sshconnect2.c - security/openssh-library - Rivoreo Source Code Repositories

 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
  *    documentation and/or other materials provided with the distribution.
  * 3. All advertising materials mentioning features or use of this software
  *    must display the following acknowledgement:
  *      This product includes software developed by Markus Friedl.
  * 4. The name of the author may not be used to endorse or promote products
  *    derived from this software without specific prior written permission.
  *
  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */

 #include "includes.h"
 RCSID("$OpenBSD: sshconnect2.c,v 1.16 2000/07/16 08:27:22 markus Exp $");

 #include <openssl/bn.h>
 #include <openssl/rsa.h>
 #include <openssl/dsa.h>
 #include <openssl/md5.h>
 #include <openssl/dh.h>
 #include <openssl/hmac.h>

 #include "ssh.h"
 #include "xmalloc.h"
 #include "rsa.h"
 #include "buffer.h"
 #include "packet.h"
 #include "cipher.h"
 #include "uidswap.h"
 #include "compat.h"
 #include "readconf.h"
 #include "bufaux.h"
 #include "ssh2.h"
 #include "kex.h"
 #include "myproposal.h"
 #include "key.h"
 #include "dsa.h"
 #include "sshconnect.h"
 #include "authfile.h"

 /* import */
 extern char *client_version_string;
 extern char *server_version_string;
 extern Options options;

 /*
  * SSH2 key exchange
  */

 unsigned char *session_id2 = NULL;
 int session_id2_len = 0;

 void
 ssh_kex_dh(Kex *kex, char *host, struct sockaddr *hostaddr,
     Buffer *client_kexinit, Buffer *server_kexinit)
 {
 	int plen, dlen;
 	unsigned int klen, kout;
 	char *signature = NULL;
 	unsigned int slen;
 	char *server_host_key_blob = NULL;
 	Key *server_host_key;
 	unsigned int sbloblen;
 	DH *dh;
 	BIGNUM *dh_server_pub = 0;
 	BIGNUM *shared_secret = 0;
 	unsigned char *kbuf;
 	unsigned char *hash;

 	debug("Sending SSH2_MSG_KEXDH_INIT.");
 	/* generate and send 'e', client DH public key */
 	dh = dh_new_group1();
 	packet_start(SSH2_MSG_KEXDH_INIT);
 	packet_put_bignum2(dh->pub_key);
 	packet_send();
 	packet_write_wait();

 #ifdef DEBUG_KEXDH
 	fprintf(stderr, "\np= ");
 	bignum_print(dh->p);
 	fprintf(stderr, "\ng= ");
 	bignum_print(dh->g);
 	fprintf(stderr, "\npub= ");
 	bignum_print(dh->pub_key);
 	fprintf(stderr, "\n");
 	DHparams_print_fp(stderr, dh);
 #endif

 	debug("Wait SSH2_MSG_KEXDH_REPLY.");

 	packet_read_expect(&plen, SSH2_MSG_KEXDH_REPLY);

 	debug("Got SSH2_MSG_KEXDH_REPLY.");

 	/* key, cert */
 	server_host_key_blob = packet_get_string(&sbloblen);
 	server_host_key = dsa_key_from_blob(server_host_key_blob, sbloblen);
 	if (server_host_key == NULL)
 		fatal("cannot decode server_host_key_blob");

 	check_host_key(host, hostaddr, server_host_key,
 	    options.user_hostfile2, options.system_hostfile2);

 	/* DH paramter f, server public DH key */
 	dh_server_pub = BN_new();
 	if (dh_server_pub == NULL)
 		fatal("dh_server_pub == NULL");
 	packet_get_bignum2(dh_server_pub, &dlen);

 #ifdef DEBUG_KEXDH
 	fprintf(stderr, "\ndh_server_pub= ");
 	bignum_print(dh_server_pub);
 	fprintf(stderr, "\n");
 	debug("bits %d", BN_num_bits(dh_server_pub));
 #endif

