ssh-rsa.c

   1 /* $OpenBSD: ssh-rsa.c,v 1.41 2010/04/16 01:47:26 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 "ssh.h"
  34
  35 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *);
  36
  37 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */
  38 int
  39 ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp,
  40     const u_char *data, u_int datalen)
  41 {
  42         const EVP_MD *evp_md;
  43         EVP_MD_CTX md;
  44         u_char digest[EVP_MAX_MD_SIZE], *sig;
  45         u_int slen, dlen, len;
  46         int ok, nid;
  47         Buffer b;
  48
  49         if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA &&
  50             key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) {
  51                 error("ssh_rsa_sign: no RSA key");
  52                 return -1;
  53         }
  54         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
  55         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
  56                 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid);
  57                 return -1;
  58         }
  59         EVP_DigestInit(&md, evp_md);
  60         EVP_DigestUpdate(&md, data, datalen);
  61         EVP_DigestFinal(&md, digest, &dlen);
  62
  63         slen = RSA_size(key->rsa);
  64         sig = xmalloc(slen);
  65
  66         ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa);
  67         memset(digest, 'd', sizeof(digest));
  68
  69         if (ok != 1) {
  70                 int ecode = ERR_get_error();
  71
  72                 error("ssh_rsa_sign: RSA_sign failed: %s",
  73                     ERR_error_string(ecode, NULL));
  74                 xfree(sig);
  75                 return -1;
  76         }
  77         if (len < slen) {
  78                 u_int diff = slen - len;
  79                 debug("slen %u > len %u", slen, len);
  80                 memmove(sig + diff, sig, len);
  81                 memset(sig, 0, diff);
  82         } else if (len > slen) {
  83                 error("ssh_rsa_sign: slen %u slen2 %u", slen, len);
  84                 xfree(sig);
  85                 return -1;
  86         }
  87         /* encode signature */
  88         buffer_init(&b);
  89         buffer_put_cstring(&b, "ssh-rsa");
  90         buffer_put_string(&b, sig, slen);
  91         len = buffer_len(&b);
  92         if (lenp != NULL)
  93                 *lenp = len;
  94         if (sigp != NULL) {
  95                 *sigp = xmalloc(len);
  96                 memcpy(*sigp, buffer_ptr(&b), len);
  97         }
  98         buffer_free(&b);
  99         memset(sig, 's', slen);
 100         xfree(sig);
 101
 102         return 0;
 103 }
 104
 105 int
 106 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen,
 107     const u_char *data, u_int datalen)
 108 {
 109         Buffer b;
 110         const EVP_MD *evp_md;
 111         EVP_MD_CTX md;
 112         char *ktype;
 113         u_char digest[EVP_MAX_MD_SIZE], *sigblob;
 114         u_int len, dlen, modlen;
 115         int rlen, ret, nid;
 116
 117         if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA &&
 118             key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) {
 119                 error("ssh_rsa_verify: no RSA key");
 120                 return -1;
 121         }
 122         if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
 123                 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits",
 124                     BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
 125                 return -1;
 126         }
 127         buffer_init(&b);
 128         buffer_append(&b, signature, signaturelen);
 129         ktype = buffer_get_string(&b, NULL);
 130         if (strcmp("ssh-rsa", ktype) != 0) {
 131                 error("ssh_rsa_verify: cannot handle type %s", ktype);
 132                 buffer_free(&b);
 133                 xfree(ktype);
 134                 return -1;
 135         }
 136         xfree(ktype);
 137         sigblob = buffer_get_string(&b, &len);
 138         rlen = buffer_len(&b);
 139         buffer_free(&b);
 140         if (rlen != 0) {
 141                 error("ssh_rsa_verify: remaining bytes in signature %d", rlen);
 142                 xfree(sigblob);
 143                 return -1;
 144         }
 145         /* RSA_verify expects a signature of RSA_size */
 146         modlen = RSA_size(key->rsa);
 147         if (len > modlen) {
 148                 error("ssh_rsa_verify: len %u > modlen %u", len, modlen);
