Annotation of src/usr.bin/ssh/sshconnect1.c, Revision 1.5
1.1 markus 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: * Created: Sat Mar 18 22:15:47 1995 ylo
6: * Code to connect to a remote host, and to perform the client side of the
7: * login (authentication) dialog.
8: *
9: */
10:
11: #include "includes.h"
1.5 ! markus 12: RCSID("$OpenBSD: sshconnect1.c,v 1.4 2000/07/16 08:27:22 markus Exp $");
1.1 markus 13:
14: #include <openssl/bn.h>
15: #include <openssl/dsa.h>
16: #include <openssl/rsa.h>
17: #include <openssl/evp.h>
18:
19: #include "xmalloc.h"
20: #include "rsa.h"
21: #include "ssh.h"
22: #include "buffer.h"
23: #include "packet.h"
24: #include "cipher.h"
25: #include "mpaux.h"
26: #include "uidswap.h"
27: #include "readconf.h"
28: #include "key.h"
1.4 markus 29: #include "authfd.h"
1.1 markus 30: #include "sshconnect.h"
31: #include "authfile.h"
32:
33: /* Session id for the current session. */
34: unsigned char session_id[16];
35: unsigned int supported_authentications = 0;
36:
37: extern Options options;
38: extern char *__progname;
39:
40: /*
41: * Checks if the user has an authentication agent, and if so, tries to
42: * authenticate using the agent.
43: */
44: int
45: try_agent_authentication()
46: {
1.5 ! markus 47: int type;
1.1 markus 48: char *comment;
49: AuthenticationConnection *auth;
50: unsigned char response[16];
51: unsigned int i;
1.5 ! markus 52: int plen, clen;
! 53: Key *key;
! 54: BIGNUM *challenge;
1.1 markus 55:
56: /* Get connection to the agent. */
57: auth = ssh_get_authentication_connection();
58: if (!auth)
59: return 0;
60:
61: challenge = BN_new();
1.5 ! markus 62: key = key_new(KEY_RSA);
1.1 markus 63:
64: /* Loop through identities served by the agent. */
1.5 ! markus 65: for (key = ssh_get_first_identity(auth, &comment, 1);
! 66: key != NULL;
! 67: key = ssh_get_next_identity(auth, &comment, 1)) {
1.1 markus 68:
69: /* Try this identity. */
70: debug("Trying RSA authentication via agent with '%.100s'", comment);
71: xfree(comment);
72:
73: /* Tell the server that we are willing to authenticate using this key. */
74: packet_start(SSH_CMSG_AUTH_RSA);
1.5 ! markus 75: packet_put_bignum(key->rsa->n);
1.1 markus 76: packet_send();
77: packet_write_wait();
78:
79: /* Wait for server's response. */
80: type = packet_read(&plen);
81:
82: /* The server sends failure if it doesn\'t like our key or
83: does not support RSA authentication. */
84: if (type == SSH_SMSG_FAILURE) {
85: debug("Server refused our key.");
1.5 ! markus 86: key_free(key);
1.1 markus 87: continue;
88: }
89: /* Otherwise it should have sent a challenge. */
90: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
91: packet_disconnect("Protocol error during RSA authentication: %d",
92: type);
93:
94: packet_get_bignum(challenge, &clen);
95:
96: packet_integrity_check(plen, clen, type);
97:
98: debug("Received RSA challenge from server.");
99:
100: /* Ask the agent to decrypt the challenge. */
1.5 ! markus 101: if (!ssh_decrypt_challenge(auth, key, challenge, session_id, 1, response)) {
! 102: /*
! 103: * The agent failed to authenticate this identifier
! 104: * although it advertised it supports this. Just
! 105: * return a wrong value.
! 106: */
1.1 markus 107: log("Authentication agent failed to decrypt challenge.");
108: memset(response, 0, sizeof(response));
109: }
1.5 ! markus 110: key_free(key);
1.1 markus 111: debug("Sending response to RSA challenge.");
112:
113: /* Send the decrypted challenge back to the server. */
114: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
115: for (i = 0; i < 16; i++)
116: packet_put_char(response[i]);
117: packet_send();
118: packet_write_wait();
119:
120: /* Wait for response from the server. */
121: type = packet_read(&plen);
122:
123: /* The server returns success if it accepted the authentication. */
124: if (type == SSH_SMSG_SUCCESS) {
1.5 ! markus 125: BN_clear_free(challenge);
1.1 markus 126: debug("RSA authentication accepted by server.");
127: return 1;
128: }
129: /* Otherwise it should return failure. */
130: if (type != SSH_SMSG_FAILURE)
131: packet_disconnect("Protocol error waiting RSA auth response: %d",
132: type);
133: }
134: BN_clear_free(challenge);
135: debug("RSA authentication using agent refused.");
136: return 0;
137: }
138:
139: /*
140: * Computes the proper response to a RSA challenge, and sends the response to
141: * the server.
