[openssh.git] / auth-rsa.c

/*
 * 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"
RCSID("$OpenBSD: auth-rsa.c,v 1.52 2002/03/18 17:50:31 provos Exp $");

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

#include "rsa.h"
#include "packet.h"
#include "xmalloc.h"
#include "ssh1.h"
#include "mpaux.h"
#include "uidswap.h"
#include "match.h"
#include "auth-options.h"
#include "pathnames.h"
#include "log.h"
#include "servconf.h"
#include "auth.h"
#include "hostfile.h"
#include "monitor_wrap.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 8000 characters.  See the documentation 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. */
	BN_rand(challenge, 256, 0, 0);
	if ((ctx = BN_CTX_new()) == NULL)
		fatal("auth_rsa_generate_challenge: BN_CTX_new() failed");
	BN_mod(challenge, challenge, key->rsa->n, ctx);
	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;

	/* 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] = 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[8192], *file;
	int allowed = 0;
	u_int bits;
	FILE *f;
	u_long linenum = 0;
	struct stat st;
	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);

	/* Fail quietly if file does not exist */
	if (stat(file, &st) < 0) {
		/* Restore the privileged uid. */
		restore_uid();
		xfree(file);
		return (NULL);
	}
	/* Open the file containing the authorized keys. */
	f = fopen(file, "r");
	if (!f) {
		/* Restore the privileged uid. */
		restore_uid();
		xfree(file);
		return (NULL);
	}
	if (options.strict_modes &&
	    secure_filename(f, file, pw, line, sizeof(line)) != 0) {
		xfree(file);
		fclose(f);
		log("Authentication refused: %s", line);
		restore_uid();
		return (NULL);
	}

	/* 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 (fgets(line, sizeof(line), f)) {
		char *cp;
		char *options;

		linenum++;

		/* 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;
			options = cp;
			for (; *cp && (quoted || (*cp != ' ' && *cp != '\t')); cp++) {
				if (*cp == '\\' && cp[1] == '"')
					cp++;	/* Skip both */
				else if (*cp == '"')
					quoted = !quoted;
			}
		} else
			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  */
		if (bits != BN_num_bits(key->rsa->n))
			log("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, 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(struct passwd *pw, BIGNUM *client_n)
{
	Key *key;
	char *fp;

