Annotation of src/usr.bin/ssh/sshconnect1.c, Revision 1.11
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: * Code to connect to a remote host, and to perform the client side of the
6: * login (authentication) dialog.
7: *
1.6 deraadt 8: * As far as I am concerned, the code I have written for this software
9: * can be used freely for any purpose. Any derived versions of this
10: * software must be clearly marked as such, and if the derived work is
11: * incompatible with the protocol description in the RFC file, it must be
12: * called by a name other than "ssh" or "Secure Shell".
1.1 markus 13: */
14:
15: #include "includes.h"
1.11 ! markus 16: RCSID("$OpenBSD: sshconnect1.c,v 1.10 2000/11/23 21:03:47 markus Exp $");
1.1 markus 17:
18: #include <openssl/bn.h>
19: #include <openssl/dsa.h>
20: #include <openssl/rsa.h>
21: #include <openssl/evp.h>
22:
23: #include "xmalloc.h"
24: #include "rsa.h"
25: #include "ssh.h"
26: #include "buffer.h"
27: #include "packet.h"
28: #include "mpaux.h"
29: #include "uidswap.h"
30: #include "readconf.h"
31: #include "key.h"
1.4 markus 32: #include "authfd.h"
1.1 markus 33: #include "sshconnect.h"
34: #include "authfile.h"
35:
36: /* Session id for the current session. */
37: unsigned char session_id[16];
38: unsigned int supported_authentications = 0;
39:
40: extern Options options;
41: extern char *__progname;
42:
43: /*
44: * Checks if the user has an authentication agent, and if so, tries to
45: * authenticate using the agent.
46: */
47: int
48: try_agent_authentication()
49: {
1.5 markus 50: int type;
1.1 markus 51: char *comment;
52: AuthenticationConnection *auth;
53: unsigned char response[16];
54: unsigned int i;
1.5 markus 55: int plen, clen;
56: Key *key;
57: BIGNUM *challenge;
1.1 markus 58:
59: /* Get connection to the agent. */
60: auth = ssh_get_authentication_connection();
61: if (!auth)
62: return 0;
63:
64: challenge = BN_new();
1.9 markus 65: key = key_new(KEY_RSA1);
1.1 markus 66:
67: /* Loop through identities served by the agent. */
1.5 markus 68: for (key = ssh_get_first_identity(auth, &comment, 1);
69: key != NULL;
70: key = ssh_get_next_identity(auth, &comment, 1)) {
1.1 markus 71:
72: /* Try this identity. */
73: debug("Trying RSA authentication via agent with '%.100s'", comment);
74: xfree(comment);
75:
76: /* Tell the server that we are willing to authenticate using this key. */
77: packet_start(SSH_CMSG_AUTH_RSA);
1.5 markus 78: packet_put_bignum(key->rsa->n);
1.1 markus 79: packet_send();
80: packet_write_wait();
81:
82: /* Wait for server's response. */
83: type = packet_read(&plen);
84:
85: /* The server sends failure if it doesn\'t like our key or
86: does not support RSA authentication. */
87: if (type == SSH_SMSG_FAILURE) {
88: debug("Server refused our key.");
1.5 markus 89: key_free(key);
1.1 markus 90: continue;
91: }
92: /* Otherwise it should have sent a challenge. */
93: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
94: packet_disconnect("Protocol error during RSA authentication: %d",
95: type);
96:
97: packet_get_bignum(challenge, &clen);
98:
99: packet_integrity_check(plen, clen, type);
100:
101: debug("Received RSA challenge from server.");
102:
103: /* Ask the agent to decrypt the challenge. */
1.5 markus 104: if (!ssh_decrypt_challenge(auth, key, challenge, session_id, 1, response)) {
105: /*
106: * The agent failed to authenticate this identifier
107: * although it advertised it supports this. Just
108: * return a wrong value.
109: */
1.1 markus 110: log("Authentication agent failed to decrypt challenge.");
111: memset(response, 0, sizeof(response));
112: }
1.5 markus 113: key_free(key);
1.1 markus 114: debug("Sending response to RSA challenge.");
115:
116: /* Send the decrypted challenge back to the server. */
117: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
118: for (i = 0; i < 16; i++)
119: packet_put_char(response[i]);
120: packet_send();
121: packet_write_wait();
122:
123: /* Wait for response from the server. */
124: type = packet_read(&plen);
125:
126: /* The server returns success if it accepted the authentication. */
127: if (type == SSH_SMSG_SUCCESS) {
1.5 markus 128: BN_clear_free(challenge);
1.1 markus 129: debug("RSA authentication accepted by server.");
130: return 1;
131: }
132: /* Otherwise it should return failure. */
133: if (type != SSH_SMSG_FAILURE)
134: packet_disconnect("Protocol error waiting RSA auth response: %d",
135: type);
136: }
137: BN_clear_free(challenge);
138: debug("RSA authentication using agent refused.");
139: return 0;
140: }
141:
142: /*
143: * Computes the proper response to a RSA challenge, and sends the response to
144: * the server.
