1 /* $OpenBSD: ssh-rsa.c,v 1.39 2006/08/03 03:34:42 deraadt 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->type != KEY_RSA || key->rsa == NULL) { 47 error("ssh_rsa_sign: no RSA key"); 48 return -1; 49 } 50 nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1; 51 if ((evp_md = EVP_get_digestbynid(nid)) == NULL) { 52 error("ssh_rsa_sign: EVP_get_digestbynid %d failed", nid); 53 return -1; 54 } 55 EVP_DigestInit(&md, evp_md); 56 EVP_DigestUpdate(&md, data, datalen); 57 EVP_DigestFinal(&md, digest, &dlen); 58 59 slen = RSA_size(key->rsa); 60 sig = xmalloc(slen); 61 62 ok = RSA_sign(nid, digest, dlen, sig, &len, key->rsa); 63 memset(digest, 'd', sizeof(digest)); 64 65 if (ok != 1) { 66 int ecode = ERR_get_error(); 67 68 error("ssh_rsa_sign: RSA_sign failed: %s", 69 ERR_error_string(ecode, NULL)); 70 xfree(sig); 71 return -1; 72 } 73 if (len < slen) { 74 u_int diff = slen - len; 75 debug("slen %u > len %u", slen, len); 76 memmove(sig + diff, sig, len); 77 memset(sig, 0, diff); 78 } else if (len > slen) { 79 error("ssh_rsa_sign: slen %u slen2 %u", slen, len); 80 xfree(sig); 81 return -1; 82 } 83 /* encode signature */ 84 buffer_init(&b); 85 buffer_put_cstring(&b, "ssh-rsa"); 86 buffer_put_string(&b, sig, slen); 87 len = buffer_len(&b); 88 if (lenp != NULL) 89 *lenp = len; 90 if (sigp != NULL) { 91 *sigp = xmalloc(len); 92 memcpy(*sigp, buffer_ptr(&b), len); 93 } 94 buffer_free(&b); 95 memset(sig, 's', slen); 96 xfree(sig); 97 98 return 0; 99 } 100 101 int 102 ssh_rsa_verify(const Key *key, const u_char *signature, u_int signaturelen, 103 const u_char *data, u_int datalen) 104 { 105 Buffer b; 106 const EVP_MD *evp_md; 107 EVP_MD_CTX md; 108 char *ktype; 109 u_char digest[EVP_MAX_MD_SIZE], *sigblob; 110 u_int len, dlen, modlen; 111 int rlen, ret, nid; 112 113 if (key == NULL || key->type != KEY_RSA || key->rsa == NULL) { 114 error("ssh_rsa_verify: no RSA key"); 115 return -1; 116 } 117 if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) { 118 error("ssh_rsa_verify: RSA modulus too small: %d < minimum %d bits", 119 BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE); 120 return -1; 121 } 122 buffer_init(&b); 123 buffer_append(&b, signature, signaturelen); 124 ktype = buffer_get_string(&b, NULL); 125 if (strcmp("ssh-rsa", ktype) != 0) { 126 error("ssh_rsa_verify: cannot handle type %s", ktype); 127 buffer_free(&b); 128 xfree(ktype); 129 return -1; 130 } 131 xfree(ktype); 132 sigblob = buffer_get_string(&b, &len); 133 rlen = buffer_len(&b); 134 buffer_free(&b); 135 if (rlen != 0) { 136 error("ssh_rsa_verify: remaining bytes in signature %d", rlen); 137 xfree(sigblob); 138 return -1; 139 } 140 /* RSA_verify expects a signature of RSA_size */ 141 modlen = RSA_size(key->rsa); 142 if (len > modlen) { 143 error("ssh_rsa_verify: len %u > modlen %u", len, modlen); 144 xfree(sigblob); 145 return -1; 146 } else if (len < modlen) { 147 u_int diff = modlen - len; 148 debug("ssh_rsa_verify: add padding: modlen %u > len %u", 149 modlen, len); 150 sigblob = xrealloc(sigblob, 1, modlen); 151 memmove(sigblob + diff, sigblob, len); 152 memset(sigblob, 