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Damien Millerce986542013-07-18 16:12:44 +10001/* $OpenBSD: auth-rsa.c,v 1.85 2013/07/12 00:19:58 djm 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 "pathnames.h"
38#include "log.h"
39#include "servconf.h"
Damien Millerd7834352006-08-05 12:39:39 +100040#include "key.h"
Damien Miller4e270b02010-04-16 15:56:21 +100041#include "auth-options.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. */
Damien Millerea1651c2010-07-16 13:58:37 +1000116 if (timingsafe_bcmp(response, mdbuf, 16) != 0) {
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000117 /* 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 Millerd8478b62011-05-29 21:39:36 +1000163static int
164rsa_key_allowed_in_file(struct passwd *pw, char *file,
165 const BIGNUM *client_n, Key **rkey)
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000166{
Darren Tucker0acca372013-06-02 07:41:51 +1000167 char *fp, line[SSH_MAX_PUBKEY_BYTES];
Damien Millerce986542013-07-18 16:12:44 +1000168 int allowed = 0, bits;
Damien Miller95def091999-11-25 00:26:21 +1100169 FILE *f;
Ben Lindstrom46c16222000-12-22 01:43:59 +0000170 u_long linenum = 0;
Damien Miller89681212001-12-21 12:52:39 +1100171 Key *key;
Damien Miller874d77b2000-10-14 16:23:11 +1100172
Ben Lindstrombfb3a0e2001-06-05 20:25:05 +0000173 debug("trying public RSA key file %s", file);
Damien Millerd8478b62011-05-29 21:39:36 +1000174 if ((f = auth_openkeyfile(file, pw, options.strict_modes)) == NULL)
175 return 0;
Damien Miller95def091999-11-25 00:26:21 +1100176
Damien Miller5428f641999-11-25 11:54:57 +1100177 /*
178 * Go though the accepted keys, looking for the current key. If
179 * found, perform a challenge-response dialog to verify that the
180 * user really has the corresponding private key.
181 */
Damien Millerd8478b62011-05-29 21:39:36 +1000182 key = key_new(KEY_RSA1);
Darren Tucker22cc7412004-12-06 22:47:41 +1100183 while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
Damien Miller95def091999-11-25 00:26:21 +1100184 char *cp;
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000185 char *key_options;
Damien Millereccb9de2005-06-17 12:59:34 +1000186 int keybits;
Damien Miller95def091999-11-25 00:26:21 +1100187
Damien Miller5428f641999-11-25 11:54:57 +1100188 /* Skip leading whitespace, empty and comment lines. */
189 for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
190 ;
Damien Miller95def091999-11-25 00:26:21 +1100191 if (!*cp || *cp == '\n' || *cp == '#')
192 continue;
193
Damien Miller5428f641999-11-25 11:54:57 +1100194 /*
195 * Check if there are options for this key, and if so,
196 * save their starting address and skip the option part
197 * for now. If there are no options, set the starting
198 * address to NULL.
199 */
Damien Miller95def091999-11-25 00:26:21 +1100200 if (*cp < '0' || *cp > '9') {
201 int quoted = 0;
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000202 key_options = cp;
Damien Miller95def091999-11-25 00:26:21 +1100203 for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
204 if (*cp == '\\' && cp[1] == '"')
205 cp++; /* Skip both */
206 else if (*cp == '"')
207 quoted = !quoted;
208 }
209 } else
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000210 key_options = NULL;
Damien Miller95def091999-11-25 00:26:21 +1100211
212 /* Parse the key from the line. */
Damien Miller89681212001-12-21 12:52:39 +1100213 if (hostfile_read_key(&cp, &bits, key) == 0) {
Ben Lindstromf96704d2001-06-25 04:17:12 +0000214 debug("%.100s, line %lu: non ssh1 key syntax",
Ben Lindstrom226cfa02001-01-22 05:34:40 +0000215 file, linenum);
Damien Miller95def091999-11-25 00:26:21 +1100216 continue;
217 }
218 /* cp now points to the comment part. */
219
Damien Millerd8478b62011-05-29 21:39:36 +1000220 /*
221 * Check if the we have found the desired key (identified
222 * by its modulus).
