Annotation of src/usr.bin/ssh/sshconnect1.c, Revision 1.2
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"
1.2 ! markus 12: RCSID("$OpenBSD: sshconnect1.c,v 1.1 2000/04/26 21:28:33 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 "authfd.h"
25: #include "cipher.h"
26: #include "mpaux.h"
27: #include "uidswap.h"
28: #include "readconf.h"
29: #include "key.h"
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: {
47: int status, type;
48: char *comment;
49: AuthenticationConnection *auth;
50: unsigned char response[16];
51: unsigned int i;
52: BIGNUM *e, *n, *challenge;
53:
54: /* Get connection to the agent. */
55: auth = ssh_get_authentication_connection();
56: if (!auth)
57: return 0;
58:
59: e = BN_new();
60: n = BN_new();
61: challenge = BN_new();
62:
63: /* Loop through identities served by the agent. */
64: for (status = ssh_get_first_identity(auth, e, n, &comment);
65: status;
66: status = ssh_get_next_identity(auth, e, n, &comment)) {
67: int plen, clen;
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);
75: packet_put_bignum(n);
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.");
86: continue;
87: }
88: /* Otherwise it should have sent a challenge. */
89: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
90: packet_disconnect("Protocol error during RSA authentication: %d",
91: type);
92:
93: packet_get_bignum(challenge, &clen);
94:
95: packet_integrity_check(plen, clen, type);
96:
97: debug("Received RSA challenge from server.");
98:
99: /* Ask the agent to decrypt the challenge. */
100: if (!ssh_decrypt_challenge(auth, e, n, challenge,
101: session_id, 1, response)) {
102: /* The agent failed to authenticate this identifier although it
103: advertised it supports this. Just return a wrong value. */
104: log("Authentication agent failed to decrypt challenge.");
105: memset(response, 0, sizeof(response));
106: }
107: debug("Sending response to RSA challenge.");
108:
109: /* Send the decrypted challenge back to the server. */
110: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
111: for (i = 0; i < 16; i++)
112: packet_put_char(response[i]);
113: packet_send();
114: packet_write_wait();
115:
116: /* Wait for response from the server. */
117: type = packet_read(&plen);
118:
119: /* The server returns success if it accepted the authentication. */
120: if (type == SSH_SMSG_SUCCESS) {
121: debug("RSA authentication accepted by server.");
122: BN_clear_free(e);
123: BN_clear_free(n);
124: BN_clear_free(challenge);
125: return 1;
126: }
127: /* Otherwise it should return failure. */
128: if (type != SSH_SMSG_FAILURE)
129: packet_disconnect("Protocol error waiting RSA auth response: %d",
130: type);
131: }
132:
133: BN_clear_free(e);
134: BN_clear_free(n);
135: BN_clear_free(challenge);
136:
137: debug("RSA authentication using agent refused.");
138: return 0;
139: }
140:
141: /*
142: * Computes the proper response to a RSA challenge, and sends the response to
143: * the server.
144: */
145: void
146: respond_to_rsa_challenge(BIGNUM * challenge, RSA * prv)
147: {
148: unsigned char buf[32], response[16];
149: MD5_CTX md;
150: int i, len;
151:
152: /* Decrypt the challenge using the private key. */
153: rsa_private_decrypt(challenge, challenge, prv);
154:
155: /* Compute the response. */
156: /* The response is MD5 of decrypted challenge plus session id. */
157: len = BN_num_bytes(challenge);
158: if (len <= 0 || len > sizeof(buf))
159: packet_disconnect("respond_to_rsa_challenge: bad challenge length %d",
160: len);
161:
162: memset(buf, 0, sizeof(buf));
163: BN_bn2bin(challenge, buf + sizeof(buf) - len);
164: MD5_Init(&md);
165: MD5_Update(&md, buf, 32);
166: MD5_Update(&md, session_id, 16);
167: MD5_Final(response, &md);
168:
169: debug("Sending response to host key RSA challenge.");
170:
171: /* Send the response back to the server. */
172: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
173: for (i = 0; i < 16; i++)
174: packet_put_char(response[i]);
175: packet_send();
176: packet_write_wait();
177:
178: memset(buf, 0, sizeof(buf));
179: memset(response, 0, sizeof(response));
180: memset(&md, 0, sizeof(md));
181: }
182:
183: /*
184: * Checks if the user has authentication file, and if so, tries to authenticate
185: * the user using it.
