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Darren Tucker33c787f2008-07-02 22:37:30 +10001/* $OpenBSD: auth-rsa.c,v 1.73 2008/07/02 12:03:51 dtucker Exp $ */
Damien Millerd4a8b7e1999-10-27 13:42:43 +10002/*
Damien Miller95def091999-11-25 00:26:21 +11003 * Author: Tatu Ylonen <ylo@cs.hut.fi>
Damien Miller95def091999-11-25 00:26:21 +11004 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5 * All rights reserved
Damien Miller95def091999-11-25 00:26:21 +11006 * 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.
Damien Miller4af51302000-04-16 11:18:38 +10009 *
Damien Millere4340be2000-09-16 13:29:08 +110010 * 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".
Damien Miller95def091999-11-25 00:26:21 +110015 */
Damien Millerd4a8b7e1999-10-27 13:42:43 +100016
17#include "includes.h"
Damien Millerf17883e2006-03-15 11:45:54 +110018
19#include <sys/types.h>
20#include <sys/stat.h>
Damien Millerd4a8b7e1999-10-27 13:42:43 +100021
22#include <openssl/rsa.h>
23#include <openssl/md5.h>
Damien Millerd4a8b7e1999-10-27 13:42:43 +100024
Damien Miller9f2abc42006-07-10 20:53:08 +100025#include <pwd.h>
Damien Millera7a73ee2006-08-05 11:37:59 +100026#include <stdio.h>
Damien Millerded319c2006-09-01 15:38:36 +100027#include <stdarg.h>
Damien Millere3476ed2006-07-24 14:13:33 +100028#include <string.h>
Damien Miller9f2abc42006-07-10 20:53:08 +100029
Damien Millerd7834352006-08-05 12:39:39 +100030#include "xmalloc.h"
Ben Lindstrom226cfa02001-01-22 05:34:40 +000031#include "rsa.h"
32#include "packet.h"
Ben Lindstrom226cfa02001-01-22 05:34:40 +000033#include "ssh1.h"
Ben Lindstrom226cfa02001-01-22 05:34:40 +000034#include "uidswap.h"
35#include "match.h"
Damien Millerd7834352006-08-05 12:39:39 +100036#include "buffer.h"
Ben Lindstrom226cfa02001-01-22 05:34:40 +000037#include "auth-options.h"
38#include "pathnames.h"
39#include "log.h"
40#include "servconf.h"
Damien Millerd7834352006-08-05 12:39:39 +100041#include "key.h"
Damien Miller89681212001-12-21 12:52:39 +110042#include "hostfile.h"
Damien Millerd7834352006-08-05 12:39:39 +100043#include "auth.h"
44#ifdef GSSAPI
45#include "ssh-gss.h"
46#endif
Ben Lindstrom7a2073c2002-03-22 02:30:41 +000047#include "monitor_wrap.h"
Ben Lindstrom03f39322002-04-02 20:43:11 +000048#include "ssh.h"
Darren Tuckerf0f90982004-12-11 13:39:50 +110049#include "misc.h"
Damien Miller874d77b2000-10-14 16:23:11 +110050
51/* import */
52extern ServerOptions options;
53
Damien Miller5428f641999-11-25 11:54:57 +110054/*
55 * Session identifier that is used to bind key exchange and authentication
56 * responses to a particular session.
57 */
Ben Lindstrom46c16222000-12-22 01:43:59 +000058extern u_char session_id[16];
Damien Millerd4a8b7e1999-10-27 13:42:43 +100059
Damien Miller5428f641999-11-25 11:54:57 +110060/*
61 * The .ssh/authorized_keys file contains public keys, one per line, in the
62 * following format:
63 * options bits e n comment
64 * where bits, e and n are decimal numbers,
65 * and comment is any string of characters up to newline. The maximum
Darren Tucker22cc7412004-12-06 22:47:41 +110066 * length of a line is SSH_MAX_PUBKEY_BYTES characters. See sshd(8) for a
Damien Miller5428f641999-11-25 11:54:57 +110067 * description of the options.