145: */
146: void
147: respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
148: {
149: unsigned char buf[32], response[16];
150: MD5_CTX md;
151: int i, len;
152:
153: /* Decrypt the challenge using the private key. */
154: rsa_private_decrypt(challenge, challenge, prv);
155:
156: /* Compute the response. */
157: /* The response is MD5 of decrypted challenge plus session id. */
158: len = BN_num_bytes(challenge);
159: if (len <= 0 || len > sizeof(buf))
160: packet_disconnect("respond_to_rsa_challenge: bad challenge length %d",
161: len);
162:
163: memset(buf, 0, sizeof(buf));
164: BN_bn2bin(challenge, buf + sizeof(buf) - len);
165: MD5_Init(&md);
166: MD5_Update(&md, buf, 32);
167: MD5_Update(&md, session_id, 16);
168: MD5_Final(response, &md);
169:
170: debug("Sending response to host key RSA challenge.");
171:
172: /* Send the response back to the server. */
173: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
174: for (i = 0; i < 16; i++)
175: packet_put_char(response[i]);
176: packet_send();
177: packet_write_wait();
178:
179: memset(buf, 0, sizeof(buf));
180: memset(response, 0, sizeof(response));
181: memset(&md, 0, sizeof(md));
182: }
183:
184: /*
185: * Checks if the user has authentication file, and if so, tries to authenticate
186: * the user using it.
187: */
188: int
189: try_rsa_authentication(const char *authfile)
190: {
191: BIGNUM *challenge;
192: Key *public;
193: Key *private;
194: char *passphrase, *comment;
195: int type, i;
196: int plen, clen;
197:
198: /* Try to load identification for the authentication key. */
1.9 markus 199: public = key_new(KEY_RSA1);
1.1 markus 200: if (!load_public_key(authfile, public, &comment)) {
201: key_free(public);
202: /* Could not load it. Fail. */
203: return 0;
204: }
205: debug("Trying RSA authentication with key '%.100s'", comment);
206:
207: /* Tell the server that we are willing to authenticate using this key. */
208: packet_start(SSH_CMSG_AUTH_RSA);
209: packet_put_bignum(public->rsa->n);
210: packet_send();
211: packet_write_wait();
212:
213: /* We no longer need the public key. */
214: key_free(public);
215:
216: /* Wait for server's response. */
217: type = packet_read(&plen);
218:
219: /*
220: * The server responds with failure if it doesn\'t like our key or
221: * doesn\'t support RSA authentication.
222: */
223: if (type == SSH_SMSG_FAILURE) {
224: debug("Server refused our key.");
225: xfree(comment);
226: return 0;
227: }
228: /* Otherwise, the server should respond with a challenge. */
229: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
230: packet_disconnect("Protocol error during RSA authentication: %d", type);
231:
232: /* Get the challenge from the packet. */
233: challenge = BN_new();
234: packet_get_bignum(challenge, &clen);
235:
236: packet_integrity_check(plen, clen, type);
237:
238: debug("Received RSA challenge from server.");
239:
1.9 markus 240: private = key_new(KEY_RSA1);
1.1 markus 241: /*
242: * Load the private key. Try first with empty passphrase; if it
243: * fails, ask for a passphrase.
244: */
245: if (!load_private_key(authfile, "", private, NULL)) {
246: char buf[300];
247: snprintf(buf, sizeof buf, "Enter passphrase for RSA key '%.100s': ",
248: comment);
249: if (!options.batch_mode)
250: passphrase = read_passphrase(buf, 0);
251: else {
252: debug("Will not query passphrase for %.100s in batch mode.",
253: comment);
254: passphrase = xstrdup("");
255: }
256:
257: /* Load the authentication file using the pasphrase. */
258: if (!load_private_key(authfile, passphrase, private, NULL)) {
259: memset(passphrase, 0, strlen(passphrase));
260: xfree(passphrase);
261: error("Bad passphrase.");
262:
263: /* Send a dummy response packet to avoid protocol error. */
264: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
265: for (i = 0; i < 16; i++)
266: packet_put_char(0);
267: packet_send();
268: packet_write_wait();
269:
270: /* Expect the server to reject it... */
271: packet_read_expect(&plen, SSH_SMSG_FAILURE);
272: xfree(comment);
273: return 0;
274: }
275: /* Destroy the passphrase. */
276: memset(passphrase, 0, strlen(passphrase));
277: xfree(passphrase);
278: }
279: /* We no longer need the comment. */
280: xfree(comment);
281:
282: /* Compute and send a response to the challenge. */
283: respond_to_rsa_challenge(challenge, private->rsa);
284:
285: /* Destroy the private key. */
286: key_free(private);
287:
288: /* We no longer need the challenge. */
289: BN_clear_free(challenge);
290:
291: /* Wait for response from the server. */
292: type = packet_read(&plen);
293: if (type == SSH_SMSG_SUCCESS) {
294: debug("RSA authentication accepted by server.");
295: return 1;
296: }
297: if (type != SSH_SMSG_FAILURE)
298: packet_disconnect("Protocol error waiting RSA auth response: %d", type);
299: debug("RSA authentication refused.");
300: return 0;
301: }
302:
303: /*
304: * Tries to authenticate the user using combined rhosts or /etc/hosts.equiv
305: * authentication and RSA host authentication.