 	/* signed H */
 	signature = packet_get_string(&slen);
 	packet_done();

 	if (!dh_pub_is_valid(dh, dh_server_pub))
 		packet_disconnect("bad server public DH value");

 	klen = DH_size(dh);
 	kbuf = xmalloc(klen);
 	kout = DH_compute_key(kbuf, dh_server_pub, dh);
 #ifdef DEBUG_KEXDH
 	debug("shared secret: len %d/%d", klen, kout);
 	fprintf(stderr, "shared secret == ");
 	for (i = 0; i< kout; i++)
 		fprintf(stderr, "%02x", (kbuf[i])&0xff);
 	fprintf(stderr, "\n");
 #endif
 	shared_secret = BN_new();

 	BN_bin2bn(kbuf, kout, shared_secret);
 	memset(kbuf, 0, klen);
 	xfree(kbuf);

 	/* calc and verify H */
 	hash = kex_hash(
 	    client_version_string,
 	    server_version_string,
 	    buffer_ptr(client_kexinit), buffer_len(client_kexinit),
 	    buffer_ptr(server_kexinit), buffer_len(server_kexinit),
 	    server_host_key_blob, sbloblen,
 	    dh->pub_key,
 	    dh_server_pub,
 	    shared_secret
 	);
 	xfree(server_host_key_blob);
 	DH_free(dh);
 #ifdef DEBUG_KEXDH
 	fprintf(stderr, "hash == ");
 	for (i = 0; i< 20; i++)
 		fprintf(stderr, "%02x", (hash[i])&0xff);
 	fprintf(stderr, "\n");
 #endif
 	if (dsa_verify(server_host_key, (unsigned char *)signature, slen, hash, 20) != 1)
 		fatal("dsa_verify failed for server_host_key");
 	key_free(server_host_key);

 	kex_derive_keys(kex, hash, shared_secret);
 	packet_set_kex(kex);

 	/* save session id */
 	session_id2_len = 20;
 	session_id2 = xmalloc(session_id2_len);
 	memcpy(session_id2, hash, session_id2_len);
 }

 void
 ssh_kex2(char *host, struct sockaddr *hostaddr)
 {
 	int i, plen;
 	Kex *kex;
 	Buffer *client_kexinit, *server_kexinit;
 	char *sprop[PROPOSAL_MAX];

 	if (options.ciphers != NULL) {
 		myproposal[PROPOSAL_ENC_ALGS_CTOS] =
 		myproposal[PROPOSAL_ENC_ALGS_STOC] = options.ciphers;
 	} else if (options.cipher == SSH_CIPHER_3DES) {
 		myproposal[PROPOSAL_ENC_ALGS_CTOS] =
 		myproposal[PROPOSAL_ENC_ALGS_STOC] =
 		    (char *) cipher_name(SSH_CIPHER_3DES_CBC);
 	} else if (options.cipher == SSH_CIPHER_BLOWFISH) {
 		myproposal[PROPOSAL_ENC_ALGS_CTOS] =
 		myproposal[PROPOSAL_ENC_ALGS_STOC] =
 		    (char *) cipher_name(SSH_CIPHER_BLOWFISH_CBC);
 	}
 	if (options.compression) {
 		myproposal[PROPOSAL_COMP_ALGS_CTOS] = "zlib";
 		myproposal[PROPOSAL_COMP_ALGS_STOC] = "zlib";
 	} else {
 		myproposal[PROPOSAL_COMP_ALGS_CTOS] = "none";
 		myproposal[PROPOSAL_COMP_ALGS_STOC] = "none";
 	}

 	/* buffers with raw kexinit messages */
 	server_kexinit = xmalloc(sizeof(*server_kexinit));
 	buffer_init(server_kexinit);
 	client_kexinit = kex_init(myproposal);

 	/* algorithm negotiation */
 	kex_exchange_kexinit(client_kexinit, server_kexinit, sprop);
 	kex = kex_choose_conf(myproposal, sprop, 0);
 	for (i = 0; i < PROPOSAL_MAX; i++)
 		xfree(sprop[i]);

