Annotation of src/usr.bin/ssh/kex.c, Revision 1.11
1.1 markus 1: /*
2: * Copyright (c) 2000 Markus Friedl. All rights reserved.
3: *
4: * Redistribution and use in source and binary forms, with or without
5: * modification, are permitted provided that the following conditions
6: * are met:
7: * 1. Redistributions of source code must retain the above copyright
8: * notice, this list of conditions and the following disclaimer.
9: * 2. Redistributions in binary form must reproduce the above copyright
10: * notice, this list of conditions and the following disclaimer in the
11: * documentation and/or other materials provided with the distribution.
12: *
13: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
14: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
15: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
16: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
17: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
18: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
19: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
20: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
21: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
22: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
23: */
24:
25: #include "includes.h"
1.11 ! provos 26: RCSID("$OpenBSD: kex.c,v 1.10 2000/09/07 20:27:51 deraadt Exp $");
1.1 markus 27:
28: #include "ssh.h"
29: #include "ssh2.h"
30: #include "xmalloc.h"
31: #include "buffer.h"
32: #include "bufaux.h"
1.7 markus 33: #include "packet.h"
1.1 markus 34: #include "cipher.h"
35: #include "compat.h"
36:
1.4 markus 37: #include <openssl/bn.h>
38: #include <openssl/dh.h>
1.1 markus 39:
1.4 markus 40: #include <openssl/crypto.h>
41: #include <openssl/bio.h>
42: #include <openssl/bn.h>
43: #include <openssl/dh.h>
44: #include <openssl/pem.h>
1.1 markus 45:
46: #include "kex.h"
47:
1.7 markus 48: #define KEX_COOKIE_LEN 16
49:
1.1 markus 50: Buffer *
51: kex_init(char *myproposal[PROPOSAL_MAX])
52: {
1.7 markus 53: int first_kex_packet_follows = 0;
54: unsigned char cookie[KEX_COOKIE_LEN];
1.1 markus 55: u_int32_t rand = 0;
56: int i;
57: Buffer *ki = xmalloc(sizeof(*ki));
1.7 markus 58: for (i = 0; i < KEX_COOKIE_LEN; i++) {
1.1 markus 59: if (i % 4 == 0)
60: rand = arc4random();
61: cookie[i] = rand & 0xff;
62: rand >>= 8;
63: }
64: buffer_init(ki);
65: buffer_append(ki, (char *)cookie, sizeof cookie);
66: for (i = 0; i < PROPOSAL_MAX; i++)
67: buffer_put_cstring(ki, myproposal[i]);
1.7 markus 68: buffer_put_char(ki, first_kex_packet_follows);
69: buffer_put_int(ki, 0); /* uint32 reserved */
1.1 markus 70: return ki;
71: }
72:
1.7 markus 73: /* send kexinit, parse and save reply */
74: void
75: kex_exchange_kexinit(
76: Buffer *my_kexinit, Buffer *peer_kexint,
77: char *peer_proposal[PROPOSAL_MAX])
78: {
79: int i;
80: char *ptr;
81: int plen;
82:
83: debug("send KEXINIT");
84: packet_start(SSH2_MSG_KEXINIT);
85: packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
86: packet_send();
87: packet_write_wait();
88: debug("done");
89:
90: /*
91: * read and save raw KEXINIT payload in buffer. this is used during
92: * computation of the session_id and the session keys.