306: */
307: int
308: try_rhosts_rsa_authentication(const char *local_user, RSA * host_key)
309: {
310: int type;
311: BIGNUM *challenge;
312: int plen, clen;
313:
314: debug("Trying rhosts or /etc/hosts.equiv with RSA host authentication.");
315:
316: /* Tell the server that we are willing to authenticate using this key. */
317: packet_start(SSH_CMSG_AUTH_RHOSTS_RSA);
318: packet_put_string(local_user, strlen(local_user));
319: packet_put_int(BN_num_bits(host_key->n));
320: packet_put_bignum(host_key->e);
321: packet_put_bignum(host_key->n);
322: packet_send();
323: packet_write_wait();
324:
325: /* Wait for server's response. */
326: type = packet_read(&plen);
327:
328: /* The server responds with failure if it doesn't admit our
329: .rhosts authentication or doesn't know our host key. */
330: if (type == SSH_SMSG_FAILURE) {
331: debug("Server refused our rhosts authentication or host key.");
332: return 0;
333: }
334: /* Otherwise, the server should respond with a challenge. */
335: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
336: packet_disconnect("Protocol error during RSA authentication: %d", type);
337:
338: /* Get the challenge from the packet. */
339: challenge = BN_new();
340: packet_get_bignum(challenge, &clen);
341:
342: packet_integrity_check(plen, clen, type);
343:
344: debug("Received RSA challenge for host key from server.");
345:
346: /* Compute a response to the challenge. */
347: respond_to_rsa_challenge(challenge, host_key);
348:
349: /* We no longer need the challenge. */
350: BN_clear_free(challenge);
351:
352: /* Wait for response from the server. */
353: type = packet_read(&plen);
354: if (type == SSH_SMSG_SUCCESS) {
355: debug("Rhosts or /etc/hosts.equiv with RSA host authentication accepted by server.");
356: return 1;
357: }
358: if (type != SSH_SMSG_FAILURE)
359: packet_disconnect("Protocol error waiting RSA auth response: %d", type);
360: debug("Rhosts or /etc/hosts.equiv with RSA host authentication refused.");
361: return 0;
362: }
363:
364: #ifdef KRB4
365: int
366: try_kerberos_authentication()
367: {
368: KTEXT_ST auth; /* Kerberos data */
369: char *reply;
370: char inst[INST_SZ];
371: char *realm;
372: CREDENTIALS cred;
373: int r, type, plen;
374: socklen_t slen;
375: Key_schedule schedule;
376: u_long checksum, cksum;
377: MSG_DAT msg_data;
378: struct sockaddr_in local, foreign;
379: struct stat st;
380:
381: /* Don't do anything if we don't have any tickets. */
382: if (stat(tkt_string(), &st) < 0)
383: return 0;
384:
385: strncpy(inst, (char *) krb_get_phost(get_canonical_hostname()), INST_SZ);
386:
387: realm = (char *) krb_realmofhost(get_canonical_hostname());
388: if (!realm) {
389: debug("Kerberos V4: no realm for %s", get_canonical_hostname());
390: return 0;
391: }
392: /* This can really be anything. */
393: checksum = (u_long) getpid();
394:
395: r = krb_mk_req(&auth, KRB4_SERVICE_NAME, inst, realm, checksum);
396: if (r != KSUCCESS) {
397: debug("Kerberos V4 krb_mk_req failed: %s", krb_err_txt[r]);
398: return 0;
399: }
400: /* Get session key to decrypt the server's reply with. */
401: r = krb_get_cred(KRB4_SERVICE_NAME, inst, realm, &cred);
402: if (r != KSUCCESS) {
403: debug("get_cred failed: %s", krb_err_txt[r]);
404: return 0;
405: }
406: des_key_sched((des_cblock *) cred.session, schedule);
407:
408: /* Send authentication info to server. */
409: packet_start(SSH_CMSG_AUTH_KERBEROS);
410: packet_put_string((char *) auth.dat, auth.length);
411: packet_send();
412: packet_write_wait();
413:
414: /* Zero the buffer. */
415: (void) memset(auth.dat, 0, MAX_KTXT_LEN);
416:
417: slen = sizeof(local);
418: memset(&local, 0, sizeof(local));
419: if (getsockname(packet_get_connection_in(),
420: (struct sockaddr *) & local, &slen) < 0)