186: */
187: int
188: try_rsa_authentication(const char *authfile)
189: {
190: BIGNUM *challenge;
191: Key *public;
192: Key *private;
193: char *passphrase, *comment;
194: int type, i;
195: int plen, clen;
196:
197: /* Try to load identification for the authentication key. */
198: public = key_new(KEY_RSA);
199: if (!load_public_key(authfile, public, &comment)) {
200: key_free(public);
201: /* Could not load it. Fail. */
202: return 0;
203: }
204: debug("Trying RSA authentication with key '%.100s'", comment);
205:
206: /* Tell the server that we are willing to authenticate using this key. */
207: packet_start(SSH_CMSG_AUTH_RSA);
208: packet_put_bignum(public->rsa->n);
209: packet_send();
210: packet_write_wait();
211:
212: /* We no longer need the public key. */
213: key_free(public);
214:
215: /* Wait for server's response. */
216: type = packet_read(&plen);
217:
218: /*
219: * The server responds with failure if it doesn\'t like our key or
220: * doesn\'t support RSA authentication.
221: */
222: if (type == SSH_SMSG_FAILURE) {
223: debug("Server refused our key.");
224: xfree(comment);
225: return 0;
226: }
227: /* Otherwise, the server should respond with a challenge. */
228: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
229: packet_disconnect("Protocol error during RSA authentication: %d", type);
230:
231: /* Get the challenge from the packet. */
232: challenge = BN_new();
233: packet_get_bignum(challenge, &clen);
234:
235: packet_integrity_check(plen, clen, type);
236:
237: debug("Received RSA challenge from server.");
238:
239: private = key_new(KEY_RSA);
240: /*
241: * Load the private key. Try first with empty passphrase; if it
242: * fails, ask for a passphrase.
243: */
244: if (!load_private_key(authfile, "", private, NULL)) {
245: char buf[300];
246: snprintf(buf, sizeof buf, "Enter passphrase for RSA key '%.100s': ",
247: comment);
248: if (!options.batch_mode)
249: passphrase = read_passphrase(buf, 0);
250: else {
251: debug("Will not query passphrase for %.100s in batch mode.",
252: comment);
253: passphrase = xstrdup("");
254: }
255:
256: /* Load the authentication file using the pasphrase. */
257: if (!load_private_key(authfile, passphrase, private, NULL)) {
258: memset(passphrase, 0, strlen(passphrase));
259: xfree(passphrase);
260: error("Bad passphrase.");
261:
262: /* Send a dummy response packet to avoid protocol error. */
263: packet_start(SSH_CMSG_AUTH_RSA_RESPONSE);
264: for (i = 0; i < 16; i++)
265: packet_put_char(0);
266: packet_send();
267: packet_write_wait();
268:
269: /* Expect the server to reject it... */
270: packet_read_expect(&plen, SSH_SMSG_FAILURE);
271: xfree(comment);
272: return 0;
273: }
274: /* Destroy the passphrase. */
275: memset(passphrase, 0, strlen(passphrase));
276: xfree(passphrase);
277: }
278: /* We no longer need the comment. */
279: xfree(comment);
280:
281: /* Compute and send a response to the challenge. */
282: respond_to_rsa_challenge(challenge, private->rsa);
283:
284: /* Destroy the private key. */
285: key_free(private);
286:
287: /* We no longer need the challenge. */
288: BN_clear_free(challenge);
289:
290: /* Wait for response from the server. */
291: type = packet_read(&plen);
292: if (type == SSH_SMSG_SUCCESS) {
293: debug("RSA authentication accepted by server.");
294: return 1;
295: }
296: if (type != SSH_SMSG_FAILURE)
297: packet_disconnect("Protocol error waiting RSA auth response: %d", type);
298: debug("RSA authentication refused.");
299: return 0;
300: }
301:
302: /*
303: * Tries to authenticate the user using combined rhosts or /etc/hosts.equiv
304: * authentication and RSA host authentication.
