ssh-rsa.c

   1 /* $OpenBSD: ssh-rsa.c,v 1.45 2010/08/31 09:58:37 djm Exp $ */
   2 /*
   3  * Copyright (c) 2000, 2003 Markus Friedl <markus@openbsd.org>
   4  *
   5  * Permission to use, copy, modify, and distribute this software for any
   6  * purpose with or without fee is hereby granted, provided that the above
   7  * copyright notice and this permission notice appear in all copies.
   8  *
   9  * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
  10  * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
  11  * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
  12  * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
  13  * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
  14  * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
  15  * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
  16  */
  17
  18 #include "includes.h"
  19
  20 #include <sys/types.h>
  21
  22 #include <openssl/evp.h>
  23 #include <openssl/err.h>
  24
  25 #include <stdarg.h>
  26 #include <string.h>
  27
  28 #include "xmalloc.h"
  29 #include "log.h"
  30 #include "buffer.h"
  31 #include "key.h"
  32 #include "compat.h"
  33 #include "misc.h"
  34 #include "ssh.h"
  35
  36 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
  37
  38 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
  39 int
  40 ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
  41     const u_char *data, u_int datalen)
  42 {
  43         const EVP_MD *evp_md;
  44         EVP_MD_CTX md;
  45         u_char digest[EVP_MAX_MD_SIZE], *sig;
  46         u_int slen, dlen, len;
  47         int ok, nid;
  48         Buffer b;
  49
  50         if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA &&
  51             key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) {
  52                 error("ssh_rsa_sign: no RSA key");
  53                 return -1;
  54         }
  55         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
  56         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
  57                 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
  58                 return -1;
  59         }
  60         EVP_DigestInit(&md, evp_md);
  61         EVP_DigestUpdate(&md, data, datalen);
  62         EVP_DigestFinal(&md, digest, &dlen);
  63
  64         slen = RSA_size(key->rsa);
  65         sig = xmalloc(slen);
  66
  67         ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
  68         memset(digest, 'd', sizeof(digest));
  69
  70         if (ok != 1) {
  71                 int ecode = ERR_get_error();
  72
  73                 error("ssh_rsa_sign: RSA_sign failed: %s",
  74                     ERR_error_string(ecode, NULL));
  75                 xfree(sig);
  76                 return -1;
  77         }
  78         if (len < slen) {
  79                 u_int diff = slen - len;
  80                 debug("slen %u > len %u", slen, len);
  81                 memmove(sig + diff, sig, len);
  82                 memset(sig, 0, diff);
  83         } else if (len > slen) {
  84                 error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
  85                 xfree(sig);
  86                 return -1;
  87         }
  88         /* encode signature */
  89         buffer_init(&b);
  90         buffer_put_cstring(&b, "ssh-rsa");
  91         buffer_put_string(&b, sig, slen);
  92         len = buffer_len(&b);
  93         if (lenp != NULL)
  94                 *lenp = len;
  95         if (sigp != NULL) {
  96                 *sigp = xmalloc(len);
  97                 memcpy(*sigp, buffer_ptr(&b), len);
  98         }
  99         buffer_free(&b);
 100         memset(sig, 's', slen);
 101         xfree(sig);
 102
 103         return 0;
 104 }
 105
 106 int
 107 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
 108     const u_char *data, u_int datalen)
 109 {
 110         Buffer b;
 111         const EVP_MD *evp_md;
 112         EVP_MD_CTX md;
 113         char *ktype;
 114         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 115         u_int len, dlen, modlen;
 116         int rlen, ret, nid;
 117
 118         if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA &&
 119             key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) {
 120                 error("ssh_rsa_verify: no RSA key");
 121                 return -1;
 122         }
 123         if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
 124                 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
 125                     BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
 126                 return -1;
 127         }
 128         buffer_init(&b);
 129         buffer_append(&b, signature, signaturelen);
 130         ktype = buffer_get_cstring(&b, NULL);
 131         if (strcmp("ssh-rsa", ktype) != 0) {
 132                 error("ssh_rsa_verify: cannot handle type %s", ktype);
 133                 buffer_free(&b);
 134                 xfree(ktype);
 135                 return -1;
 136         }
 137         xfree(ktype);
