Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 1 | /* $OpenBSD: auth-rsa.c,v 1.90 2015/01/28 22:36:00 djm Exp $ */ |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 2 | /* |
| 3 | * Author: Tatu Ylonen <ylo@cs.hut.fi> |
| 4 | * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 5 | * All rights reserved |
| 6 | * RSA-based authentication. This code determines whether to admit a login |
| 7 | * based on RSA authentication. This file also contains functions to check |
| 8 | * validity of the host key. |
| 9 | * |
| 10 | * As far as I am concerned, the code I have written for this software |
| 11 | * can be used freely for any purpose. Any derived versions of this |
| 12 | * software must be clearly marked as such, and if the derived work is |
| 13 | * incompatible with the protocol description in the RFC file, it must be |
| 14 | * called by a name other than "ssh" or "Secure Shell". |
| 15 | */ |
| 16 | |
| 17 | #include "includes.h" |
| 18 | |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 19 | #ifdef WITH_SSH1 |
| 20 | |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 21 | #include <sys/types.h> |
| 22 | #include <sys/stat.h> |
| 23 | |
| 24 | #include <openssl/rsa.h> |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 25 | |
| 26 | #include <pwd.h> |
| 27 | #include <stdio.h> |
| 28 | #include <stdarg.h> |
| 29 | #include <string.h> |
| 30 | |
| 31 | #include "xmalloc.h" |
| 32 | #include "rsa.h" |
| 33 | #include "packet.h" |
| 34 | #include "ssh1.h" |
| 35 | #include "uidswap.h" |
| 36 | #include "match.h" |
| 37 | #include "buffer.h" |
| 38 | #include "pathnames.h" |
| 39 | #include "log.h" |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 40 | #include "misc.h" |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 41 | #include "servconf.h" |
| 42 | #include "key.h" |
| 43 | #include "auth-options.h" |
| 44 | #include "hostfile.h" |
| 45 | #include "auth.h" |
| 46 | #ifdef GSSAPI |
| 47 | #include "ssh-gss.h" |
| 48 | #endif |
| 49 | #include "monitor_wrap.h" |
| 50 | #include "ssh.h" |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 51 | |
| 52 | #include "digest.h" |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 53 | |
| 54 | /* import */ |
| 55 | extern ServerOptions options; |
| 56 | |
| 57 | /* |
| 58 | * Session identifier that is used to bind key exchange and authentication |
| 59 | * responses to a particular session. |
| 60 | */ |
| 61 | extern u_char session_id[16]; |
| 62 | |
| 63 | /* |
| 64 | * The .ssh/authorized_keys file contains public keys, one per line, in the |
| 65 | * following format: |
| 66 | * options bits e n comment |
| 67 | * where bits, e and n are decimal numbers, |
| 68 | * and comment is any string of characters up to newline. The maximum |
| 69 | * length of a line is SSH_MAX_PUBKEY_BYTES characters. See sshd(8) for a |
| 70 | * description of the options. |
| 71 | */ |
| 72 | |
| 73 | BIGNUM * |
| 74 | auth_rsa_generate_challenge(Key *key) |
| 75 | { |
| 76 | BIGNUM *challenge; |
| 77 | BN_CTX *ctx; |
| 78 | |
| 79 | if ((challenge = BN_new()) == NULL) |
| 80 | fatal("auth_rsa_generate_challenge: BN_new() failed"); |
| 81 | /* Generate a random challenge. */ |
| 82 | if (BN_rand(challenge, 256, 0, 0) == 0) |
| 83 | fatal("auth_rsa_generate_challenge: BN_rand failed"); |
| 84 | if ((ctx = BN_CTX_new()) == NULL) |
| 85 | fatal("auth_rsa_generate_challenge: BN_CTX_new failed"); |
| 86 | if (BN_mod(challenge, challenge, key->rsa->n, ctx) == 0) |
| 87 | fatal("auth_rsa_generate_challenge: BN_mod failed"); |
| 88 | BN_CTX_free(ctx); |
| 89 | |
| 90 | return challenge; |
| 91 | } |
| 92 | |
| 93 | int |
| 94 | auth_rsa_verify_response(Key *key, BIGNUM *challenge, u_char response[16]) |
| 95 | { |
| 96 | u_char buf[32], mdbuf[16]; |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 97 | struct ssh_digest_ctx *md; |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 98 | int len; |
| 99 | |
| 100 | /* don't allow short keys */ |
| 101 | if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) { |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 102 | error("%s: RSA modulus too small: %d < minimum %d bits", |
| 103 | __func__, |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 104 | BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE); |
| 105 | return (0); |
| 106 | } |
| 107 | |
| 108 | /* The response is MD5 of decrypted challenge plus session id. */ |
| 109 | len = BN_num_bytes(challenge); |
| 110 | if (len <= 0 || len > 32) |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 111 | fatal("%s: bad challenge length %d", __func__, len); |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 112 | memset(buf, 0, 32); |
