flags |= FLAG_XB;
                        peer->aorg = p_xmt;
                        peer->borg = rbufp->recv_time;
                        report_event(PEVNT_XLEAVE, peer, NULL);
                        return;
                }

        /*
         * Check for bogus packet in basic mode. If found, switch to
         * interleaved mode and resynchronize, but only after confirming
         * the packet is not bogus in symmetric interleaved mode.
         */
        } else if (peer->flip == 0) {
                if (!L_ISEQU(&p_org, &peer->aorg)) {
                        peer->bogusorg++;
                        peer->flash |= TEST2;   /* bogus */
                        if (!L_ISZERO(&peer->dst) && L_ISEQU(&p_org,
                            &peer->dst)) {
                                peer->flip = 1;
                                report_event(PEVNT_XLEAVE, peer, NULL);
                        }
                } else {
                        L_CLR(&peer->aorg);
                }

        /*
         * Check for valid nonzero timestamp fields.
         */
        } else if (L_ISZERO(&p_org) || L_ISZERO(&p_rec) ||
            L_ISZERO(&peer->dst)) {
                peer->flash |= TEST3;           /* unsynch */

        /*
         * Check for bogus packet in interleaved symmetric mode. This
         * can happen if a packet is lost, duplicat or crossed. If
         * found, flip and resynchronize.
         */
        } else if (!L_ISZERO(&peer->dst) && !L_ISEQU(&p_org,
                    &peer->dst)) {
                        peer->bogusorg++;
                        peer->flags |= FLAG_XBOGUS;
                        peer->flash |= TEST2;           /* bogus */
        }

        /*
         * Update the state variables.
         */
        if (peer->flip == 0) {
                if (hismode != MODE_BROADCAST)
                        peer->rec = p_xmt;
                peer->dst = rbufp->recv_time;
        }
        peer->xmt = p_xmt;

        /*
         * If this is a crypto_NAK, the server cannot authenticate a
         * client packet. The server might have just changed keys. Clear
         * the association and restart the protocol.
         */
        if (is_authentic == AUTH_CRYPTO) {
                report_event(PEVNT_AUTH, peer, "crypto_NAK");
                peer->flash |= TEST5;           /* bad auth */
                peer->badauth++;
                if (peer->flags & FLAG_PREEMPT) {
                        unpeer(peer);
                        return;
                }
#ifdef OPENSSL
                if (peer->crypto)
                        peer_clear(peer, "AUTH");
#endif /* OPENSSL */
                return;

        /* 
         * If the digest fails, the client cannot authenticate a server
         * reply to a client packet previously sent. The loopback check
         * is designed to avoid a bait-and-switch attack, which was
         * possible in past versions. If symmetric modes, return a
         * crypto-NAK. The peer should restart the protocol.
         */
        } else if (!AUTH(has_mac || (restrict_mask & RES_DONTTRUST),
            is_authentic)) {
                report_event(PEVNT_AUTH, peer, "digest");
                peer->flash |= TEST5;           /* bad auth */
                peer->badauth++;
                if (hismode == MODE_ACTIVE || hismode == MODE_PASSIVE)
                        fast_xmit(rbufp, MODE_ACTIVE, 0, restrict_mask);
                if (peer->flags & FLAG_PREEMPT) {
                        unpeer(peer);
                        return;
                }
#ifdef OPENSSL
                if (peer->crypto)
                        peer_clear(peer, "AUTH");
#endif /* OPENSSL */
                return;
        }

        /*
         * Set the peer ppoll to the maximum of the packet ppoll and the
         * peer minpoll. If a kiss-o'-death, set the peer minpoll to
         * this maximumn and advance the headway to give the sender some
         * headroom. Very intricate.
         */
        peer->ppoll = max(peer->minpoll, pkt->ppoll);
        if (hismode == MODE_SERVER && hisleap == LEAP_NOTINSYNC &&
            hisstratum == STRATUM_UNSPEC && memcmp(&pkt->refid,
            "RATE", 4) == 0) {
                peer->selbroken++;
                report_event(PEVNT_RATE, peer, NULL);
                if (pkt->ppoll > peer->minpoll)
                        peer->minpoll = peer->ppoll;
                peer->burst = peer->retry = 0;
                peer->throttle = (NTP_SHIFT + 1) * (1 << peer->minpoll);
                poll_update(peer, pkt->ppoll);
                return;                         /* kiss-o'-death */
        }

        /*
         * That was hard and I am sweaty, but the packet is squeaky
         * clean. Get on with real work.
         */
        peer->timereceived = current_time;
        if (is_authentic == AUTH_OK)
                peer->flags |= FLAG_AUTHENTIC;
        else
                peer->flags &= ~FLAG_AUTHENTIC;

#ifdef OPENSSL
        /*
         * More autokey dance. The rules of the cha-cha are as follows:
         *
         * 1. If there is no key or the key is not auto, do nothing.
         *
         * 2. If this packet is in response to the one just previously
         *    sent or from a broadcast server, do the extension fields.
         *    Otherwise, assume bogosity and bail out.
         *
         * 3. If an extension field contains a verified signature, it is
         *    self-authenticated and we sit the dance.
         *
         * 4. If this is a server reply, check only to see that the
         *    transmitted key ID matches the received key ID.
         *
         * 5. Check to see that one or more hashes of the current key ID
         *    matches the previous key ID or ultimate original key ID
         *    obtained from the broadcaster or symmetric peer. If no
         *    match, sit the dance and call for new autokey values.
         *
         * In case of crypto error, fire the orchestra, stop dancing and
         * restart the protocol.
         */
        if (peer->flags & FLAG_SKEY) {
                /*
                 * Decrement remaining audokey hashes. This isn't
                 * perfect if a packet is lost, but results in no harm.
                 */
                ap = (struct autokey *)peer->recval.ptr;
                if (ap != NULL) {
                        if (ap->seq > 0)
                                ap->seq--;
                }
                peer->flash |= TEST8;
                rval = crypto_recv(peer, rbufp);
                if (rval == XEVNT_OK) {
                        peer->unreach = 0;
                } else {
                        if (rval == XEVNT_ERR) {
                                report_event(PEVNT_RESTART, peer,
                                    "crypto error");
                                peer_clear(peer, "CRYP");
                                peer->flash |= TEST9;   /* bad crypt */
                                if (peer->flags & FLAG_PREEMPT)
                                        unpeer(peer);
                        }
                        return;
                }

                /*
                 * If server mode, verify the receive key ID matches
                 * the transmit key ID.
                 */
                if (hismode == MODE_SERVER) {
                        if (skeyid == peer->keyid)
                                peer->flash &= ~TEST8;

                /*
                 * If an extension field is present, verify only that it
                 * has been correctly signed. We don't need a sequence
                 * check here, but the sequence continues.
                 */
                } else if (!(peer->flash & TEST8)) {
                        peer->pkeyid = skeyid;

                /*
                 * Now the fun part. Here, skeyid is the current ID in
                 * the packet, pkeyid is the ID in the last packet and
                 * tkeyid is the hash of skeyid. If the autokey values
                 * have not been received, this is an automatic error.
                 * If so, check that the tkeyid matches pkeyid. If not,
                 * hash tkeyid and try again. If the number of hashes
                 * exceeds the number remaining in the sequence, declare
                 * a successful failure and refresh the autokey values.
                 */
                } else if (ap != NULL) {
                        int i;

                        for (i = 0; ; i++) {
                                if (tkeyid == peer->pkeyid ||
                                    tkeyid == ap->key) {
                                        peer->flash &= ~TEST8;
                                        peer->pkeyid = skeyid;
                                        ap->seq -= i;
                                        break;
                                }
                                if (i > ap->seq) {
                                        peer->crypto &=
                                            ~CRYPTO_FLAG_AUTO;
                                        break;
                                }
                                tkeyid = session_key(
                                    &rbufp->recv_srcadr, dstadr_sin,
                                    tkeyid, pkeyid, 0);
                        }
                        if (peer->flash & TEST8)
                                report_event(PEVNT_AUTH, peer, "keylist");
                }
                if (!(peer->crypto & CRYPTO_FLAG_PROV)) /* test 9 */
                        peer->flash |= TEST8;   /* bad autokey */

                /*
                 * The maximum lifetime of the protocol is about one
                 * week before restarting the Autokey protocol to
                 * refreshed certificates and leapseconds values.
                 */
                if (current_time > peer->refresh) {
                        report_event(PEVNT_RESTART, peer,
                            "crypto refresh");
                        peer_clear(peer, "TIME");
                        return;
                }
        }
#endif /* OPENSSL */

        /*
         * The dance is complete and the flash bits have been lit. Toss
         * the packet over the fence for processing, which may light up
         * more flashers.
         */
        process_packet(peer, pkt, rbufp->recv_length);

        /*
         * In interleaved mode update the state variables. Also adjust the
         * transmit phase to avoid crossover.
         */
        if (peer->flip != 0) {
                peer->rec = p_rec;
                peer->dst = rbufp->recv_time;
                if (peer->nextdate - current_time < (1 << min(peer->ppoll,
                    peer->hpoll)) / 2)
                        peer->nextdate++;
                else
                        peer->nextdate--;
        }
}


/*
 * process_packet - Packet Procedure, a la Section 3.4.4 of the
 *      specification. Or almost, at least. If we're in here we have a
 *      reasonable expectation that we will be having a long term
 *      relationship with this host.
 */
void
process_packet(
        register struct peer *peer,
        register struct pkt *pkt,
        u_int   len
        )
{
        double  t34, t21;
        double  p_offset, p_del, p_disp;
        l_fp    p_rec, p_xmt, p_org, p_reftime, ci;
        u_char  pmode, pleap, pstratum;
        char    statstr[NTP_MAXSTRLEN];
#ifdef ASSYM
        int     itemp;
        double  etemp, ftemp, td;
#endif /* ASSYM */

        sys_processed++;
        peer->processed++;
        p_del = FPTOD(NTOHS_FP(pkt->rootdelay));
        p_offset = 0;
        p_disp = FPTOD(NTOHS_FP(pkt->rootdisp));
        NTOHL_FP(&pkt->reftime, &p_reftime);
        NTOHL_FP(&pkt->org, &p_org);
        NTOHL_FP(&pkt->rec, &p_rec);
        NTOHL_FP(&pkt->xmt, &p_xmt);
        pmode = PKT_MODE(pkt->li_vn_mode);
        pleap = PKT_LEAP(pkt->li_vn_mode);
        pstratum = PKT_TO_STRATUM(pkt->stratum);

        /*
         * Capture the header values in the client/peer association..
         */
        record_raw_stats(&peer->srcadr, peer->dstadr ?
            &peer->dstadr->sin : NULL, &p_org, &p_rec, &p_xmt,
            &peer->dst);
        peer->leap = pleap;
        peer->stratum = min(pstratum, STRATUM_UNSPEC);
        peer->pmode = pmode;
        peer->precision = pkt->precision;
        peer->rootdelay = p_del;
        peer->rootdisp = p_disp;
        peer->refid = pkt->refid;               /* network byte order */
        peer->reftime = p_reftime;