 	/* server authentication and session key agreement */
 	ssh_kex_dh(kex, host, hostaddr, client_kexinit, server_kexinit);

 	buffer_free(client_kexinit);
 	buffer_free(server_kexinit);
 	xfree(client_kexinit);
 	xfree(server_kexinit);

 	debug("Wait SSH2_MSG_NEWKEYS.");
 	packet_read_expect(&plen, SSH2_MSG_NEWKEYS);
 	packet_done();
 	debug("GOT SSH2_MSG_NEWKEYS.");

 	debug("send SSH2_MSG_NEWKEYS.");
 	packet_start(SSH2_MSG_NEWKEYS);
 	packet_send();
 	packet_write_wait();
 	debug("done: send SSH2_MSG_NEWKEYS.");

 #ifdef DEBUG_KEXDH
 	/* send 1st encrypted/maced/compressed message */
 	packet_start(SSH2_MSG_IGNORE);
 	packet_put_cstring("markus");
 	packet_send();
 	packet_write_wait();
 #endif
 	debug("done: KEX2.");
 }

 /*
  * Authenticate user
  */
 int
 ssh2_try_passwd(const char *server_user, const char *host, const char *service)
 {
 	static int attempt = 0;
 	char prompt[80];
 	char *password;

 	if (attempt++ >= options.number_of_password_prompts)
 		return 0;

 	if(attempt != 1)
 		error("Permission denied, please try again.");

 	snprintf(prompt, sizeof(prompt), "%.30s@%.40s's password: ",
 	    server_user, host);
 	password = read_passphrase(prompt, 0);
 	packet_start(SSH2_MSG_USERAUTH_REQUEST);
 	packet_put_cstring(server_user);
 	packet_put_cstring(service);
 	packet_put_cstring("password");
 	packet_put_char(0);
 	packet_put_cstring(password);
 	memset(password, 0, strlen(password));
 	xfree(password);
 	packet_send();
 	packet_write_wait();
 	return 1;
 }

 typedef int sign_fn(
     Key *key,
     unsigned char **sigp, int *lenp,
     unsigned char *data, int datalen);

 void
 ssh2_sign_and_send_pubkey(Key *k, sign_fn *do_sign,
     const char *server_user, const char *host, const char *service)
 {
 	Buffer b;
 	unsigned char *blob, *signature;
 	int bloblen, slen;
 	int skip = 0;

 	dsa_make_key_blob(k, &blob, &bloblen);

 	/* data to be signed */
 	buffer_init(&b);
 	if (datafellows & SSH_COMPAT_SESSIONID_ENCODING) {
 		buffer_put_string(&b, session_id2, session_id2_len);
 		skip = buffer_len(&b);
 	} else {
 		buffer_append(&b, session_id2, session_id2_len);
 		skip = session_id2_len;
 	}
 	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 	buffer_put_cstring(&b, server_user);
 	buffer_put_cstring(&b,
 	    datafellows & SSH_BUG_PUBKEYAUTH ?
 	    "ssh-userauth" :
 	    service);
 	buffer_put_cstring(&b, "publickey");
 	buffer_put_char(&b, 1);
 	buffer_put_cstring(&b, KEX_DSS);
 	buffer_put_string(&b, blob, bloblen);

 	/* generate signature */
 	do_sign(k, &signature, &slen, buffer_ptr(&b), buffer_len(&b));
 	key_free(k); /* XXX */
 #ifdef DEBUG_DSS
 	buffer_dump(&b);
 #endif
 	if (datafellows & SSH_BUG_PUBKEYAUTH) {
 		buffer_clear(&b);
 		buffer_append(&b, session_id2, session_id2_len);
 		buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
 		buffer_put_cstring(&b, server_user);
 		buffer_put_cstring(&b, service);
 		buffer_put_cstring(&b, "publickey");
 		buffer_put_char(&b, 1);
 		buffer_put_cstring(&b, KEX_DSS);
 		buffer_put_string(&b, blob, bloblen);
 	}
 	xfree(blob);
 	/* append signature */
 	buffer_put_string(&b, signature, slen);
 	xfree(signature);