93: */
94: debug("wait KEXINIT");
95: packet_read_expect(&plen, SSH2_MSG_KEXINIT);
96: ptr = packet_get_raw(&plen);
97: buffer_append(peer_kexint, ptr, plen);
98:
99: /* parse packet and save algorithm proposal */
100: /* skip cookie */
101: for (i = 0; i < KEX_COOKIE_LEN; i++)
102: packet_get_char();
103: /* extract kex init proposal strings */
104: for (i = 0; i < PROPOSAL_MAX; i++) {
105: peer_proposal[i] = packet_get_string(NULL);
106: debug("got kexinit: %s", peer_proposal[i]);
107: }
108: /* first kex follow / reserved */
109: i = packet_get_char();
110: debug("first kex follow: %d ", i);
111: i = packet_get_int();
112: debug("reserved: %d ", i);
113: packet_done();
114: debug("done");
115: }
116:
1.1 markus 117: /* diffie-hellman-group1-sha1 */
118:
1.3 markus 119: int
120: dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
121: {
122: int i;
123: int n = BN_num_bits(dh_pub);
124: int bits_set = 0;
125:
126: if (dh_pub->neg) {
127: log("invalid public DH value: negativ");
128: return 0;
129: }
130: for (i = 0; i <= n; i++)
131: if (BN_is_bit_set(dh_pub, i))
132: bits_set++;
133: debug("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
134:
135: /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
136: if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1))
137: return 1;
138: log("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
139: return 0;
140: }
141:
1.1 markus 142: DH *
1.11 ! provos 143: dh_gen_key(DH *dh)
! 144: {
! 145: int tries = 0;
! 146:
! 147: do {
! 148: if (DH_generate_key(dh) == 0)
! 149: fatal("DH_generate_key");
! 150: if (tries++ > 10)
! 151: fatal("dh_new_group1: too many bad keys: giving up");
! 152: } while (!dh_pub_is_valid(dh, dh->pub_key));
! 153: return dh;
! 154: }
! 155:
! 156: DH *
! 157: dh_new_group_asc(const char *gen, const char *modulus)
! 158: {
! 159: DH *dh;
! 160: int ret;
! 161:
! 162: dh = DH_new();
! 163: if (dh == NULL)
! 164: fatal("DH_new");
! 165:
! 166: if ((ret = BN_hex2bn(&dh->p, modulus)) < 0)
! 167: fatal("BN_hex2bn p");
! 168: if ((ret = BN_hex2bn(&dh->g, gen)) < 0)
! 169: fatal("BN_hex2bn g");
! 170:
! 171: return (dh_gen_key(dh));
! 172: }
! 173:
! 174: DH *
! 175: dh_new_group(BIGNUM *gen, BIGNUM *modulus)
! 176: {
! 177: DH *dh;
! 178:
! 179: dh = DH_new();
! 180: if (dh == NULL)
! 181: fatal("DH_new");
! 182: dh->p = modulus;
! 183: dh->g = gen;
! 184:
! 185: return (dh_gen_key(dh));
! 186: }
! 187:
! 188: DH *
1.3 markus 189: dh_new_group1()
1.1 markus 190: {
1.11 ! provos 191: static char *gen = "2", *group1 =
1.1 markus 192: "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
193: "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
194: "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
195: "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
196: "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
197: "FFFFFFFF" "FFFFFFFF";
1.11 ! provos 198:
! 199: return (dh_new_group_asc(gen, group1));
1.1 markus 200: }
201:
202: void
203: dump_digest(unsigned char *digest, int len)
204: {
205: int i;
1.5 markus 206: for (i = 0; i< len; i++){
207: fprintf(stderr, "%02x", digest[i]);
1.1 markus 208: if(i%2!=0)
209: fprintf(stderr, " ");
210: }
1.5 markus 211: fprintf(stderr, "\n");
1.1 markus 212: }
213:
214: unsigned char *
215: kex_hash(
216: char *client_version_string,
217: char *server_version_string,
