util/x509.lua

   1 -- Prosody IM
   2 -- Copyright (C) 2010 Matthew Wild
   3 -- Copyright (C) 2010 Paul Aurich
   4 --
   5 -- This project is MIT/X11 licensed. Please see the
   6 -- COPYING file in the source package for more information.
   7 --
   8
   9 -- TODO: I feel a fair amount of this logic should be integrated into Luasec,
  10 -- so that everyone isn't re-inventing the wheel.  Dependencies on
  11 -- IDN libraries complicate that.
  12
  13
  14 -- [TLS-CERTS] - http://tools.ietf.org/html/rfc6125
  15 -- [XMPP-CORE] - http://tools.ietf.org/html/rfc6120
  16 -- [SRV-ID]    - http://tools.ietf.org/html/rfc4985
  17 -- [IDNA]      - http://tools.ietf.org/html/rfc5890
  18 -- [LDAP]      - http://tools.ietf.org/html/rfc4519
  19 -- [PKIX]      - http://tools.ietf.org/html/rfc5280
  20
  21 local nameprep = require "util.encodings".stringprep.nameprep;
  22 local idna_to_ascii = require "util.encodings".idna.to_ascii;
  23 local idna_to_unicode = require "util.encodings".idna.to_unicode;
  24 local base64 = require "util.encodings".base64;
  25 local log = require "util.logger".init("x509");
  26 local mt = require "util.multitable";
  27 local s_format = string.format;
  28 local ipairs = ipairs;
  29
  30 local _ENV = nil;
  31 -- luacheck: std none
  32
  33 local oid_commonname = "2.5.4.3"; -- [LDAP] 2.3
  34 local oid_subjectaltname = "2.5.29.17"; -- [PKIX] 4.2.1.6
  35 local oid_xmppaddr = "1.3.6.1.5.5.7.8.5"; -- [XMPP-CORE]
  36 local oid_dnssrv   = "1.3.6.1.5.5.7.8.7"; -- [SRV-ID]
  37
  38 -- Compare a hostname (possibly international) with asserted names
  39 -- extracted from a certificate.
  40 -- This function follows the rules laid out in
  41 -- sections 6.4.1 and 6.4.2 of [TLS-CERTS]
  42 --
  43 -- A wildcard ("*") all by itself is allowed only as the left-most label
  44 local function compare_dnsname(host, asserted_names)
  45         -- TODO: Sufficient normalization?  Review relevant specs.
  46         local norm_host = idna_to_ascii(host)
  47         if norm_host == nil then
  48                 log("info", "Host %s failed IDNA ToASCII operation", host)
  49                 return false
  50         end
  51
  52         norm_host = norm_host:lower()
  53
  54         local host_chopped = norm_host:gsub("^[^.]+%.", "") -- everything after the first label
  55
  56         for i=1,#asserted_names do
  57                 local name = asserted_names[i]
  58                 if norm_host == name:lower() then
  59                         log("debug", "Cert dNSName %s matched hostname", name);
  60                         return true
  61                 end
  62
  63                 -- Allow the left most label to be a "*"
  64                 if name:match("^%*%.") then
  65                         local rest_name = name:gsub("^[^.]+%.", "")
  66                         if host_chopped == rest_name:lower() then
  67                                 log("debug", "Cert dNSName %s matched hostname", name);
  68                                 return true
  69                         end
  70                 end
  71         end
  72
  73         return false
  74 end
  75
  76 -- Compare an XMPP domain name with the asserted id-on-xmppAddr
  77 -- identities extracted from a certificate.  Both are UTF8 strings.
  78 --
  79 -- Per [XMPP-CORE], matches against asserted identities don't include
  80 -- wildcards, so we just do a normalize on both and then a string comparison
  81 --
  82 -- TODO: Support for full JIDs?
  83 local function compare_xmppaddr(host, asserted_names)
  84         local norm_host = nameprep(host)
  85
  86         for i=1,#asserted_names do
  87                 local name = asserted_names[i]
  88
  89                 -- We only want to match against bare domains right now, not
  90                 -- those crazy full-er JIDs.