 	/* skip session id and packet type */
 	if (buffer_len(&b) < skip + 1)
 		fatal("ssh2_try_pubkey: internal error");
 	buffer_consume(&b, skip + 1);

 	/* put remaining data from buffer into packet */
 	packet_start(SSH2_MSG_USERAUTH_REQUEST);
 	packet_put_raw(buffer_ptr(&b), buffer_len(&b));
 	buffer_free(&b);

 	/* send */
 	packet_send();
 	packet_write_wait();
 }

 int
 ssh2_try_pubkey(char *filename,
     const char *server_user, const char *host, const char *service)
 {
 	Key *k;
 	struct stat st;

 	if (stat(filename, &st) != 0) {
 		debug("key does not exist: %s", filename);
 		return 0;
 	}
 	debug("try pubkey: %s", filename);

 	k = key_new(KEY_DSA);
 	if (!load_private_key(filename, "", k, NULL)) {
 		int success = 0;
 		char *passphrase;
 		char prompt[300];
 		snprintf(prompt, sizeof prompt,
 		     "Enter passphrase for DSA key '%.100s': ",
 		     filename);
 		passphrase = read_passphrase(prompt, 0);
 		success = load_private_key(filename, passphrase, k, NULL);
 		memset(passphrase, 0, strlen(passphrase));
 		xfree(passphrase);
 		if (!success) {
 			key_free(k);
 			return 0;
 		}
 	}
 	ssh2_sign_and_send_pubkey(k, dsa_sign, server_user, host, service);
 	return 1;
 }

 void
 ssh_userauth2(const char *server_user, char *host)
 {
 	int type;
 	int plen;
 	int sent;
 	unsigned int dlen;
 	int partial;
 	int i = 0;
 	char *auths;
 	char *service = "ssh-connection";		/* service name */

 	debug("send SSH2_MSG_SERVICE_REQUEST");
 	packet_start(SSH2_MSG_SERVICE_REQUEST);
 	packet_put_cstring("ssh-userauth");
 	packet_send();
 	packet_write_wait();

 	type = packet_read(&plen);
 	if (type != SSH2_MSG_SERVICE_ACCEPT) {
 		fatal("denied SSH2_MSG_SERVICE_ACCEPT: %d", type);
 	}
 	if (packet_remaining() > 0) {
 		char *reply = packet_get_string(&plen);
 		debug("service_accept: %s", reply);
 		xfree(reply);
 	} else {
 		/* payload empty for ssh-2.0.13 ?? */
 		debug("buggy server: service_accept w/o service");
 	}
 	packet_done();
 	debug("got SSH2_MSG_SERVICE_ACCEPT");

 	/* INITIAL request for auth */
 	packet_start(SSH2_MSG_USERAUTH_REQUEST);
 	packet_put_cstring(server_user);
 	packet_put_cstring(service);
 	packet_put_cstring("none");
 	packet_send();
 	packet_write_wait();

 	for (;;) {
 		sent = 0;
 		type = packet_read(&plen);
 		if (type == SSH2_MSG_USERAUTH_SUCCESS)
 			break;
 		if (type != SSH2_MSG_USERAUTH_FAILURE)
 			fatal("access denied: %d", type);
 		/* SSH2_MSG_USERAUTH_FAILURE means: try again */
 		auths = packet_get_string(&dlen);
 		debug("authentications that can continue: %s", auths);
 		partial = packet_get_char();
 		packet_done();
 		if (partial)
 			debug("partial success");
 		if (options.dsa_authentication &&
 		    strstr(auths, "publickey") != NULL) {
 			while (i < options.num_identity_files2) {
 				sent = ssh2_try_pubkey(
 				    options.identity_files2[i++],
 				    server_user, host, service);
 				if (sent)
 					break;
 			}
 		}
 		if (!sent) {
 			if (options.password_authentication &&
 			    !options.batch_mode &&
 			    strstr(auths, "password") != NULL) {
 				sent = ssh2_try_passwd(server_user, host, service);
 			}
 		}
 		if (!sent)
 			fatal("Permission denied (%s).", auths);
 		xfree(auths);
 	}
 	packet_done();
 	debug("ssh-userauth2 successfull");
 }
	/*
	* Copyright (c) 2000 Markus Friedl. All rights reserved.
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that the following conditions
	* are met:
	* 1. Redistributions of source code must retain the above copyright
	* notice, this list of conditions and the following disclaimer.
	* 2. Redistributions in binary form must reproduce the above copyright
	* notice, this list of conditions and the following disclaimer in the
	* documentation and/or other materials provided with the distribution.
	* 3. All advertising materials mentioning features or use of this software
	* must display the following acknowledgement:
	* This product includes software developed by Markus Friedl.
	* 4. The name of the author may not be used to endorse or promote products
	* derived from this software without specific prior written permission.
	*
	* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
	* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
	* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
	* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
	* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
	* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
	* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
	* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
	* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
	* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
	*/