305: */
306: int
307: try_rhosts_rsa_authentication(const char *local_user, RSA * host_key)
308: {
309: int type;
310: BIGNUM *challenge;
311: int plen, clen;
312:
313: debug("Trying rhosts or /etc/hosts.equiv with RSA host authentication.");
314:
315: /* Tell the server that we are willing to authenticate using this key. */
316: packet_start(SSH_CMSG_AUTH_RHOSTS_RSA);
317: packet_put_string(local_user, strlen(local_user));
318: packet_put_int(BN_num_bits(host_key->n));
319: packet_put_bignum(host_key->e);
320: packet_put_bignum(host_key->n);
321: packet_send();
322: packet_write_wait();
323:
324: /* Wait for server's response. */
325: type = packet_read(&plen);
326:
327: /* The server responds with failure if it doesn't admit our
328: .rhosts authentication or doesn't know our host key. */
329: if (type == SSH_SMSG_FAILURE) {
330: debug("Server refused our rhosts authentication or host key.");
331: return 0;
332: }
333: /* Otherwise, the server should respond with a challenge. */
334: if (type != SSH_SMSG_AUTH_RSA_CHALLENGE)
335: packet_disconnect("Protocol error during RSA authentication: %d", type);
336:
337: /* Get the challenge from the packet. */
338: challenge = BN_new();
339: packet_get_bignum(challenge, &clen);
340:
341: packet_integrity_check(plen, clen, type);
342:
343: debug("Received RSA challenge for host key from server.");
344:
345: /* Compute a response to the challenge. */
346: respond_to_rsa_challenge(challenge, host_key);
347:
348: /* We no longer need the challenge. */
349: BN_clear_free(challenge);
350:
351: /* Wait for response from the server. */
352: type = packet_read(&plen);
353: if (type == SSH_SMSG_SUCCESS) {
354: debug("Rhosts or /etc/hosts.equiv with RSA host authentication accepted by server.");
355: return 1;
356: }
357: if (type != SSH_SMSG_FAILURE)
358: packet_disconnect("Protocol error waiting RSA auth response: %d", type);
359: debug("Rhosts or /etc/hosts.equiv with RSA host authentication refused.");
360: return 0;
361: }
362:
363: #ifdef KRB4
364: int
365: try_kerberos_authentication()
366: {
367: KTEXT_ST auth; /* Kerberos data */
368: char *reply;
369: char inst[INST_SZ];
370: char *realm;
371: CREDENTIALS cred;
372: int r, type, plen;
373: socklen_t slen;
374: Key_schedule schedule;
375: u_long checksum, cksum;
376: MSG_DAT msg_data;
377: struct sockaddr_in local, foreign;
378: struct stat st;
379:
380: /* Don't do anything if we don't have any tickets. */
381: if (stat(tkt_string(), &st) < 0)
382: return 0;
383:
384: strncpy(inst, (char *) krb_get_phost(get_canonical_hostname()), INST_SZ);
385:
386: realm = (char *) krb_realmofhost(get_canonical_hostname());
387: if (!realm) {
388: debug("Kerberos V4: no realm for %s", get_canonical_hostname());
389: return 0;
390: }
391: /* This can really be anything. */
392: checksum = (u_long) getpid();
393:
394: r = krb_mk_req(&auth, KRB4_SERVICE_NAME, inst, realm, checksum);
395: if (r != KSUCCESS) {
396: debug("Kerberos V4 krb_mk_req failed: %s", krb_err_txt[r]);
397: return 0;
398: }
399: /* Get session key to decrypt the server's reply with. */
400: r = krb_get_cred(KRB4_SERVICE_NAME, inst, realm, &cred);
401: if (r != KSUCCESS) {
402: debug("get_cred failed: %s", krb_err_txt[r]);
403: return 0;
404: }
405: des_key_sched((des_cblock *) cred.session, schedule);
406:
407: /* Send authentication info to server. */
408: packet_start(SSH_CMSG_AUTH_KERBEROS);
409: packet_put_string((char *) auth.dat, auth.length);
410: packet_send();
411: packet_write_wait();
412:
413: /* Zero the buffer. */
414: (void) memset(auth.dat, 0, MAX_KTXT_LEN);
415:
416: slen = sizeof(local);
417: memset(&local, 0, sizeof(local));
418: if (getsockname(packet_get_connection_in(),
419: (struct sockaddr *) & local, &slen) < 0)
420: debug("getsockname failed: %s", strerror(errno));
421:
422: slen = sizeof(foreign);
423: memset(&foreign, 0, sizeof(foreign));
424: if (getpeername(packet_get_connection_in(),
425: (struct sockaddr *) & foreign, &slen) < 0) {
426: debug("getpeername failed: %s", strerror(errno));
427: fatal_cleanup();
428: }
429: /* Get server reply. */
430: type = packet_read(&plen);
431: switch (type) {
432: case SSH_SMSG_FAILURE:
433: /* Should really be SSH_SMSG_AUTH_KERBEROS_FAILURE */
434: debug("Kerberos V4 authentication failed.");
435: return 0;
436: break;
437:
438: case SSH_SMSG_AUTH_KERBEROS_RESPONSE:
439: /* SSH_SMSG_AUTH_KERBEROS_SUCCESS */
440: debug("Kerberos V4 authentication accepted.");
441:
442: /* Get server's response. */
443: reply = packet_get_string((unsigned int *) &auth.length);
444: memcpy(auth.dat, reply, auth.length);
445: xfree(reply);
446:
447: packet_integrity_check(plen, 4 + auth.length, type);
448:
449: /*
450: * If his response isn't properly encrypted with the session
451: * key, and the decrypted checksum fails to match, he's
452: * bogus. Bail out.