421: debug("getsockname failed: %s", strerror(errno));
422:
423: slen = sizeof(foreign);
424: memset(&foreign, 0, sizeof(foreign));
425: if (getpeername(packet_get_connection_in(),
426: (struct sockaddr *) & foreign, &slen) < 0) {
427: debug("getpeername failed: %s", strerror(errno));
428: fatal_cleanup();
429: }
430: /* Get server reply. */
431: type = packet_read(&plen);
432: switch (type) {
433: case SSH_SMSG_FAILURE:
434: /* Should really be SSH_SMSG_AUTH_KERBEROS_FAILURE */
435: debug("Kerberos V4 authentication failed.");
436: return 0;
437: break;
438:
439: case SSH_SMSG_AUTH_KERBEROS_RESPONSE:
440: /* SSH_SMSG_AUTH_KERBEROS_SUCCESS */
441: debug("Kerberos V4 authentication accepted.");
442:
443: /* Get server's response. */
444: reply = packet_get_string((unsigned int *) &auth.length);
445: memcpy(auth.dat, reply, auth.length);
446: xfree(reply);
447:
448: packet_integrity_check(plen, 4 + auth.length, type);
449:
450: /*
451: * If his response isn't properly encrypted with the session
452: * key, and the decrypted checksum fails to match, he's
453: * bogus. Bail out.
454: */
455: r = krb_rd_priv(auth.dat, auth.length, schedule, &cred.session,
456: &foreign, &local, &msg_data);
457: if (r != KSUCCESS) {
458: debug("Kerberos V4 krb_rd_priv failed: %s", krb_err_txt[r]);
459: packet_disconnect("Kerberos V4 challenge failed!");
460: }
461: /* Fetch the (incremented) checksum that we supplied in the request. */
462: (void) memcpy((char *) &cksum, (char *) msg_data.app_data, sizeof(cksum));
463: cksum = ntohl(cksum);
464:
465: /* If it matches, we're golden. */
466: if (cksum == checksum + 1) {
467: debug("Kerberos V4 challenge successful.");
468: return 1;
469: } else
470: packet_disconnect("Kerberos V4 challenge failed!");
471: break;
472:
473: default:
474: packet_disconnect("Protocol error on Kerberos V4 response: %d", type);
475: }
476: return 0;
477: }
478:
479: #endif /* KRB4 */
480:
481: #ifdef AFS
482: int
483: send_kerberos_tgt()
484: {
485: CREDENTIALS *creds;
486: char pname[ANAME_SZ], pinst[INST_SZ], prealm[REALM_SZ];
487: int r, type, plen;
488: char buffer[8192];
489: struct stat st;
490:
491: /* Don't do anything if we don't have any tickets. */
492: if (stat(tkt_string(), &st) < 0)
493: return 0;
494:
495: creds = xmalloc(sizeof(*creds));
496:
497: if ((r = krb_get_tf_fullname(TKT_FILE, pname, pinst, prealm)) != KSUCCESS) {
498: debug("Kerberos V4 tf_fullname failed: %s", krb_err_txt[r]);
499: return 0;
500: }
501: if ((r = krb_get_cred("krbtgt", prealm, prealm, creds)) != GC_OK) {
502: debug("Kerberos V4 get_cred failed: %s", krb_err_txt[r]);
503: return 0;
504: }
505: if (time(0) > krb_life_to_time(creds->issue_date, creds->lifetime)) {
506: debug("Kerberos V4 ticket expired: %s", TKT_FILE);
507: return 0;
508: }
1.2 markus 509: creds_to_radix(creds, (unsigned char *)buffer, sizeof buffer);
1.1 markus 510: xfree(creds);
511:
512: packet_start(SSH_CMSG_HAVE_KERBEROS_TGT);
513: packet_put_string(buffer, strlen(buffer));
514: packet_send();
515: packet_write_wait();
516:
517: type = packet_read(&plen);
518:
519: if (type == SSH_SMSG_FAILURE)
520: debug("Kerberos TGT for realm %s rejected.", prealm);
521: else if (type != SSH_SMSG_SUCCESS)
522: packet_disconnect("Protocol error on Kerberos TGT response: %d", type);
523:
524: return 1;
525: }
526:
527: void
528: send_afs_tokens(void)
529: {
530: CREDENTIALS creds;
531: struct ViceIoctl parms;
532: struct ClearToken ct;
533: int i, type, len, plen;
534: char buf[2048], *p, *server_cell;
535: char buffer[8192];
536:
537: /* Move over ktc_GetToken, here's something leaner. */
538: for (i = 0; i < 100; i++) { /* just in case */
539: parms.in = (char *) &i;
540: parms.in_size = sizeof(i);