	#include "includes.h"
	RCSID("$OpenBSD: sshconnect2.c,v 1.16 2000/07/16 08:27:22 markus Exp $");

	#include <openssl/bn.h>
	#include <openssl/rsa.h>
	#include <openssl/dsa.h>
	#include <openssl/md5.h>
	#include <openssl/dh.h>
	#include <openssl/hmac.h>

	#include "ssh.h"
	#include "xmalloc.h"
	#include "rsa.h"
	#include "buffer.h"
	#include "packet.h"
	#include "cipher.h"
	#include "uidswap.h"
	#include "compat.h"
	#include "readconf.h"
	#include "bufaux.h"
	#include "ssh2.h"
	#include "kex.h"
	#include "myproposal.h"
	#include "key.h"
	#include "dsa.h"
	#include "sshconnect.h"
	#include "authfile.h"

	/* import */
	extern char *client_version_string;
	extern char *server_version_string;
	extern Options options;

	/*
	* SSH2 key exchange
	*/

	unsigned char *session_id2 = NULL;
	int session_id2_len = 0;

	void
	ssh_kex_dh(Kex kex, char host, struct sockaddr *hostaddr,
	Buffer client_kexinit, Buffer server_kexinit)
	{
	int plen, dlen;
	unsigned int klen, kout;
	char *signature = NULL;
	unsigned int slen;
	char *server_host_key_blob = NULL;
	Key *server_host_key;
	unsigned int sbloblen;
	DH *dh;
	BIGNUM *dh_server_pub = 0;
	BIGNUM *shared_secret = 0;
	unsigned char *kbuf;
	unsigned char *hash;

	debug("Sending SSH2_MSG_KEXDH_INIT.");
	/* generate and send 'e', client DH public key */
	dh = dh_new_group1();
	packet_start(SSH2_MSG_KEXDH_INIT);
	packet_put_bignum2(dh->pub_key);
	packet_send();
	packet_write_wait();

	#ifdef DEBUG_KEXDH
	fprintf(stderr, "\np= ");
	bignum_print(dh->p);
	fprintf(stderr, "\ng= ");
	bignum_print(dh->g);
	fprintf(stderr, "\npub= ");
	bignum_print(dh->pub_key);
	fprintf(stderr, "\n");
	DHparams_print_fp(stderr, dh);
	#endif

	debug("Wait SSH2_MSG_KEXDH_REPLY.");

	packet_read_expect(&plen, SSH2_MSG_KEXDH_REPLY);

	debug("Got SSH2_MSG_KEXDH_REPLY.");

	/* key, cert */
	server_host_key_blob = packet_get_string(&sbloblen);
	server_host_key = dsa_key_from_blob(server_host_key_blob, sbloblen);
	if (server_host_key == NULL)
	fatal("cannot decode server_host_key_blob");

	check_host_key(host, hostaddr, server_host_key,
	options.user_hostfile2, options.system_hostfile2);