68 */
Damien Millerd4a8b7e1999-10-27 13:42:43 +100069
Ben Lindstrom7a2073c2002-03-22 02:30:41 +000070BIGNUM *
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +000071auth_rsa_generate_challenge(Key *key)
72{
73 BIGNUM *challenge;
74 BN_CTX *ctx;
75
76 if ((challenge = BN_new()) == NULL)
77 fatal("auth_rsa_generate_challenge: BN_new() failed");
78 /* Generate a random challenge. */
Darren Tucker0bc85572006-11-07 23:14:41 +110079 if (BN_rand(challenge, 256, 0, 0) == 0)
80 fatal("auth_rsa_generate_challenge: BN_rand failed");
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +000081 if ((ctx = BN_CTX_new()) == NULL)
Darren Tucker0bc85572006-11-07 23:14:41 +110082 fatal("auth_rsa_generate_challenge: BN_CTX_new failed");
83 if (BN_mod(challenge, challenge, key->rsa->n, ctx) == 0)
84 fatal("auth_rsa_generate_challenge: BN_mod failed");
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +000085 BN_CTX_free(ctx);
86
87 return challenge;
88}
89
Ben Lindstrom7a2073c2002-03-22 02:30:41 +000090int
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +000091auth_rsa_verify_response(Key *key, BIGNUM *challenge, u_char response[16])
92{
93 u_char buf[32], mdbuf[16];
94 MD5_CTX md;
95 int len;
96
Ben Lindstrome1f9e322002-03-27 17:38:43 +000097 /* don't allow short keys */
Ben Lindstrom03f39322002-04-02 20:43:11 +000098 if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
Ben Lindstrom2779d282002-06-11 15:47:42 +000099 error("auth_rsa_verify_response: RSA modulus too small: %d < minimum %d bits",
100 BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
Ben Lindstrome1f9e322002-03-27 17:38:43 +0000101 return (0);
102 }
103
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000104 /* The response is MD5 of decrypted challenge plus session id. */
105 len = BN_num_bytes(challenge);
106 if (len <= 0 || len > 32)
107 fatal("auth_rsa_verify_response: bad challenge length %d", len);
108 memset(buf, 0, 32);
109 BN_bn2bin(challenge, buf + 32 - len);
110 MD5_Init(&md);
111 MD5_Update(&md, buf, 32);
112 MD5_Update(&md, session_id, 16);
113 MD5_Final(mdbuf, &md);
114
115 /* Verify that the response is the original challenge. */
116 if (memcmp(response, mdbuf, 16) != 0) {
117 /* Wrong answer. */
118 return (0);
119 }
120 /* Correct answer. */
121 return (1);
122}
123
Damien Miller5428f641999-11-25 11:54:57 +1100124/*
125 * Performs the RSA authentication challenge-response dialog with the client,
126 * and returns true (non-zero) if the client gave the correct answer to
127 * our challenge; returns zero if the client gives a wrong answer.
128 */
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000129
130int
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000131auth_rsa_challenge_dialog(Key *key)
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000132{
Damien Miller98c7ad62000-03-09 21:27:49 +1100133 BIGNUM *challenge, *encrypted_challenge;
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000134 u_char response[16];
135 int i, success;
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000136
Damien Millerda755162002-01-22 23:09:22 +1100137 if ((encrypted_challenge = BN_new()) == NULL)
138 fatal("auth_rsa_challenge_dialog: BN_new() failed");
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000139
Ben Lindstrom7a2073c2002-03-22 02:30:41 +0000140 challenge = PRIVSEP(auth_rsa_generate_challenge(key));
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000141
Damien Miller95def091999-11-25 00:26:21 +1100142 /* Encrypt the challenge with the public key. */
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000143 rsa_public_encrypt(encrypted_challenge, challenge, key->rsa);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000144
Damien Miller95def091999-11-25 00:26:21 +1100145 /* Send the encrypted challenge to the client. */
146 packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
147 packet_put_bignum(encrypted_challenge);
148 packet_send();
Damien Miller98c7ad62000-03-09 21:27:49 +1100149 BN_clear_free(encrypted_challenge);
Damien Miller95def091999-11-25 00:26:21 +1100150 packet_write_wait();
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000151