541: parms.out = buf;
542: parms.out_size = sizeof(buf);
543: if (k_pioctl(0, VIOCGETTOK, &parms, 0) != 0)
544: break;
545: p = buf;
546:
547: /* Get secret token. */
548: memcpy(&creds.ticket_st.length, p, sizeof(unsigned int));
549: if (creds.ticket_st.length > MAX_KTXT_LEN)
550: break;
551: p += sizeof(unsigned int);
552: memcpy(creds.ticket_st.dat, p, creds.ticket_st.length);
553: p += creds.ticket_st.length;
554:
555: /* Get clear token. */
556: memcpy(&len, p, sizeof(len));
557: if (len != sizeof(struct ClearToken))
558: break;
559: p += sizeof(len);
560: memcpy(&ct, p, len);
561: p += len;
562: p += sizeof(len); /* primary flag */
563: server_cell = p;
564:
565: /* Flesh out our credentials. */
566: strlcpy(creds.service, "afs", sizeof creds.service);
567: creds.instance[0] = '\0';
568: strlcpy(creds.realm, server_cell, REALM_SZ);
569: memcpy(creds.session, ct.HandShakeKey, DES_KEY_SZ);
570: creds.issue_date = ct.BeginTimestamp;
571: creds.lifetime = krb_time_to_life(creds.issue_date, ct.EndTimestamp);
572: creds.kvno = ct.AuthHandle;
573: snprintf(creds.pname, sizeof(creds.pname), "AFS ID %d", ct.ViceId);
574: creds.pinst[0] = '\0';
575:
576: /* Encode token, ship it off. */
1.2 markus 577: if (creds_to_radix(&creds, (unsigned char*) buffer, sizeof buffer) <= 0)
1.1 markus 578: break;
579: packet_start(SSH_CMSG_HAVE_AFS_TOKEN);
580: packet_put_string(buffer, strlen(buffer));
581: packet_send();
582: packet_write_wait();
583:
584: /* Roger, Roger. Clearance, Clarence. What's your vector,
585: Victor? */
586: type = packet_read(&plen);
587:
588: if (type == SSH_SMSG_FAILURE)
589: debug("AFS token for cell %s rejected.", server_cell);
590: else if (type != SSH_SMSG_SUCCESS)
591: packet_disconnect("Protocol error on AFS token response: %d", type);
592: }
593: }
594:
595: #endif /* AFS */
596:
597: /*
598: * Tries to authenticate with any string-based challenge/response system.
599: * Note that the client code is not tied to s/key or TIS.
600: */
601: int
602: try_skey_authentication()
603: {
604: int type, i;
605: int payload_len;
606: unsigned int clen;
607: char *challenge, *response;
608:
609: debug("Doing skey authentication.");
610:
611: /* request a challenge */
612: packet_start(SSH_CMSG_AUTH_TIS);
613: packet_send();
614: packet_write_wait();
615:
616: type = packet_read(&payload_len);
617: if (type != SSH_SMSG_FAILURE &&
618: type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
619: packet_disconnect("Protocol error: got %d in response "
620: "to skey-auth", type);
621: }
622: if (type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
623: debug("No challenge for skey authentication.");
624: return 0;
625: }
626: challenge = packet_get_string(&clen);
627: packet_integrity_check(payload_len, (4 + clen), type);
628: if (options.cipher == SSH_CIPHER_NONE)
629: log("WARNING: Encryption is disabled! "
630: "Reponse will be transmitted in clear text.");
631: fprintf(stderr, "%s\n", challenge);
632: xfree(challenge);
633: fflush(stderr);
634: for (i = 0; i < options.number_of_password_prompts; i++) {
635: if (i != 0)
636: error("Permission denied, please try again.");
637: response = read_passphrase("Response: ", 0);
638: packet_start(SSH_CMSG_AUTH_TIS_RESPONSE);
639: packet_put_string(response, strlen(response));
640: memset(response, 0, strlen(response));
641: xfree(response);
642: packet_send();
643: packet_write_wait();
644: type = packet_read(&payload_len);
645: if (type == SSH_SMSG_SUCCESS)
646: return 1;
647: if (type != SSH_SMSG_FAILURE)
648: packet_disconnect("Protocol error: got %d in response "
649: "to skey-auth-reponse", type);
650: }
651: /* failure */
652: return 0;
653: }
654:
655: /*
656: * Tries to authenticate with plain passwd authentication.