142: */
143: void
144: respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
145: {
146: unsigned char buf[32], response[16];
147: MD5_CTX md;
148: int i, len;
149:
150: /* Decrypt the challenge using the private key. */
151: rsa_private_decrypt(challenge, challenge, prv);
152:
153: /* Compute the response. */
154: /* The response is MD5 of decrypted challenge plus session id. */
155: len = BN_num_bytes(challenge);
156: if (len <= 0 || len > sizeof(buf))
157: packet_disconnect("respond_to_rsa_challenge: bad challenge length %d",
158: len);
159:
160: memset(buf, 0, sizeof(buf));
161: BN_bn2bin(challenge, buf + sizeof(buf) - len);
162: MD5_Init(&md);
163: MD5_Update(&md, buf, 32);
164: MD5_Update(&md, session_id, 16);
165: MD5_Final(response, &md);
166:
167: debug("Sending response to host key RSA challenge.");
168:
169: /* Send the response back to the server. */
170: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
171: for (i = 0; i < 16; i++)
172: packet_put_char(response[i]);
173: packet_send();
174: packet_write_wait();
175:
176: memset(buf, 0, sizeof(buf));
177: memset(response, 0, sizeof(response));
178: memset(&md, 0, sizeof(md));
179: }
180:
181: /*
182: * Checks if the user has authentication file, and if so, tries to authenticate
183: * the user using it.
184: */
185: int
186: try_rsa_authentication(const char *authfile)
187: {
188: BIGNUM *challenge;
189: Key *public;
190: Key *private;
191: char *passphrase, *comment;
192: int type, i;
193: int plen, clen;
194:
195: /* Try to load identification for the authentication key. */
196: public = key_new(KEY_RSA);
197: if (!load_public_key(authfile, public, &comment)) {
198: key_free(public);
199: /* Could not load it. Fail. */
200: return 0;
201: }
202: debug("Trying RSA authentication with key '%.100s'", comment);
203:
204: /* Tell the server that we are willing to authenticate using this key. */
205: packet_start(SSH_CMSG_AUTH_RSA);
206: packet_put_bignum(public->rsa->n);
207: packet_send();
208: packet_write_wait();
209:
210: /* We no longer need the public key. */
211: key_free(public);
212:
213: /* Wait for server's response. */
214: type = packet_read(&plen);
215:
216: /*
217: * The server responds with failure if it doesn\'t like our key or
218: * doesn\'t support RSA authentication.
219: */
220: if (type == SSH_SMSG_FAILURE) {
221: debug("Server refused our key.");
222: xfree(comment);
223: return 0;
224: }
225: /* Otherwise, the server should respond with a challenge. */
226: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
227: packet_disconnect("Protocol error during RSA authentication: %d", type);
228:
229: /* Get the challenge from the packet. */
230: challenge = BN_new();
231: packet_get_bignum(challenge, &clen);
232:
233: packet_integrity_check(plen, clen, type);
234:
235: debug("Received RSA challenge from server.");
236:
237: private = key_new(KEY_RSA);
238: /*
239: * Load the private key. Try first with empty passphrase; if it
240: * fails, ask for a passphrase.
241: */
242: if (!load_private_key(authfile, "", private, NULL)) {
243: char buf[300];
244: snprintf(buf, sizeof buf, "Enter passphrase for RSA key '%.100s': ",
245: comment);
246: if (!options.batch_mode)
247: passphrase = read_passphrase(buf, 0);
248: else {
249: debug("Will not query passphrase for %.100s in batch mode.",
250: comment);
251: passphrase = xstrdup("");
252: }
253:
254: /* Load the authentication file using the pasphrase. */
255: if (!load_private_key(authfile, passphrase, private, NULL)) {
256: memset(passphrase, 0, strlen(passphrase));
257: xfree(passphrase);
258: error("Bad passphrase.");
259:
260: /* Send a dummy response packet to avoid protocol error. */
261: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
262: for (i = 0; i < 16; i++)
263: packet_put_char(0);
264: packet_send();
265: packet_write_wait();
266:
267: /* Expect the server to reject it... */
268: packet_read_expect(&plen, SSH_SMSG_FAILURE);
269: xfree(comment);
270: return 0;
271: }
272: /* Destroy the passphrase. */
273: memset(passphrase, 0, strlen(passphrase));
274: xfree(passphrase);
275: }
276: /* We no longer need the comment. */
277: xfree(comment);
278:
279: /* Compute and send a response to the challenge. */
280: respond_to_rsa_challenge(challenge, private->rsa);
281:
282: /* Destroy the private key. */
283: key_free(private);
284:
285: /* We no longer need the challenge. */
286: BN_clear_free(challenge);
287:
288: /* Wait for response from the server. */
289: type = packet_read(&plen);
290: if (type == SSH_SMSG_SUCCESS) {
291: debug("RSA authentication accepted by server.");
292: return 1;
293: }
294: if (type != SSH_SMSG_FAILURE)
295: packet_disconnect("Protocol error waiting RSA auth response: %d", type);
296: debug("RSA authentication refused.");
297: return 0;
298: }
299:
300: /*
301: * Tries to authenticate the user using combined rhosts or /etc/hosts.equiv
302: * authentication and RSA host authentication.