223 */
Damien Miller89681212001-12-21 12:52:39 +1100224 if (BN_cmp(key->rsa->n, client_n) != 0)
Damien Miller5428f641999-11-25 11:54:57 +1100225 continue;
Damien Miller95def091999-11-25 00:26:21 +1100226
Damien Milleraae6c611999-12-06 11:47:28 +1100227 /* check the real bits */
Damien Millereccb9de2005-06-17 12:59:34 +1000228 keybits = BN_num_bits(key->rsa->n);
Damien Millerce986542013-07-18 16:12:44 +1000229 if (keybits < 0 || bits != keybits)
Damien Miller996acd22003-04-09 20:59:48 +1000230 logit("Warning: %s, line %lu: keysize mismatch: "
Damien Milleraae6c611999-12-06 11:47:28 +1100231 "actual %d vs. announced %d.",
Damien Miller89681212001-12-21 12:52:39 +1100232 file, linenum, BN_num_bits(key->rsa->n), bits);
Damien Milleraae6c611999-12-06 11:47:28 +1100233
Darren Tucker0acca372013-06-02 07:41:51 +1000234 fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
235 debug("matching key found: file %s, line %lu %s %s",
236 file, linenum, key_type(key), fp);
237 free(fp);
238
Darren Tuckeradab6f12010-12-05 09:01:47 +1100239 /* Never accept a revoked key */
240 if (auth_key_is_revoked(key))
241 break;
242
Damien Miller95def091999-11-25 00:26:21 +1100243 /* We have found the desired key. */
Ben Lindstrom14920292000-11-21 21:24:55 +0000244 /*
245 * If our options do not allow this key to be used,
246 * do not send challenge.
247 */
Darren Tucker3f9fdc72004-06-22 12:56:01 +1000248 if (!auth_parse_options(pw, key_options, file, linenum))
Ben Lindstrom14920292000-11-21 21:24:55 +0000249 continue;
Damien Miller3b903822010-05-21 14:56:25 +1000250 if (key_is_cert_authority)
251 continue;
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000252 /* break out, this key is allowed */
253 allowed = 1;
Damien Miller50a41ed2000-10-16 12:14:42 +1100254 break;
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000255 }
256
Damien Miller95def091999-11-25 00:26:21 +1100257 /* Close the file. */
258 fclose(f);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000259
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000260 /* return key if allowed */
261 if (allowed && rkey != NULL)
262 *rkey = key;
263 else
264 key_free(key);
Damien Millerd8478b62011-05-29 21:39:36 +1000265
266 return allowed;
267}
268
269/*
270 * check if there's user key matching client_n,
271 * return key if login is allowed, NULL otherwise
272 */
273
274int
275auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey)
276{
277 char *file;
278 u_int i, allowed = 0;
279
280 temporarily_use_uid(pw);
281
282 for (i = 0; !allowed && i < options.num_authkeys_files; i++) {
Damien Miller09d3e122012-10-31 08:58:58 +1100283 if (strcasecmp(options.authorized_keys_files[i], "none") == 0)
284 continue;
Damien Millerd8478b62011-05-29 21:39:36 +1000285 file = expand_authorized_keys(
286 options.authorized_keys_files[i], pw);
287 allowed = rsa_key_allowed_in_file(pw, file, client_n, rkey);
Darren Tuckera627d422013-06-02 07:31:17 +1000288 free(file);
Damien Millerd8478b62011-05-29 21:39:36 +1000289 }
290
291 restore_uid();
292
293 return allowed;
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000294}
295
296/*
297 * Performs the RSA authentication dialog with the client. This returns
298 * 0 if the client could not be authenticated, and 1 if authentication was
299 * successful. This may exit if there is a serious protocol violation.
300 */
301int
Damien Miller3e3b5142003-11-17 21:13:40 +1100302auth_rsa(Authctxt *authctxt, BIGNUM *client_n)
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000303{
304 Key *key;
Damien Miller3e3b5142003-11-17 21:13:40 +1100305 struct passwd *pw = authctxt->pw;
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000306
307 /* no user given */
Damien Miller3e3b5142003-11-17 21:13:40 +1100308 if (!authctxt->valid)
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000309 return 0;
310
Ben Lindstrom7a2073c2002-03-22 02:30:41 +0000311 if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) {
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000312 auth_clear_options();
313 return (0);
314 }
315
316 /* Perform the challenge-response dialog for this key. */
317 if (!auth_rsa_challenge_dialog(key)) {
318 /* Wrong response. */
319 verbose("Wrong response to RSA authentication challenge.");
320 packet_send_debug("Wrong response to RSA authentication challenge.");
321 /*
322 * Break out of the loop. Otherwise we might send
323 * another challenge and break the protocol.
324 */
325 key_free(key);
326 return (0);
327 }
328 /*
329 * Correct response. The client has been successfully
330 * authenticated. Note that we have not yet processed the
331 * options; this will be reset if the options cause the
332 * authentication to be rejected.
333 */
Damien Miller20bdcd72013-07-18 16:10:09 +1000334 pubkey_auth_info(authctxt, key, NULL);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000335
Ben Lindstrom9c8aefe2002-03-22 01:12:58 +0000336 packet_send_debug("RSA authentication accepted.");
337 return (1);
Damien Millerd4a8b7e1999-10-27 13:42:43 +1000338}