	/* DH paramter f, server public DH key */
	dh_server_pub = BN_new();
	if (dh_server_pub == NULL)
	fatal("dh_server_pub == NULL");
	packet_get_bignum2(dh_server_pub, &dlen);

	#ifdef DEBUG_KEXDH
	fprintf(stderr, "\ndh_server_pub= ");
	bignum_print(dh_server_pub);
	fprintf(stderr, "\n");
	debug("bits %d", BN_num_bits(dh_server_pub));
	#endif

	/* signed H */
	signature = packet_get_string(&slen);
	packet_done();

	if (!dh_pub_is_valid(dh, dh_server_pub))
	packet_disconnect("bad server public DH value");

	klen = DH_size(dh);
	kbuf = xmalloc(klen);
	kout = DH_compute_key(kbuf, dh_server_pub, dh);
	#ifdef DEBUG_KEXDH
	debug("shared secret: len %d/%d", klen, kout);
	fprintf(stderr, "shared secret == ");
	for (i = 0; i< kout; i++)
	fprintf(stderr, "%02x", (kbuf[i])&0xff);
	fprintf(stderr, "\n");
	#endif
	shared_secret = BN_new();

	BN_bin2bn(kbuf, kout, shared_secret);
	memset(kbuf, 0, klen);
	xfree(kbuf);

	/* calc and verify H */
	hash = kex_hash(
	client_version_string,
	server_version_string,
	buffer_ptr(client_kexinit), buffer_len(client_kexinit),
	buffer_ptr(server_kexinit), buffer_len(server_kexinit),
	server_host_key_blob, sbloblen,
	dh->pub_key,
	dh_server_pub,
	shared_secret
	);
	xfree(server_host_key_blob);
	DH_free(dh);
	#ifdef DEBUG_KEXDH
	fprintf(stderr, "hash == ");
	for (i = 0; i< 20; i++)
	fprintf(stderr, "%02x", (hash[i])&0xff);
	fprintf(stderr, "\n");
	#endif
	if (dsa_verify(server_host_key, (unsigned char *)signature, slen, hash, 20) != 1)
	fatal("dsa_verify failed for server_host_key");
	key_free(server_host_key);

	kex_derive_keys(kex, hash, shared_secret);
	packet_set_kex(kex);

	/* save session id */
	session_id2_len = 20;
	session_id2 = xmalloc(session_id2_len);
	memcpy(session_id2, hash, session_id2_len);
	}

	void
	ssh_kex2(char host, struct sockaddr hostaddr)
	{
	int i, plen;
	Kex *kex;
	Buffer client_kexinit, server_kexinit;
	char *sprop[PROPOSAL_MAX];

	if (options.ciphers != NULL) {
	myproposal[PROPOSAL_ENC_ALGS_CTOS] =
	myproposal[PROPOSAL_ENC_ALGS_STOC] = options.ciphers;
	} else if (options.cipher == SSH_CIPHER_3DES) {
	myproposal[PROPOSAL_ENC_ALGS_CTOS] =
	myproposal[PROPOSAL_ENC_ALGS_STOC] =
	(char *) cipher_name(SSH_CIPHER_3DES_CBC);
	} else if (options.cipher == SSH_CIPHER_BLOWFISH) {
	myproposal[PROPOSAL_ENC_ALGS_CTOS] =
	myproposal[PROPOSAL_ENC_ALGS_STOC] =
	(char *) cipher_name(SSH_CIPHER_BLOWFISH_CBC);
	}
	if (options.compression) {
	myproposal[PROPOSAL_COMP_ALGS_CTOS] = "zlib";
	myproposal[PROPOSAL_COMP_ALGS_STOC] = "zlib";
	} else {
	myproposal[PROPOSAL_COMP_ALGS_CTOS] = "none";
	myproposal[PROPOSAL_COMP_ALGS_STOC] = "none";
	}

	/* buffers with raw kexinit messages */
	server_kexinit = xmalloc(sizeof(*server_kexinit));
	buffer_init(server_kexinit);
	client_kexinit = kex_init(myproposal);

