summaryrefslogtreecommitdiff
path: root/sshconnect1.c
blob: c579b01cc39562ce17641dfe999658fc52123469 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
/*
 * Author: Tatu Ylonen <ylo@cs.hut.fi>
 * Copyright (c) 1995 Tatu Ylonen <ylo@cs.hut.fi>, Espoo, Finland
 *                    All rights reserved
 * Code to connect to a remote host, and to perform the client side of the
 * login (authentication) dialog.
 *
 * 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: sshconnect1.c,v 1.57 2004/05/08 00:21:31 djm Exp $");

#include <openssl/bn.h>
#include <openssl/md5.h>

#include "ssh.h"
#include "ssh1.h"
#include "xmalloc.h"
#include "rsa.h"
#include "buffer.h"
#include "packet.h"
#include "mpaux.h"
#include "uidswap.h"
#include "log.h"
#include "readconf.h"
#include "key.h"
#include "authfd.h"
#include "sshconnect.h"
#include "authfile.h"
#include "misc.h"
#include "cipher.h"
#include "canohost.h"
#include "auth.h"

/* Session id for the current session. */
u_char session_id[16];
u_int supported_authentications = 0;

extern Options options;
extern char *__progname;

/*
 * Checks if the user has an authentication agent, and if so, tries to
 * authenticate using the agent.
 */
static int
try_agent_authentication(void)
{
	int type;
	char *comment;
	AuthenticationConnection *auth;
	u_char response[16];
	u_int i;
	Key *key;
	BIGNUM *challenge;

	/* Get connection to the agent. */
	auth = ssh_get_authentication_connection();
	if (!auth)
		return 0;

	if ((challenge = BN_new()) == NULL)
		fatal("try_agent_authentication: BN_new failed");
	/* Loop through identities served by the agent. */
	for (key = ssh_get_first_identity(auth, &comment, 1);
	    key != NULL;
	    key = ssh_get_next_identity(auth, &comment, 1)) {

		/* Try this identity. */
		debug("Trying RSA authentication via agent with '%.100s'", comment);
		xfree(comment);

		/* Tell the server that we are willing to authenticate using this key. */
		packet_start(SSH_CMSG_AUTH_RSA);
		packet_put_bignum(key->rsa->n);
		packet_send();
		packet_write_wait();

		/* Wait for server's response. */
		type = packet_read();

		/* The server sends failure if it doesn\'t like our key or
		   does not support RSA authentication. */
		if (type == SSH_SMSG_FAILURE) {
			debug("Server refused our key.");
			key_free(key);
			continue;
		}
		/* Otherwise it should have sent a challenge. */
		if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
			packet_disconnect("Protocol error during RSA authentication: %d",
					  type);

		packet_get_bignum(challenge);
		packet_check_eom();

		debug("Received RSA challenge from server.");

		/* Ask the agent to decrypt the challenge. */
		if (!ssh_decrypt_challenge(auth, key, challenge, session_id, 1, response)) {
			/*
			 * The agent failed to authenticate this identifier
			 * although it advertised it supports this.  Just
			 * return a wrong value.
			 */
			logit("Authentication agent failed to decrypt challenge.");
			memset(response, 0, sizeof(response));
		}
		key_free(key);
		debug("Sending response to RSA challenge.");

		/* Send the decrypted challenge back to the server. */
		packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
		for (i = 0; i < 16; i++)
			packet_put_char(response[i]);
		packet_send();
		packet_write_wait();

		/* Wait for response from the server. */
		type = packet_read();

		/* The server returns success if it accepted the authentication. */
		if (type == SSH_SMSG_SUCCESS) {
			ssh_close_authentication_connection(auth);
			BN_clear_free(challenge);
			debug("RSA authentication accepted by server.");
			return 1;
		}
		/* Otherwise it should return failure. */
		if (type != SSH_SMSG_FAILURE)
			packet_disconnect("Protocol error waiting RSA auth response: %d",
					  type);
	}
	ssh_close_authentication_connection(auth);
	BN_clear_free(challenge);
	debug("RSA authentication using agent refused.");
	return 0;
}