 138         sigblob = buffer_get_string(&b, &len);
 139         rlen = buffer_len(&b);
 140         buffer_free(&b);
 141         if (rlen != 0) {
 142                 error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
 143                 xfree(sigblob);
 144                 return -1;
 145         }
 146         /* RSA_verify expects a signature of RSA_size */
 147         modlen = RSA_size(key->rsa);
 148         if (len > modlen) {
 149                 error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
 150                 xfree(sigblob);
 151                 return -1;
 152         } else if (len < modlen) {
 153                 u_int diff = modlen - len;
 154                 debug("ssh_rsa_verify: add padding: modlen %u > len %u",
 155                     modlen, len);
 156                 sigblob = xrealloc(sigblob, 1, modlen);
 157                 memmove(sigblob + diff, sigblob, len);
 158                 memset(sigblob, 0, diff);
 159                 len = modlen;
 160         }
 161         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
 162         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
 163                 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
 164                 xfree(sigblob);
 165                 return -1;
 166         }
 167         EVP_DigestInit(&md, evp_md);
 168         EVP_DigestUpdate(&md, data, datalen);
 169         EVP_DigestFinal(&md, digest, &dlen);
 170
 171         ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
 172         memset(digest, 'd', sizeof(digest));
 173         memset(sigblob, 's', len);
 174         xfree(sigblob);
 175         debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
 176         return ret;
 177 }
 178
 179 /*
 180  * See:
 181  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 182  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 183  */
 184 /*
 185  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 186  *      oiw(14) secsig(3) algorithms(2) 26 }
 187  */
 188 static const u_char id_sha1[] = {
 189         0x30, 0x21, /* type Sequence, length 0x21 (33) */
 190         0x30, 0x09, /* type Sequence, length 0x09 */
 191         0x06, 0x05, /* type OID, length 0x05 */
 192         0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
 193         0x05, 0x00, /* NULL */
 194         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 195 };
 196 /*
 197  * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
 198  *      rsadsi(113549) digestAlgorithm(2) 5 }
 199  */
 200 static const u_char id_md5[] = {
 201         0x30, 0x20, /* type Sequence, length 0x20 (32) */
 202         0x30, 0x0c, /* type Sequence, length 0x09 */
 203         0x06, 0x08, /* type OID, length 0x05 */
 204         0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
 205         0x05, 0x00, /* NULL */
 206         0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
 207 };
 208
 209 static int
 210 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
 211     u_char *sigbuf, u_int siglen, RSA *rsa)
 212 {
 213         u_int ret, rsasize, oidlen = 0, hlen = 0;
 214         int len, oidmatch, hashmatch;
 215         const u_char *oid = NULL;
 216         u_char *decrypted = NULL;
 217
 218         ret = 0;
 219         switch (type) {
 220         case NID_sha1:
 221                 oid = id_sha1;
 222                 oidlen = sizeof(id_sha1);
 223                 hlen = 20;
 224                 break;
 225         case NID_md5:
 226                 oid = id_md5;
 227                 oidlen = sizeof(id_md5);
 228                 hlen = 16;
 229                 break;
 230         default:
 231                 goto done;
 232         }
 233         if (hashlen != hlen) {
 234                 error("bad hashlen");
 235                 goto done;
 236         }
 237         rsasize = RSA_size(rsa);
 238         if (siglen == 0 || siglen > rsasize) {
 239                 error("bad siglen");
 240                 goto done;
 241         }
 242         decrypted = xmalloc(rsasize);
 243         if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
 244             RSA_PKCS1_PADDING)) < 0) {
 245                 error("RSA_public_decrypt failed: %s",
 246                     ERR_error_string(ERR_get_error(), NULL));
 247                 goto done;
 248         }
 249         if (len < 0 || (u_int)len != hlen + oidlen) {
 250                 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
 251                 goto done;
 252         }
 253         oidmatch = timingsafe_bcmp(decrypted, oid, oidlen) == 0;
 254         hashmatch = timingsafe_bcmp(decrypted + oidlen, hash, hlen) == 0;
 255         if (!oidmatch) {
 256                 error("oid mismatch");
 257                 goto done;
 258         }
 259         if (!hashmatch) {
 260                 error("hash mismatch");
 261                 goto done;
 262         }
 263         ret = 1;
 264 done:
 265         if (decrypted)
 266                 xfree(decrypted);
 267         return ret;
 268 }