[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 1.51 2002/03/14 16:56:33 markus 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"

/* 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.
 */

static 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;
}

static 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 = 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 = 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
 */

static int
auth_rsa_key_allowed(struct passwd *pw, BIGNUM *client_n, Key **rkey)
{
	char line[8192], *file;
	int allowed;
	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 (auth_rsa_key_allowed(pw, client_n, &key) == 0) {
		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"
46f1eece	17	RCSID("$OpenBSD: auth-rsa.c,v 1.51 2002/03/14 16:56:33 markus 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"
94ec8c6b	35
	36	/* import */
	37	extern ServerOptions options;
	38
aa3378df	39	/*
	40	* Session identifier that is used to bind key exchange and authentication
	41	* responses to a particular session.
	42	*/
1e3b8b07	43	extern u_char session_id[16];
8efc0c15	44
aa3378df	45	/*
	46	* The .ssh/authorized_keys file contains public keys, one per line, in the
	47	* following format:
	48	* options bits e n comment
	49	* where bits, e and n are decimal numbers,
	50	* and comment is any string of characters up to newline. The maximum
	51	* length of a line is 8000 characters. See the documentation for a
	52	* description of the options.
	53	*/
8efc0c15	54
46f1eece	55	static BIGNUM *
	56	auth_rsa_generate_challenge(Key *key)
	57	{
	58	BIGNUM *challenge;
	59	BN_CTX *ctx;
	60
	61	if ((challenge = BN_new()) == NULL)
	62	fatal("auth_rsa_generate_challenge: BN_new() failed");
	63	/* Generate a random challenge. */
	64	BN_rand(challenge, 256, 0, 0);
	65	if ((ctx = BN_CTX_new()) == NULL)
	66	fatal("auth_rsa_generate_challenge: BN_CTX_new() failed");
	67	BN_mod(challenge, challenge, key->rsa->n, ctx);
	68	BN_CTX_free(ctx);
	69
	70	return challenge;
	71	}
	72
	73	static int
	74	auth_rsa_verify_response(Key key, BIGNUM challenge, u_char response[16])
	75	{
	76	u_char buf[32], mdbuf[16];
	77	MD5_CTX md;
	78	int len;
	79
	80	/* The response is MD5 of decrypted challenge plus session id. */
	81	len = BN_num_bytes(challenge);
	82	if (len <= 0 \|\| len > 32)
	83	fatal("auth_rsa_verify_response: bad challenge length %d", len);
	84	memset(buf, 0, 32);
	85	BN_bn2bin(challenge, buf + 32 - len);
	86	MD5_Init(&md);
	87	MD5_Update(&md, buf, 32);
	88	MD5_Update(&md, session_id, 16);
	89	MD5_Final(mdbuf, &md);
	90
	91	/* Verify that the response is the original challenge. */
	92	if (memcmp(response, mdbuf, 16) != 0) {
	93	/* Wrong answer. */
	94	return (0);
	95	}
	96	/* Correct answer. */
	97	return (1);
	98	}
	99
aa3378df	100	/*
	101	* Performs the RSA authentication challenge-response dialog with the client,
	102	* and returns true (non-zero) if the client gave the correct answer to
	103	* our challenge; returns zero if the client gives a wrong answer.
	104	*/
8efc0c15	105
8efc0c15	106	int
46f1eece	107	auth_rsa_challenge_dialog(Key *key)
8efc0c15	108	{
c8d54615	109	BIGNUM challenge, encrypted_challenge;
46f1eece	110	u_char response[16];
46f1eece	111	int i, success;
5260325f	112
b775c6f2	113	if ((encrypted_challenge = BN_new()) == NULL)
b775c6f2	114	fatal("auth_rsa_challenge_dialog: BN_new() failed");
5260325f	115
46f1eece	116	challenge = auth_rsa_generate_challenge(key);
5260325f	117
5260325f	118	/* Encrypt the challenge with the public key. */
46f1eece	119	rsa_public_encrypt(encrypted_challenge, challenge, key->rsa);
5260325f	120
	121	/* Send the encrypted challenge to the client. */
	122	packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
	123	packet_put_bignum(encrypted_challenge);
	124	packet_send();
c8d54615	125	BN_clear_free(encrypted_challenge);
5260325f	126	packet_write_wait();
5260325f	127
c8d54615	128	/* Wait for a response. */
54a5250f	129	packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE);
c8d54615	130	for (i = 0; i < 16; i++)
c8d54615	131	response[i] = packet_get_char();
95500969	132	packet_check_eom();
c8d54615	133
46f1eece	134	success = auth_rsa_verify_response(key, challenge, response);
5260325f	135	BN_clear_free(challenge);
46f1eece	136	return (success);
8efc0c15	137	}
8efc0c15	138
aa3378df	139	/*
46f1eece	140	* check if there's user key matching client_n,
46f1eece	141	* return key if login is allowed, NULL otherwise
aa3378df	142	*/
8efc0c15	143
46f1eece	144	static int
46f1eece	145	auth_rsa_key_allowed(struct passwd pw, BIGNUM client_n, Key **rkey)
8efc0c15	146	{
c8445989	147	char line[8192], *file;
46f1eece	148	int allowed;
1e3b8b07	149	u_int bits;
5260325f	150	FILE *f;
1e3b8b07	151	u_long linenum = 0;
5260325f	152	struct stat st;
46df736f	153	Key *key;
94ec8c6b	154
5260325f	155	/* Temporarily use the user's uid. */
63bd8c36	156	temporarily_use_uid(pw);
5260325f	157
5260325f	158	/* The authorized keys. */
c8445989	159	file = authorized_keys_file(pw);