/*
 * Computes the proper response to a RSA challenge, and sends the response to
 * the server.
 */
static void
respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
{
	u_char buf[32], response[16];
	MD5_CTX md;
	int i, len;

	/* Decrypt the challenge using the private key. */
	/* XXX think about Bleichenbacher, too */
	if (rsa_private_decrypt(challenge, challenge, prv) <= 0)
		packet_disconnect(
		    "respond_to_rsa_challenge: rsa_private_decrypt failed");

	/* Compute the response. */
	/* The response is MD5 of decrypted challenge plus session id. */
	len = BN_num_bytes(challenge);
	if (len <= 0 || len > sizeof(buf))
		packet_disconnect(
		    "respond_to_rsa_challenge: bad challenge length %d", len);

	memset(buf, 0, sizeof(buf));
	BN_bn2bin(challenge, buf + sizeof(buf) - len);
	MD5_Init(&md);
	MD5_Update(&md, buf, 32);
	MD5_Update(&md, session_id, 16);
	MD5_Final(response, &md);

	debug("Sending response to host key RSA challenge.");

	/* Send the response back to the server. */
	packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
	for (i = 0; i < 16; i++)
		packet_put_char(response[i]);
	packet_send();
	packet_write_wait();

	memset(buf, 0, sizeof(buf));
	memset(response, 0, sizeof(response));
	memset(&md, 0, sizeof(md));
}

/*
 * Checks if the user has authentication file, and if so, tries to authenticate
 * the user using it.
 */
static int
try_rsa_authentication(int idx)
{
	BIGNUM *challenge;
	Key *public, *private;
	char buf[300], *passphrase, *comment, *authfile;
	int i, type, quit;

	public = options.identity_keys[idx];
	authfile = options.identity_files[idx];
	comment = xstrdup(authfile);

	debug("Trying RSA authentication with key '%.100s'", comment);

	/* Tell the server that we are willing to authenticate using this key. */
	packet_start(SSH_CMSG_AUTH_RSA);
	packet_put_bignum(public->rsa->n);
	packet_send();
	packet_write_wait();

	/* Wait for server's response. */
	type = packet_read();

	/*
	 * The server responds with failure if it doesn\'t like our key or
	 * doesn\'t support RSA authentication.
	 */
	if (type == SSH_SMSG_FAILURE) {
		debug("Server refused our key.");
		xfree(comment);
		return 0;
	}
	/* Otherwise, the server should respond with a challenge. */
	if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
		packet_disconnect("Protocol error during RSA authentication: %d", type);

	/* Get the challenge from the packet. */
	if ((challenge = BN_new()) == NULL)
		fatal("try_rsa_authentication: BN_new failed");
	packet_get_bignum(challenge);
	packet_check_eom();

	debug("Received RSA challenge from server.");

	/*
	 * If the key is not stored in external hardware, we have to
	 * load the private key.  Try first with empty passphrase; if it
	 * fails, ask for a passphrase.
	 */
	if (public->flags & KEY_FLAG_EXT)
		private = public;
	else
		private = key_load_private_type(KEY_RSA1, authfile, "", NULL);
	if (private == NULL && !options.batch_mode) {
		snprintf(buf, sizeof(buf),
		    "Enter passphrase for RSA key '%.100s': ", comment);
		for (i = 0; i < options.number_of_password_prompts; i++) {
			passphrase = read_passphrase(buf, 0);
			if (strcmp(passphrase, "") != 0) {
				private = key_load_private_type(KEY_RSA1,
				    authfile, passphrase, NULL);
				quit = 0;
			} else {
				debug2("no passphrase given, try next key");
				quit = 1;
			}
			memset(passphrase, 0, strlen(passphrase));
			xfree(passphrase);
			if (private != NULL || quit)
				break;
			debug2("bad passphrase given, try again...");
		}
	}
	/* We no longer need the comment. */
	xfree(comment);

	if (private == NULL) {
		if (!options.batch_mode)
			error("Bad passphrase.");