  91                 if name:match("[@/]") then
  92                         log("debug", "Ignoring xmppAddr %s because it's not a bare domain", name)
  93                 else
  94                         local norm_name = nameprep(name)
  95                         if norm_name == nil then
  96                                 log("info", "Ignoring xmppAddr %s, failed nameprep!", name)
  97                         else
  98                                 if norm_host == norm_name then
  99                                         log("debug", "Cert xmppAddr %s matched hostname", name)
 100                                         return true
 101                                 end
 102                         end
 103                 end
 104         end
 105
 106         return false
 107 end
 108
 109 -- Compare a host + service against the asserted id-on-dnsSRV (SRV-ID)
 110 -- identities extracted from a certificate.
 111 --
 112 -- Per [SRV-ID], the asserted identities will be encoded in ASCII via ToASCII.
 113 -- Comparison is done case-insensitively, and a wildcard ("*") all by itself
 114 -- is allowed only as the left-most non-service label.
 115 local function compare_srvname(host, service, asserted_names)
 116         local norm_host = idna_to_ascii(host)
 117         if norm_host == nil then
 118                 log("info", "Host %s failed IDNA ToASCII operation", host);
 119                 return false
 120         end
 121
 122         -- Service names start with a "_"
 123         if service:match("^_") == nil then service = "_"..service end
 124
 125         norm_host = norm_host:lower();
 126         local host_chopped = norm_host:gsub("^[^.]+%.", "") -- everything after the first label
 127
 128         for i=1,#asserted_names do
 129                 local asserted_service, name = asserted_names[i]:match("^(_[^.]+)%.(.*)");
 130                 if service == asserted_service then
 131                         if norm_host == name:lower() then
 132                                 log("debug", "Cert SRVName %s matched hostname", name);
 133                                 return true;
 134                         end
 135
 136                         -- Allow the left most label to be a "*"
 137                         if name:match("^%*%.") then
 138                                 local rest_name = name:gsub("^[^.]+%.", "")
 139                                 if host_chopped == rest_name:lower() then
 140                                         log("debug", "Cert SRVName %s matched hostname", name)
 141                                         return true
 142                                 end
 143                         end
 144                         if norm_host == name:lower() then
 145                                 log("debug", "Cert SRVName %s matched hostname", name);
 146                                 return true
 147                         end
 148                 end
 149         end
 150
 151         return false
 152 end
 153
 154 local function verify_identity(host, service, cert)
 155         if cert.setencode then
 156                 cert:setencode("utf8");
 157         end
 158         local ext = cert:extensions()
 159         if ext[oid_subjectaltname] then
 160                 local sans = ext[oid_subjectaltname];
 161
 162                 -- Per [TLS-CERTS] 6.3, 6.4.4, "a client MUST NOT seek a match for a
 163                 -- reference identifier if the presented identifiers include a DNS-ID
 164                 -- SRV-ID, URI-ID, or any application-specific identifier types"
 165                 local had_supported_altnames = false
 166
 167                 if sans[oid_xmppaddr] then
 168                         had_supported_altnames = true
 169                         if service == "_xmpp-client" or service == "_xmpp-server" then
 170                                 if compare_xmppaddr(host, sans[oid_xmppaddr]) then return true end
 171                         end
 172                 end
 173
 174                 if sans[oid_dnssrv] then
 175                         had_supported_altnames = true
 176                         -- Only check srvNames if the caller specified a service
 177                         if service and compare_srvname(host, service, sans[oid_dnssrv]) then return true end
 178                 end
 179
 180                 if sans["dNSName"] then
 181                         had_supported_altnames = true
 182                         if compare_dnsname(host, sans["dNSName"]) then return true end
 183                 end
 184
 185                 -- We don't need URIs, but [TLS-CERTS] is clear.