| 113 | BN_bn2bin(challenge, buf + 32 - len); |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 114 | if ((md = ssh_digest_start(SSH_DIGEST_MD5)) == NULL || |
| 115 | ssh_digest_update(md, buf, 32) < 0 || |
| 116 | ssh_digest_update(md, session_id, 16) < 0 || |
| 117 | ssh_digest_final(md, mdbuf, sizeof(mdbuf)) < 0) |
| 118 | fatal("%s: md5 failed", __func__); |
| 119 | ssh_digest_free(md); |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 120 | |
| 121 | /* Verify that the response is the original challenge. */ |
| 122 | if (timingsafe_bcmp(response, mdbuf, 16) != 0) { |
| 123 | /* Wrong answer. */ |
| 124 | return (0); |
| 125 | } |
| 126 | /* Correct answer. */ |
| 127 | return (1); |
| 128 | } |
| 129 | |
| 130 | /* |
| 131 | * Performs the RSA authentication challenge-response dialog with the client, |
| 132 | * and returns true (non-zero) if the client gave the correct answer to |
| 133 | * our challenge; returns zero if the client gives a wrong answer. |
| 134 | */ |
| 135 | |
| 136 | int |
| 137 | auth_rsa_challenge_dialog(Key *key) |
| 138 | { |
| 139 | BIGNUM *challenge, *encrypted_challenge; |
| 140 | u_char response[16]; |
| 141 | int i, success; |
| 142 | |
| 143 | if ((encrypted_challenge = BN_new()) == NULL) |
| 144 | fatal("auth_rsa_challenge_dialog: BN_new() failed"); |
| 145 | |
| 146 | challenge = PRIVSEP(auth_rsa_generate_challenge(key)); |
| 147 | |
| 148 | /* Encrypt the challenge with the public key. */ |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 149 | if (rsa_public_encrypt(encrypted_challenge, challenge, key->rsa) != 0) |
| 150 | fatal("%s: rsa_public_encrypt failed", __func__); |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 151 | |
| 152 | /* Send the encrypted challenge to the client. */ |
| 153 | packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE); |
| 154 | packet_put_bignum(encrypted_challenge); |
| 155 | packet_send(); |
| 156 | BN_clear_free(encrypted_challenge); |
| 157 | packet_write_wait(); |
| 158 | |
| 159 | /* Wait for a response. */ |
| 160 | packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE); |
| 161 | for (i = 0; i < 16; i++) |
| 162 | response[i] = (u_char)packet_get_char(); |
| 163 | packet_check_eom(); |
| 164 | |
| 165 | success = PRIVSEP(auth_rsa_verify_response(key, challenge, response)); |
| 166 | BN_clear_free(challenge); |
| 167 | return (success); |
| 168 | } |
| 169 | |
| 170 | static int |
| 171 | rsa_key_allowed_in_file(struct passwd *pw, char *file, |
| 172 | const BIGNUM *client_n, Key **rkey) |
| 173 | { |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 174 | char *fp, line[SSH_MAX_PUBKEY_BYTES]; |
| 175 | int allowed = 0, bits; |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 176 | FILE *f; |
| 177 | u_long linenum = 0; |
| 178 | Key *key; |
| 179 | |
| 180 | debug("trying public RSA key file %s", file); |
| 181 | if ((f = auth_openkeyfile(file, pw, options.strict_modes)) == NULL) |
| 182 | return 0; |
| 183 | |
| 184 | /* |
| 185 | * Go though the accepted keys, looking for the current key. If |
| 186 | * found, perform a challenge-response dialog to verify that the |
| 187 | * user really has the corresponding private key. |
| 188 | */ |
| 189 | key = key_new(KEY_RSA1); |
| 190 | while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) { |
| 191 | char *cp; |
| 192 | char *key_options; |
| 193 | int keybits; |
| 194 | |
| 195 | /* Skip leading whitespace, empty and comment lines. */ |
| 196 | for (cp = line; *cp == ' ' || *cp == '\t'; cp++) |
| 197 | ; |
| 198 | if (!*cp || *cp == '\n' || *cp == '#') |
| 199 | continue; |
| 200 | |
| 201 | /* |
| 202 | * Check if there are options for this key, and if so, |
| 203 | * save their starting address and skip the option part |
| 204 | * for now. If there are no options, set the starting |
| 205 | * address to NULL. |
| 206 | */ |
| 207 | if (*cp < '0' || *cp > '9') { |
| 208 | int quoted = 0; |
| 209 | key_options = cp; |
| 210 | for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { |
| 211 | if (*cp == '\\' && cp[1] == '"') |
| 212 | cp++; /* Skip both */ |
| 213 | else if (*cp == '"') |
| 214 | quoted = !quoted; |
| 215 | } |
| 216 | } else |
| 217 | key_options = NULL; |
| 218 | |
| 219 | /* Parse the key from the line. */ |
| 220 | if (hostfile_read_key(&cp, &bits, key) == 0) { |
| 221 | debug("%.100s, line %lu: non ssh1 key syntax", |
| 222 | file, linenum); |
| 223 | continue; |
| 224 | } |
| 225 | /* cp now points to the comment part. */ |
| 226 | |
| 227 | /* |