657: */
658: int
659: try_password_authentication(char *prompt)
660: {
661: int type, i, payload_len;
662: char *password;
663:
664: debug("Doing password authentication.");
665: if (options.cipher == SSH_CIPHER_NONE)
666: log("WARNING: Encryption is disabled! Password will be transmitted in clear text.");
667: for (i = 0; i < options.number_of_password_prompts; i++) {
668: if (i != 0)
669: error("Permission denied, please try again.");
670: password = read_passphrase(prompt, 0);
671: packet_start(SSH_CMSG_AUTH_PASSWORD);
672: packet_put_string(password, strlen(password));
673: memset(password, 0, strlen(password));
674: xfree(password);
675: packet_send();
676: packet_write_wait();
677:
678: type = packet_read(&payload_len);
679: if (type == SSH_SMSG_SUCCESS)
680: return 1;
681: if (type != SSH_SMSG_FAILURE)
682: packet_disconnect("Protocol error: got %d in response to passwd auth", type);
683: }
684: /* failure */
685: return 0;
686: }
687:
688: /*
689: * SSH1 key exchange
690: */
691: void
692: ssh_kex(char *host, struct sockaddr *hostaddr)
693: {
694: int i;
695: BIGNUM *key;
696: RSA *host_key;
697: RSA *public_key;
698: Key k;
699: int bits, rbits;
700: int ssh_cipher_default = SSH_CIPHER_3DES;
701: unsigned char session_key[SSH_SESSION_KEY_LENGTH];
702: unsigned char cookie[8];
703: unsigned int supported_ciphers;
704: unsigned int server_flags, client_flags;
705: int payload_len, clen, sum_len = 0;
706: u_int32_t rand = 0;
707:
708: debug("Waiting for server public key.");
709:
710: /* Wait for a public key packet from the server. */
711: packet_read_expect(&payload_len, SSH_SMSG_PUBLIC_KEY);
712:
713: /* Get cookie from the packet. */
714: for (i = 0; i < 8; i++)
715: cookie[i] = packet_get_char();
716:
717: /* Get the public key. */
718: public_key = RSA_new();
719: bits = packet_get_int();/* bits */
720: public_key->e = BN_new();
721: packet_get_bignum(public_key->e, &clen);
722: sum_len += clen;
723: public_key->n = BN_new();
724: packet_get_bignum(public_key->n, &clen);
725: sum_len += clen;
726:
727: rbits = BN_num_bits(public_key->n);
728: if (bits != rbits) {
729: log("Warning: Server lies about size of server public key: "
730: "actual size is %d bits vs. announced %d.", rbits, bits);
731: log("Warning: This may be due to an old implementation of ssh.");
732: }
733: /* Get the host key. */
734: host_key = RSA_new();
735: bits = packet_get_int();/* bits */
736: host_key->e = BN_new();
737: packet_get_bignum(host_key->e, &clen);
738: sum_len += clen;
739: host_key->n = BN_new();
740: packet_get_bignum(host_key->n, &clen);
741: sum_len += clen;
742:
743: rbits = BN_num_bits(host_key->n);
744: if (bits != rbits) {
745: log("Warning: Server lies about size of server host key: "
746: "actual size is %d bits vs. announced %d.", rbits, bits);
747: log("Warning: This may be due to an old implementation of ssh.");
748: }
749:
750: /* Get protocol flags. */
751: server_flags = packet_get_int();
752: packet_set_protocol_flags(server_flags);
753:
754: supported_ciphers = packet_get_int();
755: supported_authentications = packet_get_int();
756:
757: debug("Received server public key (%d bits) and host key (%d bits).",
758: BN_num_bits(public_key->n), BN_num_bits(host_key->n));
759:
760: packet_integrity_check(payload_len,
761: 8 + 4 + sum_len + 0 + 4 + 0 + 0 + 4 + 4 + 4,
762: SSH_SMSG_PUBLIC_KEY);
1.9 markus 763: k.type = KEY_RSA1;
1.1 markus 764: k.rsa = host_key;
765: check_host_key(host, hostaddr, &k,
766: options.user_hostfile, options.system_hostfile);
767:
768: client_flags = SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN;
769:
770: compute_session_id(session_id, cookie, host_key->n, public_key->n);
771:
772: /* Generate a session key. */
773: arc4random_stir();
774:
775: /*
776: * Generate an encryption key for the session. The key is a 256 bit
777: * random number, interpreted as a 32-byte key, with the least
778: * significant 8 bits being the first byte of the key.