		/* Send a dummy response packet to avoid protocol error. */
		packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
		for (i = 0; i < 16; i++)
			packet_put_char(0);
		packet_send();
		packet_write_wait();

		/* Expect the server to reject it... */
		packet_read_expect(SSH_SMSG_FAILURE);
		BN_clear_free(challenge);
		return 0;
	}

	/* Compute and send a response to the challenge. */
	respond_to_rsa_challenge(challenge, private->rsa);

	/* Destroy the private key unless it in external hardware. */
	if (!(private->flags & KEY_FLAG_EXT))
		key_free(private);

	/* We no longer need the challenge. */
	BN_clear_free(challenge);

	/* Wait for response from the server. */
	type = packet_read();
	if (type == SSH_SMSG_SUCCESS) {
		debug("RSA authentication accepted by server.");
		return 1;
	}
	if (type != SSH_SMSG_FAILURE)
		packet_disconnect("Protocol error waiting RSA auth response: %d", type);
	debug("RSA authentication refused.");
	return 0;
}

/*
 * Tries to authenticate the user using combined rhosts or /etc/hosts.equiv
 * authentication and RSA host authentication.
 */
static int
try_rhosts_rsa_authentication(const char *local_user, Key * host_key)
{
	int type;
	BIGNUM *challenge;

	debug("Trying rhosts or /etc/hosts.equiv with RSA host authentication.");

	/* Tell the server that we are willing to authenticate using this key. */
	packet_start(SSH_CMSG_AUTH_RHOSTS_RSA);
	packet_put_cstring(local_user);
	packet_put_int(BN_num_bits(host_key->rsa->n));
	packet_put_bignum(host_key->rsa->e);
	packet_put_bignum(host_key->rsa->n);
	packet_send();
	packet_write_wait();

	/* Wait for server's response. */
	type = packet_read();

	/* The server responds with failure if it doesn't admit our
	   .rhosts authentication or doesn't know our host key. */
	if (type == SSH_SMSG_FAILURE) {
		debug("Server refused our rhosts authentication or host key.");
		return 0;
	}
	/* Otherwise, the server should respond with a challenge. */
	if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
		packet_disconnect("Protocol error during RSA authentication: %d", type);

	/* Get the challenge from the packet. */
	if ((challenge = BN_new()) == NULL)
		fatal("try_rhosts_rsa_authentication: BN_new failed");
	packet_get_bignum(challenge);
	packet_check_eom();

	debug("Received RSA challenge for host key from server.");

	/* Compute a response to the challenge. */
	respond_to_rsa_challenge(challenge, host_key->rsa);

	/* We no longer need the challenge. */
	BN_clear_free(challenge);

	/* Wait for response from the server. */
	type = packet_read();
	if (type == SSH_SMSG_SUCCESS) {
		debug("Rhosts or /etc/hosts.equiv with RSA host authentication accepted by server.");
		return 1;
	}
	if (type != SSH_SMSG_FAILURE)
		packet_disconnect("Protocol error waiting RSA auth response: %d", type);
	debug("Rhosts or /etc/hosts.equiv with RSA host authentication refused.");
	return 0;
}

/*
 * Tries to authenticate with any string-based challenge/response system.
 * Note that the client code is not tied to s/key or TIS.
 */
static int
try_challenge_response_authentication(void)
{
	int type, i;
	u_int clen;
	char prompt[1024];
	char *challenge, *response;

	debug("Doing challenge response authentication.");

	for (i = 0; i < options.number_of_password_prompts; i++) {
		/* request a challenge */
		packet_start(SSH_CMSG_AUTH_TIS);
		packet_send();
		packet_write_wait();