        /*
         * First, if either burst mode is armed, enable the burst.
         * Compute the headway for the next packet and delay if
         * necessary to avoid exceeding the threshold.
         */
        if (peer->retry > 0) {
                peer->retry = 0;
                if (peer->reach)
                        peer->burst = min(1 << (peer->hpoll -
                            peer->minpoll), NTP_SHIFT) - 1;
                else
                        peer->burst = NTP_IBURST - 1;
                if (peer->burst > 0)
                        peer->nextdate = current_time;
        }
        poll_update(peer, peer->hpoll);

        /*
         * Verify the server is synchronized; that is, the leap bits,
         * stratum and root distance are valid.
         */
        if (pleap == LEAP_NOTINSYNC ||          /* test 6 */
            pstratum < sys_floor || pstratum >= sys_ceiling)
                peer->flash |= TEST6;           /* bad synch or strat */
        if (p_del / 2 + p_disp >= MAXDISPERSE)  /* test 7 */
                peer->flash |= TEST7;           /* bad header */

        /*
         * If any tests fail at this point, the packet is discarded.
         * Note that some flashers may have already been set in the
         * receive() routine.
         */
        if (peer->flash & PKT_TEST_MASK) {
                peer->seldisptoolarge++;
#ifdef DEBUG
                if (debug)
                        printf("packet: flash header %04x\n",
                            peer->flash);
#endif
                return;
        }

        /*
         * If the peer was previously unreachable, raise a trap. In any
         * case, mark it reachable.
         */ 
        if (!peer->reach) {
                report_event(PEVNT_REACH, peer, NULL);
                peer->timereachable = current_time;
        }
        peer->reach |= 1;

        /*
         * For a client/server association, calculate the clock offset,
         * roundtrip delay and dispersion. The equations are reordered
         * from the spec for more efficient use of temporaries. For a
         * broadcast association, offset the last measurement by the
         * computed delay during the client/server volley. Note the
         * computation of dispersion includes the system precision plus
         * that due to the frequency error since the origin time.
         *
         * It is very important to respect the hazards of overflow. The
         * only permitted operation on raw timestamps is subtraction,
         * where the result is a signed quantity spanning from 68 years
         * in the past to 68 years in the future. To avoid loss of
         * precision, these calculations are done using 64-bit integer
         * arithmetic. However, the offset and delay calculations are
         * sums and differences of these first-order differences, which
         * if done using 64-bit integer arithmetic, would be valid over
         * only half that span. Since the typical first-order
         * differences are usually very small, they are converted to 64-
         * bit doubles and all remaining calculations done in floating-
         * double arithmetic. This preserves the accuracy while
         * retaining the 68-year span.
         *
         * There are three interleaving schemes, basic, interleaved
         * symmetric and interleaved broadcast. The timestamps are
         * idioscyncratically different. See the onwire briefing/white
         * paper at www.eecis.udel.edu/~mills for details.
         *
         * Interleaved symmetric mode
         * t1 = peer->aorg/borg, t2 = peer->rec, t3 = p_xmt,
         * t4 = peer->dst
         */
        if (peer->flip != 0) {
                ci = p_xmt;                             /* t3 - t4 */
                L_SUB(&ci, &peer->dst);
                LFPTOD(&ci, t34);
                ci = p_rec;                             /* t2 - t1 */
                if (peer->flip > 0)
                        L_SUB(&ci, &peer->borg);
                else
                        L_SUB(&ci, &peer->aorg);
                LFPTOD(&ci, t21);
                p_del = t21 - t34;
                p_offset = (t21 + t34) / 2.;
                if (p_del < 0 || p_del > 1.) {
                        sprintf(statstr, "t21 %.6f t34 %.6f", t21, t34);
                        report_event(PEVNT_XERR, peer, statstr);
                        return;
                }

        /*
         * Broadcast modes
         */
        } else if (peer->pmode == MODE_BROADCAST) {

                /*
                 * Interleaved broadcast mode. Use interleaved timestamps.
                 * t1 = peer->borg, t2 = p_org, t3 = p_org, t4 = aorg
                 */
                if (peer->flags & FLAG_XB) { 
                        ci = p_org;                     /* delay */ 
                        L_SUB(&ci, &peer->aorg);
                        LFPTOD(&ci, t34);
                        ci = p_org;                     /* t2 - t1 */
                        L_SUB(&ci, &peer->borg);
                        LFPTOD(&ci, t21);
                        peer->aorg = p_xmt;
                        peer->borg = peer->dst;
                        if (t34 < 0 || t34 > 1.) {
                                sprintf(statstr,
                                    "offset %.6f delay %.6f", t21, t34);
                                report_event(PEVNT_XERR, peer, statstr);
                                return;
                        }
                        p_offset = t21;
                        peer->xleave = t34;

                /*
                 * Basic broadcast - use direct timestamps.
                 * t3 = p_xmt, t4 = peer->dst
                 */
                } else {
                        ci = p_xmt;             /* t3 - t4 */
                        L_SUB(&ci, &peer->dst);
                        LFPTOD(&ci, t34);
                        p_offset = t34;
                }

                /*
                 * When calibration is complete and the clock is
                 * synchronized, the bias is calculated as the difference
                 * between the unicast timestamp and the broadcast
                 * timestamp. This works for both basic and interleaved
                 * modes.
                 */
                if (peer->cast_flags & MDF_BCLNT) {
                        peer->cast_flags &= ~MDF_BCLNT;
                        peer->delay = (peer->offset - p_offset) * 2;
                }
                p_del = peer->delay;
                p_offset += p_del / 2;


        /*
         * Basic mode, otherwise known as the old fashioned way.
         *
         * t1 = p_org, t2 = p_rec, t3 = p_xmt, t4 = peer->dst
         */
        } else {
                ci = p_xmt;                             /* t3 - t4 */
                L_SUB(&ci, &peer->dst);
                LFPTOD(&ci, t34);
                ci = p_rec;                             /* t2 - t1 */
                L_SUB(&ci, &p_org);
                LFPTOD(&ci, t21);
                p_del = fabs(t21 - t34);
                p_offset = (t21 + t34) / 2.;
        }
        p_offset += peer->bias;
        p_disp = LOGTOD(sys_precision) + LOGTOD(peer->precision) +
            clock_phi * p_del;

#if ASSYM
        /*
         * This code calculates the outbound and inbound data rates by
         * measuring the differences between timestamps at different
         * packet lengths. This is helpful in cases of large asymmetric
         * delays commonly experienced on deep space communication
         * links.
         */
        if (peer->t21_last > 0 && peer->t34_bytes > 0) {
                itemp = peer->t21_bytes - peer->t21_last;
                if (itemp > 25) {
                        etemp = t21 - peer->t21;
                        if (fabs(etemp) > 1e-6) {
                                ftemp = itemp / etemp;
                                if (ftemp > 1000.)
                                        peer->r21 = ftemp;
                        }
                }
                itemp = len - peer->t34_bytes;
                if (itemp > 25) {
                        etemp = -t34 - peer->t34;
                        if (fabs(etemp) > 1e-6) {
                                ftemp = itemp / etemp;
                                if (ftemp > 1000.)
                                        peer->r34 = ftemp;
                        }
                }
        }

        /*
         * The following section compensates for different data rates on
         * the outbound (d21) and inbound (t34) directions. To do this,
         * it finds t such that r21 * t - r34 * (d - t) = 0, where d is
         * the roundtrip delay. Then it calculates the correction as a
         * fraction of d.
         */
        peer->t21 = t21;
        peer->t21_last = peer->t21_bytes;
        peer->t34 = -t34;
        peer->t34_bytes = len;
#ifdef DEBUG
        if (debug > 1)
                printf("packet: t21 %.9lf %d t34 %.9lf %d\n", peer->t21,
                    peer->t21_bytes, peer->t34, peer->t34_bytes);
#endif
        if (peer->r21 > 0 && peer->r34 > 0 && p_del > 0) {
                if (peer->pmode != MODE_BROADCAST)
                        td = (peer->r34 / (peer->r21 + peer->r34) -
                            .5) * p_del;
                else
                        td = 0;

                /*
                 * Unfortunately, in many cases the errors are
                 * unacceptable, so for the present the rates are not
                 * used. In future, we might find conditions where the
                 * calculations are useful, so this should be considered
                 * a work in progress.
                 */
                t21 -= td;
                t34 -= td;
#ifdef DEBUG
                if (debug > 1)
                        printf("packet: del %.6lf r21 %.1lf r34 %.1lf %.6lf\n",
                            p_del, peer->r21 / 1e3, peer->r34 / 1e3,
                            td);
#endif
        } 
#endif /* ASSYM */

        /*
         * That was awesome. Now hand off to the clock filter.
         */
        clock_filter(peer, p_offset, p_del, p_disp);

        /*
         * If we are in broadcast calibrate mode, return to broadcast
         * client mode when the client is fit and the autokey dance is
         * complete.
         */
        if ((peer->cast_flags & MDF_BCLNT) && !(peer_unfit(peer) &
            TEST11)) {
#ifdef OPENSSL
                if (peer->flags & FLAG_SKEY) {
                        if (!(~peer->crypto & CRYPTO_FLAG_ALL))
                                peer->hmode = MODE_BCLIENT;
                } else {
                        peer->hmode = MODE_BCLIENT;
                }
#else /* OPENSSL */
                peer->hmode = MODE_BCLIENT;
#endif /* OPENSSL */
        }
}


/*
 * clock_update - Called at system process update intervals.
 */
static void
clock_update(
        struct peer *peer       /* peer structure pointer */
        )
{
        double  dtemp;
        l_fp    now;
#ifdef HAVE_LIBSCF_H
        char    *fmri;
#endif /* HAVE_LIBSCF_H */

        /*
         * Update the system state variables. We do this very carefully,
         * as the poll interval might need to be clamped differently.
         */
        sys_peer = peer;
        sys_epoch = peer->epoch;
        if (sys_poll < peer->minpoll)
                sys_poll = peer->minpoll;
        if (sys_poll > peer->maxpoll)
                sys_poll = peer->maxpoll;
        poll_update(peer, sys_poll);
        sys_stratum = min(peer->stratum + 1, STRATUM_UNSPEC);
        if (peer->stratum == STRATUM_REFCLOCK ||
            peer->stratum == STRATUM_UNSPEC)
                sys_refid = peer->refid;
        else
                sys_refid = addr2refid(&peer->srcadr);
        dtemp = sys_jitter + fabs(sys_offset) + peer->disp + clock_phi *
            (current_time - peer->update);
        sys_rootdisp = dtemp + peer->rootdisp;
        sys_rootdelay = peer->delay + peer->rootdelay;
        sys_reftime = peer->dst;

#ifdef DEBUG
        if (debug)
                printf(
                    "clock_update: at %lu sample %lu associd %d\n",
                    current_time, peer->epoch, peer->associd);
#endif

        /*
         * Comes now the moment of truth. Crank the clock discipline and
         * see what comes out.
         */
        switch (local_clock(peer, sys_offset)) {