218: char *ckexinit, int ckexinitlen,
219: char *skexinit, int skexinitlen,
220: char *serverhostkeyblob, int sbloblen,
221: BIGNUM *client_dh_pub,
222: BIGNUM *server_dh_pub,
223: BIGNUM *shared_secret)
224: {
225: Buffer b;
226: static unsigned char digest[EVP_MAX_MD_SIZE];
227: EVP_MD *evp_md = EVP_sha1();
228: EVP_MD_CTX md;
229:
230: buffer_init(&b);
231: buffer_put_string(&b, client_version_string, strlen(client_version_string));
232: buffer_put_string(&b, server_version_string, strlen(server_version_string));
233:
234: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
235: buffer_put_int(&b, ckexinitlen+1);
236: buffer_put_char(&b, SSH2_MSG_KEXINIT);
237: buffer_append(&b, ckexinit, ckexinitlen);
238: buffer_put_int(&b, skexinitlen+1);
239: buffer_put_char(&b, SSH2_MSG_KEXINIT);
240: buffer_append(&b, skexinit, skexinitlen);
241:
242: buffer_put_string(&b, serverhostkeyblob, sbloblen);
243: buffer_put_bignum2(&b, client_dh_pub);
244: buffer_put_bignum2(&b, server_dh_pub);
245: buffer_put_bignum2(&b, shared_secret);
246:
247: #ifdef DEBUG_KEX
248: buffer_dump(&b);
249: #endif
250:
251: EVP_DigestInit(&md, evp_md);
252: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
253: EVP_DigestFinal(&md, digest, NULL);
254:
255: buffer_free(&b);
256:
257: #ifdef DEBUG_KEX
1.5 markus 258: dump_digest(digest, evp_md->md_size);
1.1 markus 259: #endif
260: return digest;
261: }
262:
263: unsigned char *
1.11 ! provos 264: kex_hash_gex(
! 265: char *client_version_string,
! 266: char *server_version_string,
! 267: char *ckexinit, int ckexinitlen,
! 268: char *skexinit, int skexinitlen,
! 269: char *serverhostkeyblob, int sbloblen,
! 270: int minbits, BIGNUM *prime, BIGNUM *gen,
! 271: BIGNUM *client_dh_pub,
! 272: BIGNUM *server_dh_pub,
! 273: BIGNUM *shared_secret)
! 274: {
! 275: Buffer b;
! 276: static unsigned char digest[EVP_MAX_MD_SIZE];
! 277: EVP_MD *evp_md = EVP_sha1();
! 278: EVP_MD_CTX md;
! 279:
! 280: buffer_init(&b);
! 281: buffer_put_string(&b, client_version_string, strlen(client_version_string));
! 282: buffer_put_string(&b, server_version_string, strlen(server_version_string));
! 283:
! 284: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
! 285: buffer_put_int(&b, ckexinitlen+1);
! 286: buffer_put_char(&b, SSH2_MSG_KEXINIT);
! 287: buffer_append(&b, ckexinit, ckexinitlen);
! 288: buffer_put_int(&b, skexinitlen+1);
! 289: buffer_put_char(&b, SSH2_MSG_KEXINIT);
! 290: buffer_append(&b, skexinit, skexinitlen);
! 291:
! 292: buffer_put_string(&b, serverhostkeyblob, sbloblen);
! 293: buffer_put_int(&b, minbits);
! 294: buffer_put_bignum2(&b, prime);
! 295: buffer_put_bignum2(&b, gen);
! 296: buffer_put_bignum2(&b, client_dh_pub);
! 297: buffer_put_bignum2(&b, server_dh_pub);
! 298: buffer_put_bignum2(&b, shared_secret);
! 299:
! 300: #ifdef DEBUG_KEX
! 301: buffer_dump(&b);
! 302: #endif
! 303:
! 304: EVP_DigestInit(&md, evp_md);
! 305: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
! 306: EVP_DigestFinal(&md, digest, NULL);
! 307:
! 308: buffer_free(&b);
! 309:
! 310: #ifdef DEBUG_KEX
! 311: dump_digest(digest, evp_md->md_size);
! 312: #endif
! 313: return digest;
! 314: }
! 315:
! 316: unsigned char *
1.1 markus 317: derive_key(int id, int need, char unsigned *hash, BIGNUM *shared_secret)
318: {
319: Buffer b;
320: EVP_MD *evp_md = EVP_sha1();
321: EVP_MD_CTX md;
322: char c = id;
