[openssh.git] / auth-rsa.c

/* $OpenBSD: auth-rsa.c,v 1.73 2008/07/02 12:03:51 dtucker Exp $ */
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * RSA-based authentication.  This code determines whether to admit a login
 * based on RSA authentication.  This file also contains functions to check
 * validity of the host key.
 *
 * As far as I am concerned, the code I have written for this software
 * can be used freely for any purpose.  Any derived versions of this
 * software must be clearly marked as such, and if the derived work is
 * incompatible with the protocol description in the RFC file, it must be
 * called by a name other than "ssh" or "Secure Shell".
 */

#include "includes.h"

#include <sys/types.h>
#include <sys/stat.h>

#include <openssl/rsa.h>
#include <openssl/md5.h>

#include <pwd.h>
#include <stdio.h>
#include <stdarg.h>
#include <string.h>

#include "xmalloc.h"
#include "rsa.h"
#include "packet.h"
#include "ssh1.h"
#include "uidswap.h"
#include "match.h"
#include "buffer.h"
#include "auth-options.h"
#include "pathnames.h"
#include "log.h"
#include "servconf.h"
#include "key.h"
#include "hostfile.h"
#include "auth.h"
#ifdef GSSAPI
#include "ssh-gss.h"
#endif
#include "monitor_wrap.h"
#include "ssh.h"
#include "misc.h"

/* import */
extern ServerOptions options;

/*
 * Session identifier that is used to bind key exchange and authentication
 * responses to a particular session.
 */
extern u_char session_id[16];

/*
 * The .ssh/authorized_keys file contains public keys, one per line, in the
 * following format:
 *   options bits e n comment
 * where bits, e and n are decimal numbers,
 * and comment is any string of characters up to newline.  The maximum
 * length of a line is SSH_MAX_PUBKEY_BYTES characters.  See sshd(8) for a
 * description of the options.
 */

BIGNUM *
auth_rsa_generate_challenge(Key *key)
{
	BIGNUM *challenge;
	BN_CTX *ctx;

	if ((challenge = BN_new()) == NULL)
		fatal("auth_rsa_generate_challenge: BN_new() failed");
	/* Generate a random challenge. */
	if (BN_rand(challenge, 256, 0, 0) == 0)
		fatal("auth_rsa_generate_challenge: BN_rand failed");
	if ((ctx = BN_CTX_new()) == NULL)
		fatal("auth_rsa_generate_challenge: BN_CTX_new failed");
	if (BN_mod(challenge, challenge, key->rsa->n, ctx) == 0)
		fatal("auth_rsa_generate_challenge: BN_mod failed");
	BN_CTX_free(ctx);

	return challenge;
}

int
auth_rsa_verify_response(Key *key, BIGNUM *challenge, u_char response[16])
{
	u_char buf[32], mdbuf[16];
	MD5_CTX md;
	int len;

	/* don't allow short keys */
	if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
		error("auth_rsa_verify_response: RSA modulus too small: %d < minimum %d bits",
		    BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
		return (0);
	}

	/* The response is MD5 of decrypted challenge plus session id. */
	len = BN_num_bytes(challenge);
	if (len <= 0 || len > 32)
		fatal("auth_rsa_verify_response: bad challenge length %d", len);
	memset(buf, 0, 32);
	BN_bn2bin(challenge, buf + 32 - len);
	MD5_Init(&md);
	MD5_Update(&md, buf, 32);
	MD5_Update(&md, session_id, 16);
	MD5_Final(mdbuf, &md);

	/* Verify that the response is the original challenge. */
	if (memcmp(response, mdbuf, 16) != 0) {
		/* Wrong answer. */
		return (0);
	}
	/* Correct answer. */
	return (1);
}

/*
 * Performs the RSA authentication challenge-response dialog with the client,
 * and returns true (non-zero) if the client gave the correct answer to
 * our challenge; returns zero if the client gives a wrong answer.
 */

int
auth_rsa_challenge_dialog(Key *key)
{
	BIGNUM *challenge, *encrypted_challenge;
	u_char response[16];
	int i, success;

	if ((encrypted_challenge = BN_new()) == NULL)
		fatal("auth_rsa_challenge_dialog: BN_new() failed");

	challenge = PRIVSEP(auth_rsa_generate_challenge(key));

	/* Encrypt the challenge with the public key. */
	rsa_public_encrypt(encrypted_challenge, challenge, key->rsa);

	/* Send the encrypted challenge to the client. */
	packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
	packet_put_bignum(encrypted_challenge);
	packet_send();
	BN_clear_free(encrypted_challenge);
	packet_write_wait();