        /*
         * Clock exceeds panic threshold. Life as we know it ends.
         */
        case -1:
#ifdef HAVE_LIBSCF_H
                /*
                 * For Solaris enter the maintenance mode.
                 */
                if ((fmri = getenv("SMF_FMRI")) != NULL) {
                        if (smf_maintain_instance(fmri, 0) < 0) {
                                printf("smf_maintain_instance: %s\n",
                                    scf_strerror(scf_error()));
                                exit(1);
                        }
                        /*
                         * Sleep until SMF kills us.
                         */
                        for (;;)
                                pause();
                }
#endif /* HAVE_LIBSCF_H */
                exit (-1);
                /* not reached */

        /*
         * Clock was stepped. Flush all time values of all peers.
         */
        case 2:
                clear_all();
                sys_leap = LEAP_NOTINSYNC;
                sys_stratum = STRATUM_UNSPEC;
                memcpy(&sys_refid, "STEP", 4);
                sys_rootdelay = 0;
                sys_rootdisp = 0;
                L_CLR(&sys_reftime);
                sys_jitter = LOGTOD(sys_precision);
                leapsec = 0;
                break;

        /*
         * Clock was slewed. Handle the leapsecond stuff.
         */
        case 1:

                /*
                 * If this is the first time the clock is set, reset the
                 * leap bits. If crypto, the timer will goose the setup
                 * process.
                 */
                if (sys_leap == LEAP_NOTINSYNC) {
                        sys_leap = LEAP_NOWARNING;
#ifdef OPENSSL
                        if (crypto_flags)
                                crypto_update();
#endif /* OPENSSL */
                }

                /*
                 * If the leapseconds values are from file or network
                 * and the leap is in the future, schedule a leap at the
                 * given epoch. Otherwise, if the number of survivor
                 * leap bits is greater than half the number of
                 * survivors, schedule a leap for the end of the current
                 * month.
                 */
                get_systime(&now);
                if (leap_sec > 0) {
                        if (leap_sec > now.l_ui) {
                                sys_tai = leap_tai - 1;
                                if (leapsec == 0)
                                        report_event(EVNT_ARMED, NULL,
                                            NULL);
                                leapsec = leap_sec - now.l_ui;
                        } else {
                                sys_tai = leap_tai;
                        }
                        break;

                } else if (leap_vote > sys_survivors / 2) {
                        leap_peers = now.l_ui + leap_month(now.l_ui);
                        if (leap_peers > now.l_ui) {
                                if (leapsec == 0)
                                        report_event(PEVNT_ARMED, peer,
                                            NULL);
                                leapsec = leap_peers - now.l_ui;
                        }
                } else if (leapsec > 0) {
                        report_event(EVNT_DISARMED, NULL, NULL);
                        leapsec = 0;
                }
                break;

        /*
         * Popcorn spike or step threshold exceeded. Pretend it never
         * happened.
         */
        default:
                break;
        }
}


/*
 * poll_update - update peer poll interval
 */
void
poll_update(
        struct peer *peer,      /* peer structure pointer */
        int     mpoll
        )
{
        int     hpoll, minpkt;
        u_long  next, utemp;

        /*
         * This routine figures out when the next poll should be sent.
         * That turns out to be wickedly complicated. One problem is
         * that sometimes the time for the next poll is in the past when
         * the poll interval is reduced. We watch out for races here
         * between the receive process and the poll process.
         *
         * First, bracket the poll interval according to the type of
         * association and options. If a fixed interval is configured,
         * use minpoll. This primarily is for reference clocks, but
         * works for any association. Otherwise, clamp the poll interval
         * between minpoll and maxpoll.
         */
        if (peer->cast_flags & MDF_BCLNT)
                hpoll = peer->minpoll;
        else
                hpoll = max(min(peer->maxpoll, mpoll), peer->minpoll);

#ifdef OPENSSL
        /*
         * If during the crypto protocol the poll interval has changed,
         * the lifetimes in the key list are probably bogus. Purge the
         * the key list and regenerate it later.
         */
        if ((peer->flags & FLAG_SKEY) && hpoll != peer->hpoll)
                key_expire(peer);
#endif /* OPENSSL */
        peer->hpoll = hpoll;

        /*
         * There are three variables important for poll scheduling, the
         * current time (current_time), next scheduled time (nextdate)
         * and the earliest time (utemp). The earliest time is 2 s
         * seconds, but could be more due to rate management. When
         * sending in a burst, use the earliest time. When not in a
         * burst but with a reply pending, send at the earliest time
         * unless the next scheduled time has not advanced. This can
         * only happen if multiple replies are peinding in the same
         * response interval. Otherwise, send at the later of the next
         * scheduled time and the earliest time.
         *
         * Now we figure out if there is an override. If a burst is in
         * progress and we get called from the receive process, just
         * slink away. If called from the poll process, delay 1 s for a
         * reference clock, otherwise 2 s.
         */
        minpkt = 1 << ntp_minpkt;
        utemp = current_time + max(peer->throttle - (NTP_SHIFT - 1) *
            (1 << peer->minpoll), minpkt);
        if (peer->burst > 0) {
                if (peer->nextdate > current_time)
                        return;
#ifdef REFCLOCK
                else if (peer->flags & FLAG_REFCLOCK)
                        peer->nextdate = current_time + RESP_DELAY;
#endif /* REFCLOCK */
                else
                        peer->nextdate = utemp;

#ifdef OPENSSL
        /*
         * If a burst is not in progress and a crypto response message
         * is pending, delay 2 s, but only if this is a new interval.
         */
        } else if (peer->cmmd != NULL) {
                if (peer->nextdate > current_time) {
                        if (peer->nextdate + minpkt != utemp)
                                peer->nextdate = utemp;
                } else {
                        peer->nextdate = utemp;
                }
#endif /* OPENSSL */

        /*
         * The ordinary case. If a retry, use minpoll; if unreachable,
         * use host poll; otherwise, use the minimum of host and peer
         * polls; In other words, oversampling is okay but
         * understampling is evil. Use the maximum of this value and the
         * headway. If the average headway is greater than the headway
         * threshold, increase the headway by the minimum interval.
         */
        } else {
                if (peer->retry > 0)
                        hpoll = peer->minpoll;
                else if (!(peer->reach))
                        hpoll = peer->hpoll;
                else
                        hpoll = min(peer->ppoll, peer->hpoll);
#ifdef REFCLOCK
                if (peer->flags & FLAG_REFCLOCK)
                        next = 1 << hpoll;
                else
                        next = ((0x1000UL | (ntp_random() & 0x0ff)) <<
                            hpoll) >> 12;
#else /* REFCLOCK */
                next = ((0x1000UL | (ntp_random() & 0x0ff)) << hpoll) >>
                    12;
#endif /* REFCLOCK */
                next += peer->outdate;
                if (next > utemp)
                        peer->nextdate = next;
                else
                        peer->nextdate = utemp;
                hpoll = peer->throttle - (1 << peer->minpoll);
                if (hpoll > 0)
                        peer->nextdate += minpkt;
        }
#ifdef DEBUG
        if (debug > 1)
                printf("poll_update: at %lu %s poll %d burst %d retry %d head %d early %lu next %lu\n",
                    current_time, ntoa(&peer->srcadr), peer->hpoll,
                    peer->burst, peer->retry, peer->throttle,
                    utemp - current_time, peer->nextdate -
                    current_time);
#endif
}


/*
 * peer_clear - clear peer filter registers.  See Section 3.4.8 of the
 * spec.
 */
void
peer_clear(
        struct peer *peer,              /* peer structure */
        char    *ident                  /* tally lights */
        )
{
        int     i;

#ifdef OPENSSL
        /*
         * If cryptographic credentials have been acquired, toss them to
         * Valhalla. Note that autokeys are ephemeral, in that they are
         * tossed immediately upon use. Therefore, the keylist can be
         * purged anytime without needing to preserve random keys. Note
         * that, if the peer is purged, the cryptographic variables are
         * purged, too. This makes it much harder to sneak in some
         * unauthenticated data in the clock filter.
         */
        key_expire(peer);
        if (peer->iffval != NULL)
                BN_free(peer->iffval);
        value_free(&peer->cookval);
        value_free(&peer->recval);
        value_free(&peer->encrypt);
        value_free(&peer->sndval);
        if (peer->cmmd != NULL)
                free(peer->cmmd);
        if (peer->subject != NULL)
                free(peer->subject);
        if (peer->issuer != NULL)
                free(peer->issuer);
#endif /* OPENSSL */

        /*
         * Clear all values, including the optional crypto values above.
         */
        memset(CLEAR_TO_ZERO(peer), 0, LEN_CLEAR_TO_ZERO);
        peer->ppoll = peer->maxpoll;
        peer->hpoll = peer->minpoll;
        peer->disp = MAXDISPERSE;
        peer->flash = peer_unfit(peer);
        peer->jitter = LOGTOD(sys_precision);

        /*
         * If interleave mode, initialize the alternate origin switch.
         */
        if (peer->flags & FLAG_XLEAVE)
                peer->flip = 1;
        for (i = 0; i < NTP_SHIFT; i++) {
                peer->filter_order[i] = i;
                peer->filter_disp[i] = MAXDISPERSE;
        }
#ifdef REFCLOCK
        if (!(peer->flags & FLAG_REFCLOCK)) {
                peer->leap = LEAP_NOTINSYNC;
                peer->stratum = STRATUM_UNSPEC;
                memcpy(&peer->refid, ident, 4);
        }
#else
        peer->leap = LEAP_NOTINSYNC;
        peer->stratum = STRATUM_UNSPEC;
        memcpy(&peer->refid, ident, 4);
#endif /* REFCLOCK */

        /*
         * During initialization use the association count to spread out
         * the polls at one-second intervals. Otherwise, randomize over
         * the minimum poll interval in order to avoid broadcast
         * implosion.
         */
        peer->nextdate = peer->update = peer->outdate = current_time;
        if (initializing) {
                peer->nextdate += peer_associations;
        } else if (peer->hmode == MODE_PASSIVE) {
                peer->nextdate += 1 << ntp_minpkt;
        } else {
                peer->nextdate += ntp_random() % peer_associations;
        }
#ifdef OPENSSL
        peer->refresh = current_time + (1 << NTP_REFRESH);
#endif /* OPENSSL */
#ifdef DEBUG
        if (debug)
                printf(
                    "peer_clear: at %ld next %ld associd %d refid %s\n",
                    current_time, peer->nextdate, peer->associd,
                    ident);
#endif
}


/*
 * clock_filter - add incoming clock sample to filter register and run
 *                the filter procedure to find the best sample.
 */
void
clock_filter(
        struct peer *peer,              /* peer structure pointer */
        double  sample_offset,          /* clock offset */
        double  sample_delay,           /* roundtrip delay */
        double  sample_disp             /* dispersion */
        )
{
        double  dst[NTP_SHIFT];         /* distance vector */
        int     ord[NTP_SHIFT];         /* index vector */
        int     i, j, k, m;
        double  dtemp, etemp;
        char    tbuf[80];

