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 <sys/types.h> 19 20 #include <openssl/evp.h> 21 #include <openssl/err.h> 22 23 #include <string.h> 24 25 #include "xmalloc.h" 26 #include "log.h" 27 #include "buffer.h" 28 #include "key.h" 29 #include "compat.h" 30 #include "ssh.h" 31 32 static int openssh_RSA_verify(int, u_char *, u_int, u_char *, u_int, RSA *); 33 34 /* RSASSA-PKCS1-v1_5 (PKCS #1 v2.0 signature) with SHA1 */ 35 int 36 ssh_rsa_sign(const Key *key, u_char **sigp, u_int *lenp, 37 const u_char *data, u_int datalen) 38 { 39 const EVP_MD *evp_md; 40 EVP_MD_CTX md; 41 u_char digest[EVP_MAX_MD_SIZE], *sig; 42 u_int slen, dlen, len; 43 int ok, nid; 44 Buffer b; 45 46 if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA && 47 key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) { 48 error("ssh_rsa_sign: no RSA key"); 49 return -1; 50 } 51 nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1; 52 if ((evp_md = EVP_get_digestbynid(nid)) == NULL) { 53 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid); 54 return -1; 55 } 56 EVP_DigestInit(&md, evp_md); 57 EVP_DigestUpdate(&md, data, datalen); 58 EVP_DigestFinal(&md, digest, &dlen); 59 60 slen = RSA_size(key->rsa); 61 sig = xmalloc(slen); 62 63 ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa); 64 memset(digest, 'd', sizeof(digest)); 65 66 if (ok != 1) { 67 int ecode = ERR_get_error(); 68 69 error("ssh_rsa_sign: RSA_sign failed: %s", 70 ERR_error_string(ecode, NULL)); 71 xfree(sig); 72 return -1; 73 } 74 if (len < slen) { 75 u_int diff = slen - len; 76 debug("slen %u > len %u", slen, len); 77 memmove(sig + diff, sig, len); 78 memset(sig, 0, diff); 79 } else if (len > slen) { 80 error("ssh_rsa_sign: slen %u slen2 %u", slen, len); 81 xfree(sig); 82 return -1; 83 } 84 /* encode signature */ 85 buffer_init(&b); 86 buffer_put_cstring(&b, "ssh-rsa"); 87 buffer_put_string(&b, sig, slen); 88 len = buffer_len(&b); 89 if (lenp != NULL) 90 *lenp = len; 91 if (sigp != NULL) { 92 *sigp = xmalloc(len); 93 memcpy(*sigp, buffer_ptr(&b), len); 94 } 95 buffer_free(&b); 96 memset(sig, 's', slen); 97 xfree(sig); 98 99 return 0; 100 } 101 102 int 103 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen, 104 const u_char *data, u_int datalen) 105 { 106 Buffer b; 107 const EVP_MD *evp_md; 108 EVP_MD_CTX md; 109 char *ktype; 110 u_char digest[EVP_MAX_MD_SIZE], *sigblob; 111 u_int len, dlen, modlen; 112 int rlen, ret, nid; 113 114 if (key == NULL || key->rsa == NULL || (key->type != KEY_RSA && 115 key->type != KEY_RSA_CERT && key->type != KEY_RSA_CERT_V00)) { 116 error("ssh_rsa_verify: no RSA key"); 117 return -1; 118 } 119 if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) { 120 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits", 121 BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE); 122 return -1; 123 } 124 buffer_init(&b); 125 buffer_append(&b, signature, signaturelen); 126 ktype = buffer_get_string(&b, NULL); 127 if (strcmp("ssh-rsa", ktype) != 0) { 128 error("ssh_rsa_verify: cannot handle type %s", ktype); 129 buffer_free(&b); 130 xfree(ktype); 131 return -1; 132 } 133 xfree(ktype); 134 sigblob = buffer_get_string(&b, &len); 135 rlen = buffer_len(&b); 136 buffer_free(&b); 137 if (rlen != 0) { 138 error("ssh_rsa_verify: remaining bytes in signature %d", rlen); 139 xfree(sigblob); 140 return -1; 141 } 142 /* RSA_verify expects a signature of RSA_size */ 143 modlen = RSA_size(key->rsa); 