0, diff); 153 len = modlen; 154 } 155 nid = (datafellows & SSH_BUG_RSASIGMD5) ? NID_md5 : NID_sha1; 156 if ((evp_md = EVP_get_digestbynid(nid)) == NULL) { 157 error("ssh_rsa_verify: EVP_get_digestbynid %d failed", nid); 158 xfree(sigblob); 159 return -1; 160 } 161 EVP_DigestInit(&md, evp_md); 162 EVP_DigestUpdate(&md, data, datalen); 163 EVP_DigestFinal(&md, digest, &dlen); 164 165 ret = openssh_RSA_verify(nid, digest, dlen, sigblob, len, key->rsa); 166 memset(digest, 'd', sizeof(digest)); 167 memset(sigblob, 's', len); 168 xfree(sigblob); 169 debug("ssh_rsa_verify: signature %scorrect", (ret==0) ? "in" : ""); 170 return ret; 171 } 172 173 /* 174 * See: 175 * http://www.rsasecurity.com/rsalabs/pkcs/pkcs-1/ 176 * ftp://ftp.rsasecurity.com/pub/pkcs/pkcs-1/pkcs-1v2-1.asn 177 */ 178 /* 179 * id-sha1 OBJECT IDENTIFIER ::= { iso(1) identified-organization(3) 180 * oiw(14) secsig(3) algorithms(2) 26 } 181 */ 182 static const u_char id_sha1[] = { 183 0x30, 0x21, /* type Sequence, length 0x21 (33) */ 184 0x30, 0x09, /* type Sequence, length 0x09 */ 185 0x06, 0x05, /* type OID, length 0x05 */ 186 0x2b, 0x0e, 0x03, 0x02, 0x1a, /* id-sha1 OID */ 187 0x05, 0x00, /* NULL */ 188 0x04, 0x14 /* Octet string, length 0x14 (20), followed by sha1 hash */ 189 }; 190 /* 191 * id-md5 OBJECT IDENTIFIER ::= { iso(1) member-body(2) us(840) 192 * rsadsi(113549) digestAlgorithm(2) 5 } 193 */ 194 static const u_char id_md5[] = { 195 0x30, 0x20, /* type Sequence, length 0x20 (32) */ 196 0x30, 0x0c, /* type Sequence, length 0x09 */ 197 0x06, 0x08, /* type OID, length 0x05 */ 198 0x2a, 0x86, 0x48, 0x86, 0xF7, 0x0D, 0x02, 0x05, /* id-md5 */ 199 0x05, 0x00, /* NULL */ 200 0x04, 0x10 /* Octet string, length 0x10 (16), followed by md5 hash */ 201 }; 202 203 static int 204 openssh_RSA_verify(int type, u_char *hash, u_int hashlen, 205 u_char *sigbuf, u_int siglen, RSA *rsa) 206 { 207 u_int ret, rsasize, oidlen = 0, hlen = 0; 208 int len; 209 const u_char *oid = NULL; 210 u_char *decrypted = NULL; 211 212 ret = 0; 213 switch (type) { 214 case NID_sha1: 215 oid = id_sha1; 216 oidlen = sizeof(id_sha1); 217 hlen = 20; 218 break; 219 case NID_md5: 220 oid = id_md5; 221 oidlen = sizeof(id_md5); 222 hlen = 16; 223 break; 224 default: 225 goto done; 226 } 227 if (hashlen != hlen) { 228 error("bad hashlen"); 229 goto done; 230 } 231 rsasize = RSA_size(rsa); 232 if (siglen == 0 || siglen > rsasize) { 233 error("bad siglen"); 234 goto done; 235 } 236 decrypted = xmalloc(rsasize); 237 if ((len = RSA_public_decrypt(siglen, sigbuf, decrypted, rsa, 238 RSA_PKCS1_PADDING)) < 0) { 239 error("RSA_public_decrypt failed: %s", 240 ERR_error_string(ERR_get_error(), NULL)); 241 goto done; 242 } 243 if (len < 0 || (u_int)len != hlen + oidlen) { 244 error("bad decrypted len: %d != %d + %d", len, hlen, oidlen); 245 goto done; 246 } 247 if (memcmp(decrypted, oid, oidlen) != 0) { 248 error("oid mismatch"); 249 goto done; 250 } 251 if (memcmp(decrypted + oidlen, hash, hlen) != 0) { 252 error("hash mismatch"); 253 goto done; 254 } 255 ret = 1; 256 done: 257 if (decrypted) 258 xfree(decrypted); 259 return ret; 260 } 261