303: */
304: int
305: try_rhosts_rsa_authentication(const char *local_user, RSA * host_key)
306: {
307: int type;
308: BIGNUM *challenge;
309: int plen, clen;
310:
311: debug("Trying rhosts or /etc/hosts.equiv with RSA host authentication.");
312:
313: /* Tell the server that we are willing to authenticate using this key. */
314: packet_start(SSH_CMSG_AUTH_RHOSTS_RSA);
315: packet_put_string(local_user, strlen(local_user));
316: packet_put_int(BN_num_bits(host_key->n));
317: packet_put_bignum(host_key->e);
318: packet_put_bignum(host_key->n);
319: packet_send();
320: packet_write_wait();
321:
322: /* Wait for server's response. */
323: type = packet_read(&plen);
324:
325: /* The server responds with failure if it doesn't admit our
326: .rhosts authentication or doesn't know our host key. */
327: if (type == SSH_SMSG_FAILURE) {
328: debug("Server refused our rhosts authentication or host key.");
329: return 0;
330: }
331: /* Otherwise, the server should respond with a challenge. */
332: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
333: packet_disconnect("Protocol error during RSA authentication: %d", type);
334:
335: /* Get the challenge from the packet. */
336: challenge = BN_new();
337: packet_get_bignum(challenge, &clen);
338:
339: packet_integrity_check(plen, clen, type);
340:
341: debug("Received RSA challenge for host key from server.");
342:
343: /* Compute a response to the challenge. */
344: respond_to_rsa_challenge(challenge, host_key);
345:
346: /* We no longer need the challenge. */
347: BN_clear_free(challenge);
348:
349: /* Wait for response from the server. */
350: type = packet_read(&plen);
351: if (type == SSH_SMSG_SUCCESS) {
352: debug("Rhosts or /etc/hosts.equiv with RSA host authentication accepted by server.");
353: return 1;
354: }
355: if (type != SSH_SMSG_FAILURE)
356: packet_disconnect("Protocol error waiting RSA auth response: %d", type);
357: debug("Rhosts or /etc/hosts.equiv with RSA host authentication refused.");
358: return 0;
359: }
360:
361: #ifdef KRB4
362: int
363: try_kerberos_authentication()
364: {
365: KTEXT_ST auth; /* Kerberos data */
366: char *reply;
367: char inst[INST_SZ];
368: char *realm;
369: CREDENTIALS cred;
370: int r, type, plen;
371: socklen_t slen;
372: Key_schedule schedule;
373: u_long checksum, cksum;
374: MSG_DAT msg_data;
375: struct sockaddr_in local, foreign;
376: struct stat st;
377:
378: /* Don't do anything if we don't have any tickets. */
379: if (stat(tkt_string(), &st) < 0)
380: return 0;
381:
382: strncpy(inst, (char *) krb_get_phost(get_canonical_hostname()), INST_SZ);
383:
384: realm = (char *) krb_realmofhost(get_canonical_hostname());
385: if (!realm) {
386: debug("Kerberos V4: no realm for %s", get_canonical_hostname());
387: return 0;
388: }
389: /* This can really be anything. */
390: checksum = (u_long) getpid();
391:
392: r = krb_mk_req(&auth, KRB4_SERVICE_NAME, inst, realm, checksum);
393: if (r != KSUCCESS) {
394: debug("Kerberos V4 krb_mk_req failed: %s", krb_err_txt[r]);
395: return 0;
396: }
397: /* Get session key to decrypt the server's reply with. */
398: r = krb_get_cred(KRB4_SERVICE_NAME, inst, realm, &cred);
399: if (r != KSUCCESS) {
400: debug("get_cred failed: %s", krb_err_txt[r]);
401: return 0;
402: }
403: des_key_sched((des_cblock *) cred.session, schedule);
404:
405: /* Send authentication info to server. */
406: packet_start(SSH_CMSG_AUTH_KERBEROS);
407: packet_put_string((char *) auth.dat, auth.length);
408: packet_send();
409: packet_write_wait();
410:
411: /* Zero the buffer. */
412: (void) memset(auth.dat, 0, MAX_KTXT_LEN);
413:
414: slen = sizeof(local);
415: memset(&local, 0, sizeof(local));
416: if (getsockname(packet_get_connection_in(),
417: (struct sockaddr *) & local, &slen) < 0)