	/* algorithm negotiation */
	kex_exchange_kexinit(client_kexinit, server_kexinit, sprop);
	kex = kex_choose_conf(myproposal, sprop, 0);
	for (i = 0; i < PROPOSAL_MAX; i++)
	xfree(sprop[i]);

	/* server authentication and session key agreement */
	ssh_kex_dh(kex, host, hostaddr, client_kexinit, server_kexinit);

	buffer_free(client_kexinit);
	buffer_free(server_kexinit);
	xfree(client_kexinit);
	xfree(server_kexinit);

	debug("Wait SSH2_MSG_NEWKEYS.");
	packet_read_expect(&plen, SSH2_MSG_NEWKEYS);
	packet_done();
	debug("GOT SSH2_MSG_NEWKEYS.");

	debug("send SSH2_MSG_NEWKEYS.");
	packet_start(SSH2_MSG_NEWKEYS);
	packet_send();
	packet_write_wait();
	debug("done: send SSH2_MSG_NEWKEYS.");

	#ifdef DEBUG_KEXDH
	/* send 1st encrypted/maced/compressed message */
	packet_start(SSH2_MSG_IGNORE);
	packet_put_cstring("markus");
	packet_send();
	packet_write_wait();
	#endif
	debug("done: KEX2.");
	}

	/*
	* Authenticate user
	*/
	int
	ssh2_try_passwd(const char server_user, const char host, const char *service)
	{
	static int attempt = 0;
	char prompt[80];
	char *password;

	if (attempt++ >= options.number_of_password_prompts)
	return 0;

	if(attempt != 1)
	error("Permission denied, please try again.");

	snprintf(prompt, sizeof(prompt), "%.30s@%.40s's password: ",
	server_user, host);
	password = read_passphrase(prompt, 0);
	packet_start(SSH2_MSG_USERAUTH_REQUEST);
	packet_put_cstring(server_user);
	packet_put_cstring(service);
	packet_put_cstring("password");
	packet_put_char(0);
	packet_put_cstring(password);
	memset(password, 0, strlen(password));
	xfree(password);
	packet_send();
	packet_write_wait();
	return 1;
	}

	typedef int sign_fn(
	Key *key,
	unsigned char *sigp, int lenp,
	unsigned char *data, int datalen);

	void
	ssh2_sign_and_send_pubkey(Key k, sign_fn do_sign,
	const char server_user, const char host, const char *service)
	{
	Buffer b;
	unsigned char blob, signature;
	int bloblen, slen;
	int skip = 0;

	dsa_make_key_blob(k, &blob, &bloblen);

	/* data to be signed */
	buffer_init(&b);
	if (datafellows & SSH_COMPAT_SESSIONID_ENCODING) {
	buffer_put_string(&b, session_id2, session_id2_len);
	skip = buffer_len(&b);
	} else {
	buffer_append(&b, session_id2, session_id2_len);
	skip = session_id2_len;
	}
	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
	buffer_put_cstring(&b, server_user);
	buffer_put_cstring(&b,
	datafellows & SSH_BUG_PUBKEYAUTH ?
	"ssh-userauth" :
	service);
	buffer_put_cstring(&b, "publickey");
	buffer_put_char(&b, 1);
	buffer_put_cstring(&b, KEX_DSS);
	buffer_put_string(&b, blob, bloblen);

	/* generate signature */
	do_sign(k, &signature, &slen, buffer_ptr(&b), buffer_len(&b));
	key_free(k); /* XXX */
	#ifdef DEBUG_DSS
	buffer_dump(&b);
	#endif
	if (datafellows & SSH_BUG_PUBKEYAUTH) {
	buffer_clear(&b);
	buffer_append(&b, session_id2, session_id2_len);
	buffer_put_char(&b, SSH2_MSG_USERAUTH_REQUEST);
	buffer_put_cstring(&b, server_user);
	buffer_put_cstring(&b, service);
	buffer_put_cstring(&b, "publickey");
	buffer_put_char(&b, 1);
	buffer_put_cstring(&b, KEX_DSS);
	buffer_put_string(&b, blob, bloblen);
	}
	xfree(blob);
	/* append signature */
	buffer_put_string(&b, signature, slen);
	xfree(signature);