| 228 | * Check if the we have found the desired key (identified |
| 229 | * by its modulus). |
| 230 | */ |
| 231 | if (BN_cmp(key->rsa->n, client_n) != 0) |
| 232 | continue; |
| 233 | |
| 234 | /* check the real bits */ |
| 235 | keybits = BN_num_bits(key->rsa->n); |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 236 | if (keybits < 0 || bits != keybits) |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 237 | logit("Warning: %s, line %lu: keysize mismatch: " |
| 238 | "actual %d vs. announced %d.", |
| 239 | file, linenum, BN_num_bits(key->rsa->n), bits); |
| 240 | |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 241 | if ((fp = sshkey_fingerprint(key, options.fingerprint_hash, |
| 242 | SSH_FP_DEFAULT)) == NULL) |
| 243 | continue; |
| 244 | debug("matching key found: file %s, line %lu %s %s", |
| 245 | file, linenum, key_type(key), fp); |
| 246 | free(fp); |
| 247 | |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 248 | /* Never accept a revoked key */ |
| 249 | if (auth_key_is_revoked(key)) |
| 250 | break; |
| 251 | |
| 252 | /* We have found the desired key. */ |
| 253 | /* |
| 254 | * If our options do not allow this key to be used, |
| 255 | * do not send challenge. |
| 256 | */ |
| 257 | if (!auth_parse_options(pw, key_options, file, linenum)) |
| 258 | continue; |
| 259 | if (key_is_cert_authority) |
| 260 | continue; |
| 261 | /* break out, this key is allowed */ |
| 262 | allowed = 1; |
| 263 | break; |
| 264 | } |
| 265 | |
| 266 | /* Close the file. */ |
| 267 | fclose(f); |
| 268 | |
| 269 | /* return key if allowed */ |
| 270 | if (allowed && rkey != NULL) |
| 271 | *rkey = key; |
| 272 | else |
| 273 | key_free(key); |
| 274 | |
| 275 | return allowed; |
| 276 | } |
| 277 | |
| 278 | /* |
| 279 | * check if there's user key matching client_n, |
| 280 | * return key if login is allowed, NULL otherwise |
| 281 | */ |
| 282 | |
| 283 | int |
| 284 | auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey) |
| 285 | { |
| 286 | char *file; |
| 287 | u_int i, allowed = 0; |
| 288 | |
| 289 | temporarily_use_uid(pw); |
| 290 | |
| 291 | for (i = 0; !allowed && i < options.num_authkeys_files; i++) { |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 292 | if (strcasecmp(options.authorized_keys_files[i], "none") == 0) |
| 293 | continue; |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 294 | file = expand_authorized_keys( |
| 295 | options.authorized_keys_files[i], pw); |
| 296 | allowed = rsa_key_allowed_in_file(pw, file, client_n, rkey); |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 297 | free(file); |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 298 | } |
| 299 | |
| 300 | restore_uid(); |
| 301 | |
| 302 | return allowed; |
| 303 | } |
| 304 | |
| 305 | /* |
| 306 | * Performs the RSA authentication dialog with the client. This returns |
| 307 | * 0 if the client could not be authenticated, and 1 if authentication was |
| 308 | * successful. This may exit if there is a serious protocol violation. |
| 309 | */ |
| 310 | int |
| 311 | auth_rsa(Authctxt *authctxt, BIGNUM *client_n) |
| 312 | { |
| 313 | Key *key; |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 314 | struct passwd *pw = authctxt->pw; |
| 315 | |
| 316 | /* no user given */ |
| 317 | if (!authctxt->valid) |
| 318 | return 0; |
| 319 | |
| 320 | if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) { |
| 321 | auth_clear_options(); |
| 322 | return (0); |
| 323 | } |
| 324 | |
| 325 | /* Perform the challenge-response dialog for this key. */ |
| 326 | if (!auth_rsa_challenge_dialog(key)) { |
| 327 | /* Wrong response. */ |
| 328 | verbose("Wrong response to RSA authentication challenge."); |
| 329 | packet_send_debug("Wrong response to RSA authentication challenge."); |
| 330 | /* |
| 331 | * Break out of the loop. Otherwise we might send |
| 332 | * another challenge and break the protocol. |
| 333 | */ |
| 334 | key_free(key); |
| 335 | return (0); |
| 336 | } |
| 337 | /* |
| 338 | * Correct response. The client has been successfully |
| 339 | * authenticated. Note that we have not yet processed the |
| 340 | * options; this will be reset if the options cause the |
| 341 | * authentication to be rejected. |
| 342 | */ |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 343 | pubkey_auth_info(authctxt, key, NULL); |
Greg Hartman | bd77cf7 | 2015-02-25 13:21:06 -0800 | [diff] [blame] | 344 | |
| 345 | packet_send_debug("RSA authentication accepted."); |
| 346 | return (1); |
| 347 | } |
Adam Langley | d059297 | 2015-03-30 14:49:51 -0700 | [diff] [blame^] | 348 | |
| 349 | #endif /* WITH_SSH1 */ |