418: debug("getsockname failed: %s", strerror(errno));
419:
420: slen = sizeof(foreign);
421: memset(&foreign, 0, sizeof(foreign));
422: if (getpeername(packet_get_connection_in(),
423: (struct sockaddr *) & foreign, &slen) < 0) {
424: debug("getpeername failed: %s", strerror(errno));
425: fatal_cleanup();
426: }
427: /* Get server reply. */
428: type = packet_read(&plen);
429: switch (type) {
430: case SSH_SMSG_FAILURE:
431: /* Should really be SSH_SMSG_AUTH_KERBEROS_FAILURE */
432: debug("Kerberos V4 authentication failed.");
433: return 0;
434: break;
435:
436: case SSH_SMSG_AUTH_KERBEROS_RESPONSE:
437: /* SSH_SMSG_AUTH_KERBEROS_SUCCESS */
438: debug("Kerberos V4 authentication accepted.");
439:
440: /* Get server's response. */
441: reply = packet_get_string((unsigned int *) &auth.length);
442: memcpy(auth.dat, reply, auth.length);
443: xfree(reply);
444:
445: packet_integrity_check(plen, 4 + auth.length, type);
446:
447: /*
448: * If his response isn't properly encrypted with the session
449: * key, and the decrypted checksum fails to match, he's
450: * bogus. Bail out.
451: */
452: r = krb_rd_priv(auth.dat, auth.length, schedule, &cred.session,
453: &foreign, &local, &msg_data);
454: if (r != KSUCCESS) {
455: debug("Kerberos V4 krb_rd_priv failed: %s", krb_err_txt[r]);
456: packet_disconnect("Kerberos V4 challenge failed!");
457: }
458: /* Fetch the (incremented) checksum that we supplied in the request. */
459: (void) memcpy((char *) &cksum, (char *) msg_data.app_data, sizeof(cksum));
460: cksum = ntohl(cksum);
461:
462: /* If it matches, we're golden. */
463: if (cksum == checksum + 1) {
464: debug("Kerberos V4 challenge successful.");
465: return 1;
466: } else
467: packet_disconnect("Kerberos V4 challenge failed!");
468: break;
469:
470: default:
471: packet_disconnect("Protocol error on Kerberos V4 response: %d", type);
472: }
473: return 0;
474: }
475:
476: #endif /* KRB4 */
477:
478: #ifdef AFS
479: int
480: send_kerberos_tgt()
481: {
482: CREDENTIALS *creds;
483: char pname[ANAME_SZ], pinst[INST_SZ], prealm[REALM_SZ];
484: int r, type, plen;
485: char buffer[8192];
486: struct stat st;
487:
488: /* Don't do anything if we don't have any tickets. */
489: if (stat(tkt_string(), &st) < 0)
490: return 0;
491:
492: creds = xmalloc(sizeof(*creds));
493:
494: if ((r = krb_get_tf_fullname(TKT_FILE, pname, pinst, prealm)) != KSUCCESS) {
495: debug("Kerberos V4 tf_fullname failed: %s", krb_err_txt[r]);
496: return 0;
497: }
498: if ((r = krb_get_cred("krbtgt", prealm, prealm, creds)) != GC_OK) {
499: debug("Kerberos V4 get_cred failed: %s", krb_err_txt[r]);
500: return 0;
501: }
502: if (time(0) > krb_life_to_time(creds->issue_date, creds->lifetime)) {
503: debug("Kerberos V4 ticket expired: %s", TKT_FILE);
504: return 0;
505: }
1.2 markus 506: creds_to_radix(creds, (unsigned char *)buffer, sizeof buffer);
1.1 markus 507: xfree(creds);
508:
509: packet_start(SSH_CMSG_HAVE_KERBEROS_TGT);
510: packet_put_string(buffer, strlen(buffer));
511: packet_send();
512: packet_write_wait();
513:
514: type = packet_read(&plen);
515:
516: if (type == SSH_SMSG_FAILURE)
517: debug("Kerberos TGT for realm %s rejected.", prealm);
518: else if (type != SSH_SMSG_SUCCESS)
519: packet_disconnect("Protocol error on Kerberos TGT response: %d", type);
520:
521: return 1;
522: }
523:
524: void
525: send_afs_tokens(void)
526: {
527: CREDENTIALS creds;
528: struct ViceIoctl parms;
529: struct ClearToken ct;
530: int i, type, len, plen;
531: char buf[2048], *p, *server_cell;
532: char buffer[8192];
533:
534: /* Move over ktc_GetToken, here's something leaner. */
535: for (i = 0; i < 100; i++) { /* just in case */
536: parms.in = (char *) &i;
537: parms.in_size = sizeof(i);