144 if (len > modlen) { 145 error("ssh_rsa_verify: len %u > modlen %u", len, modlen); 146 xfree(sigblob); 147 return -1; 148 } else if (len < modlen) { 149 u_int diff = modlen - len; 150 debug("ssh_rsa_verify: add padding: modlen %u > len %u", 151 modlen, len); 152 sigblob = xrealloc(sigblob, 1, modlen); 153 memmove(sigblob + diff, sigblob, len); 154 memset(sigblob, 0, diff); 155 len = modlen; 156 } 157 nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1; 158 if ((evp_md = EVP_get_digestbynid(nid)) == NULL) { 159 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid); 160 xfree(sigblob); 161 return -1; 162 } 163 EVP_DigestInit(&md, evp_md); 164 EVP_DigestUpdate(&md, data, datalen); 165 EVP_DigestFinal(&md, digest, &dlen); 166 167 ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa); 168 memset(digest, 'd', sizeof(digest)); 169 memset(sigblob, 's', len); 170 xfree(sigblob); 171 debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : ""); 172 return ret; 173 } 174 175 /* 176 * See: 177 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/ 178 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn 179 */ 180 /* 181 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) 182 * oiw(14) secsig(3) algorithms(2) 26 } 183 */ 184 static const u_char id_sha1[] = { 185 0x30, 0x21, /* type Sequence, length 0x21 (33) */ 186 0x30, 0x09, /* type Sequence, length 0x09 */ 187 0x06, 0x05, /* type OID, length 0x05 */ 188 0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */ 189 0x05, 0x00, /* NULL */ 190 0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */ 191 }; 192 /* 193 * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) 194 * rsadsi(113549) digestAlgorithm(2) 5 } 195 */ 196 static const u_char id_md5[] = { 197 0x30, 0x20, /* type Sequence, length 0x20 (32) */ 198 0x30, 0x0c, /* type Sequence, length 0x09 */ 199 0x06, 0x08, /* type OID, length 0x05 */ 200 0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */ 201 0x05, 0x00, /* NULL */ 202 0x04, 0x10 /* Octet string, length 0x10 (16), followed by md5 hash */ 203 }; 204 205 static int 206 openssh_RSA_verify(int type, u_char *hash, u_int hashlen, 207 u_char *sigbuf, u_int siglen, RSA *rsa) 208 { 209 u_int ret, rsasize, oidlen = 0, hlen = 0; 210 int len; 211 const u_char *oid = NULL; 212 u_char *decrypted = NULL; 213 214 ret = 0; 215 switch (type) { 216 case NID_sha1: 217 oid = id_sha1; 218 oidlen = sizeof(id_sha1); 219 hlen = 20; 220 break; 221 case NID_md5: 222 oid = id_md5; 223 oidlen = sizeof(id_md5); 224 hlen = 16; 225 break; 226 default: 227 goto done; 228 } 229 if (hashlen != hlen) { 230 error("bad hashlen"); 231 goto done; 232 } 233 rsasize = RSA_size(rsa); 234 if (siglen == 0 || siglen > rsasize) { 235 error("bad siglen"); 236 goto done; 237 } 238 decrypted = xmalloc(rsasize); 239 if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa, 240 RSA_PKCS1_PADDING)) < 0) { 241 error("RSA_public_decrypt failed: %s", 242 ERR_error_string(ERR_get_error(), NULL)); 243 goto done; 244 } 245 if (len < 0 || (u_int)len != hlen + oidlen) { 246 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen); 247 goto done; 248 } 249 if (memcmp(decrypted, oid, oidlen) != 0) { 250 error("oid mismatch"); 251 goto done; 252 } 253 if (memcmp(decrypted + oidlen, hash, hlen) != 0) { 254 error("hash mismatch"); 255 goto done; 256 } 257 ret = 1; 258 done: 259 if (decrypted) 260 xfree(decrypted); 261 return ret; 262 } 263