        /*
         * A sample consists of the offset, delay, dispersion and epoch
         * of arrival. The offset and delay are determined by the on-
         * wire protcol. The dispersion grows from the last outbound
         * packet to the arrival of this one increased by the sum of the
         * peer precision and the system precision as required by the
         * error budget. First, shift the new arrival into the shift
         * register discarding the oldest one.
         */
        j = peer->filter_nextpt;
        peer->filter_offset[j] = sample_offset;
        peer->filter_delay[j] = sample_delay;
        peer->filter_disp[j] = sample_disp;
        peer->filter_epoch[j] = current_time;
        j = (j + 1) % NTP_SHIFT;
        peer->filter_nextpt = j;

        /*
         * Update dispersions since the last update and at the same
         * time initialize the distance and index lists. Since samples
         * become increasingly uncorrelated beyond the Allan intercept,
         * only under exceptional cases will an older sample be used.
         * Therefore, the distance list uses a compound metric. If the
         * dispersion is greater than the maximum dispersion, clamp the
         * distance at that value. If the time since the last update is
         * less than the Allan intercept use the delay; otherwise, use
         * the sum of the delay and dispersion.
         */
        dtemp = clock_phi * (current_time - peer->update);
        peer->update = current_time;
        for (i = NTP_SHIFT - 1; i >= 0; i--) {
                if (i != 0)
                        peer->filter_disp[j] += dtemp;
                if (peer->filter_disp[j] >= MAXDISPERSE) { 
                        peer->filter_disp[j] = MAXDISPERSE;
                        dst[i] = MAXDISPERSE;
                } else if (peer->update - peer->filter_epoch[j] >
                    ULOGTOD(allan_xpt)) {
                        dst[i] = peer->filter_delay[j] +
                            peer->filter_disp[j];
                } else {
                        dst[i] = peer->filter_delay[j];
                }
                ord[i] = j;
                j = (j + 1) % NTP_SHIFT;
        }

        /*
         * If the clock discipline has stabilized, sort the samples by
         * distance.  
         */
        if (sys_leap != LEAP_NOTINSYNC) {
                for (i = 1; i < NTP_SHIFT; i++) {
                        for (j = 0; j < i; j++) {
                                if (dst[j] > dst[i]) {
                                        k = ord[j];
                                        ord[j] = ord[i];
                                        ord[i] = k;
                                        etemp = dst[j];
                                        dst[j] = dst[i];
                                        dst[i] = etemp;
                                }
                        }
                }
        }

        /*
         * Copy the index list to the association structure so ntpq
         * can see it later. Prune the distance list to leave only
         * samples less than the maximum dispersion, which disfavors
         * uncorrelated samples older than the Allan intercept. To
         * further improve the jitter estimate, of the remainder leave
         * only samples less than the maximum distance, but keep at
         * least two samples for jitter calculation.
         */
        m = 0;
        for (i = 0; i < NTP_SHIFT; i++) {
                peer->filter_order[i] = (u_char) ord[i];
                if (dst[i] >= MAXDISPERSE || (m >= 2 && dst[i] >=
                    sys_maxdist))
                        continue;
                m++;
        }
        
        /*
         * Compute the dispersion and jitter. The dispersion is weighted
         * exponentially by NTP_FWEIGHT (0.5) so it is normalized close
         * to 1.0. The jitter is the RMS differences relative to the
         * lowest delay sample.
         */
        peer->disp = peer->jitter = 0;
        k = ord[0];
        for (i = NTP_SHIFT - 1; i >= 0; i--) {
                j = ord[i];
                peer->disp = NTP_FWEIGHT * (peer->disp +
                    peer->filter_disp[j]);
                if (i < m)
                        peer->jitter += DIFF(peer->filter_offset[j],
                            peer->filter_offset[k]);
        }

        /*
         * If no acceptable samples remain in the shift register,
         * quietly tiptoe home leaving only the dispersion. Otherwise,
         * save the offset, delay and jitter. Note the jitter must not
         * be less than the precision.
         */
        if (m == 0)
                return;

        etemp = fabs(peer->offset - peer->filter_offset[k]);
        peer->offset = peer->filter_offset[k];
        peer->delay = peer->filter_delay[k];
        if (m > 1)
                peer->jitter /= m - 1;
        peer->jitter = max(SQRT(peer->jitter), LOGTOD(sys_precision));

        /*
         * If the the new sample and the current sample are both valid
         * and the difference between their offsets exceeds CLOCK_SGATE
         * (3) times the jitter and the interval between them is less
         * than twice the host poll interval, consider the new sample
         * a popcorn spike and ignore it.
         */
        if (peer->disp < sys_maxdist && peer->filter_disp[k] <
            sys_maxdist && etemp > CLOCK_SGATE * peer->jitter &&
            peer->filter_epoch[k] - peer->epoch < 2. *
            ULOGTOD(peer->hpoll)) {
                snprintf(tbuf, sizeof(tbuf), "%.6f s", etemp);
                report_event(PEVNT_POPCORN, peer, tbuf);
                return;
        }

        /*
         * A new minimum sample is useful only if it is later than the
         * last one used. In this design the maximum lifetime of any
         * sample is not greater than eight times the poll interval, so
         * the maximum interval between minimum samples is eight
         * packets.
         */
        if (peer->filter_epoch[k] <= peer->epoch) {
#if DEBUG
        if (debug)
                printf("clock_filter: old sample %lu\n", current_time -
                    peer->filter_epoch[k]);
#endif
                return;
        }
        peer->epoch = peer->filter_epoch[k];

        /*
         * The mitigated sample statistics are saved for later
         * processing. If not synchronized or not in a burst, tickle the
         * clock select algorithm.
         */
        record_peer_stats(&peer->srcadr, ctlpeerstatus(peer),
            peer->offset, peer->delay, peer->disp, peer->jitter);
#ifdef DEBUG
        if (debug)
                printf(
                    "clock_filter: n %d off %.6f del %.6f dsp %.6f jit %.6f\n",
                    m, peer->offset, peer->delay, peer->disp,
                    peer->jitter);
#endif
        if (peer->burst == 0 || sys_leap == LEAP_NOTINSYNC)
                clock_select();
}


/*
 * clock_select - find the pick-of-the-litter clock
 *
 * LOCKCLOCK: (1) If the local clock is the prefer peer, it will always
 * be enabled, even if declared falseticker, (2) only the prefer peer
 * caN Be selected as the system peer, (3) if the external source is
 * down, the system leap bits are set to 11 and the stratum set to
 * infinity.
 */
void
clock_select(void)
{
        struct peer *peer;
        int     i, j, k, n;
        int     nlist, nl3;
        int     allow, osurv;
        double  d, e, f, g;
        double  high, low;
        double  seljitter;
        double  synch[NTP_MAXASSOC], error[NTP_MAXASSOC];
        double  orphdist = 1e10;
        struct peer *osys_peer = NULL;
        struct peer *sys_prefer = NULL; /* prefer peer */
        struct peer *typesystem = NULL;
        struct peer *typeorphan = NULL;
#ifdef REFCLOCK
        struct peer *typeacts = NULL;
        struct peer *typelocal = NULL;
        struct peer *typepps = NULL;
#endif /* REFCLOCK */

        static int list_alloc = 0;
        static struct endpoint *endpoint = NULL;
        static int *indx = NULL;
        static struct peer **peer_list = NULL;
        static u_int endpoint_size = 0;
        static u_int indx_size = 0;
        static u_int peer_list_size = 0;

        /*
         * Initialize and create endpoint, index and peer lists big
         * enough to handle all associations.
         */
        osys_peer = sys_peer;
        osurv = sys_survivors;
        sys_survivors = 0;
#ifdef LOCKCLOCK
        sys_leap = LEAP_NOTINSYNC;
        sys_stratum = STRATUM_UNSPEC;
        memcpy(&sys_refid, "DOWN", 4);
#endif /* LOCKCLOCK */
        nlist = 0;
        for (n = 0; n < NTP_HASH_SIZE; n++)
                nlist += peer_hash_count[n];
        if (nlist > list_alloc) {
                if (list_alloc > 0) {
                        free(endpoint);
                        free(indx);
                        free(peer_list);
                }
                while (list_alloc < nlist) {
                        list_alloc += 5;
                        endpoint_size += 5 * 3 * sizeof(*endpoint);
                        indx_size += 5 * 3 * sizeof(*indx);
                        peer_list_size += 5 * sizeof(*peer_list);
                }
                endpoint = (struct endpoint *)emalloc(endpoint_size);
                indx = (int *)emalloc(indx_size);
                peer_list = (struct peer **)emalloc(peer_list_size);
        }

        /*
         * Initially, we populate the island with all the rifraff peers
         * that happen to be lying around. Those with seriously
         * defective clocks are immediately booted off the island. Then,
         * the falsetickers are culled and put to sea. The truechimers
         * remaining are subject to repeated rounds where the most
         * unpopular at each round is kicked off. When the population
         * has dwindled to sys_minclock, the survivors split a million
         * bucks and collectively crank the chimes.
         */
        nlist = nl3 = 0;        /* none yet */
        for (n = 0; n < NTP_HASH_SIZE; n++) {
                for (peer = peer_hash[n]; peer != NULL; peer =
                    peer->next) {
                        peer->flags &= ~FLAG_SYSPEER;
                        peer->status = CTL_PST_SEL_REJECT;

                        /*
                         * Leave the island immediately if the peer is
                         * unfit to synchronize.
                         */
                        if (peer_unfit(peer))
                                continue;

                        /*
                         * If this is an orphan, choose the one with
                         * the lowest metric defined as the IPv4 address
                         * or the first 64 bits of the hashed IPv6 address.
                         */
                        if (peer->stratum == sys_orphan) {
                                double  ftemp;

                                ftemp = addr2refid(&peer->srcadr);
                                if (ftemp < orphdist) {
                                        typeorphan = peer;
                                        orphdist = ftemp;
                                }
                                continue;
                        }
#ifdef REFCLOCK
                        /*
                         * The following are special cases. We deal
                         * with them later.
                         */
                        switch (peer->refclktype) { 
                        case REFCLK_LOCALCLOCK:
                                if (typelocal == NULL &&
                                    !(peer->flags & FLAG_PREFER))
                                        typelocal = peer;
                                continue;

                        case REFCLK_ACTS:
                                if (typeacts == NULL &&
                                    !(peer->flags & FLAG_PREFER))
                                        typeacts = peer;
                                continue;
                        }
#endif /* REFCLOCK */

                        /*
                         * If we get this far, the peer can stay on the
                         * island, but does not yet have the immunity
                         * idol.
                         */
                        peer->status = CTL_PST_SEL_SANE;
                        peer_list[nlist++] = peer;

                        /*
                         * Insert each interval endpoint on the sorted
                         * list.
                         */
                        e = peer->offset;        /* Upper end */
                        f = root_distance(peer);
                        e = e + f;
                        for (i = nl3 - 1; i >= 0; i--) {
                                if (e >= endpoint[indx[i]].val)
                                        break;

                                indx[i + 3] = indx[i];
                        }
                        indx[i + 3] = nl3;
                        endpoint[nl3].type = 1;
                        endpoint[nl3++].val = e;

                        e = e - f;              /* Center point */
                        for (; i >= 0; i--) {
                                if (e >= endpoint[indx[i]].val)
                                        break;