538: parms.out = buf;
539: parms.out_size = sizeof(buf);
540: if (k_pioctl(0, VIOCGETTOK, &parms, 0) != 0)
541: break;
542: p = buf;
543:
544: /* Get secret token. */
545: memcpy(&creds.ticket_st.length, p, sizeof(unsigned int));
546: if (creds.ticket_st.length > MAX_KTXT_LEN)
547: break;
548: p += sizeof(unsigned int);
549: memcpy(creds.ticket_st.dat, p, creds.ticket_st.length);
550: p += creds.ticket_st.length;
551:
552: /* Get clear token. */
553: memcpy(&len, p, sizeof(len));
554: if (len != sizeof(struct ClearToken))
555: break;
556: p += sizeof(len);
557: memcpy(&ct, p, len);
558: p += len;
559: p += sizeof(len); /* primary flag */
560: server_cell = p;
561:
562: /* Flesh out our credentials. */
563: strlcpy(creds.service, "afs", sizeof creds.service);
564: creds.instance[0] = '\0';
565: strlcpy(creds.realm, server_cell, REALM_SZ);
566: memcpy(creds.session, ct.HandShakeKey, DES_KEY_SZ);
567: creds.issue_date = ct.BeginTimestamp;
568: creds.lifetime = krb_time_to_life(creds.issue_date, ct.EndTimestamp);
569: creds.kvno = ct.AuthHandle;
570: snprintf(creds.pname, sizeof(creds.pname), "AFS ID %d", ct.ViceId);
571: creds.pinst[0] = '\0';
572:
573: /* Encode token, ship it off. */
1.2 markus 574: if (creds_to_radix(&creds, (unsigned char*) buffer, sizeof buffer) <= 0)
1.1 markus 575: break;
576: packet_start(SSH_CMSG_HAVE_AFS_TOKEN);
577: packet_put_string(buffer, strlen(buffer));
578: packet_send();
579: packet_write_wait();
580:
581: /* Roger, Roger. Clearance, Clarence. What's your vector,
582: Victor? */
583: type = packet_read(&plen);
584:
585: if (type == SSH_SMSG_FAILURE)
586: debug("AFS token for cell %s rejected.", server_cell);
587: else if (type != SSH_SMSG_SUCCESS)
588: packet_disconnect("Protocol error on AFS token response: %d", type);
589: }
590: }
591:
592: #endif /* AFS */
593:
594: /*
595: * Tries to authenticate with any string-based challenge/response system.
596: * Note that the client code is not tied to s/key or TIS.
597: */
598: int
599: try_skey_authentication()
600: {
601: int type, i;
602: int payload_len;
603: unsigned int clen;
604: char *challenge, *response;
605:
606: debug("Doing skey authentication.");
607:
608: /* request a challenge */
609: packet_start(SSH_CMSG_AUTH_TIS);
610: packet_send();
611: packet_write_wait();
612:
613: type = packet_read(&payload_len);
614: if (type != SSH_SMSG_FAILURE &&
615: type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
616: packet_disconnect("Protocol error: got %d in response "
617: "to skey-auth", type);
618: }
619: if (type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
620: debug("No challenge for skey authentication.");
621: return 0;
622: }
623: challenge = packet_get_string(&clen);
624: packet_integrity_check(payload_len, (4 + clen), type);
625: if (options.cipher == SSH_CIPHER_NONE)
626: log("WARNING: Encryption is disabled! "
627: "Reponse will be transmitted in clear text.");
628: fprintf(stderr, "%s\n", challenge);
629: xfree(challenge);
630: fflush(stderr);
631: for (i = 0; i < options.number_of_password_prompts; i++) {
632: if (i != 0)
633: error("Permission denied, please try again.");
634: response = read_passphrase("Response: ", 0);
635: packet_start(SSH_CMSG_AUTH_TIS_RESPONSE);
636: packet_put_string(response, strlen(response));
637: memset(response, 0, strlen(response));
638: xfree(response);
639: packet_send();
640: packet_write_wait();
641: type = packet_read(&payload_len);
642: if (type == SSH_SMSG_SUCCESS)
643: return 1;
644: if (type != SSH_SMSG_FAILURE)
645: packet_disconnect("Protocol error: got %d in response "
646: "to skey-auth-reponse", type);
647: }
648: /* failure */
649: return 0;
650: }
651:
652: /*
653: * Tries to authenticate with plain passwd authentication.