		type = packet_read();
		if (type != SSH_SMSG_FAILURE &&
		    type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
			packet_disconnect("Protocol error: got %d in response "
			    "to SSH_CMSG_AUTH_TIS", type);
		}
		if (type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
			debug("No challenge.");
			return 0;
		}
		challenge = packet_get_string(&clen);
		packet_check_eom();
		snprintf(prompt, sizeof prompt, "%s%s", challenge,
		    strchr(challenge, '\n') ? "" : "\nResponse: ");
		xfree(challenge);
		if (i != 0)
			error("Permission denied, please try again.");
		if (options.cipher == SSH_CIPHER_NONE)
			logit("WARNING: Encryption is disabled! "
			    "Response will be transmitted in clear text.");
		response = read_passphrase(prompt, 0);
		if (strcmp(response, "") == 0) {
			xfree(response);
			break;
		}
		packet_start(SSH_CMSG_AUTH_TIS_RESPONSE);
		ssh_put_password(response);
		memset(response, 0, strlen(response));
		xfree(response);
		packet_send();
		packet_write_wait();
		type = packet_read();
		if (type == SSH_SMSG_SUCCESS)
			return 1;
		if (type != SSH_SMSG_FAILURE)
			packet_disconnect("Protocol error: got %d in response "
			    "to SSH_CMSG_AUTH_TIS_RESPONSE", type);
	}
	/* failure */
	return 0;
}

/*
 * Tries to authenticate with plain passwd authentication.
 */
static int
try_password_authentication(char *prompt)
{
	int type, i;
	char *password;

	debug("Doing password authentication.");
	if (options.cipher == SSH_CIPHER_NONE)
		logit("WARNING: Encryption is disabled! Password will be transmitted in clear text.");
	for (i = 0; i < options.number_of_password_prompts; i++) {
		if (i != 0)
			error("Permission denied, please try again.");
		password = read_passphrase(prompt, 0);
		packet_start(SSH_CMSG_AUTH_PASSWORD);
		ssh_put_password(password);
		memset(password, 0, strlen(password));
		xfree(password);
		packet_send();
		packet_write_wait();

		type = packet_read();
		if (type == SSH_SMSG_SUCCESS)
			return 1;
		if (type != SSH_SMSG_FAILURE)
			packet_disconnect("Protocol error: got %d in response to passwd auth", type);
	}
	/* failure */
	return 0;
}

/*
 * SSH1 key exchange
 */
void
ssh_kex(char *host, struct sockaddr *hostaddr)
{
	int i;
	BIGNUM *key;
	Key *host_key, *server_key;
	int bits, rbits;
	int ssh_cipher_default = SSH_CIPHER_3DES;
	u_char session_key[SSH_SESSION_KEY_LENGTH];
	u_char cookie[8];
	u_int supported_ciphers;
	u_int server_flags, client_flags;
	u_int32_t rand = 0;

	debug("Waiting for server public key.");

	/* Wait for a public key packet from the server. */
	packet_read_expect(SSH_SMSG_PUBLIC_KEY);

	/* Get cookie from the packet. */
	for (i = 0; i < 8; i++)
		cookie[i] = packet_get_char();

	/* Get the public key. */
	server_key = key_new(KEY_RSA1);
	bits = packet_get_int();
	packet_get_bignum(server_key->rsa->e);
	packet_get_bignum(server_key->rsa->n);

	rbits = BN_num_bits(server_key->rsa->n);
	if (bits != rbits) {
		logit("Warning: Server lies about size of server public key: "
		    "actual size is %d bits vs. announced %d.", rbits, bits);
		logit("Warning: This may be due to an old implementation of ssh.");
	}
	/* Get the host key. */
	host_key = key_new(KEY_RSA1);
	bits = packet_get_int();
	packet_get_bignum(host_key->rsa->e);
	packet_get_bignum(host_key->rsa->n);

	rbits = BN_num_bits(host_key->rsa->n);
	if (bits != rbits) {
		logit("Warning: Server lies about size of server host key: "
		    "actual size is %d bits vs. announced %d.", rbits, bits);
		logit("Warning: This may be due to an old implementation of ssh.");
	}