                                indx[i + 2] = indx[i];
                        }
                        indx[i + 2] = nl3;
                        endpoint[nl3].type = 0;
                        endpoint[nl3++].val = e;

                        e = e - f;              /* Lower end */
                        for (; i >= 0; i--) {
                                if (e >= endpoint[indx[i]].val)
                                        break;

                                indx[i + 1] = indx[i];
                        }
                        indx[i + 1] = nl3;
                        endpoint[nl3].type = -1;
                        endpoint[nl3++].val = e;
                }
        }
#ifdef DEBUG
        if (debug > 2)
                for (i = 0; i < nl3; i++)
                        printf("select: endpoint %2d %.6f\n",
                           endpoint[indx[i]].type,
                           endpoint[indx[i]].val);
#endif
        /*
         * This is the actual algorithm that cleaves the truechimers
         * from the falsetickers. The original algorithm was described
         * in Keith Marzullo's dissertation, but has been modified for
         * better accuracy.
         *
         * Briefly put, we first assume there are no falsetickers, then
         * scan the candidate list first from the low end upwards and
         * then from the high end downwards. The scans stop when the
         * number of intersections equals the number of candidates less
         * the number of falsetickers. If this doesn't happen for a
         * given number of falsetickers, we bump the number of
         * falsetickers and try again. If the number of falsetickers
         * becomes equal to or greater than half the number of
         * candidates, the Albanians have won the Byzantine wars and
         * correct synchronization is not possible.
         *
         * Here, nlist is the number of candidates and allow is the
         * number of falsetickers. Upon exit, the truechimers are the
         * susvivors with offsets not less than low and not greater than
         * high. There may be none of them.
         */
        low = 1e9;
        high = -1e9;
        for (allow = 0; 2 * allow < nlist; allow++) {
                int     found;

                /*
                 * Bound the interval (low, high) as the largest
                 * interval containing points from presumed truechimers.
                 */
                found = 0;
                n = 0;
                for (i = 0; i < nl3; i++) {
                        low = endpoint[indx[i]].val;
                        n -= endpoint[indx[i]].type;
                        if (n >= nlist - allow)
                                break;
                        if (endpoint[indx[i]].type == 0)
                                found++;
                }
                n = 0;
                for (j = nl3 - 1; j >= 0; j--) {
                        high = endpoint[indx[j]].val;
                        n += endpoint[indx[j]].type;
                        if (n >= nlist - allow)
                                break;
                        if (endpoint[indx[j]].type == 0)
                                found++;
                }

                /*
                 * If the number of candidates found outside the
                 * interval is greater than the number of falsetickers,
                 * then at least one truechimer is outside the interval,
                 * so go around again. This is what makes this algorithm
                 * different than Marzullo's.
                 */
                if (found > allow)
                        continue;

                /*
                 * If an interval containing truechimers is found, stop.
                 * If not, increase the number of falsetickers and go
                 * around again.
                 */
                if (high > low)
                        break;
        }

        /*
         * Clustering algorithm. Construct candidate list in order first
         * by stratum then by root distance, but keep only the best
         * NTP_MAXASSOC of them. Scan the list to find falsetickers, who
         * leave the island immediately. The TRUE peer is always a
         * truechimer. We must leave at least one peer to collect the
         * million bucks.
         */
        j = 0;
        for (i = 0; i < nlist; i++) {
                peer = peer_list[i];
                if (nlist > 1 && (peer->offset <= low || peer->offset >=
                    high) && !(peer->flags & FLAG_TRUE))
                        continue;

#ifdef REFCLOCK
                /*
                 * Elegible PPS peers must survive the intersection
                 * algorithm. Use the first one found, but don't
                 * include any of them in the cluster population.
                 */
                if (peer->flags & FLAG_PPS) {
                        if (typepps == NULL) 
                                typepps = peer;
                        continue;
                }
#endif /* REFCLOCK */

                /*
                 * The metric is the scaled root distance at the next
                 * poll interval plus the peer stratum.
                 */
                d = (root_distance(peer) + clock_phi * (peer->nextdate -
                    current_time)) / sys_maxdist + peer->stratum;
                if (j >= NTP_MAXASSOC) {
                        if (d >= synch[j - 1])
                                continue;
                        else
                                j--;
                }
                for (k = j; k > 0; k--) {
                        if (d >= synch[k - 1])
                                break;

                        peer_list[k] = peer_list[k - 1];
                        error[k] = error[k - 1];
                        synch[k] = synch[k - 1];
                }
                peer_list[k] = peer;
                error[k] = peer->jitter;
                synch[k] = d;
                j++;
        }
        nlist = j;

        /*
         * If no survivors remain at this point, check if the modem 
         * driver, local driver or orphan parent in that order. If so,
         * nominate the first one found as the only survivor.
         * Otherwise, give up and leave the island to the rats.
         */
        if (nlist == 0) {
                error[0] = 0;
                synch[0] = 0;
#ifdef REFCLOCK
                if (typeacts != NULL) {
                        peer_list[0] = typeacts;
                        nlist = 1;
                } else if (typelocal != NULL) {
                        peer_list[0] = typelocal;
                        nlist = 1;
                }
#endif /* REFCLOCK */
                if (typeorphan != NULL) {
                        peer_list[0] = typeorphan;
                        nlist = 1;
                }
        }

        /*
         * Mark the candidates at this point as truechimers.
         */
        for (i = 0; i < nlist; i++) {
                peer_list[i]->status = CTL_PST_SEL_SELCAND;
#ifdef DEBUG
                if (debug > 1)
                        printf("select: survivor %s %f\n",
                            stoa(&peer_list[i]->srcadr), synch[i]);
#endif
        }

        /*
         * Now, vote outlyers off the island by select jitter weighted
         * by root distance. Continue voting as long as there are more
         * than sys_minclock survivors and the minimum select jitter is
         * greater than the maximum peer jitter. Stop if we are about to
         * discard a TRUE or PREFER  peer, who of course has the
         * immunity idol.
         */
        seljitter = 0;
        while (1) {
                d = 1e9;
                e = -1e9;
                f = g = 0;
                k = 0;
                for (i = 0; i < nlist; i++) {
                        if (error[i] < d)
                                d = error[i];
                        f = 0;
                        if (nlist > 1) {
                                for (j = 0; j < nlist; j++)
                                        f += DIFF(peer_list[j]->offset,
                                            peer_list[i]->offset);
                                f = SQRT(f / (nlist - 1));
                        }
                        if (f * synch[i] > e) {
                                g = f;
                                e = f * synch[i];
                                k = i;
                        }
                }
                f = max(f, LOGTOD(sys_precision));
                if (nlist <= sys_minsane || nlist <= sys_minclock) {
                        break;

                } else if (f <= d || peer_list[k]->flags &
                    (FLAG_TRUE | FLAG_PREFER)) {
                        seljitter = f;
                        break;
                }
#ifdef DEBUG
                if (debug > 2)
                        printf(
                            "select: drop %s seljit %.6f jit %.6f\n",
                            ntoa(&peer_list[k]->srcadr), g, d);
#endif
                if (nlist > sys_maxclock)
                        peer_list[k]->status = CTL_PST_SEL_EXCESS;
                for (j = k + 1; j < nlist; j++) {
                        peer_list[j - 1] = peer_list[j];
                        synch[j - 1] = synch[j];
                        error[j - 1] = error[j];
                }
                nlist--;
        }

        /*
         * What remains is a list usually not greater than sys_minclock
         * peers. Note that the head of the list is the system peer at
         * the lowest stratum and that unsynchronized peers cannot
         * survive this far.
         *
         * While at it, count the number of leap warning bits found.
         * This will be used later to vote the system leap warning bit.
         * If a leap warning bit is found on a reference clock, the vote
         * is always won.
         */
        leap_vote = 0;
        for (i = 0; i < nlist; i++) {
                peer = peer_list[i];
                peer->unreach = 0;
                peer->status = CTL_PST_SEL_SYNCCAND;
                sys_survivors++;
                if (peer->leap == LEAP_ADDSECOND) {
                        if (peer->flags & FLAG_REFCLOCK)
                                leap_vote = nlist;
                        else 
                                leap_vote++;
                }
                if (peer->flags & FLAG_PREFER)
                        sys_prefer = peer;
        }

        /*
         * Unless there are at least sys_misane survivors, leave the
         * building dark. Otherwise, do a clockhop dance. Ordinarily,
         * use the first survivor on the survivor list. However, if the
         * last selection is not first on the list, use it as long as
         * it doesn't get too old or too ugly.
         */
        if (nlist > 0 && nlist >= sys_minsane) {
                double  x;

                typesystem = peer_list[0];
                if (osys_peer == NULL || osys_peer == typesystem) {
                        sys_clockhop = 0; 
                } else if ((x = fabs(typesystem->offset -
                    osys_peer->offset)) < sys_mindisp) {
                        if (sys_clockhop == 0)
                                sys_clockhop = sys_mindisp;
                        else
                                sys_clockhop *= .5;
#ifdef DEBUG
                        if (debug)
                                printf("select: clockhop %d %.6f %.6f\n",
                                    j, x, sys_clockhop);
#endif
                        if (fabs(x) < sys_clockhop)
                                typesystem = osys_peer;
                        else
                                sys_clockhop = 0;
                } else {
                        sys_clockhop = 0;
                }
        }

        /*
         * Mitigation rules of the game. We have the pick of the
         * litter in typesystem if any survivors are left. If
         * there is a prefer peer, use its offset and jitter.
         * Otherwise, use the combined offset and jitter of all kitters.
         */
        if (typesystem != NULL) {
                if (sys_prefer == NULL) {
                        typesystem->status = CTL_PST_SEL_SYSPEER;
                        clock_combine(peer_list, sys_survivors);
                        sys_jitter = SQRT(SQUARE(typesystem->jitter) +
                            SQUARE(sys_jitter) + SQUARE(seljitter));
                } else {
                        typesystem = sys_prefer;
                        sys_clockhop = 0;
                        typesystem->status = CTL_PST_SEL_SYSPEER;
                        sys_offset = typesystem->offset;
                        sys_jitter = typesystem->jitter;
                }
#ifdef DEBUG
                if (debug)
                        printf("select: combine offset %.9f jitter %.9f\n",
                            sys_offset, sys_jitter);
#endif
        }
#ifdef REFCLOCK
        /*
         * If a PPS driver is lit and the combined offset is less than
         * 0.4 s, select the driver as the PPS peer and use its offset
         * and jitter. However, if this is the atom driver, use it only
         * if there is a prefer peer or there are no survivors and none
         * are required.
         */
        if (typepps != NULL && fabs(sys_offset < 0.4) &&
            (typepps->refclktype != REFCLK_ATOM_PPS ||
            (typepps->refclktype == REFCLK_ATOM_PPS && (sys_prefer !=
            NULL || (typesystem == NULL && sys_minsane == 0))))) {
                typesystem = typepps;
                sys_clockhop = 0;
                typesystem->status = CTL_PST_SEL_PPS;
                sys_offset = typesystem->offset;
                sys_jitter = typesystem->jitter;
#ifdef DEBUG
                if (debug)
                        printf("select: pps offset %.9f jitter %.9f\n",
                            sys_offset, sys_jitter);
#endif
        }
#endif /* REFCLOCK */