779: */
780: for (i = 0; i < 32; i++) {
781: if (i % 4 == 0)
782: rand = arc4random();
783: session_key[i] = rand & 0xff;
784: rand >>= 8;
785: }
786:
787: /*
788: * According to the protocol spec, the first byte of the session key
789: * is the highest byte of the integer. The session key is xored with
790: * the first 16 bytes of the session id.
791: */
792: key = BN_new();
793: BN_set_word(key, 0);
794: for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
795: BN_lshift(key, key, 8);
796: if (i < 16)
797: BN_add_word(key, session_key[i] ^ session_id[i]);
798: else
799: BN_add_word(key, session_key[i]);
800: }
801:
802: /*
803: * Encrypt the integer using the public key and host key of the
804: * server (key with smaller modulus first).
805: */
806: if (BN_cmp(public_key->n, host_key->n) < 0) {
807: /* Public key has smaller modulus. */
808: if (BN_num_bits(host_key->n) <
809: BN_num_bits(public_key->n) + SSH_KEY_BITS_RESERVED) {
810: fatal("respond_to_rsa_challenge: host_key %d < public_key %d + "
811: "SSH_KEY_BITS_RESERVED %d",
812: BN_num_bits(host_key->n),
813: BN_num_bits(public_key->n),
814: SSH_KEY_BITS_RESERVED);
815: }
816: rsa_public_encrypt(key, key, public_key);
817: rsa_public_encrypt(key, key, host_key);
818: } else {
819: /* Host key has smaller modulus (or they are equal). */
820: if (BN_num_bits(public_key->n) <
821: BN_num_bits(host_key->n) + SSH_KEY_BITS_RESERVED) {
822: fatal("respond_to_rsa_challenge: public_key %d < host_key %d + "
823: "SSH_KEY_BITS_RESERVED %d",
824: BN_num_bits(public_key->n),
825: BN_num_bits(host_key->n),
826: SSH_KEY_BITS_RESERVED);
827: }
828: rsa_public_encrypt(key, key, host_key);
829: rsa_public_encrypt(key, key, public_key);
830: }
831:
832: /* Destroy the public keys since we no longer need them. */
833: RSA_free(public_key);
834: RSA_free(host_key);
835:
1.11 ! markus 836: if (options.cipher == SSH_CIPHER_NOT_SET) {
! 837: if (cipher_mask_ssh1(1) & supported_ciphers & (1 << ssh_cipher_default))
! 838: options.cipher = ssh_cipher_default;
! 839: } else if (options.cipher == SSH_CIPHER_ILLEGAL ||
1.10 markus 840: !(cipher_mask_ssh1(1) & (1 << options.cipher))) {
1.3 markus 841: log("No valid SSH1 cipher, using %.100s instead.",
1.7 markus 842: cipher_name(ssh_cipher_default));
843: options.cipher = ssh_cipher_default;
1.1 markus 844: }
845: /* Check that the selected cipher is supported. */
846: if (!(supported_ciphers & (1 << options.cipher)))
847: fatal("Selected cipher type %.100s not supported by server.",
848: cipher_name(options.cipher));
849:
850: debug("Encryption type: %.100s", cipher_name(options.cipher));
851:
852: /* Send the encrypted session key to the server. */
853: packet_start(SSH_CMSG_SESSION_KEY);
854: packet_put_char(options.cipher);
855:
856: /* Send the cookie back to the server. */
857: for (i = 0; i < 8; i++)
858: packet_put_char(cookie[i]);
859:
860: /* Send and destroy the encrypted encryption key integer. */
861: packet_put_bignum(key);
862: BN_clear_free(key);
863:
864: /* Send protocol flags. */
865: packet_put_int(client_flags);
866:
867: /* Send the packet now. */
868: packet_send();
869: packet_write_wait();
870:
871: debug("Sent encrypted session key.");
872:
873: /* Set the encryption key. */
874: packet_set_encryption_key(session_key, SSH_SESSION_KEY_LENGTH, options.cipher);
875:
876: /* We will no longer need the session key here. Destroy any extra copies. */
877: memset(session_key, 0, sizeof(session_key));
878:
879: /*
880: * Expect a success message from the server. Note that this message
881: * will be received in encrypted form.
882: */
883: packet_read_expect(&payload_len, SSH_SMSG_SUCCESS);
884:
885: debug("Received encrypted confirmation.");
886: }
887:
888: /*
889: * Authenticate user
890: */
891: void
892: ssh_userauth(
893: const char* local_user,
894: const char* server_user,
895: char *host,
896: int host_key_valid, RSA *own_host_key)
897: {
898: int i, type;
899: int payload_len;
900:
901: if (supported_authentications == 0)
902: fatal("ssh_userauth: server supports no auth methods");
903:
904: /* Send the name of the user to log in as on the server. */
905: packet_start(SSH_CMSG_USER);
906: packet_put_string(server_user, strlen(server_user));
907: packet_send();
908: packet_write_wait();
909:
910: /*
911: * The server should respond with success if no authentication is
912: * needed (the user has no password). Otherwise the server responds
913: * with failure.
