auth-rsa.c - security/openssh-library - Rivoreo Source Code Repositories

 /*
  * 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;
 }
	/*
	* 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;
	}