[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 1.39 2001/03/01 02:45:10 deraadt 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"

/* 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.
 */

/*
 * 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(RSA *pk)
{
	BIGNUM *challenge, *encrypted_challenge;
	BN_CTX *ctx;
	u_char buf[32], mdbuf[16], response[16];
	MD5_CTX md;
	u_int i;
	int plen, len;

	encrypted_challenge = BN_new();
	challenge = BN_new();

	/* Generate a random challenge. */
	BN_rand(challenge, 256, 0, 0);
	ctx = BN_CTX_new();
	BN_mod(challenge, challenge, pk->n, ctx);
	BN_CTX_free(ctx);

	/* Encrypt the challenge with the public key. */
	rsa_public_encrypt(encrypted_challenge, challenge, pk);

	/* 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(&plen, SSH_CMSG_AUTH_RSA_RESPONSE);
	packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE);
	for (i = 0; i < 16; i++)
		response[i] = packet_get_char();

	/* The response is MD5 of decrypted challenge plus session id. */
	len = BN_num_bytes(challenge);
	if (len <= 0 || len > 32)
		fatal("auth_rsa_challenge_dialog: 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);
	BN_clear_free(challenge);

	/* 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 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)
{
	char line[8192], file[MAXPATHLEN];
	int authenticated;
	u_int bits;
	FILE *f;
	u_long linenum = 0;
	struct stat st;
	RSA *pk;

	/* no user given */
	if (pw == NULL)
		return 0;

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

	/* The authorized keys. */
	snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir,
		 _PATH_SSH_USER_PERMITTED_KEYS);

	/* Fail quietly if file does not exist */
	if (stat(file, &st) < 0) {
		/* Restore the privileged uid. */
		restore_uid();
		return 0;
	}
	/* Open the file containing the authorized keys. */
	f = fopen(file, "r");
	if (!f) {
		/* Restore the privileged uid. */
		restore_uid();
		packet_send_debug("Could not open %.900s for reading.", file);
		packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
		return 0;
	}
	if (options.strict_modes) {
		int fail = 0;
		char buf[1024];
		/* Check open file in order to avoid open/stat races */
		if (fstat(fileno(f), &st) < 0 ||
		    (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
		    (st.st_mode & 022) != 0) {
			snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
				 "bad ownership or modes for '%s'.", pw->pw_name, file);
			fail = 1;
		} else {
			/* Check path to _PATH_SSH_USER_PERMITTED_KEYS */
			int i;
			static const char *check[] = {
				"", _PATH_SSH_USER_DIR, NULL
			};
			for (i = 0; check[i]; i++) {
				snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]);
				if (stat(line, &st) < 0 ||
				    (st.st_uid != 0 && st.st_uid != pw->pw_uid) ||
				    (st.st_mode & 022) != 0) {
					snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
						 "bad ownership or modes for '%s'.", pw->pw_name, line);
					fail = 1;
					break;
				}
			}
		}
		if (fail) {
			fclose(f);
			log("%s", buf);
			packet_send_debug("%s", buf);
			restore_uid();
			return 0;
		}
	}
	/* Flag indicating whether authentication has succeeded. */
	authenticated = 0;

	pk = RSA_new();
	pk->e = BN_new();
	pk->n = BN_new();

	/*
	 * 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 (!auth_rsa_read_key(&cp, &bits, pk->e, pk->n)) {
			debug("%.100s, line %lu: bad key syntax",
			    file, linenum);
			packet_send_debug("%.100s, line %lu: bad 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(pk->n, client_n) != 0)
			continue;

		/* check the real bits  */
		if (bits != BN_num_bits(pk->n))
			log("Warning: %s, line %ld: keysize mismatch: "
			    "actual %d vs. announced %d.",
			    file, linenum, BN_num_bits(pk->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;

		/* Perform the challenge-response dialog for this key. */
		if (!auth_rsa_challenge_dialog(pk)) {
			/* Wrong response. */
			verbose("Wrong response to RSA authentication challenge.");
			packet_send_debug("Wrong response to RSA authentication challenge.");
			continue;
		}
		/*
		 * 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.
		 * Break out of the loop if authentication was successful;
		 * otherwise continue searching.
		 */
		authenticated = 1;
		break;
	}

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

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

	RSA_free(pk);

	if (authenticated)
		packet_send_debug("RSA authentication accepted.");
	else
		auth_clear_options();