	/* no user given */
	if (pw == NULL)
		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
8efc0c15	1	/*
5260325f	2	* Author: Tatu Ylonen <ylo@cs.hut.fi>
5260325f	3	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
5260325f	4	* All rights reserved
5260325f	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.
6ae2364d	8	*
bcbf86ec	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".
5260325f	14	*/
8efc0c15	15
8efc0c15	16	#include "includes.h"
1853d1ef	17	RCSID("$OpenBSD: auth-rsa.c,v 1.52 2002/03/18 17:50:31 provos Exp $");
42f11eb2	18
	19	#include <openssl/rsa.h>
	20	#include <openssl/md5.h>
8efc0c15	21
	22	#include "rsa.h"
	23	#include "packet.h"
	24	#include "xmalloc.h"
42f11eb2	25	#include "ssh1.h"
8efc0c15	26	#include "mpaux.h"
8efc0c15	27	#include "uidswap.h"
4fe2af09	28	#include "match.h"
38c295d6	29	#include "auth-options.h"
42f11eb2	30	#include "pathnames.h"
	31	#include "log.h"
	32	#include "servconf.h"
	33	#include "auth.h"
46df736f	34	#include "hostfile.h"
1853d1ef	35	#include "monitor_wrap.h"
94ec8c6b	36
	37	/* import */
	38	extern ServerOptions options;
	39
aa3378df	40	/*
	41	* Session identifier that is used to bind key exchange and authentication
	42	* responses to a particular session.
	43	*/
1e3b8b07	44	extern u_char session_id[16];
8efc0c15	45
aa3378df	46	/*
	47	* The .ssh/authorized_keys file contains public keys, one per line, in the
	48	* following format:
	49	* options bits e n comment
	50	* where bits, e and n are decimal numbers,
	51	* and comment is any string of characters up to newline. The maximum
	52	* length of a line is 8000 characters. See the documentation for a
	53	* description of the options.
	54	*/
8efc0c15	55
1853d1ef	56	BIGNUM *
46f1eece	57	auth_rsa_generate_challenge(Key *key)
	58	{
	59	BIGNUM *challenge;
	60	BN_CTX *ctx;
	61
	62	if ((challenge = BN_new()) == NULL)
	63	fatal("auth_rsa_generate_challenge: BN_new() failed");
	64	/* Generate a random challenge. */
	65	BN_rand(challenge, 256, 0, 0);
	66	if ((ctx = BN_CTX_new()) == NULL)
	67	fatal("auth_rsa_generate_challenge: BN_CTX_new() failed");
	68	BN_mod(challenge, challenge, key->rsa->n, ctx);
	69	BN_CTX_free(ctx);
	70
	71	return challenge;
	72	}
	73
1853d1ef	74	int
46f1eece	75	auth_rsa_verify_response(Key key, BIGNUM challenge, u_char response[16])
	76	{
	77	u_char buf[32], mdbuf[16];
	78	MD5_CTX md;
	79	int len;
	80
	81	/* The response is MD5 of decrypted challenge plus session id. */
	82	len = BN_num_bytes(challenge);
	83	if (len <= 0 \|\| len > 32)
	84	fatal("auth_rsa_verify_response: bad challenge length %d", len);
	85	memset(buf, 0, 32);
	86	BN_bn2bin(challenge, buf + 32 - len);
	87	MD5_Init(&md);
	88	MD5_Update(&md, buf, 32);
	89	MD5_Update(&md, session_id, 16);
	90	MD5_Final(mdbuf, &md);
	91
	92	/* Verify that the response is the original challenge. */
	93	if (memcmp(response, mdbuf, 16) != 0) {
	94	/* Wrong answer. */
	95	return (0);
	96	}
	97	/* Correct answer. */
	98	return (1);
	99	}
	100
aa3378df	101	/*
	102	* Performs the RSA authentication challenge-response dialog with the client,
	103	* and returns true (non-zero) if the client gave the correct answer to
	104	* our challenge; returns zero if the client gives a wrong answer.
	105	*/
8efc0c15	106
8efc0c15	107	int
46f1eece	108	auth_rsa_challenge_dialog(Key *key)
8efc0c15	109	{
c8d54615	110	BIGNUM challenge, encrypted_challenge;
46f1eece	111	u_char response[16];
46f1eece	112	int i, success;
5260325f	113
b775c6f2	114	if ((encrypted_challenge = BN_new()) == NULL)
b775c6f2	115	fatal("auth_rsa_challenge_dialog: BN_new() failed");
5260325f	116
1853d1ef	117	challenge = PRIVSEP(auth_rsa_generate_challenge(key));
5260325f	118
5260325f	119	/* Encrypt the challenge with the public key. */
46f1eece	120	rsa_public_encrypt(encrypted_challenge, challenge, key->rsa);
5260325f	121
	122	/* Send the encrypted challenge to the client. */
	123	packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
	124	packet_put_bignum(encrypted_challenge);
	125	packet_send();
c8d54615	126	BN_clear_free(encrypted_challenge);
5260325f	127	packet_write_wait();
5260325f	128
c8d54615	129	/* Wait for a response. */
54a5250f	130	packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE);
c8d54615	131	for (i = 0; i < 16; i++)
c8d54615	132	response[i] = packet_get_char();
95500969	133	packet_check_eom();
c8d54615	134
1853d1ef	135	success = PRIVSEP(auth_rsa_verify_response(key, challenge, response));
5260325f	136	BN_clear_free(challenge);
46f1eece	137	return (success);
8efc0c15	138	}
8efc0c15	139
aa3378df	140	/*
46f1eece	141	* check if there's user key matching client_n,
46f1eece	142	* return key if login is allowed, NULL otherwise
aa3378df	143	*/
8efc0c15	144
1853d1ef	145	int
46f1eece	146	auth_rsa_key_allowed(struct passwd pw, BIGNUM client_n, Key **rkey)
8efc0c15	147	{
c8445989	148	char line[8192], *file;
1853d1ef	149	int allowed = 0;
1e3b8b07	150	u_int bits;
5260325f	151	FILE *f;
1e3b8b07	152	u_long linenum = 0;
5260325f	153	struct stat st;
46df736f	154	Key *key;
94ec8c6b	155
5260325f	156	/* Temporarily use the user's uid. */
63bd8c36	157	temporarily_use_uid(pw);
5260325f	158