453: */
454: r = krb_rd_priv(auth.dat, auth.length, schedule, &cred.session,
455: &foreign, &local, &msg_data);
456: if (r != KSUCCESS) {
457: debug("Kerberos V4 krb_rd_priv failed: %s", krb_err_txt[r]);
458: packet_disconnect("Kerberos V4 challenge failed!");
459: }
460: /* Fetch the (incremented) checksum that we supplied in the request. */
461: (void) memcpy((char *) &cksum, (char *) msg_data.app_data, sizeof(cksum));
462: cksum = ntohl(cksum);
463:
464: /* If it matches, we're golden. */
465: if (cksum == checksum + 1) {
466: debug("Kerberos V4 challenge successful.");
467: return 1;
468: } else
469: packet_disconnect("Kerberos V4 challenge failed!");
470: break;
471:
472: default:
473: packet_disconnect("Protocol error on Kerberos V4 response: %d", type);
474: }
475: return 0;
476: }
477:
478: #endif /* KRB4 */
479:
480: #ifdef AFS
481: int
482: send_kerberos_tgt()
483: {
484: CREDENTIALS *creds;
485: char pname[ANAME_SZ], pinst[INST_SZ], prealm[REALM_SZ];
486: int r, type, plen;
487: char buffer[8192];
488: struct stat st;
489:
490: /* Don't do anything if we don't have any tickets. */
491: if (stat(tkt_string(), &st) < 0)
492: return 0;
493:
494: creds = xmalloc(sizeof(*creds));
495:
496: if ((r = krb_get_tf_fullname(TKT_FILE, pname, pinst, prealm)) != KSUCCESS) {
497: debug("Kerberos V4 tf_fullname failed: %s", krb_err_txt[r]);
498: return 0;
499: }
500: if ((r = krb_get_cred("krbtgt", prealm, prealm, creds)) != GC_OK) {
501: debug("Kerberos V4 get_cred failed: %s", krb_err_txt[r]);
502: return 0;
503: }
504: if (time(0) > krb_life_to_time(creds->issue_date, creds->lifetime)) {
505: debug("Kerberos V4 ticket expired: %s", TKT_FILE);
506: return 0;
507: }
1.2 ! markus 508: creds_to_radix(creds, (unsigned char *)buffer, sizeof buffer);
1.1 markus 509: xfree(creds);
510:
511: packet_start(SSH_CMSG_HAVE_KERBEROS_TGT);
512: packet_put_string(buffer, strlen(buffer));
513: packet_send();
514: packet_write_wait();
515:
516: type = packet_read(&plen);
517:
518: if (type == SSH_SMSG_FAILURE)
519: debug("Kerberos TGT for realm %s rejected.", prealm);
520: else if (type != SSH_SMSG_SUCCESS)
521: packet_disconnect("Protocol error on Kerberos TGT response: %d", type);
522:
523: return 1;
524: }
525:
526: void
527: send_afs_tokens(void)
528: {
529: CREDENTIALS creds;
530: struct ViceIoctl parms;
531: struct ClearToken ct;
532: int i, type, len, plen;
533: char buf[2048], *p, *server_cell;
534: char buffer[8192];
535:
536: /* Move over ktc_GetToken, here's something leaner. */
537: for (i = 0; i < 100; i++) { /* just in case */
538: parms.in = (char *) &i;
539: parms.in_size = sizeof(i);
540: parms.out = buf;
541: parms.out_size = sizeof(buf);
542: if (k_pioctl(0, VIOCGETTOK, &parms, 0) != 0)
543: break;
544: p = buf;
545:
546: /* Get secret token. */
547: memcpy(&creds.ticket_st.length, p, sizeof(unsigned int));
548: if (creds.ticket_st.length > MAX_KTXT_LEN)
549: break;
550: p += sizeof(unsigned int);
551: memcpy(creds.ticket_st.dat, p, creds.ticket_st.length);
552: p += creds.ticket_st.length;
553:
554: /* Get clear token. */
555: memcpy(&len, p, sizeof(len));
556: if (len != sizeof(struct ClearToken))
557: break;
