[gssapi-openssh.git] / openssh / 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 1.50 2001/12/28 14:50:54 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.
 */

/*
 * 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 len;

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

	/* Generate a random challenge. */
	BN_rand(challenge, 256, 0, 0);
	if ((ctx = BN_CTX_new()) == NULL)
		fatal("auth_rsa_challenge_dialog: BN_CTX_new() failed");
	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(SSH_CMSG_AUTH_RSA_RESPONSE);
	for (i = 0; i < 16; i++)
		response[i] = packet_get_char();
	packet_check_eom();

	/* 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;
	int authenticated;
	u_int bits;
	FILE *f;
	u_long linenum = 0;
	struct stat st;
	Key *key;
	char *fp;

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

	/* 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();
		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.");
		xfree(file);
		return 0;
	}
	if (options.strict_modes &&
	    secure_filename(f, file, pw, line, sizeof(line)) != 0) {
		xfree(file);
		fclose(f);
		log("Authentication refused: %s", line);
		packet_send_debug("Authentication refused: %s", line);
		restore_uid();
		return 0;
	}
	/* Flag indicating whether authentication has succeeded. */
	authenticated = 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;

		/* Perform the challenge-response dialog for this key. */
		if (!auth_rsa_challenge_dialog(key->rsa)) {
			/* 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.
			 */
			break;
		}
		/*
		 * 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;

	 	fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
		verbose("Found matching %s key: %s",
		    key_type(key), fp);
		xfree(fp);

		break;
	}

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

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

	key_free(key);

