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