558: p += sizeof(len);
559: memcpy(&ct, p, len);
560: p += len;
561: p += sizeof(len); /* primary flag */
562: server_cell = p;
563:
564: /* Flesh out our credentials. */
565: strlcpy(creds.service, "afs", sizeof creds.service);
566: creds.instance[0] = '\0';
567: strlcpy(creds.realm, server_cell, REALM_SZ);
568: memcpy(creds.session, ct.HandShakeKey, DES_KEY_SZ);
569: creds.issue_date = ct.BeginTimestamp;
570: creds.lifetime = krb_time_to_life(creds.issue_date, ct.EndTimestamp);
571: creds.kvno = ct.AuthHandle;
572: snprintf(creds.pname, sizeof(creds.pname), "AFS ID %d", ct.ViceId);
573: creds.pinst[0] = '\0';
574:
575: /* Encode token, ship it off. */
1.2 ! markus 576: if (creds_to_radix(&creds, (unsigned char*) buffer, sizeof buffer) <= 0)
1.1 markus 577: break;
578: packet_start(SSH_CMSG_HAVE_AFS_TOKEN);
579: packet_put_string(buffer, strlen(buffer));
580: packet_send();
581: packet_write_wait();
582:
583: /* Roger, Roger. Clearance, Clarence. What's your vector,
584: Victor? */
585: type = packet_read(&plen);
586:
587: if (type == SSH_SMSG_FAILURE)
588: debug("AFS token for cell %s rejected.", server_cell);
589: else if (type != SSH_SMSG_SUCCESS)
590: packet_disconnect("Protocol error on AFS token response: %d", type);
591: }
592: }
593:
594: #endif /* AFS */
595:
596: /*
597: * Tries to authenticate with any string-based challenge/response system.
598: * Note that the client code is not tied to s/key or TIS.
599: */
600: int
601: try_skey_authentication()
602: {
603: int type, i;
604: int payload_len;
605: unsigned int clen;
606: char *challenge, *response;
607:
608: debug("Doing skey authentication.");
609:
610: /* request a challenge */
611: packet_start(SSH_CMSG_AUTH_TIS);
612: packet_send();
613: packet_write_wait();
614:
615: type = packet_read(&payload_len);
616: if (type != SSH_SMSG_FAILURE &&
617: type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
618: packet_disconnect("Protocol error: got %d in response "
619: "to skey-auth", type);
620: }
621: if (type != SSH_SMSG_AUTH_TIS_CHALLENGE) {
622: debug("No challenge for skey authentication.");
623: return 0;
624: }
625: challenge = packet_get_string(&clen);
626: packet_integrity_check(payload_len, (4 + clen), type);
627: if (options.cipher == SSH_CIPHER_NONE)
628: log("WARNING: Encryption is disabled! "
629: "Reponse will be transmitted in clear text.");
630: fprintf(stderr, "%s\n", challenge);
631: xfree(challenge);
632: fflush(stderr);
633: for (i = 0; i < options.number_of_password_prompts; i++) {
634: if (i != 0)
635: error("Permission denied, please try again.");
636: response = read_passphrase("Response: ", 0);
637: packet_start(SSH_CMSG_AUTH_TIS_RESPONSE);
638: packet_put_string(response, strlen(response));
639: memset(response, 0, strlen(response));
640: xfree(response);
641: packet_send();
642: packet_write_wait();
643: type = packet_read(&payload_len);
644: if (type == SSH_SMSG_SUCCESS)
645: return 1;
646: if (type != SSH_SMSG_FAILURE)
647: packet_disconnect("Protocol error: got %d in response "
648: "to skey-auth-reponse", type);
649: }
650: /* failure */
651: return 0;
652: }
653:
654: /*
655: * Tries to authenticate with plain passwd authentication.
