[openssh.git] / auth-rsa.c

/* $OpenBSD: auth-rsa.c,v 1.69 2006/07/22 20:48:22 stevesk 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 <string.h>

#include "rsa.h"
#include "packet.h"
#include "xmalloc.h"
#include "ssh1.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"
#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. */
	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;

	/* 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;
	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 (0);
	}
	/* Open the file containing the authorized keys. */
	f = fopen(file, "r");
	if (!f) {
		/* Restore the privileged uid. */
		restore_uid();
		xfree(file);
		return (0);
	}
	if (options.strict_modes &&
	    secure_filename(f, file, pw, line, sizeof(line)) != 0) {
		xfree(file);
		fclose(f);
		logit("Authentication refused: %s", line);
		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
00146caa	1	/* $OpenBSD: auth-rsa.c,v 1.69 2006/07/22 20:48:22 stevesk 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>
00146caa	26	#include <string.h>
b1842393	27
8efc0c15	28	#include "rsa.h"
	29	#include "packet.h"
	30	#include "xmalloc.h"
42f11eb2	31	#include "ssh1.h"
8efc0c15	32	#include "uidswap.h"
4fe2af09	33	#include "match.h"
38c295d6	34	#include "auth-options.h"
42f11eb2	35	#include "pathnames.h"
	36	#include "log.h"
	37	#include "servconf.h"
	38	#include "auth.h"
46df736f	39	#include "hostfile.h"
1853d1ef	40	#include "monitor_wrap.h"
82b00264	41	#include "ssh.h"
41feb690	42	#include "misc.h"
94ec8c6b	43
	44	/* import */
	45	extern ServerOptions options;
	46
aa3378df	47	/*
	48	* Session identifier that is used to bind key exchange and authentication
	49	* responses to a particular session.
	50	*/
1e3b8b07	51	extern u_char session_id[16];
8efc0c15	52
aa3378df	53	/*
	54	* The .ssh/authorized_keys file contains public keys, one per line, in the
	55	* following format:
	56	* options bits e n comment
	57	* where bits, e and n are decimal numbers,
	58	* and comment is any string of characters up to newline. The maximum
ea067773	59	* length of a line is SSH_MAX_PUBKEY_BYTES characters. See sshd(8) for a
aa3378df	60	* description of the options.
aa3378df	61	*/
8efc0c15	62
1853d1ef	63	BIGNUM *
46f1eece	64	auth_rsa_generate_challenge(Key *key)
	65	{
	66	BIGNUM *challenge;
	67	BN_CTX *ctx;
	68
	69	if ((challenge = BN_new()) == NULL)
	70	fatal("auth_rsa_generate_challenge: BN_new() failed");
	71	/* Generate a random challenge. */
	72	BN_rand(challenge, 256, 0, 0);
	73	if ((ctx = BN_CTX_new()) == NULL)
	74	fatal("auth_rsa_generate_challenge: BN_CTX_new() failed");
	75	BN_mod(challenge, challenge, key->rsa->n, ctx);
	76	BN_CTX_free(ctx);
	77
	78	return challenge;
	79	}
	80
1853d1ef	81	int
46f1eece	82	auth_rsa_verify_response(Key key, BIGNUM challenge, u_char response[16])
	83	{
	84	u_char buf[32], mdbuf[16];
	85	MD5_CTX md;
	86	int len;
	87
52103b10	88	/* don't allow short keys */
82b00264	89	if (BN_num_bits(key->rsa->n) < SSH_RSA_MINIMUM_MODULUS_SIZE) {
b7ced7d1	90	error("auth_rsa_verify_response: RSA modulus too small: %d < minimum %d bits",
b7ced7d1	91	BN_num_bits(key->rsa->n), SSH_RSA_MINIMUM_MODULUS_SIZE);
52103b10	92	return (0);
	93	}
	94
46f1eece	95	/* The response is MD5 of decrypted challenge plus session id. */
	96	len = BN_num_bytes(challenge);
	97	if (len <= 0 \|\| len > 32)
	98	fatal("auth_rsa_verify_response: bad challenge length %d", len);
	99	memset(buf, 0, 32);
	100	BN_bn2bin(challenge, buf + 32 - len);
	101	MD5_Init(&md);
	102	MD5_Update(&md, buf, 32);
	103	MD5_Update(&md, session_id, 16);
	104	MD5_Final(mdbuf, &md);
	105
	106	/* Verify that the response is the original challenge. */
	107	if (memcmp(response, mdbuf, 16) != 0) {
	108	/* Wrong answer. */
	109	return (0);
	110	}
	111	/* Correct answer. */
	112	return (1);
	113	}
	114
aa3378df	115	/*
	116	* Performs the RSA authentication challenge-response dialog with the client,
	117	* and returns true (non-zero) if the client gave the correct answer to
	118	* our challenge; returns zero if the client gives a wrong answer.
