[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 1.44 2001/07/23 18:14:58 stevesk 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;
	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);

	/* 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;

	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: 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(pk->n, client_n) != 0)
			continue;

		/* check the real bits  */
		if (bits != BN_num_bits(pk->n))
			log("Warning: %s, line %lu: 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. */
	xfree(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
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"
	17	RCSID("$OpenBSD: auth-rsa.c,v 1.44 2001/07/23 18:14:58 stevesk Exp $");
	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"
	34
	35	/* import */
	36	extern ServerOptions options;
	37
	38	/*
	39	* Session identifier that is used to bind key exchange and authentication
	40	* responses to a particular session.
	41	*/
	42	extern u_char session_id[16];
	43
	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	*/
	53
	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	*/
	59
	60	int
	61	auth_rsa_challenge_dialog(RSA *pk)
	62	{
	63	BIGNUM challenge, encrypted_challenge;
	64	BN_CTX *ctx;
65	u_char buf[32], mdbuf[16], response[16];
66	MD5_CTX md;
67	u_int i;
68	int plen, len;
69
70	encrypted_challenge = BN_new();
71	challenge = BN_new();
72
73	/* Generate a random challenge. */
74	BN_rand(challenge, 256, 0, 0);
75	ctx = BN_CTX_new();
76	BN_mod(challenge, challenge, pk->n, ctx);
77	BN_CTX_free(ctx);
78
79	/* Encrypt the challenge with the public key. */
80	rsa_public_encrypt(encrypted_challenge, challenge, pk);
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();
86	BN_clear_free(encrypted_challenge);
87	packet_write_wait();
88
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
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);
105	BN_clear_free(challenge);
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;
114	}
115
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	*/
121
122	int
123	auth_rsa(struct passwd pw, BIGNUM client_n)
124	{
125	char line[8192], *file;
126	int authenticated;
127	u_int bits;
128	FILE *f;
129	u_long linenum = 0;
130	struct stat st;
131	RSA *pk;
132
133	/* no user given */
134	if (pw == NULL)
135	return 0;
136
137	/* Temporarily use the user's uid. */
138	temporarily_use_uid(pw);
139
140	/* The authorized keys. */
141	file = authorized_keys_file(pw);
142	debug("trying public RSA key file %s", file);
143
144	/* Fail quietly if file does not exist */
145	if (stat(file, &st) < 0) {
146	/* Restore the privileged uid. */
147	restore_uid();
148	xfree(file);
149	return 0;
150	}
151	/* Open the file containing the authorized keys. */
152	f = fopen(file, "r");
153	if (!f) {
154	/* Restore the privileged uid. */
155	restore_uid();
156	packet_send_debug("Could not open %.900s for reading.", file);
157	packet_send_debug("If your home is on an NFS volume, it may need to be world-readable.");
158	xfree(file);
159	return 0;
160	}
161	if (options.strict_modes &&
162	secure_filename(f, file, pw, line, sizeof(line)) != 0) {
163	xfree(file);
164	fclose(f);
165	log("Authentication refused: %s", line);
166	packet_send_debug("Authentication refused: %s", line);
167	restore_uid();
168	return 0;
169	}
170	/* Flag indicating whether authentication has succeeded. */
171	authenticated = 0;
172
173	pk = RSA_new();
174	pk->e = BN_new();
175	pk->n = BN_new();
176
177	/*
178	* Go though the accepted keys, looking for the current key. If
179	* found, perform a challenge-response dialog to verify that the
180	* user really has the corresponding private key.
181	*/
182	while (fgets(line, sizeof(line), f)) {
183	char *cp;
184	char *options;
185
186	linenum++;
187
188	/* Skip leading whitespace, empty and comment lines. */
189	for (cp = line; cp == ' ' \|\| cp == '\t'; cp++)
190	;
191	if (!cp \|\| cp == '\n' \|\| *cp == '#')
192	continue;
193
194	/*
195	* Check if there are options for this key, and if so,
196	* save their starting address and skip the option part
197	* for now. If there are no options, set the starting
198	* address to NULL.
199	*/
200	if (cp < '0' \|\| cp > '9') {
201	int quoted = 0;
202	options = cp;
203	for (; cp && (quoted \|\| (cp != ' ' && *cp != '\t')); cp++) {
204	if (*cp == '\\' && cp[1] == '"')
205	cp++; /* Skip both */
206	else if (*cp == '"')
207	quoted = !quoted;
208	}
209	} else
210	options = NULL;
211
212	/* Parse the key from the line. */
213	if (!auth_rsa_read_key(&cp, &bits, pk->e, pk->n)) {
214	debug("%.100s, line %lu: non ssh1 key syntax",
215	file, linenum);
216	continue;
217	}
218	/* cp now points to the comment part. */
219
220	/* Check if the we have found the desired key (identified by its modulus). */
221	if (BN_cmp(pk->n, client_n) != 0)
222	continue;
223
224	/* check the real bits */
225	if (bits != BN_num_bits(pk->n))
226	log("Warning: %s, line %lu: keysize mismatch: "
227	"actual %d vs. announced %d.",
228	file, linenum, BN_num_bits(pk->n), bits);
229
230	/* We have found the desired key. */
231	/*
232	* If our options do not allow this key to be used,
233	* do not send challenge.
234	*/
235	if (!auth_parse_options(pw, options, file, linenum))
236	continue;
237
238	/* Perform the challenge-response dialog for this key. */
239	if (!auth_rsa_challenge_dialog(pk)) {
240	/* Wrong response. */
241	verbose("Wrong response to RSA authentication challenge.");
242	packet_send_debug("Wrong response to RSA authentication challenge.");
243	continue;
244	}
245	/*
246	* Correct response. The client has been successfully
247	* authenticated. Note that we have not yet processed the
248	* options; this will be reset if the options cause the
249	* authentication to be rejected.
250	* Break out of the loop if authentication was successful;
251	* otherwise continue searching.
252	*/
253	authenticated = 1;
254	break;
255	}
256
257	/* Restore the privileged uid. */
258	restore_uid();
259
260	/* Close the file. */
261	xfree(file);
262	fclose(f);
263
264	RSA_free(pk);
265
266	if (authenticated)
267	packet_send_debug("RSA authentication accepted.");
268	else
269	auth_clear_options();
270
271	/* Return authentication result. */
272	return authenticated;
273	}