Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 1 | /* |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 2 | * Author: Tatu Ylonen <ylo@cs.hut.fi> |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 3 | * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland |
| 4 | * All rights reserved |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 5 | * RSA-based authentication. This code determines whether to admit a login |
| 6 | * based on RSA authentication. This file also contains functions to check |
| 7 | * validity of the host key. |
Damien Miller | 4af5130 | 2000-04-16 11:18:38 +1000 | [diff] [blame] | 8 | * |
Damien Miller | e4340be | 2000-09-16 13:29:08 +1100 | [diff] [blame] | 9 | * As far as I am concerned, the code I have written for this software |
| 10 | * can be used freely for any purpose. Any derived versions of this |
| 11 | * software must be clearly marked as such, and if the derived work is |
| 12 | * incompatible with the protocol description in the RFC file, it must be |
| 13 | * called by a name other than "ssh" or "Secure Shell". |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 14 | */ |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 15 | |
| 16 | #include "includes.h" |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 17 | RCSID("$OpenBSD: auth-rsa.c,v 1.31 2000/10/11 19:59:52 markus Exp $"); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 18 | |
| 19 | #include "rsa.h" |
| 20 | #include "packet.h" |
| 21 | #include "xmalloc.h" |
| 22 | #include "ssh.h" |
| 23 | #include "mpaux.h" |
| 24 | #include "uidswap.h" |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 25 | #include "match.h" |
Damien Miller | 6d7b2cd | 1999-11-12 15:19:27 +1100 | [diff] [blame] | 26 | #include "servconf.h" |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 27 | #include "auth-options.h" |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 28 | |
| 29 | #include <openssl/rsa.h> |
| 30 | #include <openssl/md5.h> |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 31 | |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 32 | |
| 33 | /* import */ |
| 34 | extern ServerOptions options; |
| 35 | |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 36 | /* |
| 37 | * Session identifier that is used to bind key exchange and authentication |
| 38 | * responses to a particular session. |
| 39 | */ |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 40 | extern unsigned char session_id[16]; |
| 41 | |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 42 | /* |
| 43 | * The .ssh/authorized_keys file contains public keys, one per line, in the |
| 44 | * following format: |
| 45 | * options bits e n comment |
| 46 | * where bits, e and n are decimal numbers, |
| 47 | * and comment is any string of characters up to newline. The maximum |
| 48 | * length of a line is 8000 characters. See the documentation for a |
| 49 | * description of the options. |
| 50 | */ |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 51 | |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 52 | /* |
| 53 | * Performs the RSA authentication challenge-response dialog with the client, |
| 54 | * and returns true (non-zero) if the client gave the correct answer to |
| 55 | * our challenge; returns zero if the client gives a wrong answer. |
| 56 | */ |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 57 | |
| 58 | int |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 59 | auth_rsa_challenge_dialog(RSA *pk) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 60 | { |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 61 | BIGNUM *challenge, *encrypted_challenge; |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 62 | BN_CTX *ctx; |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 63 | unsigned char buf[32], mdbuf[16], response[16]; |
| 64 | MD5_CTX md; |
| 65 | unsigned int i; |
| 66 | int plen, len; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 67 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 68 | encrypted_challenge = BN_new(); |
| 69 | challenge = BN_new(); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 70 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 71 | /* Generate a random challenge. */ |
| 72 | BN_rand(challenge, 256, 0, 0); |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 73 | ctx = BN_CTX_new(); |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 74 | BN_mod(challenge, challenge, pk->n, ctx); |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 75 | BN_CTX_free(ctx); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 76 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 77 | /* Encrypt the challenge with the public key. */ |
| 78 | rsa_public_encrypt(encrypted_challenge, challenge, pk); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 79 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 80 | /* Send the encrypted challenge to the client. */ |
| 81 | packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE); |
| 82 | packet_put_bignum(encrypted_challenge); |
| 83 | packet_send(); |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 84 | BN_clear_free(encrypted_challenge); |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 85 | packet_write_wait(); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 86 | |
Damien Miller | 98c7ad6 | 2000-03-09 21:27:49 +1100 | [diff] [blame] | 87 | /* Wait for a response. */ |
| 88 | packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE); |