	/* skip session id and packet type */
	if (buffer_len(&b) < skip + 1)
	fatal("ssh2_try_pubkey: internal error");
	buffer_consume(&b, skip + 1);

	/* put remaining data from buffer into packet */
	packet_start(SSH2_MSG_USERAUTH_REQUEST);
	packet_put_raw(buffer_ptr(&b), buffer_len(&b));
	buffer_free(&b);

	/* send */
	packet_send();
	packet_write_wait();
	}

	int
	ssh2_try_pubkey(char *filename,
	const char server_user, const char host, const char *service)
	{
	Key *k;
	struct stat st;

	if (stat(filename, &st) != 0) {
	debug("key does not exist: %s", filename);
	return 0;
	}
	debug("try pubkey: %s", filename);

	k = key_new(KEY_DSA);
	if (!load_private_key(filename, "", k, NULL)) {
	int success = 0;
	char *passphrase;
	char prompt[300];
	snprintf(prompt, sizeof prompt,
	"Enter passphrase for DSA key '%.100s': ",
	filename);
	passphrase = read_passphrase(prompt, 0);
	success = load_private_key(filename, passphrase, k, NULL);
	memset(passphrase, 0, strlen(passphrase));
	xfree(passphrase);
	if (!success) {
	key_free(k);
	return 0;
	}
	}
	ssh2_sign_and_send_pubkey(k, dsa_sign, server_user, host, service);
	return 1;
	}

	void
	ssh_userauth2(const char server_user, char host)
	{
	int type;
	int plen;
	int sent;
	unsigned int dlen;
	int partial;
	int i = 0;
	char *auths;
	char service = "ssh-connection"; / service name */

	debug("send SSH2_MSG_SERVICE_REQUEST");
	packet_start(SSH2_MSG_SERVICE_REQUEST);
	packet_put_cstring("ssh-userauth");
	packet_send();
	packet_write_wait();

	type = packet_read(&plen);
	if (type != SSH2_MSG_SERVICE_ACCEPT) {
	fatal("denied SSH2_MSG_SERVICE_ACCEPT: %d", type);
	}
	if (packet_remaining() > 0) {
	char *reply = packet_get_string(&plen);
	debug("service_accept: %s", reply);
	xfree(reply);
	} else {
	/* payload empty for ssh-2.0.13 ?? */
	debug("buggy server: service_accept w/o service");
	}
	packet_done();
	debug("got SSH2_MSG_SERVICE_ACCEPT");

	/* INITIAL request for auth */
	packet_start(SSH2_MSG_USERAUTH_REQUEST);
	packet_put_cstring(server_user);
	packet_put_cstring(service);
	packet_put_cstring("none");
	packet_send();
	packet_write_wait();

	for (;;) {
	sent = 0;
	type = packet_read(&plen);
	if (type == SSH2_MSG_USERAUTH_SUCCESS)
	break;
	if (type != SSH2_MSG_USERAUTH_FAILURE)
	fatal("access denied: %d", type);
	/* SSH2_MSG_USERAUTH_FAILURE means: try again */
	auths = packet_get_string(&dlen);
	debug("authentications that can continue: %s", auths);
	partial = packet_get_char();
	packet_done();
	if (partial)
	debug("partial success");
	if (options.dsa_authentication &&
	strstr(auths, "publickey") != NULL) {
	while (i < options.num_identity_files2) {
	sent = ssh2_try_pubkey(
	options.identity_files2[i++],
	server_user, host, service);
	if (sent)
	break;
	}
	}
	if (!sent) {
	if (options.password_authentication &&
	!options.batch_mode &&
	strstr(auths, "password") != NULL) {
	sent = ssh2_try_passwd(server_user, host, service);
	}
	}
	if (!sent)
	fatal("Permission denied (%s).", auths);
	xfree(auths);
	}
	packet_done();
	debug("ssh-userauth2 successfull");
	}