654: */
655: int
656: try_password_authentication(char *prompt)
657: {
658: int type, i, payload_len;
659: char *password;
660:
661: debug("Doing password authentication.");
662: if (options.cipher == SSH_CIPHER_NONE)
663: log("WARNING: Encryption is disabled! Password will be transmitted in clear text.");
664: for (i = 0; i < options.number_of_password_prompts; i++) {
665: if (i != 0)
666: error("Permission denied, please try again.");
667: password = read_passphrase(prompt, 0);
668: packet_start(SSH_CMSG_AUTH_PASSWORD);
669: packet_put_string(password, strlen(password));
670: memset(password, 0, strlen(password));
671: xfree(password);
672: packet_send();
673: packet_write_wait();
674:
675: type = packet_read(&payload_len);
676: if (type == SSH_SMSG_SUCCESS)
677: return 1;
678: if (type != SSH_SMSG_FAILURE)
679: packet_disconnect("Protocol error: got %d in response to passwd auth", type);
680: }
681: /* failure */
682: return 0;
683: }
684:
685: /*
686: * SSH1 key exchange
687: */
688: void
689: ssh_kex(char *host, struct sockaddr *hostaddr)
690: {
691: int i;
692: BIGNUM *key;
693: RSA *host_key;
694: RSA *public_key;
695: Key k;
696: int bits, rbits;
697: int ssh_cipher_default = SSH_CIPHER_3DES;
698: unsigned char session_key[SSH_SESSION_KEY_LENGTH];
699: unsigned char cookie[8];
700: unsigned int supported_ciphers;
701: unsigned int server_flags, client_flags;
702: int payload_len, clen, sum_len = 0;
703: u_int32_t rand = 0;
704:
705: debug("Waiting for server public key.");
706:
707: /* Wait for a public key packet from the server. */
708: packet_read_expect(&payload_len, SSH_SMSG_PUBLIC_KEY);
709:
710: /* Get cookie from the packet. */
711: for (i = 0; i < 8; i++)
712: cookie[i] = packet_get_char();
713:
714: /* Get the public key. */
715: public_key = RSA_new();
716: bits = packet_get_int();/* bits */
717: public_key->e = BN_new();
718: packet_get_bignum(public_key->e, &clen);
719: sum_len += clen;
720: public_key->n = BN_new();
721: packet_get_bignum(public_key->n, &clen);
722: sum_len += clen;
723:
724: rbits = BN_num_bits(public_key->n);
725: if (bits != rbits) {
726: log("Warning: Server lies about size of server public key: "
727: "actual size is %d bits vs. announced %d.", rbits, bits);
728: log("Warning: This may be due to an old implementation of ssh.");
729: }
730: /* Get the host key. */
731: host_key = RSA_new();
732: bits = packet_get_int();/* bits */
733: host_key->e = BN_new();
734: packet_get_bignum(host_key->e, &clen);
735: sum_len += clen;
736: host_key->n = BN_new();
737: packet_get_bignum(host_key->n, &clen);
738: sum_len += clen;
739:
740: rbits = BN_num_bits(host_key->n);
741: if (bits != rbits) {
742: log("Warning: Server lies about size of server host key: "
743: "actual size is %d bits vs. announced %d.", rbits, bits);
744: log("Warning: This may be due to an old implementation of ssh.");
745: }
746:
747: /* Get protocol flags. */
748: server_flags = packet_get_int();
749: packet_set_protocol_flags(server_flags);
750:
751: supported_ciphers = packet_get_int();
752: supported_authentications = packet_get_int();
753:
754: debug("Received server public key (%d bits) and host key (%d bits).",
755: BN_num_bits(public_key->n), BN_num_bits(host_key->n));
756:
757: packet_integrity_check(payload_len,
758: 8 + 4 + sum_len + 0 + 4 + 0 + 0 + 4 + 4 + 4,
759: SSH_SMSG_PUBLIC_KEY);
760: k.type = KEY_RSA;
761: k.rsa = host_key;
762: check_host_key(host, hostaddr, &k,
763: options.user_hostfile, options.system_hostfile);
764:
765: client_flags = SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN;
766:
767: compute_session_id(session_id, cookie, host_key->n, public_key->n);
768:
769: /* Generate a session key. */
770: arc4random_stir();
771:
772: /*
773: * Generate an encryption key for the session. The key is a 256 bit
774: * random number, interpreted as a 32-byte key, with the least
775: * significant 8 bits being the first byte of the key.
776: */
777: for (i = 0; i < 32; i++) {
778: if (i % 4 == 0)
779: rand = arc4random();
780: session_key[i] = rand & 0xff;
781: rand >>= 8;
782: }
783:
784: /*
785: * According to the protocol spec, the first byte of the session key
786: * is the highest byte of the integer. The session key is xored with
787: * the first 16 bytes of the session id.