| 89 | packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE); |
| 90 | for (i = 0; i < 16; i++) |
| 91 | response[i] = packet_get_char(); |
| 92 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 93 | /* The response is MD5 of decrypted challenge plus session id. */ |
| 94 | len = BN_num_bytes(challenge); |
| 95 | if (len <= 0 || len > 32) |
| 96 | fatal("auth_rsa_challenge_dialog: bad challenge length %d", len); |
| 97 | memset(buf, 0, 32); |
| 98 | BN_bn2bin(challenge, buf + 32 - len); |
| 99 | MD5_Init(&md); |
| 100 | MD5_Update(&md, buf, 32); |
| 101 | MD5_Update(&md, session_id, 16); |
| 102 | MD5_Final(mdbuf, &md); |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 103 | BN_clear_free(challenge); |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 104 | |
| 105 | /* Verify that the response is the original challenge. */ |
| 106 | if (memcmp(response, mdbuf, 16) != 0) { |
| 107 | /* Wrong answer. */ |
| 108 | return 0; |
| 109 | } |
| 110 | /* Correct answer. */ |
| 111 | return 1; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 112 | } |
| 113 | |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 114 | /* |
| 115 | * Performs the RSA authentication dialog with the client. This returns |
| 116 | * 0 if the client could not be authenticated, and 1 if authentication was |
| 117 | * successful. This may exit if there is a serious protocol violation. |
| 118 | */ |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 119 | |
| 120 | int |
Damien Miller | 6d7b2cd | 1999-11-12 15:19:27 +1100 | [diff] [blame] | 121 | auth_rsa(struct passwd *pw, BIGNUM *client_n) |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 122 | { |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 123 | char line[8192], file[1024]; |
| 124 | int authenticated; |
| 125 | unsigned int bits; |
| 126 | FILE *f; |
| 127 | unsigned long linenum = 0; |
| 128 | struct stat st; |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 129 | RSA *pk; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 130 | |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 131 | /* no user given */ |
| 132 | if (pw == NULL) |
| 133 | return 0; |
| 134 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 135 | /* Temporarily use the user's uid. */ |
| 136 | temporarily_use_uid(pw->pw_uid); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 137 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 138 | /* The authorized keys. */ |
| 139 | snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir, |
| 140 | SSH_USER_PERMITTED_KEYS); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 141 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 142 | /* Fail quietly if file does not exist */ |
| 143 | if (stat(file, &st) < 0) { |
| 144 | /* Restore the privileged uid. */ |
| 145 | restore_uid(); |
| 146 | return 0; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 147 | } |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 148 | /* Open the file containing the authorized keys. */ |
| 149 | f = fopen(file, "r"); |
| 150 | if (!f) { |
| 151 | /* Restore the privileged uid. */ |
| 152 | restore_uid(); |
| 153 | packet_send_debug("Could not open %.900s for reading.", file); |
| 154 | packet_send_debug("If your home is on an NFS volume, it may need to be world-readable."); |
| 155 | return 0; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 156 | } |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 157 | if (options.strict_modes) { |
| 158 | int fail = 0; |
| 159 | char buf[1024]; |
| 160 | /* Check open file in order to avoid open/stat races */ |
| 161 | if (fstat(fileno(f), &st) < 0 || |
| 162 | (st.st_uid != 0 && st.st_uid != pw->pw_uid) || |
| 163 | (st.st_mode & 022) != 0) { |
| 164 | snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: " |
| 165 | "bad ownership or modes for '%s'.", pw->pw_name, file); |
| 166 | fail = 1; |
| 167 | } else { |
| 168 | /* Check path to SSH_USER_PERMITTED_KEYS */ |
| 169 | int i; |
| 170 | static const char *check[] = { |
| 171 | "", SSH_USER_DIR, NULL |
| 172 | }; |
| 173 | for (i = 0; check[i]; i++) { |
| 174 | snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]); |
| 175 | if (stat(line, &st) < 0 || |
| 176 | (st.st_uid != 0 && st.st_uid != pw->pw_uid) || |
| 177 | (st.st_mode & 022) != 0) { |
| 178 | snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: " |
| 179 | "bad ownership or modes for '%s'.", pw->pw_name, line); |
| 180 | fail = 1; |
| 181 | break; |
| 182 | } |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 183 | } |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 184 | } |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 185 | if (fail) { |
Damien Miller | eba71ba | 2000-04-29 23:57:08 +1000 | [diff] [blame] | 186 | fclose(f); |
Damien Miller | 3702396 | 2000-07-11 17:31:38 +1000 | [diff] [blame] | 187 | log("%s",buf); |
| 188 | packet_send_debug("%s",buf); |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 189 | restore_uid(); |
| 190 | return 0; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 191 | } |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 192 | } |
| 193 | /* Flag indicating whether authentication has succeeded. */ |
| 194 | authenticated = 0; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 195 | |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 196 | pk = RSA_new(); |
| 197 | pk->e = BN_new(); |