	/* Get protocol flags. */
	server_flags = packet_get_int();
	packet_set_protocol_flags(server_flags);

	supported_ciphers = packet_get_int();
	supported_authentications = packet_get_int();
	packet_check_eom();

	debug("Received server public key (%d bits) and host key (%d bits).",
	    BN_num_bits(server_key->rsa->n), BN_num_bits(host_key->rsa->n));

	if (verify_host_key(host, hostaddr, host_key) == -1)
		fatal("Host key verification failed.");

	client_flags = SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN;

	compute_session_id(session_id, cookie, host_key->rsa->n, server_key->rsa->n);

	/* Generate a session key. */
	arc4random_stir();

	/*
	 * Generate an encryption key for the session.   The key is a 256 bit
	 * random number, interpreted as a 32-byte key, with the least
	 * significant 8 bits being the first byte of the key.
	 */
	for (i = 0; i < 32; i++) {
		if (i % 4 == 0)
			rand = arc4random();
		session_key[i] = rand & 0xff;
		rand >>= 8;
	}

	/*
	 * According to the protocol spec, the first byte of the session key
	 * is the highest byte of the integer.  The session key is xored with
	 * the first 16 bytes of the session id.
	 */
	if ((key = BN_new()) == NULL)
		fatal("respond_to_rsa_challenge: BN_new failed");
	BN_set_word(key, 0);
	for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
		BN_lshift(key, key, 8);
		if (i < 16)
			BN_add_word(key, session_key[i] ^ session_id[i]);
		else
			BN_add_word(key, session_key[i]);
	}

	/*
	 * Encrypt the integer using the public key and host key of the
	 * server (key with smaller modulus first).
	 */
	if (BN_cmp(server_key->rsa->n, host_key->rsa->n) < 0) {
		/* Public key has smaller modulus. */
		if (BN_num_bits(host_key->rsa->n) <
		    BN_num_bits(server_key->rsa->n) + SSH_KEY_BITS_RESERVED) {
			fatal("respond_to_rsa_challenge: host_key %d < server_key %d + "
			    "SSH_KEY_BITS_RESERVED %d",
			    BN_num_bits(host_key->rsa->n),
			    BN_num_bits(server_key->rsa->n),
			    SSH_KEY_BITS_RESERVED);
		}
		rsa_public_encrypt(key, key, server_key->rsa);
		rsa_public_encrypt(key, key, host_key->rsa);
	} else {
		/* Host key has smaller modulus (or they are equal). */
		if (BN_num_bits(server_key->rsa->n) <
		    BN_num_bits(host_key->rsa->n) + SSH_KEY_BITS_RESERVED) {
			fatal("respond_to_rsa_challenge: server_key %d < host_key %d + "
			    "SSH_KEY_BITS_RESERVED %d",
			    BN_num_bits(server_key->rsa->n),
			    BN_num_bits(host_key->rsa->n),
			    SSH_KEY_BITS_RESERVED);
		}
		rsa_public_encrypt(key, key, host_key->rsa);
		rsa_public_encrypt(key, key, server_key->rsa);
	}

	/* Destroy the public keys since we no longer need them. */
	key_free(server_key);
	key_free(host_key);

	if (options.cipher == SSH_CIPHER_NOT_SET) {
		if (cipher_mask_ssh1(1) & supported_ciphers & (1 << ssh_cipher_default))
			options.cipher = ssh_cipher_default;
	} else if (options.cipher == SSH_CIPHER_ILLEGAL ||
	    !(cipher_mask_ssh1(1) & (1 << options.cipher))) {
		logit("No valid SSH1 cipher, using %.100s instead.",
		    cipher_name(ssh_cipher_default));
		options.cipher = ssh_cipher_default;
	}
	/* Check that the selected cipher is supported. */
	if (!(supported_ciphers & (1 << options.cipher)))
		fatal("Selected cipher type %.100s not supported by server.",
		    cipher_name(options.cipher));

	debug("Encryption type: %.100s", cipher_name(options.cipher));