Damien Miller98c7ad62000-03-09 21:27:49 +1100152 /* Wait for a response. */
Damien Millerdff50992002-01-22 23:16:32 +1100153 packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE);
Damien Miller98c7ad62000-03-09 21:27:49 +1100154 for (i = 0; i < 16; i++)
Damien Miller8ba29fe2006-03-26 14:25:19 +1100155 response[i] = (u_char)packet_get_char();
Damien Miller48b03fc2002-01-22 23:11:40 +1100156 packet_check_eom();
Damien Miller98c7ad62000-03-09 21:27:49 +1100157
Ben Lindstrom7a2073c2002-03-22 02:30:41 +0000158 success = PRIVSEP(auth_rsa_verify_response(key, challenge, response));
Damien Miller95def091999-11-25 00:26:21 +1100159 BN_clear_free(challenge);
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000160 return (success);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000161}
162
Damien Miller5428f641999-11-25 11:54:57 +1100163/*
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000164 * check if there's user key matching client_n,
165 * return key if login is allowed, NULL otherwise
Damien Miller5428f641999-11-25 11:54:57 +1100166 */
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000167
Ben Lindstrom7a2073c2002-03-22 02:30:41 +0000168int
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000169auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey)
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000170{
Darren Tucker22cc7412004-12-06 22:47:41 +1100171 char line[SSH_MAX_PUBKEY_BYTES], *file;
Ben Lindstrom7a2073c2002-03-22 02:30:41 +0000172 int allowed = 0;
Ben Lindstrom46c16222000-12-22 01:43:59 +0000173 u_int bits;
Damien Miller95def091999-11-25 00:26:21 +1100174 FILE *f;
Ben Lindstrom46c16222000-12-22 01:43:59 +0000175 u_long linenum = 0;
Damien Miller89681212001-12-21 12:52:39 +1100176 Key *key;
Damien Miller874d77b2000-10-14 16:23:11 +1100177
Damien Miller95def091999-11-25 00:26:21 +1100178 /* Temporarily use the user's uid. */
Ben Lindstrom3fcf1a22001-04-08 18:26:59 +0000179 temporarily_use_uid(pw);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000180
Damien Miller95def091999-11-25 00:26:21 +1100181 /* The authorized keys. */
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000182 file = authorized_keys_file(pw);
183 debug("trying public RSA key file %s", file);
Darren Tucker33c787f2008-07-02 22:37:30 +1000184 f = auth_openkeyfile(file, pw, options.strict_modes);
Damien Miller95def091999-11-25 00:26:21 +1100185 if (!f) {
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000186 xfree(file);
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000187 restore_uid();
Ben Lindstromf6d367b2002-03-26 02:59:31 +0000188 return (0);
Damien Miller95def091999-11-25 00:26:21 +1100189 }
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000190
191 /* Flag indicating whether the key is allowed. */
192 allowed = 0;
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000193
Damien Miller89681212001-12-21 12:52:39 +1100194 key = key_new(KEY_RSA1);
Damien Miller95def091999-11-25 00:26:21 +1100195
Damien Miller5428f641999-11-25 11:54:57 +1100196 /*
197 * Go though the accepted keys, looking for the current key. If
198 * found, perform a challenge-response dialog to verify that the
199 * user really has the corresponding private key.
200 */
Darren Tucker22cc7412004-12-06 22:47:41 +1100201 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
Damien Miller95def091999-11-25 00:26:21 +1100202 char *cp;
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000203 char *key_options;
Damien Millereccb9de2005-06-17 12:59:34 +1000204 int keybits;
Damien Miller95def091999-11-25 00:26:21 +1100205
Damien Miller5428f641999-11-25 11:54:57 +1100206 /* Skip leading whitespace, empty and comment lines. */
207 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
208 ;
Damien Miller95def091999-11-25 00:26:21 +1100209 if (!*cp || *cp == '\n' || *cp == '#')
210 continue;
211
Damien Miller5428f641999-11-25 11:54:57 +1100212 /*
213 * Check if there are options for this key, and if so,
214 * save their starting address and skip the option part
215 * for now. If there are no options, set the starting
216 * address to NULL.