| 198 | pk->n = BN_new(); |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 199 | |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 200 | /* |
| 201 | * Go though the accepted keys, looking for the current key. If |
| 202 | * found, perform a challenge-response dialog to verify that the |
| 203 | * user really has the corresponding private key. |
| 204 | */ |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 205 | while (fgets(line, sizeof(line), f)) { |
| 206 | char *cp; |
| 207 | char *options; |
| 208 | |
| 209 | linenum++; |
| 210 | |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 211 | /* Skip leading whitespace, empty and comment lines. */ |
| 212 | for (cp = line; *cp == ' ' || *cp == '\t'; cp++) |
| 213 | ; |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 214 | if (!*cp || *cp == '\n' || *cp == '#') |
| 215 | continue; |
| 216 | |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 217 | /* |
| 218 | * Check if there are options for this key, and if so, |
| 219 | * save their starting address and skip the option part |
| 220 | * for now. If there are no options, set the starting |
| 221 | * address to NULL. |
| 222 | */ |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 223 | if (*cp < '0' || *cp > '9') { |
| 224 | int quoted = 0; |
| 225 | options = cp; |
| 226 | for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) { |
| 227 | if (*cp == '\\' && cp[1] == '"') |
| 228 | cp++; /* Skip both */ |
| 229 | else if (*cp == '"') |
| 230 | quoted = !quoted; |
| 231 | } |
| 232 | } else |
| 233 | options = NULL; |
| 234 | |
| 235 | /* Parse the key from the line. */ |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 236 | if (!auth_rsa_read_key(&cp, &bits, pk->e, pk->n)) { |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 237 | debug("%.100s, line %lu: bad key syntax", |
| 238 | SSH_USER_PERMITTED_KEYS, linenum); |
| 239 | packet_send_debug("%.100s, line %lu: bad key syntax", |
Damien Miller | 4af5130 | 2000-04-16 11:18:38 +1000 | [diff] [blame] | 240 | SSH_USER_PERMITTED_KEYS, linenum); |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 241 | continue; |
| 242 | } |
| 243 | /* cp now points to the comment part. */ |
| 244 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 245 | /* Check if the we have found the desired key (identified by its modulus). */ |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 246 | if (BN_cmp(pk->n, client_n) != 0) |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 247 | continue; |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 248 | |
Damien Miller | aae6c61 | 1999-12-06 11:47:28 +1100 | [diff] [blame] | 249 | /* check the real bits */ |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 250 | if (bits != BN_num_bits(pk->n)) |
Damien Miller | aae6c61 | 1999-12-06 11:47:28 +1100 | [diff] [blame] | 251 | log("Warning: %s, line %ld: keysize mismatch: " |
| 252 | "actual %d vs. announced %d.", |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 253 | file, linenum, BN_num_bits(pk->n), bits); |
Damien Miller | aae6c61 | 1999-12-06 11:47:28 +1100 | [diff] [blame] | 254 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 255 | /* We have found the desired key. */ |
| 256 | |
| 257 | /* Perform the challenge-response dialog for this key. */ |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 258 | if (!auth_rsa_challenge_dialog(pk)) { |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 259 | /* Wrong response. */ |
| 260 | verbose("Wrong response to RSA authentication challenge."); |
| 261 | packet_send_debug("Wrong response to RSA authentication challenge."); |
| 262 | continue; |
| 263 | } |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 264 | /* |
| 265 | * Correct response. The client has been successfully |
| 266 | * authenticated. Note that we have not yet processed the |
| 267 | * options; this will be reset if the options cause the |
| 268 | * authentication to be rejected. |
Damien Miller | 5428f64 | 1999-11-25 11:54:57 +1100 | [diff] [blame] | 269 | * Break out of the loop if authentication was successful; |
| 270 | * otherwise continue searching. |
| 271 | */ |
Damien Miller | f6d9e22 | 2000-06-18 14:50:44 +1000 | [diff] [blame] | 272 | authenticated = auth_parse_options(pw, options, linenum); |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 273 | if (authenticated) |
| 274 | break; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 275 | } |
| 276 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 277 | /* Restore the privileged uid. */ |
| 278 | restore_uid(); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 279 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 280 | /* Close the file. */ |
| 281 | fclose(f); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 282 | |
Damien Miller | 450a7a1 | 2000-03-26 13:04:51 +1000 | [diff] [blame] | 283 | RSA_free(pk); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 284 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 285 | if (authenticated) |
| 286 | packet_send_debug("RSA authentication accepted."); |
Damien Miller | 874d77b | 2000-10-14 16:23:11 +1100 | [diff] [blame] | 287 | else |
| 288 | auth_clear_options(); |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 289 | |
Damien Miller | 95def09 | 1999-11-25 00:26:21 +1100 | [diff] [blame] | 290 | /* Return authentication result. */ |
| 291 | return authenticated; |
Damien Miller | d4a8b7e | 1999-10-27 13:42:43 +1000 | [diff] [blame] | 292 | } |