 149                 xfree(sigblob);
 150                 return -1;
 151         } else if (len < modlen) {
 152                 u_int diff = modlen - len;
 153                 debug("ssh_rsa_verify: add padding: modlen %u > len %u",
 154                     modlen, len);
 155                 sigblob = xrealloc(sigblob, 1, modlen);
 156                 memmove(sigblob + diff, sigblob, len);
 157                 memset(sigblob, 0, diff);
 158                 len = modlen;
 159         }
 160         nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1;
 161         if ((evp_md = EVP_get_digestbynid(nid)) == NULL) {
 162                 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid);
 163                 xfree(sigblob);
 164                 return -1;
 165         }
 166         EVP_DigestInit(&md, evp_md);
 167         EVP_DigestUpdate(&md, data, datalen);
 168         EVP_DigestFinal(&md, digest, &dlen);
 169
 170         ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa);
 171         memset(digest, 'd', sizeof(digest));
 172         memset(sigblob, 's', len);
 173         xfree(sigblob);
 174         debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : "");
 175         return ret;
 176 }
 177
 178 /*
 179  * See:
 180  * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/
 181  * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn
 182  */
 183 /*
 184  * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3)
 185  *      oiw(14) secsig(3) algorithms(2) 26 }
 186  */
 187 static const u_char id_sha1[] = {
 188         0x30, 0x21, /* type Sequence, length 0x21 (33) */
 189         0x30, 0x09, /* type Sequence, length 0x09 */
 190         0x06, 0x05, /* type OID, length 0x05 */
 191         0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */
 192         0x05, 0x00, /* NULL */
 193         0x04, 0x14  /* Octet string, length 0x14 (20), followed by sha1 hash */
 194 };
 195 /*
 196  * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840)
 197  *      rsadsi(113549) digestAlgorithm(2) 5 }
 198  */
 199 static const u_char id_md5[] = {
 200         0x30, 0x20, /* type Sequence, length 0x20 (32) */
 201         0x30, 0x0c, /* type Sequence, length 0x09 */
 202         0x06, 0x08, /* type OID, length 0x05 */
 203         0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */
 204         0x05, 0x00, /* NULL */
 205         0x04, 0x10  /* Octet string, length 0x10 (16), followed by md5 hash */
 206 };
 207
 208 static int
 209 openssh_RSA_verify(int type, u_char *hash, u_int hashlen,
 210     u_char *sigbuf, u_int siglen, RSA *rsa)
 211 {
 212         u_int ret, rsasize, oidlen = 0, hlen = 0;
 213         int len;
 214         const u_char *oid = NULL;
 215         u_char *decrypted = NULL;
 216
 217         ret = 0;
 218         switch (type) {
 219         case NID_sha1:
 220                 oid = id_sha1;
 221                 oidlen = sizeof(id_sha1);
 222                 hlen = 20;
 223                 break;
 224         case NID_md5:
 225                 oid = id_md5;
 226                 oidlen = sizeof(id_md5);
 227                 hlen = 16;
 228                 break;
 229         default:
 230                 goto done;
 231         }
 232         if (hashlen != hlen) {
 233                 error("bad hashlen");
 234                 goto done;
 235         }
 236         rsasize = RSA_size(rsa);
 237         if (siglen == 0 || siglen > rsasize) {
 238                 error("bad siglen");
 239                 goto done;
 240         }
 241         decrypted = xmalloc(rsasize);
 242         if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa,
 243             RSA_PKCS1_PADDING)) < 0) {
 244                 error("RSA_public_decrypt failed: %s",
 245                     ERR_error_string(ERR_get_error(), NULL));
 246                 goto done;
 247         }
 248         if (len < 0 || (u_int)len != hlen + oidlen) {
 249                 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen);
 250                 goto done;
 251         }
 252         if (memcmp(decrypted, oid, oidlen) != 0) {
 253                 error("oid mismatch");
 254                 goto done;
 255         }
 256         if (memcmp(decrypted + oidlen, hash, hlen) != 0) {
 257                 error("hash mismatch");
 258                 goto done;
 259         }
 260         ret = 1;
 261 done:
 262         if (decrypted)
 263                 xfree(decrypted);
 264         return ret;
 265 }