c8445989	160	debug("trying public RSA key file %s", file);
5260325f	161
	162	/* Fail quietly if file does not exist */
	163	if (stat(file, &st) < 0) {
	164	/* Restore the privileged uid. */
	165	restore_uid();
c8445989	166	xfree(file);
46f1eece	167	return (NULL);
8efc0c15	168	}
5260325f	169	/* Open the file containing the authorized keys. */
	170	f = fopen(file, "r");
	171	if (!f) {
	172	/* Restore the privileged uid. */
	173	restore_uid();
c8445989	174	xfree(file);
46f1eece	175	return (NULL);
8efc0c15	176	}
c8445989	177	if (options.strict_modes &&
6978866a	178	secure_filename(f, file, pw, line, sizeof(line)) != 0) {
c8445989	179	xfree(file);
	180	fclose(f);
	181	log("Authentication refused: %s", line);
c8445989	182	restore_uid();
46f1eece	183	return (NULL);
5260325f	184	}
46f1eece	185
	186	/* Flag indicating whether the key is allowed. */
	187	allowed = 0;
5260325f	188
46df736f	189	key = key_new(KEY_RSA1);
5260325f	190
aa3378df	191	/*
	192	* Go though the accepted keys, looking for the current key. If
	193	* found, perform a challenge-response dialog to verify that the
	194	* user really has the corresponding private key.
	195	*/
5260325f	196	while (fgets(line, sizeof(line), f)) {
	197	char *cp;
	198	char *options;
	199
	200	linenum++;
	201
aa3378df	202	/* Skip leading whitespace, empty and comment lines. */
	203	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	204	;
5260325f	205	if (!cp \|\| cp == '\n' \|\| *cp == '#')
	206	continue;
	207
aa3378df	208	/*
	209	* Check if there are options for this key, and if so,
	210	* save their starting address and skip the option part
	211	* for now. If there are no options, set the starting
	212	* address to NULL.
	213	*/
5260325f	214	if (cp < '0' \|\| cp > '9') {
	215	int quoted = 0;
	216	options = cp;
	217	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
	218	if (*cp == '\\' && cp[1] == '"')
	219	cp++; /* Skip both */
	220	else if (*cp == '"')
	221	quoted = !quoted;
8efc0c15	222	}
5260325f	223	} else
	224	options = NULL;
	225
	226	/* Parse the key from the line. */
46df736f	227	if (hostfile_read_key(&cp, &bits, key) == 0) {
96a7b0cc	228	debug("%.100s, line %lu: non ssh1 key syntax",
42f11eb2	229	file, linenum);
5260325f	230	continue;
8efc0c15	231	}
5260325f	232	/* cp now points to the comment part. */
5260325f	233
5260325f	234	/* Check if the we have found the desired key (identified by its modulus). */
46df736f	235	if (BN_cmp(key->rsa->n, client_n) != 0)
aa3378df	236	continue;
5260325f	237
57112b5a	238	/* check the real bits */
46df736f	239	if (bits != BN_num_bits(key->rsa->n))
1bdee08c	240	log("Warning: %s, line %lu: keysize mismatch: "
57112b5a	241	"actual %d vs. announced %d.",
46df736f	242	file, linenum, BN_num_bits(key->rsa->n), bits);
57112b5a	243
5260325f	244	/* We have found the desired key. */
d343d900	245	/*
	246	* If our options do not allow this key to be used,
	247	* do not send challenge.
	248	*/
42f11eb2	249	if (!auth_parse_options(pw, options, file, linenum))
d343d900	250	continue;
5260325f	251
46f1eece	252	/* break out, this key is allowed */
46f1eece	253	allowed = 1;
33de75a3	254	break;
8efc0c15	255	}
8efc0c15	256
5260325f	257	/* Restore the privileged uid. */
5260325f	258	restore_uid();
8efc0c15	259
5260325f	260	/* Close the file. */
c8445989	261	xfree(file);
5260325f	262	fclose(f);
8efc0c15	263
46f1eece	264	/* return key if allowed */
	265	if (allowed && rkey != NULL)
	266	*rkey = key;
94ec8c6b	267	else
46f1eece	268	key_free(key);
	269	return (allowed);
	270	}
	271
	272	/*
	273	* Performs the RSA authentication dialog with the client. This returns
	274	* 0 if the client could not be authenticated, and 1 if authentication was
	275	* successful. This may exit if there is a serious protocol violation.
	276	*/
	277	int
	278	auth_rsa(struct passwd pw, BIGNUM client_n)
	279	{
	280	Key *key;
	281	char *fp;
	282
	283	/* no user given */
	284	if (pw == NULL)
	285	return 0;
	286
	287	if (auth_rsa_key_allowed(pw, client_n, &key) == 0) {
94ec8c6b	288	auth_clear_options();
46f1eece	289	return (0);
	290	}
	291
	292	/* Perform the challenge-response dialog for this key. */
	293	if (!auth_rsa_challenge_dialog(key)) {
	294	/* Wrong response. */
	295	verbose("Wrong response to RSA authentication challenge.");
	296	packet_send_debug("Wrong response to RSA authentication challenge.");
	297	/*
	298	* Break out of the loop. Otherwise we might send
	299	* another challenge and break the protocol.
	300	*/
	301	key_free(key);
	302	return (0);
	303	}
	304	/*
	305	* Correct response. The client has been successfully
	306	* authenticated. Note that we have not yet processed the
	307	* options; this will be reset if the options cause the
	308	* authentication to be rejected.
	309	*/
	310	fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
	311	verbose("Found matching %s key: %s",
	312	key_type(key), fp);
	313	xfree(fp);
	314	key_free(key);
8efc0c15	315
46f1eece	316	packet_send_debug("RSA authentication accepted.");
46f1eece	317	return (1);
8efc0c15	318	}