        /*
         * If there are no survivors at this point, there is no
         * system peer. If so and this is an old update, keep the
         * current statistics, but do not update the clock.
         */
        if (typesystem == NULL) {
                if (osys_peer != NULL)
                        report_event(EVNT_NOPEER, NULL, NULL);
                sys_peer = NULL;                        
                return;
        }

        /*
         * Do not use old data, as this may mess up the clock discipline
         * stability.
         */
        if (typesystem->epoch <= sys_epoch)
                return;

        /*
         * We have found the alpha male. Wind the clock.
         */
        if (osys_peer != typesystem)
                report_event(PEVNT_NEWPEER, typesystem, NULL);
        typesystem->flags |= FLAG_SYSPEER;
        clock_update(typesystem);
}


/*
 * clock_combine - compute system offset and jitter from selected peers
 */
static void
clock_combine(
        struct peer **peers,    /* survivor list */
        int     npeers          /* number of survivors */
        )
{
        int     i;
        double  x, y, z, w;

        y = z = w = 0;
        for (i = 0; i < npeers; i++) {
                x = root_distance(peers[i]);
                y += 1. / x;
                z += peers[i]->offset / x;
                w += SQUARE(peers[i]->offset - peers[0]->offset) / x;
        }
        sys_offset = z / y;
        sys_jitter = SQRT(w / y);
}


/*
 * root_distance - compute synchronization distance from peer to root
 */
static double
root_distance(
        struct peer *peer       /* peer structure pointer */
        )
{
        double  dtemp;

        /*
         * Careful squeak here. The value returned must be greater than
         * the minimum root dispersion in order to avoid clockhop with
         * highly precise reference clocks. Note that the root distance
         * cannot exceed the sys_maxdist, as this is the cutoff by the
         * selection algorithm.
         */
        dtemp = (peer->delay + peer->rootdelay) / 2 + peer->disp +
            peer->rootdisp + clock_phi * (current_time - peer->update) +
            peer->jitter;
        if (dtemp < sys_mindisp)
                dtemp = sys_mindisp;
        return (dtemp);
}


/*
 * peer_xmit - send packet for persistent association.
 */
static void
peer_xmit(
        struct peer *peer       /* peer structure pointer */
        )
{
        struct pkt xpkt;        /* transmit packet */
        int     sendlen, authlen;
        keyid_t xkeyid = 0;     /* transmit key ID */
        l_fp    xmt_tx, xmt_ty;

        if (!peer->dstadr)      /* drop peers without interface */
                return;

        xpkt.li_vn_mode = PKT_LI_VN_MODE(sys_leap, peer->version,
            peer->hmode);
        xpkt.stratum = STRATUM_TO_PKT(sys_stratum);
        xpkt.ppoll = peer->hpoll;
        xpkt.precision = sys_precision;
        xpkt.refid = sys_refid;
        xpkt.rootdelay = HTONS_FP(DTOFP(sys_rootdelay));
        xpkt.rootdisp =  HTONS_FP(DTOUFP(sys_rootdisp));
        HTONL_FP(&sys_reftime, &xpkt.reftime);
        HTONL_FP(&peer->rec, &xpkt.org);
        HTONL_FP(&peer->dst, &xpkt.rec);

        /*
         * If the received packet contains a MAC, the transmitted packet
         * is authenticated and contains a MAC. If not, the transmitted
         * packet is not authenticated.
         *
         * It is most important when autokey is in use that the local
         * interface IP address be known before the first packet is
         * sent. Otherwise, it is not possible to compute a correct MAC
         * the recipient will accept. Thus, the I/O semantics have to do
         * a little more work. In particular, the wildcard interface
         * might not be usable.
         */
        sendlen = LEN_PKT_NOMAC;
#ifdef OPENSSL
        if (!(peer->flags & FLAG_SKEY) && peer->keyid == 0) {
#else
        if (peer->keyid == 0) {
#endif /* OPENSSL */

                /*
                 * Transmit a-priori timestamps
                 */
                get_systime(&xmt_tx);
                if (peer->flip == 0) {  /* basic mode */
                        peer->aorg = xmt_tx;
                        HTONL_FP(&xmt_tx, &xpkt.xmt);
                } else {                /* interleaved modes */
                        if (peer->hmode == MODE_BROADCAST) { /* bcst */
                                HTONL_FP(&xmt_tx, &xpkt.xmt);
                                if (peer->flip > 0)
                                        HTONL_FP(&peer->borg,
                                            &xpkt.org);
                                else
                                        HTONL_FP(&peer->aorg,
                                            &xpkt.org);
                        } else {        /* symmetric */
                                if (peer->flip > 0)
                                        HTONL_FP(&peer->borg,
                                            &xpkt.xmt);
                                else
                                        HTONL_FP(&peer->aorg,
                                            &xpkt.xmt);
                        }
                }
                peer->t21_bytes = sendlen;
                sendpkt(&peer->srcadr, peer->dstadr, sys_ttl[peer->ttl],
                    &xpkt, sendlen);
                peer->sent++;
                peer->throttle += (1 << peer->minpoll) - 2;

                /*
                 * Capture a-posteriori timestamps
                 */
                get_systime(&xmt_ty);
                if (peer->flip != 0) {          /* interleaved modes */
                        if (peer->flip > 0)
                                peer->aorg = xmt_ty;
                        else
                                peer->borg = xmt_ty;
                        peer->flip = -peer->flip;
                }
                L_SUB(&xmt_ty, &xmt_tx);
                LFPTOD(&xmt_ty, peer->xleave);
#ifdef DEBUG
                if (debug)
                        printf("transmit: at %ld %s->%s mode %d len %d\n",
                            current_time, peer->dstadr ?
                            stoa(&peer->dstadr->sin) : "-",
                            stoa(&peer->srcadr), peer->hmode, sendlen);
#endif
                return;
        }

        /*
         * Authentication is enabled, so the transmitted packet must be
         * authenticated. If autokey is enabled, fuss with the various
         * modes; otherwise, symmetric key cryptography is used.
         */
#ifdef OPENSSL
        if (peer->flags & FLAG_SKEY) {
                struct exten *exten;    /* extension field */

                /*
                 * The Public Key Dance (PKD): Cryptographic credentials
                 * are contained in extension fields, each including a
                 * 4-octet length/code word followed by a 4-octet
                 * association ID and optional additional data. Optional
                 * data includes a 4-octet data length field followed by
                 * the data itself. Request messages are sent from a
                 * configured association; response messages can be sent
                 * from a configured association or can take the fast
                 * path without ever matching an association. Response
                 * messages have the same code as the request, but have
                 * a response bit and possibly an error bit set. In this
                 * implementation, a message may contain no more than
                 * one command and one or more responses.
                 *
                 * Cryptographic session keys include both a public and
                 * a private componet. Request and response messages
                 * using extension fields are always sent with the
                 * private component set to zero. Packets without
                 * extension fields indlude the private component when
                 * the session key is generated.
                 */
                while (1) {
                
                        /*
                         * Allocate and initialize a keylist if not
                         * already done. Then, use the list in inverse
                         * order, discarding keys once used. Keep the
                         * latest key around until the next one, so
                         * clients can use client/server packets to
                         * compute propagation delay.
                         *
                         * Note that once a key is used from the list,
                         * it is retained in the key cache until the
                         * next key is used. This is to allow a client
                         * to retrieve the encrypted session key
                         * identifier to verify authenticity.
                         *
                         * If for some reason a key is no longer in the
                         * key cache, a birthday has happened or the key
                         * has expired, so the pseudo-random sequence is
                         * broken. In that case, purge the keylist and
                         * regenerate it.
                         */
                        if (peer->keynumber == 0)
                                make_keylist(peer, peer->dstadr);
                        else
                                peer->keynumber--;
                        xkeyid = peer->keylist[peer->keynumber];
                        if (authistrusted(xkeyid))
                                break;
                        else
                                key_expire(peer);
                }
                peer->keyid = xkeyid;
                exten = NULL;
                switch (peer->hmode) {

                /*
                 * In broadcast server mode the autokey values are
                 * required by the broadcast clients. Push them when a
                 * new keylist is generated; otherwise, push the
                 * association message so the client can request them at
                 * other times.
                 */
                case MODE_BROADCAST:
                        if (peer->flags & FLAG_ASSOC)
                                exten = crypto_args(peer, CRYPTO_AUTO |
                                    CRYPTO_RESP, peer->associd, NULL);
                        else
                                exten = crypto_args(peer, CRYPTO_ASSOC |
                                    CRYPTO_RESP, peer->associd, NULL);
                        break;

                /*
                 * In symmetric modes the parameter, certificate, 
                 * identity, cookie and autokey exchanges are
                 * required. The leapsecond exchange is optional. But, a
                 * peer will not believe the other peer until the other
                 * peer has synchronized, so the certificate exchange
                 * might loop until then. If a peer finds a broken
                 * autokey sequence, it uses the autokey exchange to
                 * retrieve the autokey values. In any case, if a new
                 * keylist is generated, the autokey values are pushed.
                 */
                case MODE_ACTIVE:
                case MODE_PASSIVE:

                        /*
                         * Parameter, certificate and identity.
                         */
                        if (!peer->crypto)
                                exten = crypto_args(peer, CRYPTO_ASSOC,
                                    peer->associd, sys_hostname);
                        else if (!(peer->crypto & CRYPTO_FLAG_CERT))
                                exten = crypto_args(peer, CRYPTO_CERT,
                                    peer->associd, peer->issuer);
                        else if (!(peer->crypto & CRYPTO_FLAG_VRFY))
                                exten = crypto_args(peer,
                                    crypto_ident(peer), peer->associd,
                                    NULL);

                        /*
                         * Cookie and autokey. We request the cookie
                         * only when the this peer and the other peer
                         * are synchronized. But, this peer needs the
                         * autokey values when the cookie is zero. Any
                         * time we regenerate the key list, we offer the
                         * autokey values without being asked. If for
                         * some reason either peer finds a broken
                         * autokey sequence, the autokey exchange is
                         * used to retrieve the autokey values.
                         */
                        else if (sys_leap != LEAP_NOTINSYNC &&
                            peer->leap != LEAP_NOTINSYNC &&
                            !(peer->crypto & CRYPTO_FLAG_COOK))
                                exten = crypto_args(peer, CRYPTO_COOK,
                                    peer->associd, NULL);
                        else if (!(peer->crypto & CRYPTO_FLAG_AUTO))
                                exten = crypto_args(peer, CRYPTO_AUTO,
                                    peer->associd, NULL);
                        else if (peer->flags & FLAG_ASSOC &&
                            peer->crypto & CRYPTO_FLAG_SIGN)
                                exten = crypto_args(peer, CRYPTO_AUTO |
                                    CRYPTO_RESP, peer->assoc, NULL);

                        /*
                         * Wait for clock sync, then sign the
                         * certificate and retrieve the leapsecond
                         * values.
                         */
                        else if (sys_leap == LEAP_NOTINSYNC)
                                break;