788: */
789: key = BN_new();
790: BN_set_word(key, 0);
791: for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
792: BN_lshift(key, key, 8);
793: if (i < 16)
794: BN_add_word(key, session_key[i] ^ session_id[i]);
795: else
796: BN_add_word(key, session_key[i]);
797: }
798:
799: /*
800: * Encrypt the integer using the public key and host key of the
801: * server (key with smaller modulus first).
802: */
803: if (BN_cmp(public_key->n, host_key->n) < 0) {
804: /* Public key has smaller modulus. */
805: if (BN_num_bits(host_key->n) <
806: BN_num_bits(public_key->n) + SSH_KEY_BITS_RESERVED) {
807: fatal("respond_to_rsa_challenge: host_key %d < public_key %d + "
808: "SSH_KEY_BITS_RESERVED %d",
809: BN_num_bits(host_key->n),
810: BN_num_bits(public_key->n),
811: SSH_KEY_BITS_RESERVED);
812: }
813: rsa_public_encrypt(key, key, public_key);
814: rsa_public_encrypt(key, key, host_key);
815: } else {
816: /* Host key has smaller modulus (or they are equal). */
817: if (BN_num_bits(public_key->n) <
818: BN_num_bits(host_key->n) + SSH_KEY_BITS_RESERVED) {
819: fatal("respond_to_rsa_challenge: public_key %d < host_key %d + "
820: "SSH_KEY_BITS_RESERVED %d",
821: BN_num_bits(public_key->n),
822: BN_num_bits(host_key->n),
823: SSH_KEY_BITS_RESERVED);
824: }
825: rsa_public_encrypt(key, key, host_key);
826: rsa_public_encrypt(key, key, public_key);
827: }
828:
829: /* Destroy the public keys since we no longer need them. */
830: RSA_free(public_key);
831: RSA_free(host_key);
832:
1.3 markus 833: if (options.cipher == SSH_CIPHER_ILLEGAL) {
834: log("No valid SSH1 cipher, using %.100s instead.",
835: cipher_name(SSH_FALLBACK_CIPHER));
836: options.cipher = SSH_FALLBACK_CIPHER;
837: } else if (options.cipher == SSH_CIPHER_NOT_SET) {
1.1 markus 838: if (cipher_mask1() & supported_ciphers & (1 << ssh_cipher_default))
839: options.cipher = ssh_cipher_default;
840: else {
841: debug("Cipher %s not supported, using %.100s instead.",
1.3 markus 842: cipher_name(ssh_cipher_default),
843: cipher_name(SSH_FALLBACK_CIPHER));
1.1 markus 844: options.cipher = SSH_FALLBACK_CIPHER;
845: }
846: }
847: /* Check that the selected cipher is supported. */
848: if (!(supported_ciphers & (1 << options.cipher)))
849: fatal("Selected cipher type %.100s not supported by server.",
850: cipher_name(options.cipher));
851:
852: debug("Encryption type: %.100s", cipher_name(options.cipher));
853:
854: /* Send the encrypted session key to the server. */
855: packet_start(SSH_CMSG_SESSION_KEY);
856: packet_put_char(options.cipher);
857:
858: /* Send the cookie back to the server. */
859: for (i = 0; i < 8; i++)
860: packet_put_char(cookie[i]);
861:
862: /* Send and destroy the encrypted encryption key integer. */
863: packet_put_bignum(key);
864: BN_clear_free(key);
865:
866: /* Send protocol flags. */
867: packet_put_int(client_flags);
868:
869: /* Send the packet now. */
870: packet_send();
871: packet_write_wait();
872:
873: debug("Sent encrypted session key.");
874:
875: /* Set the encryption key. */
876: packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, options.cipher);
877:
878: /* We will no longer need the session key here. Destroy any extra copies. */
879: memset(session_key, 0, sizeof(session_key));
880:
881: /*
882: * Expect a success message from the server. Note that this message
883: * will be received in encrypted form.
884: */
885: packet_read_expect(&payload_len, SSH_SMSG_SUCCESS);
886:
887: debug("Received encrypted confirmation.");
888: }
889:
890: /*
891: * Authenticate user
892: */
893: void
894: ssh_userauth(
895: const char* local_user,
896: const char* server_user,
897: char *host,
898: int host_key_valid, RSA *own_host_key)
899: {
900: int i, type;
901: int payload_len;
902:
903: if (supported_authentications == 0)
904: fatal("ssh_userauth: server supports no auth methods");
905:
906: /* Send the name of the user to log in as on the server. */
907: packet_start(SSH_CMSG_USER);
908: packet_put_string(server_user, strlen(server_user));
909: packet_send();
910: packet_write_wait();
911:
912: /*
913: * The server should respond with success if no authentication is
914: * needed (the user has no password). Otherwise the server responds
915: * with failure.