323: int have;
324: int mdsz = evp_md->md_size;
325: unsigned char *digest = xmalloc(((need+mdsz-1)/mdsz)*mdsz);
326:
327: buffer_init(&b);
328: buffer_put_bignum2(&b, shared_secret);
329:
330: EVP_DigestInit(&md, evp_md);
331: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); /* shared_secret K */
332: EVP_DigestUpdate(&md, hash, mdsz); /* transport-06 */
333: EVP_DigestUpdate(&md, &c, 1); /* key id */
334: EVP_DigestUpdate(&md, hash, mdsz); /* session id */
335: EVP_DigestFinal(&md, digest, NULL);
336:
337: /* expand */
338: for (have = mdsz; need > have; have += mdsz) {
339: EVP_DigestInit(&md, evp_md);
340: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
341: EVP_DigestUpdate(&md, hash, mdsz);
342: EVP_DigestUpdate(&md, digest, have);
343: EVP_DigestFinal(&md, digest + have, NULL);
344: }
345: buffer_free(&b);
346: #ifdef DEBUG_KEX
347: fprintf(stderr, "Digest '%c'== ", c);
348: dump_digest(digest, need);
349: #endif
350: return digest;
351: }
352:
353: #define NKEYS 6
354:
355: #define MAX_PROP 20
356: #define SEP ","
357:
358: char *
359: get_match(char *client, char *server)
360: {
361: char *sproposals[MAX_PROP];
1.9 ho 362: char *c, *s, *p, *ret, *cp, *sp;
1.1 markus 363: int i, j, nproposals;
364:
1.9 ho 365: c = cp = xstrdup(client);
366: s = sp = xstrdup(server);
1.7 markus 367:
1.9 ho 368: for ((p = strsep(&sp, SEP)), i=0; p && *p != '\0';
369: (p = strsep(&sp, SEP)), i++) {
1.1 markus 370: if (i < MAX_PROP)
371: sproposals[i] = p;
372: else
373: break;
374: }
375: nproposals = i;
376:
1.9 ho 377: for ((p = strsep(&cp, SEP)), i=0; p && *p != '\0';
378: (p = strsep(&cp, SEP)), i++) {
1.7 markus 379: for (j = 0; j < nproposals; j++) {
380: if (strcmp(p, sproposals[j]) == 0) {
381: ret = xstrdup(p);
382: xfree(c);
383: xfree(s);
384: return ret;
385: }
386: }
1.1 markus 387: }
1.7 markus 388: xfree(c);
389: xfree(s);
1.1 markus 390: return NULL;
391: }
392: void
393: choose_enc(Enc *enc, char *client, char *server)
394: {
395: char *name = get_match(client, server);
396: if (name == NULL)
397: fatal("no matching cipher found: client %s server %s", client, server);
398: enc->type = cipher_number(name);
399:
400: switch (enc->type) {
401: case SSH_CIPHER_3DES_CBC:
402: enc->key_len = 24;
403: enc->iv_len = 8;
404: enc->block_size = 8;
405: break;
406: case SSH_CIPHER_BLOWFISH_CBC:
407: case SSH_CIPHER_CAST128_CBC:
408: enc->key_len = 16;
409: enc->iv_len = 8;
410: enc->block_size = 8;
411: break;
412: case SSH_CIPHER_ARCFOUR:
413: enc->key_len = 16;
414: enc->iv_len = 0;
415: enc->block_size = 8;
416: break;
417: default:
418: fatal("unsupported cipher %s", name);
419: }
420: enc->name = name;
421: enc->enabled = 0;
422: enc->iv = NULL;
423: enc->key = NULL;
424: }
425: void
426: choose_mac(Mac *mac, char *client, char *server)
427: {
428: char *name = get_match(client, server);
429: if (name == NULL)
430: fatal("no matching mac found: client %s server %s", client, server);
431: if (strcmp(name, "hmac-md5") == 0) {
432: mac->md = EVP_md5();
433: } else if (strcmp(name, "hmac-sha1") == 0) {
434: mac->md = EVP_sha1();
435: } else if (strcmp(name, "hmac-ripemd160@openssh.com") == 0) {
436: mac->md = EVP_ripemd160();
437: } else {
438: fatal("unsupported mac %s", name);
439: }
440: mac->name = name;
441: mac->mac_len = mac->md->md_size;
1.6 markus 442: mac->key_len = (datafellows & SSH_BUG_HMAC) ? 16 : mac->mac_len;