	/* Return authentication result. */
	return authenticated;
}
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"
12bf85ed	17	RCSID("$OpenBSD: auth-rsa.c,v 1.39 2001/03/01 02:45:10 deraadt 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"
94ec8c6b	34
	35	/* import */
	36	extern ServerOptions options;
	37
aa3378df	38	/*
	39	* Session identifier that is used to bind key exchange and authentication
	40	* responses to a particular session.
	41	*/
1e3b8b07	42	extern u_char session_id[16];
8efc0c15	43
aa3378df	44	/*
	45	* The .ssh/authorized_keys file contains public keys, one per line, in the
	46	* following format:
	47	* options bits e n comment
	48	* where bits, e and n are decimal numbers,
	49	* and comment is any string of characters up to newline. The maximum
	50	* length of a line is 8000 characters. See the documentation for a
	51	* description of the options.
	52	*/
8efc0c15	53
aa3378df	54	/*
	55	* Performs the RSA authentication challenge-response dialog with the client,
	56	* and returns true (non-zero) if the client gave the correct answer to
	57	* our challenge; returns zero if the client gives a wrong answer.
	58	*/
8efc0c15	59
8efc0c15	60	int
4fe2af09	61	auth_rsa_challenge_dialog(RSA *pk)
8efc0c15	62	{
c8d54615	63	BIGNUM challenge, encrypted_challenge;
c8d54615	64	BN_CTX *ctx;
1e3b8b07	65	u_char buf[32], mdbuf[16], response[16];
5260325f	66	MD5_CTX md;
1e3b8b07	67	u_int i;
5260325f	68	int plen, len;
	69
	70	encrypted_challenge = BN_new();
	71	challenge = BN_new();
5260325f	72
	73	/* Generate a random challenge. */
	74	BN_rand(challenge, 256, 0, 0);
c8d54615	75	ctx = BN_CTX_new();
4fe2af09	76	BN_mod(challenge, challenge, pk->n, ctx);
c8d54615	77	BN_CTX_free(ctx);
5260325f	78
5260325f	79	/* Encrypt the challenge with the public key. */
5260325f	80	rsa_public_encrypt(encrypted_challenge, challenge, pk);
5260325f	81
	82	/* Send the encrypted challenge to the client. */
	83	packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
	84	packet_put_bignum(encrypted_challenge);
	85	packet_send();
c8d54615	86	BN_clear_free(encrypted_challenge);
5260325f	87	packet_write_wait();
5260325f	88
c8d54615	89	/* Wait for a response. */
	90	packet_read_expect(&plen, SSH_CMSG_AUTH_RSA_RESPONSE);
	91	packet_integrity_check(plen, 16, SSH_CMSG_AUTH_RSA_RESPONSE);
	92	for (i = 0; i < 16; i++)
	93	response[i] = packet_get_char();
	94
5260325f	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_challenge_dialog: 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);
5260325f	105	BN_clear_free(challenge);
5260325f	106
	107	/* Verify that the response is the original challenge. */
	108	if (memcmp(response, mdbuf, 16) != 0) {
	109	/* Wrong answer. */
	110	return 0;
	111	}
	112	/* Correct answer. */
	113	return 1;
8efc0c15	114	}
8efc0c15	115
aa3378df	116	/*
	117	* Performs the RSA authentication dialog with the client. This returns
	118	* 0 if the client could not be authenticated, and 1 if authentication was
	119	* successful. This may exit if there is a serious protocol violation.
	120	*/
8efc0c15	121
8efc0c15	122	int
6fa724bc	123	auth_rsa(struct passwd pw, BIGNUM client_n)
8efc0c15	124	{
42f11eb2	125	char line[8192], file[MAXPATHLEN];
5260325f	126	int authenticated;
1e3b8b07	127	u_int bits;
5260325f	128	FILE *f;
1e3b8b07	129	u_long linenum = 0;
5260325f	130	struct stat st;
4fe2af09	131	RSA *pk;
5260325f	132
94ec8c6b	133	/* no user given */
	134	if (pw == NULL)
	135	return 0;
	136
5260325f	137	/* Temporarily use the user's uid. */
	138	temporarily_use_uid(pw->pw_uid);
	139
	140	/* The authorized keys. */
	141	snprintf(file, sizeof file, "%.500s/%.100s", pw->pw_dir,
42f11eb2	142	_PATH_SSH_USER_PERMITTED_KEYS);
5260325f	143
	144	/* Fail quietly if file does not exist */
	145	if (stat(file, &st) < 0) {
	146	/* Restore the privileged uid. */
	147	restore_uid();
	148	return 0;
8efc0c15	149	}
5260325f	150	/* Open the file containing the authorized keys. */
	151	f = fopen(file, "r");
	152	if (!f) {
	153	/* Restore the privileged uid. */
	154	restore_uid();
	155	packet_send_debug("Could not open %.900s for reading.", file);
	156	packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
	157	return 0;
8efc0c15	158	}
5260325f	159	if (options.strict_modes) {
	160	int fail = 0;
	161	char buf[1024];
	162	/* Check open file in order to avoid open/stat races */
	163	if (fstat(fileno(f), &st) < 0 \|\|
	164	(st.st_uid != 0 && st.st_uid != pw->pw_uid) \|\|
	165	(st.st_mode & 022) != 0) {
	166	snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