 186                 if sans["uniformResourceIdentifier"] then
 187                         had_supported_altnames = true
 188                 end
 189
 190                 if had_supported_altnames then return false end
 191         end
 192
 193         -- Extract a common name from the certificate, and check it as if it were
 194         -- a dNSName subjectAltName (wildcards may apply for, and receive,
 195         -- cat treats)
 196         --
 197         -- Per [TLS-CERTS] 1.8, a CN-ID is the Common Name from a cert subject
 198         -- which has one and only one Common Name
 199         local subject = cert:subject()
 200         local cn = nil
 201         for i=1,#subject do
 202                 local dn = subject[i]
 203                 if dn["oid"] == oid_commonname then
 204                         if cn then
 205                                 log("info", "Certificate has multiple common names")
 206                                 return false
 207                         end
 208
 209                         cn = dn["value"];
 210                 end
 211         end
 212
 213         if cn then
 214                 -- Per [TLS-CERTS] 6.4.4, follow the comparison rules for dNSName SANs.
 215                 return compare_dnsname(host, { cn })
 216         end
 217
 218         -- If all else fails, well, why should we be any different?
 219         return false
 220 end
 221
 222 -- TODO Support other SANs
 223 local function get_identities(cert) --> map of names to sets of services
 224         if cert.setencode then
 225                 cert:setencode("utf8");
 226         end
 227
 228         local names = mt.new();
 229
 230         local ext = cert:extensions();
 231         local sans = ext[oid_subjectaltname];
 232         if sans then
 233                 if sans["dNSName"] then -- Valid for any service
 234                         for _, name in ipairs(sans["dNSName"]) do
 235                                 name = idna_to_unicode(nameprep(name));
 236                                 if name then
 237                                         names:set(name, "*", true);
 238                                 end
 239                         end
 240                 end
 241                 if sans[oid_xmppaddr] then
 242                         for _, name in ipairs(sans[oid_xmppaddr]) do
 243                                 name = nameprep(name);
 244                                 if name then
 245                                         names:set(name, "xmpp-client", true);
 246                                         names:set(name, "xmpp-server", true);
 247                                 end
 248                         end
 249                 end
 250                 if sans[oid_dnssrv] then
 251                         for _, srvname in ipairs(sans[oid_dnssrv]) do
 252                                 local srv, name = srvname:match("^_([^.]+)%.(.*)");
 253                                 if srv then
 254                                         name = nameprep(name);
 255                                         if name then
 256                                                 names:set(name, srv, true);
 257                                         end
 258                                 end
 259                         end
 260                 end
 261         end
 262
 263         local subject = cert:subject();
 264         for i = 1, #subject do
 265                 local dn = subject[i];
 266                 if dn.oid == oid_commonname then
 267                         local name = nameprep(dn.value);
 268                         if name and idna_to_ascii(name) then
 269                                 names:set("*", name, true);
 270                         end
 271                 end
 272         end
 273         return names.data;
 274 end
 275
 276 local pat = "%-%-%-%-%-BEGIN ([A-Z ]+)%-%-%-%-%-\r?\n"..
 277 "([0-9A-Za-z+/=\r\n]*)\r?\n%-%-%-%-%-END %1%-%-%-%-%-";
 278
 279 local function pem2der(pem)
 280         local typ, data = pem:match(pat);
 281         if typ and data then
 282                 return base64.decode(data), typ;
 283         end
 284 end
 285
 286 local wrap = ('.'):rep(64);
 287 local envelope = "-----BEGIN %s-----\n%s\n-----END %s-----\n"
 288
 289 local function der2pem(data, typ)
 290         typ = typ and typ:upper() or "CERTIFICATE";
 291         data = base64.encode(data);
 292         return s_format(envelope, typ, data:gsub(wrap, '%0\n', (#data-1)/64), typ);
 293 end
 294
 295 return {
 296         verify_identity = verify_identity;
 297         get_identities = get_identities;
 298         pem2der = pem2der;
 299         der2pem = der2pem;
 300 };