916: */
917: type = packet_read(&payload_len);
918:
919: /* check whether the connection was accepted without authentication. */
920: if (type == SSH_SMSG_SUCCESS)
921: return;
922: if (type != SSH_SMSG_FAILURE)
923: packet_disconnect("Protocol error: got %d in response to SSH_CMSG_USER",
924: type);
925:
926: #ifdef AFS
927: /* Try Kerberos tgt passing if the server supports it. */
928: if ((supported_authentications & (1 << SSH_PASS_KERBEROS_TGT)) &&
929: options.kerberos_tgt_passing) {
930: if (options.cipher == SSH_CIPHER_NONE)
931: log("WARNING: Encryption is disabled! Ticket will be transmitted in the clear!");
932: (void) send_kerberos_tgt();
933: }
934: /* Try AFS token passing if the server supports it. */
935: if ((supported_authentications & (1 << SSH_PASS_AFS_TOKEN)) &&
936: options.afs_token_passing && k_hasafs()) {
937: if (options.cipher == SSH_CIPHER_NONE)
938: log("WARNING: Encryption is disabled! Token will be transmitted in the clear!");
939: send_afs_tokens();
940: }
941: #endif /* AFS */
942:
943: #ifdef KRB4
944: if ((supported_authentications & (1 << SSH_AUTH_KERBEROS)) &&
945: options.kerberos_authentication) {
946: debug("Trying Kerberos authentication.");
947: if (try_kerberos_authentication()) {
948: /* The server should respond with success or failure. */
949: type = packet_read(&payload_len);
950: if (type == SSH_SMSG_SUCCESS)
951: return;
952: if (type != SSH_SMSG_FAILURE)
953: packet_disconnect("Protocol error: got %d in response to Kerberos auth", type);
954: }
955: }
956: #endif /* KRB4 */
957:
958: /*
959: * Use rhosts authentication if running in privileged socket and we
960: * do not wish to remain anonymous.
961: */
962: if ((supported_authentications & (1 << SSH_AUTH_RHOSTS)) &&
963: options.rhosts_authentication) {
964: debug("Trying rhosts authentication.");
965: packet_start(SSH_CMSG_AUTH_RHOSTS);
966: packet_put_string(local_user, strlen(local_user));
967: packet_send();
968: packet_write_wait();
969:
970: /* The server should respond with success or failure. */
971: type = packet_read(&payload_len);
972: if (type == SSH_SMSG_SUCCESS)
973: return;
974: if (type != SSH_SMSG_FAILURE)
975: packet_disconnect("Protocol error: got %d in response to rhosts auth",
976: type);
977: }
978: /*
979: * Try .rhosts or /etc/hosts.equiv authentication with RSA host
980: * authentication.
981: */
982: if ((supported_authentications & (1 << SSH_AUTH_RHOSTS_RSA)) &&
983: options.rhosts_rsa_authentication && host_key_valid) {
984: if (try_rhosts_rsa_authentication(local_user, own_host_key))
985: return;
986: }
987: /* Try RSA authentication if the server supports it. */
988: if ((supported_authentications & (1 << SSH_AUTH_RSA)) &&
989: options.rsa_authentication) {
990: /*
991: * Try RSA authentication using the authentication agent. The
992: * agent is tried first because no passphrase is needed for
993: * it, whereas identity files may require passphrases.
994: */
995: if (try_agent_authentication())
996: return;
997:
998: /* Try RSA authentication for each identity. */
999: for (i = 0; i < options.num_identity_files; i++)
1000: if (try_rsa_authentication(options.identity_files[i]))
1001: return;
1002: }
1003: /* Try skey authentication if the server supports it. */
1004: if ((supported_authentications & (1 << SSH_AUTH_TIS)) &&
1005: options.skey_authentication && !options.batch_mode) {
1006: if (try_skey_authentication())
1007: return;
1008: }
1009: /* Try password authentication if the server supports it. */
1010: if ((supported_authentications & (1 << SSH_AUTH_PASSWORD)) &&
1011: options.password_authentication && !options.batch_mode) {
1012: char prompt[80];
1013:
1014: snprintf(prompt, sizeof(prompt), "%.30s@%.40s's password: ",
1015: server_user, host);
1016: if (try_password_authentication(prompt))
1017: return;
1018: }
1019: /* All authentication methods have failed. Exit with an error message. */
1020: fatal("Permission denied.");
1021: /* NOTREACHED */
1022: }
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