	/* Wait for a response. */
	packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE);
	for (i = 0; i < 16; i++)
		response[i] = (u_char)packet_get_char();
	packet_check_eom();

	success = PRIVSEP(auth_rsa_verify_response(key, challenge, response));
	BN_clear_free(challenge);
	return (success);
}

/*
 * check if there's user key matching client_n,
 * return key if login is allowed, NULL otherwise
 */

int
auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey)
{
	char line[SSH_MAX_PUBKEY_BYTES], *file;
	int allowed = 0;
	u_int bits;
	FILE *f;
	u_long linenum = 0;
	Key *key;

	/* Temporarily use the user's uid. */
	temporarily_use_uid(pw);

	/* The authorized keys. */
	file = authorized_keys_file(pw);
	debug("trying public RSA key file %s", file);
	f = auth_openkeyfile(file, pw, options.strict_modes);
	if (!f) {
		xfree(file);
		restore_uid();
		return (0);
	}

	/* Flag indicating whether the key is allowed. */
	allowed = 0;

	key = key_new(KEY_RSA1);

	/*
	 * Go though the accepted keys, looking for the current key.  If
	 * found, perform a challenge-response dialog to verify that the
	 * user really has the corresponding private key.
	 */
	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
		char *cp;
		char *key_options;
		int keybits;

		/* Skip leading whitespace, empty and comment lines. */
		for (cp = line; *cp == ' ' || *cp == '\t'; cp++)
			;
		if (!*cp || *cp == '\n' || *cp == '#')
			continue;

		/*
		 * Check if there are options for this key, and if so,
		 * save their starting address and skip the option part
		 * for now.  If there are no options, set the starting
		 * address to NULL.
		 */
		if (*cp < '0' || *cp > '9') {
			int quoted = 0;
			key_options = cp;
			for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
				if (*cp == '\\' && cp[1] == '"')
					cp++;	/* Skip both */
				else if (*cp == '"')
					quoted = !quoted;
			}
		} else
			key_options = NULL;

		/* Parse the key from the line. */
		if (hostfile_read_key(&cp, &bits, key) == 0) {
			debug("%.100s, line %lu: non ssh1 key syntax",
			    file, linenum);
			continue;
		}
		/* cp now points to the comment part. */

		/* Check if the we have found the desired key (identified by its modulus). */
		if (BN_cmp(key->rsa->n, client_n) != 0)
			continue;

		/* check the real bits  */
		keybits = BN_num_bits(key->rsa->n);
		if (keybits < 0 || bits != (u_int)keybits)
			logit("Warning: %s, line %lu: keysize mismatch: "
			    "actual %d vs. announced %d.",
			    file, linenum, BN_num_bits(key->rsa->n), bits);

		/* We have found the desired key. */
		/*
		 * If our options do not allow this key to be used,
		 * do not send challenge.
		 */
		if (!auth_parse_options(pw, key_options, file, linenum))
			continue;

		/* break out, this key is allowed */
		allowed = 1;
		break;
	}

	/* Restore the privileged uid. */
	restore_uid();

	/* Close the file. */
	xfree(file);
	fclose(f);

	/* return key if allowed */
	if (allowed && rkey != NULL)
		*rkey = key;
	else
		key_free(key);
	return (allowed);
}

/*
 * Performs the RSA authentication dialog with the client.  This returns
 * 0 if the client could not be authenticated, and 1 if authentication was
 * successful.  This may exit if there is a serious protocol violation.
 */
int
auth_rsa(Authctxt *authctxt, BIGNUM *client_n)
{
	Key *key;
	char *fp;
	struct passwd *pw = authctxt->pw;

	/* no user given */
	if (!authctxt->valid)
		return 0;

	if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) {
		auth_clear_options();
		return (0);
	}

	/* Perform the challenge-response dialog for this key. */
	if (!auth_rsa_challenge_dialog(key)) {
		/* Wrong response. */
		verbose("Wrong response to RSA authentication challenge.");
		packet_send_debug("Wrong response to RSA authentication challenge.");
		/*
		 * Break out of the loop. Otherwise we might send
		 * another challenge and break the protocol.
		 */
		key_free(key);
		return (0);
	}
	/*
	 * Correct response.  The client has been successfully
	 * authenticated. Note that we have not yet processed the
	 * options; this will be reset if the options cause the
	 * authentication to be rejected.
	 */
	fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
	verbose("Found matching %s key: %s",
	    key_type(key), fp);
	xfree(fp);
	key_free(key);