	/* Send the encrypted session key to the server. */
	packet_start(SSH_CMSG_SESSION_KEY);
	packet_put_char(options.cipher);

	/* Send the cookie back to the server. */
	for (i = 0; i < 8; i++)
		packet_put_char(cookie[i]);

	/* Send and destroy the encrypted encryption key integer. */
	packet_put_bignum(key);
	BN_clear_free(key);

	/* Send protocol flags. */
	packet_put_int(client_flags);

	/* Send the packet now. */
	packet_send();
	packet_write_wait();

	debug("Sent encrypted session key.");

	/* Set the encryption key. */
	packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, options.cipher);

	/* We will no longer need the session key here.  Destroy any extra copies. */
	memset(session_key, 0, sizeof(session_key));

	/*
	 * Expect a success message from the server.  Note that this message
	 * will be received in encrypted form.
	 */
	packet_read_expect(SSH_SMSG_SUCCESS);

	debug("Received encrypted confirmation.");
}

/*
 * Authenticate user
 */
void
ssh_userauth1(const char *local_user, const char *server_user, char *host,
    Sensitive *sensitive)
{
	int i, type;

	if (supported_authentications == 0)
		fatal("ssh_userauth1: server supports no auth methods");

	/* Send the name of the user to log in as on the server. */
	packet_start(SSH_CMSG_USER);
	packet_put_cstring(server_user);
	packet_send();
	packet_write_wait();

	/*
	 * The server should respond with success if no authentication is
	 * needed (the user has no password).  Otherwise the server responds
	 * with failure.
	 */
	type = packet_read();

	/* check whether the connection was accepted without authentication. */
	if (type == SSH_SMSG_SUCCESS)
		goto success;
	if (type != SSH_SMSG_FAILURE)
		packet_disconnect("Protocol error: got %d in response to SSH_CMSG_USER", type);

	/*
	 * Try .rhosts or /etc/hosts.equiv authentication with RSA host
	 * authentication.
	 */
	if ((supported_authentications & (1 << SSH_AUTH_RHOSTS_RSA)) &&
	    options.rhosts_rsa_authentication) {
		for (i = 0; i < sensitive->nkeys; i++) {
			if (sensitive->keys[i] != NULL &&
			    sensitive->keys[i]->type == KEY_RSA1 &&
			    try_rhosts_rsa_authentication(local_user,
			    sensitive->keys[i]))
				goto success;
		}
	}
	/* Try RSA authentication if the server supports it. */
	if ((supported_authentications & (1 << SSH_AUTH_RSA)) &&
	    options.rsa_authentication) {
		/*
		 * Try RSA authentication using the authentication agent. The
		 * agent is tried first because no passphrase is needed for
		 * it, whereas identity files may require passphrases.
		 */
		if (try_agent_authentication())
			goto success;

		/* Try RSA authentication for each identity. */
		for (i = 0; i < options.num_identity_files; i++)
			if (options.identity_keys[i] != NULL &&
			    options.identity_keys[i]->type == KEY_RSA1 &&
			    try_rsa_authentication(i))
				goto success;
	}
	/* Try challenge response authentication if the server supports it. */
	if ((supported_authentications & (1 << SSH_AUTH_TIS)) &&
	    options.challenge_response_authentication && !options.batch_mode) {
		if (try_challenge_response_authentication())
			goto success;
	}
	/* Try password authentication if the server supports it. */
	if ((supported_authentications & (1 << SSH_AUTH_PASSWORD)) &&
	    options.password_authentication && !options.batch_mode) {
		char prompt[80];

		snprintf(prompt, sizeof(prompt), "%.30s@%.128s's password: ",
		    server_user, host);
		if (try_password_authentication(prompt))
			goto success;
	}
	/* All authentication methods have failed.  Exit with an error message. */
	fatal("Permission denied.");
	/* NOTREACHED */

 success:
	return;	/* need statement after label */
}