5260325f	159	/* The authorized keys. */
c8445989	160	file = authorized_keys_file(pw);
c8445989	161	debug("trying public RSA key file %s", file);
5260325f	162
	163	/* Fail quietly if file does not exist */
	164	if (stat(file, &st) < 0) {
	165	/* Restore the privileged uid. */
	166	restore_uid();
c8445989	167	xfree(file);
46f1eece	168	return (NULL);
8efc0c15	169	}
5260325f	170	/* Open the file containing the authorized keys. */
	171	f = fopen(file, "r");
	172	if (!f) {
	173	/* Restore the privileged uid. */
	174	restore_uid();
c8445989	175	xfree(file);
46f1eece	176	return (NULL);
8efc0c15	177	}
c8445989	178	if (options.strict_modes &&
6978866a	179	secure_filename(f, file, pw, line, sizeof(line)) != 0) {
c8445989	180	xfree(file);
	181	fclose(f);
	182	log("Authentication refused: %s", line);
c8445989	183	restore_uid();
46f1eece	184	return (NULL);
5260325f	185	}
46f1eece	186
	187	/* Flag indicating whether the key is allowed. */
	188	allowed = 0;
5260325f	189
46df736f	190	key = key_new(KEY_RSA1);
5260325f	191
aa3378df	192	/*
	193	* Go though the accepted keys, looking for the current key. If
	194	* found, perform a challenge-response dialog to verify that the
	195	* user really has the corresponding private key.
	196	*/
5260325f	197	while (fgets(line, sizeof(line), f)) {
	198	char *cp;
	199	char *options;
	200
	201	linenum++;
	202
aa3378df	203	/* Skip leading whitespace, empty and comment lines. */
	204	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	205	;
5260325f	206	if (!cp \|\| cp == '\n' \|\| *cp == '#')
	207	continue;
	208
aa3378df	209	/*
	210	* Check if there are options for this key, and if so,
	211	* save their starting address and skip the option part
	212	* for now. If there are no options, set the starting
	213	* address to NULL.
	214	*/
5260325f	215	if (cp < '0' \|\| cp > '9') {
	216	int quoted = 0;
	217	options = cp;
	218	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
	219	if (*cp == '\\' && cp[1] == '"')
	220	cp++; /* Skip both */
	221	else if (*cp == '"')
	222	quoted = !quoted;
8efc0c15	223	}
5260325f	224	} else
	225	options = NULL;
	226
	227	/* Parse the key from the line. */
46df736f	228	if (hostfile_read_key(&cp, &bits, key) == 0) {
96a7b0cc	229	debug("%.100s, line %lu: non ssh1 key syntax",
42f11eb2	230	file, linenum);
5260325f	231	continue;
8efc0c15	232	}
5260325f	233	/* cp now points to the comment part. */
5260325f	234
5260325f	235	/* Check if the we have found the desired key (identified by its modulus). */
46df736f	236	if (BN_cmp(key->rsa->n, client_n) != 0)
aa3378df	237	continue;
5260325f	238
57112b5a	239	/* check the real bits */
46df736f	240	if (bits != BN_num_bits(key->rsa->n))
1bdee08c	241	log("Warning: %s, line %lu: keysize mismatch: "
57112b5a	242	"actual %d vs. announced %d.",
46df736f	243	file, linenum, BN_num_bits(key->rsa->n), bits);
57112b5a	244
5260325f	245	/* We have found the desired key. */
d343d900	246	/*
	247	* If our options do not allow this key to be used,
	248	* do not send challenge.
	249	*/
42f11eb2	250	if (!auth_parse_options(pw, options, file, linenum))
d343d900	251	continue;
5260325f	252
46f1eece	253	/* break out, this key is allowed */
46f1eece	254	allowed = 1;
33de75a3	255	break;
8efc0c15	256	}
8efc0c15	257
5260325f	258	/* Restore the privileged uid. */
5260325f	259	restore_uid();
8efc0c15	260
5260325f	261	/* Close the file. */
c8445989	262	xfree(file);
5260325f	263	fclose(f);
8efc0c15	264
46f1eece	265	/* return key if allowed */
	266	if (allowed && rkey != NULL)
	267	*rkey = key;
94ec8c6b	268	else
46f1eece	269	key_free(key);
	270	return (allowed);
	271	}
	272
	273	/*
	274	* Performs the RSA authentication dialog with the client. This returns
	275	* 0 if the client could not be authenticated, and 1 if authentication was
	276	* successful. This may exit if there is a serious protocol violation.
	277	*/
	278	int
	279	auth_rsa(struct passwd pw, BIGNUM client_n)
	280	{
	281	Key *key;
	282	char *fp;
	283
	284	/* no user given */
	285	if (pw == NULL)
	286	return 0;
	287
1853d1ef	288	if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) {
94ec8c6b	289	auth_clear_options();
46f1eece	290	return (0);
	291	}
	292
	293	/* Perform the challenge-response dialog for this key. */
	294	if (!auth_rsa_challenge_dialog(key)) {
	295	/* Wrong response. */
	296	verbose("Wrong response to RSA authentication challenge.");
	297	packet_send_debug("Wrong response to RSA authentication challenge.");
	298	/*
	299	* Break out of the loop. Otherwise we might send
	300	* another challenge and break the protocol.
	301	*/
	302	key_free(key);
	303	return (0);
	304	}
	305	/*
	306	* Correct response. The client has been successfully
	307	* authenticated. Note that we have not yet processed the
	308	* options; this will be reset if the options cause the
	309	* authentication to be rejected.
	310	*/
	311	fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
	312	verbose("Found matching %s key: %s",
	313	key_type(key), fp);
	314	xfree(fp);
	315	key_free(key);
8efc0c15	316
46f1eece	317	packet_send_debug("RSA authentication accepted.");
46f1eece	318	return (1);
8efc0c15	319	}