217 */
Damien Miller95def091999-11-25 00:26:21 +1100218 if (*cp < '0' || *cp > '9') {
219 int quoted = 0;
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000220 key_options = cp;
Damien Miller95def091999-11-25 00:26:21 +1100221 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
222 if (*cp == '\\' && cp[1] == '"')
223 cp++; /* Skip both */
224 else if (*cp == '"')
225 quoted = !quoted;
226 }
227 } else
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000228 key_options = NULL;
Damien Miller95def091999-11-25 00:26:21 +1100229
230 /* Parse the key from the line. */
Damien Miller89681212001-12-21 12:52:39 +1100231 if (hostfile_read_key(&cp, &bits, key) == 0) {
Ben Lindstromf96704d2001-06-25 04:17:12 +0000232 debug("%.100s, line %lu: non ssh1 key syntax",
Ben Lindstrom226cfa02001-01-22 05:34:40 +0000233 file, linenum);
Damien Miller95def091999-11-25 00:26:21 +1100234 continue;
235 }
236 /* cp now points to the comment part. */
237
Damien Miller95def091999-11-25 00:26:21 +1100238 /* Check if the we have found the desired key (identified by its modulus). */
Damien Miller89681212001-12-21 12:52:39 +1100239 if (BN_cmp(key->rsa->n, client_n) != 0)
Damien Miller5428f641999-11-25 11:54:57 +1100240 continue;
Damien Miller95def091999-11-25 00:26:21 +1100241
Damien Milleraae6c611999-12-06 11:47:28 +1100242 /* check the real bits */
Damien Millereccb9de2005-06-17 12:59:34 +1000243 keybits = BN_num_bits(key->rsa->n);
244 if (keybits < 0 || bits != (u_int)keybits)
Damien Miller996acd22003-04-09 20:59:48 +1000245 logit("Warning: %s, line %lu: keysize mismatch: "
Damien Milleraae6c611999-12-06 11:47:28 +1100246 "actual %d vs. announced %d.",
Damien Miller89681212001-12-21 12:52:39 +1100247 file, linenum, BN_num_bits(key->rsa->n), bits);
Damien Milleraae6c611999-12-06 11:47:28 +1100248
Damien Miller95def091999-11-25 00:26:21 +1100249 /* We have found the desired key. */
Ben Lindstrom14920292000-11-21 21:24:55 +0000250 /*
251 * If our options do not allow this key to be used,
252 * do not send challenge.
253 */
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000254 if (!auth_parse_options(pw, key_options, file, linenum))
Ben Lindstrom14920292000-11-21 21:24:55 +0000255 continue;
Damien Miller95def091999-11-25 00:26:21 +1100256
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000257 /* break out, this key is allowed */
258 allowed = 1;
Damien Miller50a41ed2000-10-16 12:14:42 +1100259 break;
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000260 }
261
Damien Miller95def091999-11-25 00:26:21 +1100262 /* Restore the privileged uid. */
263 restore_uid();
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000264
Damien Miller95def091999-11-25 00:26:21 +1100265 /* Close the file. */
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000266 xfree(file);
Damien Miller95def091999-11-25 00:26:21 +1100267 fclose(f);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000268
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000269 /* return key if allowed */
270 if (allowed && rkey != NULL)
271 *rkey = key;
272 else
273 key_free(key);
274 return (allowed);
275}
276
277/*
278 * Performs the RSA authentication dialog with the client. This returns
279 * 0 if the client could not be authenticated, and 1 if authentication was
280 * successful. This may exit if there is a serious protocol violation.
281 */
282int
Damien Miller3e3b5142003-11-17 21:13:40 +1100283auth_rsa(Authctxt *authctxt, BIGNUM *client_n)
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000284{
285 Key *key;
286 char *fp;
Damien Miller3e3b5142003-11-17 21:13:40 +1100287 struct passwd *pw = authctxt->pw;
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000288
289 /* no user given */
Damien Miller3e3b5142003-11-17 21:13:40 +1100290 if (!authctxt->valid)
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000291 return 0;
292
Ben Lindstrom7a2073c2002-03-22 02:30:41 +0000293 if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) {
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000294 auth_clear_options();
295 return (0);
296 }
297
298 /* Perform the challenge-response dialog for this key. */
299 if (!auth_rsa_challenge_dialog(key)) {
300 /* Wrong response. */
301 verbose("Wrong response to RSA authentication challenge.");
302 packet_send_debug("Wrong response to RSA authentication challenge.");
303 /*
304 * Break out of the loop. Otherwise we might send
305 * another challenge and break the protocol.
306 */
307 key_free(key);
308 return (0);
309 }
310 /*
311 * Correct response. The client has been successfully
312 * authenticated. Note that we have not yet processed the
313 * options; this will be reset if the options cause the
314 * authentication to be rejected.
315 */
316 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
317 verbose("Found matching %s key: %s",
318 key_type(key), fp);
319 xfree(fp);
Damien Miller89681212001-12-21 12:52:39 +1100320 key_free(key);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000321
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000322 packet_send_debug("RSA authentication accepted.");
323 return (1);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000324}