1.1 markus 443: mac->key = NULL;
444: mac->enabled = 0;
445: }
446: void
447: choose_comp(Comp *comp, char *client, char *server)
448: {
449: char *name = get_match(client, server);
450: if (name == NULL)
451: fatal("no matching comp found: client %s server %s", client, server);
452: if (strcmp(name, "zlib") == 0) {
453: comp->type = 1;
454: } else if (strcmp(name, "none") == 0) {
455: comp->type = 0;
456: } else {
457: fatal("unsupported comp %s", name);
458: }
459: comp->name = name;
460: }
461: void
462: choose_kex(Kex *k, char *client, char *server)
463: {
464: k->name = get_match(client, server);
465: if (k->name == NULL)
466: fatal("no kex alg");
1.11 ! provos 467: if (strcmp(k->name, KEX_DH1) == 0) {
! 468: k->kex_type = DH_GRP1_SHA1;
! 469: } else if (strcmp(k->name, KEX_DHGEX) == 0) {
! 470: k->kex_type = DH_GEX_SHA1;
! 471: } else
1.1 markus 472: fatal("bad kex alg %s", k->name);
473: }
474: void
475: choose_hostkeyalg(Kex *k, char *client, char *server)
476: {
477: k->hostkeyalg = get_match(client, server);
478: if (k->hostkeyalg == NULL)
479: fatal("no hostkey alg");
480: if (strcmp(k->hostkeyalg, KEX_DSS) != 0)
481: fatal("bad hostkey alg %s", k->hostkeyalg);
482: }
483:
484: Kex *
485: kex_choose_conf(char *cprop[PROPOSAL_MAX], char *sprop[PROPOSAL_MAX], int server)
486: {
487: int mode;
488: int ctos; /* direction: if true client-to-server */
489: int need;
490: Kex *k;
491:
492: k = xmalloc(sizeof(*k));
493: memset(k, 0, sizeof(*k));
494: k->server = server;
495:
496: for (mode = 0; mode < MODE_MAX; mode++) {
497: int nenc, nmac, ncomp;
498: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
499: nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
500: nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
501: ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
502: choose_enc (&k->enc [mode], cprop[nenc], sprop[nenc]);
503: choose_mac (&k->mac [mode], cprop[nmac], sprop[nmac]);
504: choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
1.2 markus 505: debug("kex: %s %s %s %s",
1.1 markus 506: ctos ? "client->server" : "server->client",
507: k->enc[mode].name,
508: k->mac[mode].name,
509: k->comp[mode].name);
510: }
511: choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
512: choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
513: sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
514: need = 0;
515: for (mode = 0; mode < MODE_MAX; mode++) {
516: if (need < k->enc[mode].key_len)
517: need = k->enc[mode].key_len;
518: if (need < k->enc[mode].iv_len)
519: need = k->enc[mode].iv_len;
520: if (need < k->mac[mode].key_len)
521: need = k->mac[mode].key_len;
522: }
1.7 markus 523: /* XXX need runden? */
1.1 markus 524: k->we_need = need;
525: return k;
526: }
527:
528: int
529: kex_derive_keys(Kex *k, unsigned char *hash, BIGNUM *shared_secret)
530: {
531: int i;
532: int mode;
533: int ctos;
534: unsigned char *keys[NKEYS];
535:
536: for (i = 0; i < NKEYS; i++)
537: keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);
538:
539: for (mode = 0; mode < MODE_MAX; mode++) {
540: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
541: k->enc[mode].iv = keys[ctos ? 0 : 1];
542: k->enc[mode].key = keys[ctos ? 2 : 3];
543: k->mac[mode].key = keys[ctos ? 4 : 5];
544: }
545: return 0;
546: }
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