656: */
657: int
658: try_password_authentication(char *prompt)
659: {
660: int type, i, payload_len;
661: char *password;
662:
663: debug("Doing password authentication.");
664: if (options.cipher == SSH_CIPHER_NONE)
665: log("WARNING: Encryption is disabled! Password will be transmitted in clear text.");
666: for (i = 0; i < options.number_of_password_prompts; i++) {
667: if (i != 0)
668: error("Permission denied, please try again.");
669: password = read_passphrase(prompt, 0);
670: packet_start(SSH_CMSG_AUTH_PASSWORD);
671: packet_put_string(password, strlen(password));
672: memset(password, 0, strlen(password));
673: xfree(password);
674: packet_send();
675: packet_write_wait();
676:
677: type = packet_read(&payload_len);
678: if (type == SSH_SMSG_SUCCESS)
679: return 1;
680: if (type != SSH_SMSG_FAILURE)
681: packet_disconnect("Protocol error: got %d in response to passwd auth", type);
682: }
683: /* failure */
684: return 0;
685: }
686:
687: /*
688: * SSH1 key exchange
689: */
690: void
691: ssh_kex(char *host, struct sockaddr *hostaddr)
692: {
693: int i;
694: BIGNUM *key;
695: RSA *host_key;
696: RSA *public_key;
697: Key k;
698: int bits, rbits;
699: int ssh_cipher_default = SSH_CIPHER_3DES;
700: unsigned char session_key[SSH_SESSION_KEY_LENGTH];
701: unsigned char cookie[8];
702: unsigned int supported_ciphers;
703: unsigned int server_flags, client_flags;
704: int payload_len, clen, sum_len = 0;
705: u_int32_t rand = 0;
706:
707: debug("Waiting for server public key.");
708:
709: /* Wait for a public key packet from the server. */
710: packet_read_expect(&payload_len, SSH_SMSG_PUBLIC_KEY);
711:
712: /* Get cookie from the packet. */
713: for (i = 0; i < 8; i++)
714: cookie[i] = packet_get_char();
715:
716: /* Get the public key. */
717: public_key = RSA_new();
718: bits = packet_get_int();/* bits */
719: public_key->e = BN_new();
720: packet_get_bignum(public_key->e, &clen);
721: sum_len += clen;
722: public_key->n = BN_new();
723: packet_get_bignum(public_key->n, &clen);
724: sum_len += clen;
725:
726: rbits = BN_num_bits(public_key->n);
727: if (bits != rbits) {
728: log("Warning: Server lies about size of server public key: "
729: "actual size is %d bits vs. announced %d.", rbits, bits);
730: log("Warning: This may be due to an old implementation of ssh.");
731: }
732: /* Get the host key. */
733: host_key = RSA_new();
734: bits = packet_get_int();/* bits */
735: host_key->e = BN_new();
736: packet_get_bignum(host_key->e, &clen);
737: sum_len += clen;
738: host_key->n = BN_new();
739: packet_get_bignum(host_key->n, &clen);
740: sum_len += clen;
741:
742: rbits = BN_num_bits(host_key->n);
743: if (bits != rbits) {
744: log("Warning: Server lies about size of server host key: "
745: "actual size is %d bits vs. announced %d.", rbits, bits);
746: log("Warning: This may be due to an old implementation of ssh.");
747: }
748:
749: /* Get protocol flags. */
750: server_flags = packet_get_int();
751: packet_set_protocol_flags(server_flags);
752:
753: supported_ciphers = packet_get_int();
754: supported_authentications = packet_get_int();
755:
756: debug("Received server public key (%d bits) and host key (%d bits).",
757: BN_num_bits(public_key->n), BN_num_bits(host_key->n));
758:
759: packet_integrity_check(payload_len,
760: 8 + 4 + sum_len + 0 + 4 + 0 + 0 + 4 + 4 + 4,
761: SSH_SMSG_PUBLIC_KEY);
762: k.type = KEY_RSA;
763: k.rsa = host_key;
764: check_host_key(host, hostaddr, &k,
765: options.user_hostfile, options.system_hostfile);
766:
767: client_flags = SSH_PROTOFLAG_SCREEN_NUMBER | SSH_PROTOFLAG_HOST_IN_FWD_OPEN;
768:
769: compute_session_id(session_id, cookie, host_key->n, public_key->n);
770:
771: /* Generate a session key. */
772: arc4random_stir();
773:
774: /*
775: * Generate an encryption key for the session. The key is a 256 bit
776: * random number, interpreted as a 32-byte key, with the least
777: * significant 8 bits being the first byte of the key.