	119	*/
8efc0c15	120
8efc0c15	121	int
46f1eece	122	auth_rsa_challenge_dialog(Key *key)
8efc0c15	123	{
c8d54615	124	BIGNUM challenge, encrypted_challenge;
46f1eece	125	u_char response[16];
46f1eece	126	int i, success;
5260325f	127
b775c6f2	128	if ((encrypted_challenge = BN_new()) == NULL)
b775c6f2	129	fatal("auth_rsa_challenge_dialog: BN_new() failed");
5260325f	130
1853d1ef	131	challenge = PRIVSEP(auth_rsa_generate_challenge(key));
5260325f	132
5260325f	133	/* Encrypt the challenge with the public key. */
46f1eece	134	rsa_public_encrypt(encrypted_challenge, challenge, key->rsa);
5260325f	135
	136	/* Send the encrypted challenge to the client. */
	137	packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
	138	packet_put_bignum(encrypted_challenge);
	139	packet_send();
c8d54615	140	BN_clear_free(encrypted_challenge);
5260325f	141	packet_write_wait();
5260325f	142
c8d54615	143	/* Wait for a response. */
54a5250f	144	packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE);
c8d54615	145	for (i = 0; i < 16; i++)
febd6f21	146	response[i] = (u_char)packet_get_char();
95500969	147	packet_check_eom();
c8d54615	148
1853d1ef	149	success = PRIVSEP(auth_rsa_verify_response(key, challenge, response));
5260325f	150	BN_clear_free(challenge);
46f1eece	151	return (success);
8efc0c15	152	}
8efc0c15	153
aa3378df	154	/*
46f1eece	155	* check if there's user key matching client_n,
46f1eece	156	* return key if login is allowed, NULL otherwise
aa3378df	157	*/
8efc0c15	158
1853d1ef	159	int
46f1eece	160	auth_rsa_key_allowed(struct passwd pw, BIGNUM client_n, Key **rkey)
8efc0c15	161	{
ea067773	162	char line[SSH_MAX_PUBKEY_BYTES], *file;
1853d1ef	163	int allowed = 0;
1e3b8b07	164	u_int bits;
5260325f	165	FILE *f;
1e3b8b07	166	u_long linenum = 0;
5260325f	167	struct stat st;
46df736f	168	Key *key;
94ec8c6b	169
5260325f	170	/* Temporarily use the user's uid. */
63bd8c36	171	temporarily_use_uid(pw);
5260325f	172
5260325f	173	/* The authorized keys. */
c8445989	174	file = authorized_keys_file(pw);
c8445989	175	debug("trying public RSA key file %s", file);
5260325f	176
	177	/* Fail quietly if file does not exist */
	178	if (stat(file, &st) < 0) {
	179	/* Restore the privileged uid. */
	180	restore_uid();
c8445989	181	xfree(file);
159897f3	182	return (0);
8efc0c15	183	}
5260325f	184	/* Open the file containing the authorized keys. */
	185	f = fopen(file, "r");
	186	if (!f) {
	187	/* Restore the privileged uid. */
	188	restore_uid();
c8445989	189	xfree(file);
159897f3	190	return (0);
8efc0c15	191	}
c8445989	192	if (options.strict_modes &&
6978866a	193	secure_filename(f, file, pw, line, sizeof(line)) != 0) {
c8445989	194	xfree(file);
c8445989	195	fclose(f);
bbe88b6d	196	logit("Authentication refused: %s", line);
c8445989	197	restore_uid();
159897f3	198	return (0);
5260325f	199	}
46f1eece	200
	201	/* Flag indicating whether the key is allowed. */
	202	allowed = 0;
5260325f	203
46df736f	204	key = key_new(KEY_RSA1);
5260325f	205
aa3378df	206	/*
	207	* Go though the accepted keys, looking for the current key. If
	208	* found, perform a challenge-response dialog to verify that the
	209	* user really has the corresponding private key.
	210	*/
ea067773	211	while (read_keyfile_line(f, file, line, sizeof(line), &linenum) != -1) {
5260325f	212	char *cp;
ca75d7de	213	char *key_options;
2ceb8101	214	int keybits;
5260325f	215
aa3378df	216	/* Skip leading whitespace, empty and comment lines. */
	217	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	218	;
5260325f	219	if (!cp \|\| cp == '\n' \|\| *cp == '#')
	220	continue;
	221
aa3378df	222	/*
	223	* Check if there are options for this key, and if so,
	224	* save their starting address and skip the option part
	225	* for now. If there are no options, set the starting
	226	* address to NULL.