914: */
915: type = packet_read(&payload_len);
916:
917: /* check whether the connection was accepted without authentication. */
918: if (type == SSH_SMSG_SUCCESS)
919: return;
920: if (type != SSH_SMSG_FAILURE)
921: packet_disconnect("Protocol error: got %d in response to SSH_CMSG_USER",
922: type);
923:
924: #ifdef AFS
925: /* Try Kerberos tgt passing if the server supports it. */
926: if ((supported_authentications & (1 << SSH_PASS_KERBEROS_TGT)) &&
927: options.kerberos_tgt_passing) {
928: if (options.cipher == SSH_CIPHER_NONE)
929: log("WARNING: Encryption is disabled! Ticket will be transmitted in the clear!");
930: (void) send_kerberos_tgt();
931: }
932: /* Try AFS token passing if the server supports it. */
933: if ((supported_authentications & (1 << SSH_PASS_AFS_TOKEN)) &&
934: options.afs_token_passing && k_hasafs()) {
935: if (options.cipher == SSH_CIPHER_NONE)
936: log("WARNING: Encryption is disabled! Token will be transmitted in the clear!");
937: send_afs_tokens();
938: }
939: #endif /* AFS */
940:
941: #ifdef KRB4
942: if ((supported_authentications & (1 << SSH_AUTH_KERBEROS)) &&
943: options.kerberos_authentication) {
944: debug("Trying Kerberos authentication.");
945: if (try_kerberos_authentication()) {
946: /* The server should respond with success or failure. */
947: type = packet_read(&payload_len);
948: if (type == SSH_SMSG_SUCCESS)
949: return;
950: if (type != SSH_SMSG_FAILURE)
951: packet_disconnect("Protocol error: got %d in response to Kerberos auth", type);
952: }
953: }
954: #endif /* KRB4 */
955:
956: /*
957: * Use rhosts authentication if running in privileged socket and we
958: * do not wish to remain anonymous.
959: */
960: if ((supported_authentications & (1 << SSH_AUTH_RHOSTS)) &&
961: options.rhosts_authentication) {
962: debug("Trying rhosts authentication.");
963: packet_start(SSH_CMSG_AUTH_RHOSTS);
964: packet_put_string(local_user, strlen(local_user));
965: packet_send();
966: packet_write_wait();
967:
968: /* The server should respond with success or failure. */
969: type = packet_read(&payload_len);
970: if (type == SSH_SMSG_SUCCESS)
971: return;
972: if (type != SSH_SMSG_FAILURE)
973: packet_disconnect("Protocol error: got %d in response to rhosts auth",
974: type);
975: }
976: /*
977: * Try .rhosts or /etc/hosts.equiv authentication with RSA host
978: * authentication.
979: */
980: if ((supported_authentications & (1 << SSH_AUTH_RHOSTS_RSA)) &&
981: options.rhosts_rsa_authentication && host_key_valid) {
982: if (try_rhosts_rsa_authentication(local_user, own_host_key))
983: return;
984: }
985: /* Try RSA authentication if the server supports it. */
986: if ((supported_authentications & (1 << SSH_AUTH_RSA)) &&
987: options.rsa_authentication) {
988: /*
989: * Try RSA authentication using the authentication agent. The
990: * agent is tried first because no passphrase is needed for
991: * it, whereas identity files may require passphrases.
992: */
993: if (try_agent_authentication())
994: return;
995:
996: /* Try RSA authentication for each identity. */
997: for (i = 0; i < options.num_identity_files; i++)
1.9 markus 998: if (options.identity_files_type[i] == KEY_RSA1 &&
999: try_rsa_authentication(options.identity_files[i]))
1.1 markus 1000: return;
1001: }
1002: /* Try skey authentication if the server supports it. */
1003: if ((supported_authentications & (1 << SSH_AUTH_TIS)) &&
1004: options.skey_authentication && !options.batch_mode) {
1005: if (try_skey_authentication())
1006: return;
1007: }
1008: /* Try password authentication if the server supports it. */
1009: if ((supported_authentications & (1 << SSH_AUTH_PASSWORD)) &&
1010: options.password_authentication && !options.batch_mode) {
1011: char prompt[80];
1012:
1013: snprintf(prompt, sizeof(prompt), "%.30s@%.40s's password: ",
1014: server_user, host);
1015: if (try_password_authentication(prompt))
1016: return;
1017: }
1018: /* All authentication methods have failed. Exit with an error message. */
1019: fatal("Permission denied.");
1020: /* NOTREACHED */
1021: }
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