	167	"bad ownership or modes for '%s'.", pw->pw_name, file);
	168	fail = 1;
	169	} else {
42f11eb2	170	/* Check path to _PATH_SSH_USER_PERMITTED_KEYS */
5260325f	171	int i;
5260325f	172	static const char *check[] = {
42f11eb2	173	"", _PATH_SSH_USER_DIR, NULL
5260325f	174	};
	175	for (i = 0; check[i]; i++) {
	176	snprintf(line, sizeof line, "%.500s/%.100s", pw->pw_dir, check[i]);
	177	if (stat(line, &st) < 0 \|\|
	178	(st.st_uid != 0 && st.st_uid != pw->pw_uid) \|\|
	179	(st.st_mode & 022) != 0) {
	180	snprintf(buf, sizeof buf, "RSA authentication refused for %.100s: "
	181	"bad ownership or modes for '%s'.", pw->pw_name, line);
	182	fail = 1;
	183	break;
	184	}
	185	}
8efc0c15	186	}
5260325f	187	if (fail) {
a306f2dd	188	fclose(f);
12bf85ed	189	log("%s", buf);
12bf85ed	190	packet_send_debug("%s", buf);
5260325f	191	restore_uid();
5260325f	192	return 0;
8efc0c15	193	}
5260325f	194	}
	195	/* Flag indicating whether authentication has succeeded. */
	196	authenticated = 0;
	197
4fe2af09	198	pk = RSA_new();
	199	pk->e = BN_new();
	200	pk->n = BN_new();
5260325f	201
aa3378df	202	/*
	203	* Go though the accepted keys, looking for the current key. If
	204	* found, perform a challenge-response dialog to verify that the
	205	* user really has the corresponding private key.
	206	*/
5260325f	207	while (fgets(line, sizeof(line), f)) {
	208	char *cp;
	209	char *options;
	210
	211	linenum++;
	212
aa3378df	213	/* Skip leading whitespace, empty and comment lines. */
	214	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	215	;
5260325f	216	if (!cp \|\| cp == '\n' \|\| *cp == '#')
	217	continue;
	218
aa3378df	219	/*
	220	* Check if there are options for this key, and if so,
	221	* save their starting address and skip the option part
	222	* for now. If there are no options, set the starting
	223	* address to NULL.
	224	*/
5260325f	225	if (cp < '0' \|\| cp > '9') {
	226	int quoted = 0;
	227	options = cp;
	228	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
	229	if (*cp == '\\' && cp[1] == '"')
	230	cp++; /* Skip both */
	231	else if (*cp == '"')
	232	quoted = !quoted;
8efc0c15	233	}
5260325f	234	} else
	235	options = NULL;
	236
	237	/* Parse the key from the line. */
4fe2af09	238	if (!auth_rsa_read_key(&cp, &bits, pk->e, pk->n)) {
5260325f	239	debug("%.100s, line %lu: bad key syntax",
42f11eb2	240	file, linenum);
5260325f	241	packet_send_debug("%.100s, line %lu: bad key syntax",
42f11eb2	242	file, linenum);
5260325f	243	continue;
8efc0c15	244	}
5260325f	245	/* cp now points to the comment part. */
5260325f	246
5260325f	247	/* Check if the we have found the desired key (identified by its modulus). */
4fe2af09	248	if (BN_cmp(pk->n, client_n) != 0)
aa3378df	249	continue;
5260325f	250
57112b5a	251	/* check the real bits */
4fe2af09	252	if (bits != BN_num_bits(pk->n))
57112b5a	253	log("Warning: %s, line %ld: keysize mismatch: "
57112b5a	254	"actual %d vs. announced %d.",
4fe2af09	255	file, linenum, BN_num_bits(pk->n), bits);
57112b5a	256
5260325f	257	/* We have found the desired key. */
d343d900	258	/*
	259	* If our options do not allow this key to be used,
	260	* do not send challenge.
	261	*/
42f11eb2	262	if (!auth_parse_options(pw, options, file, linenum))
d343d900	263	continue;
5260325f	264
5260325f	265	/* Perform the challenge-response dialog for this key. */
4fe2af09	266	if (!auth_rsa_challenge_dialog(pk)) {
5260325f	267	/* Wrong response. */
	268	verbose("Wrong response to RSA authentication challenge.");
	269	packet_send_debug("Wrong response to RSA authentication challenge.");
	270	continue;
8efc0c15	271	}
aa3378df	272	/*
	273	* Correct response. The client has been successfully
	274	* authenticated. Note that we have not yet processed the
	275	* options; this will be reset if the options cause the
	276	* authentication to be rejected.
aa3378df	277	* Break out of the loop if authentication was successful;
	278	* otherwise continue searching.
	279	*/
33de75a3	280	authenticated = 1;
33de75a3	281	break;
8efc0c15	282	}
8efc0c15	283
5260325f	284	/* Restore the privileged uid. */
5260325f	285	restore_uid();
8efc0c15	286
5260325f	287	/* Close the file. */
5260325f	288	fclose(f);
8efc0c15	289
4fe2af09	290	RSA_free(pk);
8efc0c15	291
5260325f	292	if (authenticated)
5260325f	293	packet_send_debug("RSA authentication accepted.");
94ec8c6b	294	else
94ec8c6b	295	auth_clear_options();
8efc0c15	296
5260325f	297	/* Return authentication result. */
5260325f	298	return authenticated;
8efc0c15	299	}