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 ssh_rsa_sign(const Key * key,u_char ** sigp,u_int * lenp,const u_char * data,u_int datalen)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 ssh_rsa_verify(const Key * key,const u_char * signature,u_int signaturelen,const u_char * data,u_int datalen)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 openssh_RSA_verify(int type,u_char * hash,u_int hashlen,u_char * sigbuf,u_int siglen,RSA * rsa)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 } 269