                        else if (!(peer->crypto & CRYPTO_FLAG_SIGN))
                                exten = crypto_args(peer, CRYPTO_SIGN,
                                    peer->associd, sys_hostname);
                        else if (!(peer->crypto & CRYPTO_FLAG_LEAP))
                                exten = crypto_args(peer, CRYPTO_LEAP,
                                    peer->associd, NULL);
                        break;

                /*
                 * In client mode the parameter, certificate, identity,
                 * cookie and sign exchanges are required. The
                 * leapsecond exchange is optional. If broadcast client
                 * mode the same exchanges are required, except that the
                 * autokey exchange is substitutes for the cookie
                 * exchange, since the cookie is always zero. If the
                 * broadcast client finds a broken autokey sequence, it
                 * uses the autokey exchange to retrieve the autokey
                 * values.
                 */
                case MODE_CLIENT:

                        /*
                         * Parameter, certificate and identity.
                         */
                        if (!peer->crypto)
                                exten = crypto_args(peer, CRYPTO_ASSOC,
                                    peer->associd, sys_hostname);
                        else if (!(peer->crypto & CRYPTO_FLAG_CERT))
                                exten = crypto_args(peer, CRYPTO_CERT,
                                    peer->associd, peer->issuer);
                        else if (!(peer->crypto & CRYPTO_FLAG_VRFY))
                                exten = crypto_args(peer,
                                    crypto_ident(peer), peer->associd,
                                    NULL);

                        /*
                         * Cookie and autokey. These are requests, but
                         * we use the peer association ID with autokey
                         * rather than our own.
                         */
                        else if (!(peer->crypto & CRYPTO_FLAG_COOK))
                                exten = crypto_args(peer, CRYPTO_COOK,
                                    peer->associd, NULL);
                        else if (!(peer->crypto & CRYPTO_FLAG_AUTO))
                                exten = crypto_args(peer, CRYPTO_AUTO,
                                    peer->assoc, NULL);

                        /*
                         * Wait for clock sync, then sign the
                         * certificate and retrieve the leapsecond
                         * values.
                         */
                        else if (sys_leap == LEAP_NOTINSYNC)
                                break;

                        else if (!(peer->crypto & CRYPTO_FLAG_SIGN))
                                exten = crypto_args(peer, CRYPTO_SIGN,
                                    peer->associd, sys_hostname);
                        else if (!(peer->crypto & CRYPTO_FLAG_LEAP))
                                exten = crypto_args(peer, CRYPTO_LEAP,
                                    peer->associd, NULL);
                        break;
                }

                /*
                 * Add a queued extension field if present. This is
                 * always a request message, so the reply ID is already
                 * in the message. If an error occurs, the error bit is
                 * lit in the response.
                 */
                if (peer->cmmd != NULL) {
                        u_int32 temp32;

                        temp32 = CRYPTO_RESP;
                        peer->cmmd->opcode |= htonl(temp32);
                        sendlen += crypto_xmit(peer, &xpkt, NULL,
                            sendlen, peer->cmmd, 0);
                        free(peer->cmmd);
                        peer->cmmd = NULL;
                }

                /*
                 * Add an extension field created above. All but the
                 * autokey response message are request messages.
                 */
                if (exten != NULL) {
                        if (exten->opcode != 0)
                                sendlen += crypto_xmit(peer, &xpkt,
                                    NULL, sendlen, exten, 0);
                        free(exten);
                }

                /*
                 * Calculate the next session key. Since extension
                 * fields are present, the cookie value is zero.
                 */
                if (sendlen > LEN_PKT_NOMAC) {
                        session_key(&peer->dstadr->sin, &peer->srcadr,
                            xkeyid, 0, 2);
                }
        } 
#endif /* OPENSSL */

        /*
         * Transmit a-priori timestamps
         */
        get_systime(&xmt_tx);
        if (peer->flip == 0) {          /* basic mode */
                peer->aorg = xmt_tx;
                HTONL_FP(&xmt_tx, &xpkt.xmt);
        } else {                        /* interleaved modes */
                if (peer->hmode == MODE_BROADCAST) { /* bcst */
                        HTONL_FP(&xmt_tx, &xpkt.xmt);
                        if (peer->flip > 0)
                                HTONL_FP(&peer->borg, &xpkt.org);
                        else
                                HTONL_FP(&peer->aorg, &xpkt.org);
                } else {                /* symmetric */
                        if (peer->flip > 0)
                                HTONL_FP(&peer->borg, &xpkt.xmt);
                        else
                                HTONL_FP(&peer->aorg, &xpkt.xmt);
                }
        }
        xkeyid = peer->keyid;
        authlen = authencrypt(xkeyid, (u_int32 *)&xpkt, sendlen);
        if (authlen == 0) {
                report_event(PEVNT_AUTH, peer, "no key");
                peer->flash |= TEST5;           /* auth error */
                peer->badauth++;
                return;
        }
        sendlen += authlen;
#ifdef OPENSSL
        if (xkeyid > NTP_MAXKEY)
                authtrust(xkeyid, 0);
#endif /* OPENSSL */
        if (sendlen > sizeof(xpkt)) {
                msyslog(LOG_ERR, "proto: buffer overflow %u", sendlen);
                exit (-1);
        }
        peer->t21_bytes = sendlen;
        sendpkt(&peer->srcadr, peer->dstadr, sys_ttl[peer->ttl], &xpkt,
            sendlen);
        peer->sent++;
        peer->throttle += (1 << peer->minpoll) - 2;

        /*
         * Capture a-posteriori timestamps
         */
        get_systime(&xmt_ty);
        if (peer->flip != 0) {                  /* interleaved modes */
                if (peer->flip > 0)
                        peer->aorg = xmt_ty;
                else
                        peer->borg = xmt_ty;
                peer->flip = -peer->flip;
        }
        L_SUB(&xmt_ty, &xmt_tx);
        LFPTOD(&xmt_ty, peer->xleave);
#ifdef OPENSSL
#ifdef DEBUG
        if (debug)
                printf("transmit: at %ld %s->%s mode %d keyid %08x len %d index %d\n",
                    current_time, peer->dstadr ?
                    ntoa(&peer->dstadr->sin) : "-",
                    ntoa(&peer->srcadr), peer->hmode, xkeyid, sendlen,
                    peer->keynumber);
#endif
#else /* OPENSSL */
#ifdef DEBUG
        if (debug)
                printf("transmit: at %ld %s->%s mode %d keyid %08x len %d\n",
                    current_time, peer->dstadr ?
                    ntoa(&peer->dstadr->sin) : "-",
                    ntoa(&peer->srcadr), peer->hmode, xkeyid, sendlen);
#endif
#endif /* OPENSSL */
}


/*
 * fast_xmit - Send packet for nonpersistent association. Note that
 * neither the source or destination can be a broadcast address.
 */
static void
fast_xmit(
        struct recvbuf *rbufp,  /* receive packet pointer */
        int     xmode,          /* receive mode */
        keyid_t xkeyid,         /* transmit key ID */
        int     flags           /* restrict mask */
        )
{
        struct pkt xpkt;        /* transmit packet structure */
        struct pkt *rpkt;       /* receive packet structure */
        l_fp    xmt_tx, xmt_ty;
        int     sendlen;
#ifdef OPENSSL
        u_int32 temp32;
#endif

        /*
         * Initialize transmit packet header fields from the receive
         * buffer provided. We leave the fields intact as received, but
         * set the peer poll at the maximum of the receive peer poll and
         * the system minimum poll (ntp_minpoll). This is for KoD rate
         * control and not strictly specification compliant, but doesn't
         * break anything.
         *
         * If the gazinta was from a multicast address, the gazoutta
         * must go out another way.
         */
        rpkt = &rbufp->recv_pkt;
        if (rbufp->dstadr->flags & INT_MCASTOPEN)
                rbufp->dstadr = findinterface(&rbufp->recv_srcadr);

        /*
         * If this is a kiss-o'-death (KoD) packet, show leap
         * unsynchronized, stratum zero, reference ID the four-character
         * kiss code and system root delay. Note we don't reveal the
         * local time, so these packets can't be used for
         * synchronization.
         */
        if (flags & RES_KOD) {
                sys_kodsent++;
                xpkt.li_vn_mode = PKT_LI_VN_MODE(LEAP_NOTINSYNC,
                    PKT_VERSION(rpkt->li_vn_mode), xmode);
                xpkt.stratum = STRATUM_PKT_UNSPEC;
                xpkt.ppoll = max(rpkt->ppoll, ntp_minpoll);
                memcpy(&xpkt.refid, "RATE", 4);
                xpkt.org = rpkt->xmt;
                xpkt.rec = rpkt->xmt;
                xpkt.xmt = rpkt->xmt;

        /*
         * This is a normal packet. Use the system variables.
         */
        } else {
                xpkt.li_vn_mode = PKT_LI_VN_MODE(sys_leap,
                    PKT_VERSION(rpkt->li_vn_mode), xmode);
                xpkt.stratum = STRATUM_TO_PKT(sys_stratum);
                xpkt.ppoll = max(rpkt->ppoll, ntp_minpoll);
                xpkt.precision = sys_precision;
                xpkt.refid = sys_refid;
                xpkt.rootdelay = HTONS_FP(DTOFP(sys_rootdelay));
                xpkt.rootdisp = HTONS_FP(DTOUFP(sys_rootdisp));
                HTONL_FP(&sys_reftime, &xpkt.reftime);
                xpkt.org = rpkt->xmt;
                HTONL_FP(&rbufp->recv_time, &xpkt.rec);
                get_systime(&xmt_tx);
                HTONL_FP(&xmt_tx, &xpkt.xmt);
        }

#ifdef HAVE_NTP_SIGND
        if (flags & RES_MSSNTP) {
                send_via_ntp_signd(rbufp, xmode, xkeyid, flags, &xpkt);
                return;
        }
#endif /* HAVE_NTP_SIGND */

        /*
         * If the received packet contains a MAC, the transmitted packet
         * is authenticated and contains a MAC. If not, the transmitted
         * packet is not authenticated.
         */
        sendlen = LEN_PKT_NOMAC;
        if (rbufp->recv_length == sendlen) {
                sendpkt(&rbufp->recv_srcadr, rbufp->dstadr, 0, &xpkt,
                    sendlen);
#ifdef DEBUG
                if (debug)
                        printf(
                            "transmit: at %ld %s->%s mode %d len %d\n",
                            current_time, stoa(&rbufp->dstadr->sin),
                            stoa(&rbufp->recv_srcadr), xmode, sendlen);
#endif
                return;
        }

        /*
         * The received packet contains a MAC, so the transmitted packet
         * must be authenticated. For symmetric key cryptography, use
         * the predefined and trusted symmetric keys to generate the
         * cryptosum. For autokey cryptography, use the server private
         * value to generate the cookie, which is unique for every
         * source-destination-key ID combination.
         */
#ifdef OPENSSL
        if (xkeyid > NTP_MAXKEY) {
                keyid_t cookie;