	packet_send_debug("RSA authentication accepted.");
	return (1);
}
Commit	Line	Data
f7c2a004	1	/* $OpenBSD: auth-rsa.c,v 1.73 2008/07/02 12:03:51 dtucker Exp $ */
8efc0c15	2	/*
5260325f	3	* Author: Tatu Ylonen <ylo@cs.hut.fi>
5260325f	4	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5260325f	5	* All rights reserved
5260325f	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.
6ae2364d	9	*
bcbf86ec	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".
5260325f	15	*/
8efc0c15	16
8efc0c15	17	#include "includes.h"
4095f623	18
	19	#include <sys/types.h>
	20	#include <sys/stat.h>
42f11eb2	21
	22	#include <openssl/rsa.h>
	23	#include <openssl/md5.h>
8efc0c15	24
b1842393	25	#include <pwd.h>
cf851879	26	#include <stdio.h>
24436b92	27	#include <stdarg.h>
00146caa	28	#include <string.h>
b1842393	29
31652869	30	#include "xmalloc.h"
8efc0c15	31	#include "rsa.h"
8efc0c15	32	#include "packet.h"
42f11eb2	33	#include "ssh1.h"
8efc0c15	34	#include "uidswap.h"
4fe2af09	35	#include "match.h"
31652869	36	#include "buffer.h"
38c295d6	37	#include "auth-options.h"
42f11eb2	38	#include "pathnames.h"
	39	#include "log.h"
	40	#include "servconf.h"
31652869	41	#include "key.h"
46df736f	42	#include "hostfile.h"
31652869	43	#include "auth.h"
	44	#ifdef GSSAPI
	45	#include "ssh-gss.h"
	46	#endif
1853d1ef	47	#include "monitor_wrap.h"
82b00264	48	#include "ssh.h"
41feb690	49	#include "misc.h"
94ec8c6b	50
	51	/* import */
	52	extern ServerOptions options;
	53
aa3378df	54	/*
	55	* Session identifier that is used to bind key exchange and authentication
	56	* responses to a particular session.
	57	*/
1e3b8b07	58	extern u_char session_id[16];
8efc0c15	59
aa3378df	60	/*
	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
ea067773	66	* length of a line is SSH_MAX_PUBKEY_BYTES characters. See sshd(8) for a
aa3378df	67	* description of the options.
aa3378df	68	*/
8efc0c15	69
1853d1ef	70	BIGNUM *
46f1eece	71	auth_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. */
e516451d	79	if (BN_rand(challenge, 256, 0, 0) == 0)
e516451d	80	fatal("auth_rsa_generate_challenge: BN_rand failed");
46f1eece	81	if ((ctx = BN_CTX_new()) == NULL)
e516451d	82	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");
46f1eece	85	BN_CTX_free(ctx);
	86
	87	return challenge;
	88	}
	89
1853d1ef	90	int
46f1eece	91	auth_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
52103b10	97	/* don't allow short keys */
82b00264	98	if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
b7ced7d1	99	error("auth_rsa_verify_response: RSA modulus too small: %d < minimum %d bits",
b7ced7d1	100	BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
52103b10	101	return (0);
	102	}
	103
46f1eece	104	/* 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
aa3378df	124	/*
	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	*/
8efc0c15	129
8efc0c15	130	int
46f1eece	131	auth_rsa_challenge_dialog(Key *key)
8efc0c15	132	{
c8d54615	133	BIGNUM challenge, encrypted_challenge;
46f1eece	134	u_char response[16];
46f1eece	135	int i, success;
5260325f	136
b775c6f2	137	if ((encrypted_challenge = BN_new()) == NULL)
b775c6f2	138	fatal("auth_rsa_challenge_dialog: BN_new() failed");
5260325f	139
1853d1ef	140	challenge = PRIVSEP(auth_rsa_generate_challenge(key));
5260325f	141
5260325f	142	/* Encrypt the challenge with the public key. */
46f1eece	143	rsa_public_encrypt(encrypted_challenge, challenge, key->rsa);
5260325f	144
	145	/* Send the encrypted challenge to the client. */
	146	packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
	147	packet_put_bignum(encrypted_challenge);
	148	packet_send();
c8d54615	149	BN_clear_free(encrypted_challenge);
5260325f	150	packet_write_wait();
5260325f	151
c8d54615	152	/* Wait for a response. */
54a5250f	153	packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE);
c8d54615	154	for (i = 0; i < 16; i++)
febd6f21	155	response[i] = (u_char)packet_get_char();
95500969	156	packet_check_eom();
c8d54615	157
1853d1ef	158	success = PRIVSEP(auth_rsa_verify_response(key, challenge, response));
5260325f	159	BN_clear_free(challenge);
46f1eece	160	return (success);
8efc0c15	161	}