	227	*/
5260325f	228	if (cp < '0' \|\| cp > '9') {
5260325f	229	int quoted = 0;
ca75d7de	230	key_options = cp;
5260325f	231	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
	232	if (*cp == '\\' && cp[1] == '"')
	233	cp++; /* Skip both */
	234	else if (*cp == '"')
	235	quoted = !quoted;
8efc0c15	236	}
5260325f	237	} else
ca75d7de	238	key_options = NULL;
5260325f	239
5260325f	240	/* Parse the key from the line. */
46df736f	241	if (hostfile_read_key(&cp, &bits, key) == 0) {
96a7b0cc	242	debug("%.100s, line %lu: non ssh1 key syntax",
42f11eb2	243	file, linenum);
5260325f	244	continue;
8efc0c15	245	}
5260325f	246	/* cp now points to the comment part. */
5260325f	247
5260325f	248	/* Check if the we have found the desired key (identified by its modulus). */
46df736f	249	if (BN_cmp(key->rsa->n, client_n) != 0)
aa3378df	250	continue;
5260325f	251
57112b5a	252	/* check the real bits */
2ceb8101	253	keybits = BN_num_bits(key->rsa->n);
2ceb8101	254	if (keybits < 0 \|\| bits != (u_int)keybits)
bbe88b6d	255	logit("Warning: %s, line %lu: keysize mismatch: "
57112b5a	256	"actual %d vs. announced %d.",
46df736f	257	file, linenum, BN_num_bits(key->rsa->n), bits);
57112b5a	258
5260325f	259	/* We have found the desired key. */
d343d900	260	/*
	261	* If our options do not allow this key to be used,
	262	* do not send challenge.
	263	*/
ca75d7de	264	if (!auth_parse_options(pw, key_options, file, linenum))
d343d900	265	continue;
5260325f	266
46f1eece	267	/* break out, this key is allowed */
46f1eece	268	allowed = 1;
33de75a3	269	break;
8efc0c15	270	}
8efc0c15	271
5260325f	272	/* Restore the privileged uid. */
5260325f	273	restore_uid();
8efc0c15	274
5260325f	275	/* Close the file. */
c8445989	276	xfree(file);
5260325f	277	fclose(f);
8efc0c15	278
46f1eece	279	/* return key if allowed */
	280	if (allowed && rkey != NULL)
	281	*rkey = key;
94ec8c6b	282	else
46f1eece	283	key_free(key);
	284	return (allowed);
	285	}
	286
	287	/*
	288	* Performs the RSA authentication dialog with the client. This returns
	289	* 0 if the client could not be authenticated, and 1 if authentication was
	290	* successful. This may exit if there is a serious protocol violation.
	291	*/
	292	int
fdaef11e	293	auth_rsa(Authctxt authctxt, BIGNUM client_n)
46f1eece	294	{
	295	Key *key;
	296	char *fp;
fdaef11e	297	struct passwd *pw = authctxt->pw;
46f1eece	298
46f1eece	299	/* no user given */
fdaef11e	300	if (!authctxt->valid)
46f1eece	301	return 0;
46f1eece	302
1853d1ef	303	if (!PRIVSEP(auth_rsa_key_allowed(pw, client_n, &key))) {
94ec8c6b	304	auth_clear_options();
46f1eece	305	return (0);
	306	}
	307
	308	/* Perform the challenge-response dialog for this key. */
	309	if (!auth_rsa_challenge_dialog(key)) {
	310	/* Wrong response. */
	311	verbose("Wrong response to RSA authentication challenge.");
	312	packet_send_debug("Wrong response to RSA authentication challenge.");
	313	/*
	314	* Break out of the loop. Otherwise we might send
	315	* another challenge and break the protocol.
	316	*/
	317	key_free(key);
	318	return (0);
	319	}
	320	/*
	321	* Correct response. The client has been successfully
	322	* authenticated. Note that we have not yet processed the
	323	* options; this will be reset if the options cause the
	324	* authentication to be rejected.
	325	*/
	326	fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
	327	verbose("Found matching %s key: %s",
	328	key_type(key), fp);
	329	xfree(fp);
	330	key_free(key);
8efc0c15	331
46f1eece	332	packet_send_debug("RSA authentication accepted.");
46f1eece	333	return (1);
8efc0c15	334	}