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

	/* Return authentication result. */
	return authenticated;
}
Commit	Line	Data
3c0ef626	1	/*
	2	* Author: Tatu Ylonen <ylo@cs.hut.fi>
	3	* Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
	4	* All rights reserved
	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.
	8	*
	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".
	14	*/
	15
	16	#include "includes.h"
e9a17296	17	RCSID("$OpenBSD: auth-rsa.c,v 1.50 2001/12/28 14:50:54 markus Exp $");
3c0ef626	18
	19	#include <openssl/rsa.h>
	20	#include <openssl/md5.h>
	21
	22	#include "rsa.h"
	23	#include "packet.h"
	24	#include "xmalloc.h"
	25	#include "ssh1.h"
	26	#include "mpaux.h"
	27	#include "uidswap.h"
	28	#include "match.h"
	29	#include "auth-options.h"
	30	#include "pathnames.h"
	31	#include "log.h"
	32	#include "servconf.h"
	33	#include "auth.h"
e9a17296	34	#include "hostfile.h"
3c0ef626	35
	36	/* import */
	37	extern ServerOptions options;
	38
	39	/*
	40	* Session identifier that is used to bind key exchange and authentication
	41	* responses to a particular session.
	42	*/
	43	extern u_char session_id[16];
	44
	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	*/
	54
	55	/*
	56	* Performs the RSA authentication challenge-response dialog with the client,
	57	* and returns true (non-zero) if the client gave the correct answer to
	58	* our challenge; returns zero if the client gives a wrong answer.
	59	*/
	60
	61	int
	62	auth_rsa_challenge_dialog(RSA *pk)
	63	{
	64	BIGNUM challenge, encrypted_challenge;
	65	BN_CTX *ctx;
	66	u_char buf[32], mdbuf[16], response[16];
	67	MD5_CTX md;
	68	u_int i;
e9a17296	69	int len;
3c0ef626	70
e9a17296	71	if ((encrypted_challenge = BN_new()) == NULL)
	72	fatal("auth_rsa_challenge_dialog: BN_new() failed");
	73	if ((challenge = BN_new()) == NULL)
	74	fatal("auth_rsa_challenge_dialog: BN_new() failed");
3c0ef626	75
	76	/* Generate a random challenge. */
	77	BN_rand(challenge, 256, 0, 0);
e9a17296	78	if ((ctx = BN_CTX_new()) == NULL)
e9a17296	79	fatal("auth_rsa_challenge_dialog: BN_CTX_new() failed");
3c0ef626	80	BN_mod(challenge, challenge, pk->n, ctx);
	81	BN_CTX_free(ctx);
	82
	83	/* Encrypt the challenge with the public key. */
	84	rsa_public_encrypt(encrypted_challenge, challenge, pk);
	85
	86	/* Send the encrypted challenge to the client. */
	87	packet_start(SSH_SMSG_AUTH_RSA_CHALLENGE);
	88	packet_put_bignum(encrypted_challenge);
	89	packet_send();
	90	BN_clear_free(encrypted_challenge);
	91	packet_write_wait();
	92
	93	/* Wait for a response. */
e9a17296	94	packet_read_expect(SSH_CMSG_AUTH_RSA_RESPONSE);
3c0ef626	95	for (i = 0; i < 16; i++)
3c0ef626	96	response[i] = packet_get_char();
e9a17296	97	packet_check_eom();
3c0ef626	98
	99	/* The response is MD5 of decrypted challenge plus session id. */
	100	len = BN_num_bytes(challenge);
	101	if (len <= 0 \|\| len > 32)
	102	fatal("auth_rsa_challenge_dialog: bad challenge length %d", len);
	103	memset(buf, 0, 32);
	104	BN_bn2bin(challenge, buf + 32 - len);
	105	MD5_Init(&md);
	106	MD5_Update(&md, buf, 32);
	107	MD5_Update(&md, session_id, 16);
	108	MD5_Final(mdbuf, &md);
	109	BN_clear_free(challenge);
	110
	111	/* Verify that the response is the original challenge. */
	112	if (memcmp(response, mdbuf, 16) != 0) {
	113	/* Wrong answer. */
	114	return 0;
	115	}
	116	/* Correct answer. */
	117	return 1;
	118	}
	119
	120	/*
	121	* Performs the RSA authentication dialog with the client. This returns
	122	* 0 if the client could not be authenticated, and 1 if authentication was
	123	* successful. This may exit if there is a serious protocol violation.
	124	*/
	125
	126	int
	127	auth_rsa(struct passwd pw, BIGNUM client_n)
	128	{
	129	char line[8192], *file;
	130	int authenticated;
	131	u_int bits;
	132	FILE *f;
	133	u_long linenum = 0;
	134	struct stat st;
e9a17296	135	Key *key;
e9a17296	136	char *fp;
3c0ef626	137
	138	/* no user given */
	139	if (pw == NULL)
	140	return 0;
	141
	142	/* Temporarily use the user's uid. */
	143	temporarily_use_uid(pw);
	144
	145	/* The authorized keys. */
	146	file = authorized_keys_file(pw);
	147	debug("trying public RSA key file %s", file);
	148
	149	/* Fail quietly if file does not exist */
	150	if (stat(file, &st) < 0) {
	151	/* Restore the privileged uid. */
	152	restore_uid();
	153	xfree(file);
	154	return 0;
	155	}
	156	/* Open the file containing the authorized keys. */
	157	f = fopen(file, "r");
	158	if (!f) {
	159	/* Restore the privileged uid. */
	160	restore_uid();
	161	packet_send_debug("Could not open %.900s for reading.", file);
	162	packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
	163	xfree(file);
	164	return 0;
	165	}
	166	if (options.strict_modes &&
	167	secure_filename(f, file, pw, line, sizeof(line)) != 0) {
	168	xfree(file);
	169	fclose(f);
	170	log("Authentication refused: %s", line);
	171	packet_send_debug("Authentication refused: %s", line);
	172	restore_uid();
	173	return 0;
	174	}
	175	/* Flag indicating whether authentication has succeeded. */
	176	authenticated = 0;
	177
e9a17296	178	key = key_new(KEY_RSA1);
3c0ef626	179
	180	/*
	181	* Go though the accepted keys, looking for the current key. If
	182	* found, perform a challenge-response dialog to verify that the
	183	* user really has the corresponding private key.
	184	*/
	185	while (fgets(line, sizeof(line), f)) {
	186	char *cp;
	187	char *options;
	188
	189	linenum++;
	190
	191	/* Skip leading whitespace, empty and comment lines. */
	192	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
	193	;
	194	if (!cp \|\| cp == '\n' \|\| *cp == '#')
	195	continue;
	196
	197	/*
	198	* Check if there are options for this key, and if so,
	199	* save their starting address and skip the option part
	200	* for now. If there are no options, set the starting
	201	* address to NULL.
	202	*/
	203	if (cp < '0' \|\| cp > '9') {
	204	int quoted = 0;
	205	options = cp;
	206	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
	207	if (*cp == '\\' && cp[1] == '"')
	208	cp++; /* Skip both */
	209	else if (*cp == '"')
	210	quoted = !quoted;
	211	}
	212	} else
	213	options = NULL;
	214
	215	/* Parse the key from the line. */
e9a17296	216	if (hostfile_read_key(&cp, &bits, key) == 0) {
3c0ef626	217	debug("%.100s, line %lu: non ssh1 key syntax",
	218	file, linenum);
	219	continue;
	220	}
	221	/* cp now points to the comment part. */
	222
	223	/* Check if the we have found the desired key (identified by its modulus). */
e9a17296	224	if (BN_cmp(key->rsa->n, client_n) != 0)
3c0ef626	225	continue;
	226
	227	/* check the real bits */
e9a17296	228	if (bits != BN_num_bits(key->rsa->n))
3c0ef626	229	log("Warning: %s, line %lu: keysize mismatch: "
3c0ef626	230	"actual %d vs. announced %d.",
e9a17296	231	file, linenum, BN_num_bits(key->rsa->n), bits);
3c0ef626	232
	233	/* We have found the desired key. */
	234	/*
	235	* If our options do not allow this key to be used,
	236	* do not send challenge.
	237	*/
	238	if (!auth_parse_options(pw, options, file, linenum))
	239	continue;
	240
	241	/* Perform the challenge-response dialog for this key. */
e9a17296	242	if (!auth_rsa_challenge_dialog(key->rsa)) {
3c0ef626	243	/* Wrong response. */
	244	verbose("Wrong response to RSA authentication challenge.");
	245	packet_send_debug("Wrong response to RSA authentication challenge.");
e9a17296	246	/*
	247	* Break out of the loop. Otherwise we might send
	248	* another challenge and break the protocol.
	249	*/
	250	break;
3c0ef626	251	}
	252	/*
	253	* Correct response. The client has been successfully
	254	* authenticated. Note that we have not yet processed the
	255	* options; this will be reset if the options cause the
	256	* authentication to be rejected.
	257	* Break out of the loop if authentication was successful;
	258	* otherwise continue searching.
	259	*/
	260	authenticated = 1;
e9a17296	261
	262	fp = key_fingerprint(key, SSH_FP_MD5, SSH_FP_HEX);
	263	verbose("Found matching %s key: %s",
	264	key_type(key), fp);
	265	xfree(fp);
	266
3c0ef626	267	break;
	268	}
	269
	270	/* Restore the privileged uid. */
	271	restore_uid();
	272
	273	/* Close the file. */
	274	xfree(file);
	275	fclose(f);
	276
e9a17296	277	key_free(key);
3c0ef626	278
	279	if (authenticated)
	280	packet_send_debug("RSA authentication accepted.");
	281	else
	282	auth_clear_options();
	283
	284	/* Return authentication result. */
	285	return authenticated;
	286	}