8efc0c15	162
aa3378df	163	/*
46f1eece	164	* check if there's user key matching client_n,
46f1eece	165	* return key if login is allowed, NULL otherwise
aa3378df	166	*/
8efc0c15	167
1853d1ef	168	int
46f1eece	169	auth_rsa_key_allowed(struct passwd pw, BIGNUM client_n, Key **rkey)
8efc0c15	170	{
ea067773	171	char line[SSH_MAX_PUBKEY_BYTES], *file;
1853d1ef	172	int allowed = 0;
1e3b8b07	173	u_int bits;
5260325f	174	FILE *f;
1e3b8b07	175	u_long linenum = 0;
46df736f	176	Key *key;
94ec8c6b	177
5260325f	178	/* Temporarily use the user's uid. */
63bd8c36	179	temporarily_use_uid(pw);
5260325f	180
5260325f	181	/* The authorized keys. */
c8445989	182	file = authorized_keys_file(pw);
c8445989	183	debug("trying public RSA key file %s", file);
f7c2a004	184	f = auth_openkeyfile(file, pw, options.strict_modes);
5260325f	185	if (!f) {
c8445989	186	xfree(file);
c8445989	187	restore_uid();
159897f3	188	return (0);
5260325f	189	}
46f1eece	190
	191	/* Flag indicating whether the key is allowed. */
	192	allowed = 0;
5260325f	193
46df736f	194	key = key_new(KEY_RSA1);
5260325f	195
aa3378df	196	/*
	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	*/
ea067773	201	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
5260325f	202	char *cp;
ca75d7de	203	char *key_options;
2ceb8101	204	int keybits;
5260325f	205
aa3378df	206	/* Skip leading whitespace, empty and comment lines. */
	207	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	208	;
5260325f	209	if (!cp \|\| cp == '\n' \|\| *cp == '#')
	210	continue;
	211
aa3378df	212	/*
	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	*/
5260325f	218	if (cp < '0' \|\| cp > '9') {
5260325f	219	int quoted = 0;
ca75d7de	220	key_options = cp;
5260325f	221	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
	222	if (*cp == '\\' && cp[1] == '"')
	223	cp++; /* Skip both */
	224	else if (*cp == '"')
	225	quoted = !quoted;
8efc0c15	226	}
5260325f	227	} else
ca75d7de	228	key_options = NULL;
5260325f	229
5260325f	230	/* Parse the key from the line. */
46df736f	231	if (hostfile_read_key(&cp, &bits, key) == 0) {
96a7b0cc	232	debug("%.100s, line %lu: non ssh1 key syntax",
42f11eb2	233	file, linenum);
5260325f	234	continue;
8efc0c15	235	}
5260325f	236	/* cp now points to the comment part. */
5260325f	237
5260325f	238	/* Check if the we have found the desired key (identified by its modulus). */
46df736f	239	if (BN_cmp(key->rsa->n, client_n) != 0)
aa3378df	240	continue;
5260325f	241
57112b5a	242	/* check the real bits */
2ceb8101	243	keybits = BN_num_bits(key->rsa->n);
2ceb8101	244	if (keybits < 0 \|\| bits != (u_int)keybits)
bbe88b6d	245	logit("Warning: %s, line %lu: keysize mismatch: "
57112b5a	246	"actual %d vs. announced %d.",
46df736f	247	file, linenum, BN_num_bits(key->rsa->n), bits);
57112b5a	248
5260325f	249	/* We have found the desired key. */
d343d900	250	/*
	251	* If our options do not allow this key to be used,
	252	* do not send challenge.
	253	*/
ca75d7de	254	if (!auth_parse_options(pw, key_options, file, linenum))
d343d900	255	continue;
5260325f	256
46f1eece	257	/* break out, this key is allowed */
46f1eece	258	allowed = 1;
33de75a3	259	break;
8efc0c15	260	}
8efc0c15	261
5260325f	262	/* Restore the privileged uid. */
5260325f	263	restore_uid();
8efc0c15	264
5260325f	265	/* Close the file. */
c8445989	266	xfree(file);
5260325f	267	fclose(f);
8efc0c15	268
46f1eece	269	/* return key if allowed */
	270	if (allowed && rkey != NULL)
	271	*rkey = key;
94ec8c6b	272	else
46f1eece	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	*/
	282	int
fdaef11e	283	auth_rsa(Authctxt authctxt, BIGNUM client_n)
46f1eece	284	{
	285	Key *key;
	286	char *fp;
fdaef11e	287	struct passwd *pw = authctxt->pw;
46f1eece	288
46f1eece	289	/* no user given */
fdaef11e	290	if (!authctxt->valid)
46f1eece	291	return 0;
46f1eece	292
1853d1ef	293	if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) {
94ec8c6b	294	auth_clear_options();
46f1eece	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);
	320	key_free(key);
8efc0c15	321
46f1eece	322	packet_send_debug("RSA authentication accepted.");
46f1eece	323	return (1);
8efc0c15	324	}