                /*
                 * The only way to get here is a reply to a legitimate
                 * client request message, so the mode must be
                 * MODE_SERVER. If an extension field is present, there
                 * can be only one and that must be a command. Do what
                 * needs, but with private value of zero so the poor
                 * jerk can decode it. If no extension field is present,
                 * use the cookie to generate the session key.
                 */
                cookie = session_key(&rbufp->recv_srcadr,
                    &rbufp->dstadr->sin, 0, sys_private, 0);
                if (rbufp->recv_length > sendlen + MAX_MAC_LEN) {
                        session_key(&rbufp->dstadr->sin,
                            &rbufp->recv_srcadr, xkeyid, 0, 2);
                        temp32 = CRYPTO_RESP;
                        rpkt->exten[0] |= htonl(temp32);
                        sendlen += crypto_xmit(NULL, &xpkt, rbufp,
                            sendlen, (struct exten *)rpkt->exten,
                            cookie);
                } else {
                        session_key(&rbufp->dstadr->sin,
                            &rbufp->recv_srcadr, xkeyid, cookie, 2);
                }
        }
#endif /* OPENSSL */
        get_systime(&xmt_tx);
        sendlen += authencrypt(xkeyid, (u_int32 *)&xpkt, sendlen);
#ifdef OPENSSL
        if (xkeyid > NTP_MAXKEY)
                authtrust(xkeyid, 0);
#endif /* OPENSSL */
        sendpkt(&rbufp->recv_srcadr, rbufp->dstadr, 0, &xpkt, sendlen);
        get_systime(&xmt_ty);
        L_SUB(&xmt_ty, &xmt_tx);
        sys_authdelay = xmt_ty;
#ifdef DEBUG
        if (debug)
                printf(
                    "transmit: at %ld %s->%s mode %d keyid %08x len %d\n",
                    current_time, ntoa(&rbufp->dstadr->sin),
                    ntoa(&rbufp->recv_srcadr), xmode, xkeyid, sendlen);
#endif
}


#ifdef OPENSSL
/*
 * key_expire - purge the key list
 */
void
key_expire(
        struct peer *peer       /* peer structure pointer */
        )
{
        int i;

        if (peer->keylist != NULL) {
                for (i = 0; i <= peer->keynumber; i++)
                        authtrust(peer->keylist[i], 0);
                free(peer->keylist);
                peer->keylist = NULL;
        }
        value_free(&peer->sndval);
        peer->keynumber = 0;
        peer->flags &= ~FLAG_ASSOC;
#ifdef DEBUG
        if (debug)
                printf("key_expire: at %lu associd %d\n", current_time,
                    peer->associd);
#endif
}
#endif /* OPENSSL */


/*
 * Determine if the peer is unfit for synchronization
 *
 * A peer is unfit for synchronization if
 * > TEST10 bad leap or stratum below floor or at or above ceiling
 * > TEST11 root distance exceeded for remote peer
 * > TEST12 a direct or indirect synchronization loop would form
 * > TEST13 unreachable or noselect
 */
int                             /* FALSE if fit, TRUE if unfit */
peer_unfit(
        struct peer *peer       /* peer structure pointer */
        )
{
        int     rval = 0;

        /*
         * A stratum error occurs if (1) the server has never been
         * synchronized, (2) the server stratum is below the floor or
         * greater than or equal to the ceiling.
         */
        if (peer->leap == LEAP_NOTINSYNC || peer->stratum < sys_floor ||
            peer->stratum >= sys_ceiling)
                rval |= TEST10;         /* bad synch or stratum */

        /*
         * A distance error for a remote peer occurs if the root
         * distance is greater than or equal to the distance threshold
         * plus the increment due to one host poll interval.
         */
        if (!(peer->flags & FLAG_REFCLOCK) && root_distance(peer) >=
            sys_maxdist + clock_phi * ULOGTOD(peer->hpoll))
                rval |= TEST11;         /* distance exceeded */

        /*
         * A loop error occurs if the remote peer is synchronized to the
         * local peer or if the remote peer is synchronized to the same
         * server as the local peer but only if the remote peer is
         * neither a reference clock nor an orphan.
         */
        if (peer->stratum > 1 && peer->refid != htonl(LOOPBACKADR) &&
            (peer->refid == (peer->dstadr ? peer->dstadr->addr_refid :
            0) || peer->refid == sys_refid))
                rval |= TEST12;         /* synchronization loop */

        /*
         * An unreachable error occurs if the server is unreachable or
         * the noselect bit is set.
         */
        if (!peer->reach || (peer->flags & FLAG_NOSELECT))
                rval |= TEST13;         /* unreachable */

        peer->flash &= ~PEER_TEST_MASK;
        peer->flash |= rval;
        return (rval);
}


/*
 * Find the precision of this particular machine
 */
#define MINSTEP 100e-9          /* minimum clock increment (s) */
#define MAXSTEP 20e-3           /* maximum clock increment (s) */
#define MINLOOPS 5              /* minimum number of step samples */

/*
 * This routine measures the system precision defined as the minimum of
 * a sequence of differences between successive readings of the system
 * clock. However, if a difference is less than MINSTEP, the clock has
 * been read more than once during a clock tick and the difference is
 * ignored. We set MINSTEP greater than zero in case something happens
 * like a cache miss.
 */
int
default_get_precision(void)
{
        l_fp    val;            /* current seconds fraction */
        l_fp    last;           /* last seconds fraction */
        l_fp    diff;           /* difference */
        double  tick;           /* computed tick value */
        double  dtemp;          /* scratch */
        int     i;              /* log2 precision */

        /*
         * Loop to find precision value in seconds.
         */
        tick = MAXSTEP;
        i = 0;
        get_systime(&last);
        while (1) {
                get_systime(&val);
                diff = val;
                L_SUB(&diff, &last);
                last = val;
                LFPTOD(&diff, dtemp);
                if (dtemp < MINSTEP)
                        continue;

                if (dtemp < tick)
                        tick = dtemp;
                if (++i >= MINLOOPS)
                        break;
        }
        sys_tick = tick;

        /*
         * Find the nearest power of two.
         */
        msyslog(LOG_NOTICE, "proto: precision = %.3f usec", tick * 1e6);
        for (i = 0; tick <= 1; i++)
                tick *= 2;
        if (tick - 1 > 1 - tick / 2)
                i--;
        return (-i);
}


/*
 * init_proto - initialize the protocol module's data
 */
void
init_proto(void)
{
        l_fp    dummy;
        int     i;

        /*
         * Fill in the sys_* stuff.  Default is don't listen to
         * broadcasting, require authentication.
         */
        sys_leap = LEAP_NOTINSYNC;
        sys_stratum = STRATUM_UNSPEC;
        memcpy(&sys_refid, "INIT", 4);
        sys_peer = NULL;
        sys_rootdelay = 0;
        sys_rootdisp = 0;
        L_CLR(&sys_reftime);
        sys_jitter = 0;
        sys_precision = (s_char)default_get_precision();
        get_systime(&dummy);
        sys_survivors = 0;
        sys_manycastserver = 0;
        sys_bclient = 0;
        sys_bdelay = 0;
        sys_authenticate = 1;
        sys_stattime = current_time;
        proto_clr_stats();
        for (i = 0; i < MAX_TTL; i++) {
                sys_ttl[i] = (u_char)((i * 256) / MAX_TTL);
                sys_ttlmax = i;
        }
        pps_enable = 0;
        stats_control = 1;
}


/*
 * proto_config - configure the protocol module
 */
void
proto_config(
        int     item,
        u_long  value,
        double  dvalue,
        sockaddr_u *svalue
        )
{
        /*
         * Figure out what he wants to change, then do it
         */
        DPRINTF(2, ("proto_config: code %d value %lu dvalue %lf\n",
                    item, value, dvalue));

        switch (item) {

        /*
         * enable and disable commands - arguments are Boolean.
         */
        case PROTO_AUTHENTICATE: /* authentication (auth) */
                sys_authenticate = value;
                break;

        case PROTO_BROADCLIENT: /* broadcast client (bclient) */
                sys_bclient = (int)value;
                if (sys_bclient == 0)
                        io_unsetbclient();
                else
                        io_setbclient();
                break;

#ifdef REFCLOCK
        case PROTO_CAL:         /* refclock calibrate (calibrate) */
                cal_enable = value;
                break;
#endif /* REFCLOCK */

        case PROTO_KERNEL:      /* kernel discipline (kernel) */
                kern_enable = value;
                break;

        case PROTO_MONITOR:     /* monitoring (monitor) */
                if (value)
                        mon_start(MON_ON);
                else
                        mon_stop(MON_ON);
                break;

        case PROTO_NTP:         /* NTP discipline (ntp) */
                ntp_enable = value;
                break;

        case PROTO_PPS:         /* PPS discipline (pps) */
                pps_enable = value;
                break;

        case PROTO_FILEGEN:     /* statistics (stats) */
                stats_control = value;
                break;

        /*
         * tos command - arguments are double, sometimes cast to int
         */
        case PROTO_BEACON:      /* manycast beacon (beacon) */
                sys_beacon = (int)dvalue;
                break;

        case PROTO_BROADDELAY:  /* default broadcast delay (bdelay) */
                sys_bdelay = dvalue;
                break;

        case PROTO_CEILING:     /* stratum ceiling (ceiling) */
                sys_ceiling = (int)dvalue;
                break;

        case PROTO_COHORT:      /* cohort switch (cohort) */
                sys_cohort = (int)dvalue;
                break;

        case PROTO_FLOOR:       /* stratum floor (floor) */
                sys_floor = (int)dvalue;
                break;

        case PROTO_MAXCLOCK:    /* maximum candidates (maxclock) */
                sys_maxclock = (int)dvalue;
                break;

        case PROTO_MAXDIST:     /* select threshold (maxdist) */
                sys_maxdist = dvalue;
                break;

        case PROTO_CALLDELAY:   /* modem call delay (mdelay) */
                break;          /* NOT USED */

        case PROTO_MINCLOCK:    /* minimum candidates (minclock) */
                sys_minclock = (int)dvalue;
                break;

        case PROTO_MINDISP:     /* minimum distance (mindist) */
                sys_mindisp = dvalue;
                break;

        case PROTO_MINSANE:     /* minimum survivors (minsane) */
                sys_minsane = (int)dvalue;
                break;

        case PROTO_ORPHAN:      /* orphan stratum (orphan) */
                sys_orphan = (int)dvalue;
                break;

        case PROTO_ADJ:         /* tick increment (tick) */
                sys_tick = dvalue;
                break;

        /*
         * Miscellaneous commands
         */
        case PROTO_MULTICAST_ADD: /* add group address */
                if (svalue != NULL)
                        io_multicast_add(svalue);
                sys_bclient = 1;
                break;

        case PROTO_MULTICAST_DEL: /* delete group address */
                if (svalue != NULL)
                        io_multicast_del(svalue);
                break;

        default:
                msyslog(LOG_NOTICE,
                    "proto: unsupported option %d", item);
        }
}


/*
 * proto_clr_stats - clear protocol stat counters
 */
void
proto_clr_stats(void)
{
        sys_stattime = current_time;
        sys_received = 0;
        sys_processed = 0;
        sys_newversion = 0;
        sys_oldversion = 0;
        sys_declined = 0;
        sys_restricted = 0;
        sys_badlength = 0;
        sys_badauth = 0;
        sys_limitrejected = 0;
}