778: */
779: for (i = 0; i < 32; i++) {
780: if (i % 4 == 0)
781: rand = arc4random();
782: session_key[i] = rand & 0xff;
783: rand >>= 8;
784: }
785:
786: /*
787: * According to the protocol spec, the first byte of the session key
788: * is the highest byte of the integer. The session key is xored with
789: * the first 16 bytes of the session id.
790: */
791: key = BN_new();
792: BN_set_word(key, 0);
793: for (i = 0; i < SSH_SESSION_KEY_LENGTH; i++) {
794: BN_lshift(key, key, 8);
795: if (i < 16)
796: BN_add_word(key, session_key[i] ^ session_id[i]);
797: else
798: BN_add_word(key, session_key[i]);
799: }
800:
801: /*
802: * Encrypt the integer using the public key and host key of the
803: * server (key with smaller modulus first).
804: */
805: if (BN_cmp(public_key->n, host_key->n) < 0) {
806: /* Public key has smaller modulus. */
807: if (BN_num_bits(host_key->n) <
808: BN_num_bits(public_key->n) + SSH_KEY_BITS_RESERVED) {
809: fatal("respond_to_rsa_challenge: host_key %d < public_key %d + "
810: "SSH_KEY_BITS_RESERVED %d",
811: BN_num_bits(host_key->n),
812: BN_num_bits(public_key->n),
813: SSH_KEY_BITS_RESERVED);
814: }
815: rsa_public_encrypt(key, key, public_key);
816: rsa_public_encrypt(key, key, host_key);
817: } else {
818: /* Host key has smaller modulus (or they are equal). */
819: if (BN_num_bits(public_key->n) <
820: BN_num_bits(host_key->n) + SSH_KEY_BITS_RESERVED) {
821: fatal("respond_to_rsa_challenge: public_key %d < host_key %d + "
822: "SSH_KEY_BITS_RESERVED %d",
823: BN_num_bits(public_key->n),
824: BN_num_bits(host_key->n),
825: SSH_KEY_BITS_RESERVED);
826: }
827: rsa_public_encrypt(key, key, host_key);
828: rsa_public_encrypt(key, key, public_key);
829: }
830:
831: /* Destroy the public keys since we no longer need them. */
832: RSA_free(public_key);
833: RSA_free(host_key);
834:
835: if (options.cipher == SSH_CIPHER_NOT_SET) {
836: if (cipher_mask1() & supported_ciphers & (1 << ssh_cipher_default))
837: options.cipher = ssh_cipher_default;
838: else {
839: debug("Cipher %s not supported, using %.100s instead.",
840: cipher_name(ssh_cipher_default),
841: cipher_name(SSH_FALLBACK_CIPHER));
842: options.cipher = SSH_FALLBACK_CIPHER;
843: }
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++)
998: if (try_rsa_authentication(options.identity_files[i]))
999: return;
1000: }
1001: /* Try skey authentication if the server supports it. */
1002: if ((supported_authentications & (1 << SSH_AUTH_TIS)) &&
1003: options.skey_authentication && !options.batch_mode) {
1004: if (try_skey_authentication())
1005: return;
1006: }
1007: /* Try password authentication if the server supports it. */
1008: if ((supported_authentications & (1 << SSH_AUTH_PASSWORD)) &&
1009: options.password_authentication && !options.batch_mode) {
1010: char prompt[80];
1011:
1012: snprintf(prompt, sizeof(prompt), "%.30s@%.40s's password: ",
1013: server_user, host);
1014: if (try_password_authentication(prompt))
1015: return;
1016: }
1017: /* All authentication methods have failed. Exit with an error message. */
1018: fatal("Permission denied.");
1019: /* NOTREACHED */
1020: }
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