Annotation of src/usr.bin/ssh/kex.c, Revision 1.6.2.2
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: * 3. All advertising materials mentioning features or use of this software
13: * must display the following acknowledgement:
14: * This product includes software developed by Markus Friedl.
15: * 4. The name of the author may not be used to endorse or promote products
16: * derived from this software without specific prior written permission.
17: *
18: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
19: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
20: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
21: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
22: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
23: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
24: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
25: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
26: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
27: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
28: */
29:
30: #include "includes.h"
1.6.2.2 ! jason 31: RCSID("$OpenBSD: kex.c,v 1.9 2000/07/10 16:30:25 ho Exp $");
1.1 markus 32:
33: #include "ssh.h"
34: #include "ssh2.h"
35: #include "xmalloc.h"
36: #include "buffer.h"
37: #include "bufaux.h"
1.6.2.1 jason 38: #include "packet.h"
1.1 markus 39: #include "cipher.h"
40: #include "compat.h"
41:
1.4 markus 42: #include <openssl/bn.h>
43: #include <openssl/dh.h>
1.1 markus 44:
1.4 markus 45: #include <openssl/crypto.h>
46: #include <openssl/bio.h>
47: #include <openssl/bn.h>
48: #include <openssl/dh.h>
49: #include <openssl/pem.h>
1.1 markus 50:
51: #include "kex.h"
52:
1.6.2.1 jason 53: #define KEX_COOKIE_LEN 16
54:
1.1 markus 55: Buffer *
56: kex_init(char *myproposal[PROPOSAL_MAX])
57: {
1.6.2.1 jason 58: int first_kex_packet_follows = 0;
59: unsigned char cookie[KEX_COOKIE_LEN];
1.1 markus 60: u_int32_t rand = 0;
61: int i;
62: Buffer *ki = xmalloc(sizeof(*ki));
1.6.2.1 jason 63: for (i = 0; i < KEX_COOKIE_LEN; i++) {
1.1 markus 64: if (i % 4 == 0)
65: rand = arc4random();
66: cookie[i] = rand & 0xff;
67: rand >>= 8;
68: }
69: buffer_init(ki);
70: buffer_append(ki, (char *)cookie, sizeof cookie);
71: for (i = 0; i < PROPOSAL_MAX; i++)
72: buffer_put_cstring(ki, myproposal[i]);
1.6.2.1 jason 73: buffer_put_char(ki, first_kex_packet_follows);
74: buffer_put_int(ki, 0); /* uint32 reserved */
1.1 markus 75: return ki;
76: }
77:
1.6.2.1 jason 78: /* send kexinit, parse and save reply */
79: void
80: kex_exchange_kexinit(
81: Buffer *my_kexinit, Buffer *peer_kexint,
82: char *peer_proposal[PROPOSAL_MAX])
83: {
84: int i;
85: char *ptr;
86: int plen;
87:
88: debug("send KEXINIT");
89: packet_start(SSH2_MSG_KEXINIT);
90: packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
91: packet_send();
92: packet_write_wait();
93: debug("done");
94:
95: /*
96: * read and save raw KEXINIT payload in buffer. this is used during
97: * computation of the session_id and the session keys.
98: */
99: debug("wait KEXINIT");
100: packet_read_expect(&plen, SSH2_MSG_KEXINIT);
101: ptr = packet_get_raw(&plen);
102: buffer_append(peer_kexint, ptr, plen);
103:
104: /* parse packet and save algorithm proposal */
105: /* skip cookie */
106: for (i = 0; i < KEX_COOKIE_LEN; i++)
107: packet_get_char();
108: /* extract kex init proposal strings */
109: for (i = 0; i < PROPOSAL_MAX; i++) {
110: peer_proposal[i] = packet_get_string(NULL);
111: debug("got kexinit: %s", peer_proposal[i]);
112: }
113: /* first kex follow / reserved */
114: i = packet_get_char();
115: debug("first kex follow: %d ", i);
116: i = packet_get_int();
117: debug("reserved: %d ", i);
118: packet_done();
119: debug("done");
120: }
121:
1.1 markus 122: /* diffie-hellman-group1-sha1 */
123:
1.3 markus 124: int
125: dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
126: {
127: int i;
128: int n = BN_num_bits(dh_pub);
129: int bits_set = 0;
130:
131: /* we only accept g==2 */
132: if (!BN_is_word(dh->g, 2)) {
133: log("invalid DH base != 2");
134: return 0;
135: }
136: if (dh_pub->neg) {
137: log("invalid public DH value: negativ");
138: return 0;
139: }
140: for (i = 0; i <= n; i++)
141: if (BN_is_bit_set(dh_pub, i))
142: bits_set++;
143: debug("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
144:
145: /* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
146: if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1))
147: return 1;
148: log("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
149: return 0;
150: }
151:
1.1 markus 152: DH *
1.3 markus 153: dh_new_group1()
1.1 markus 154: {
155: static char *group1 =
156: "FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
157: "29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
158: "EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
159: "E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
160: "EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
161: "FFFFFFFF" "FFFFFFFF";
162: DH *dh;
1.3 markus 163: int ret, tries = 0;
1.1 markus 164: dh = DH_new();
165: if(dh == NULL)
166: fatal("DH_new");
1.3 markus 167: ret = BN_hex2bn(&dh->p, group1);
1.1 markus 168: if(ret<0)
169: fatal("BN_hex2bn");
170: dh->g = BN_new();
171: if(dh->g == NULL)
172: fatal("DH_new g");
1.3 markus 173: BN_set_word(dh->g, 2);
174: do {
175: if (DH_generate_key(dh) == 0)
176: fatal("DH_generate_key");
177: if (tries++ > 10)
178: fatal("dh_new_group1: too many bad keys: giving up");
179: } while (!dh_pub_is_valid(dh, dh->pub_key));
1.1 markus 180: return dh;
181: }
182:
183: void
184: dump_digest(unsigned char *digest, int len)
185: {
186: int i;
1.5 markus 187: for (i = 0; i< len; i++){
188: fprintf(stderr, "%02x", digest[i]);
1.1 markus 189: if(i%2!=0)
190: fprintf(stderr, " ");
191: }
1.5 markus 192: fprintf(stderr, "\n");
1.1 markus 193: }
194:
195: unsigned char *
196: kex_hash(
197: char *client_version_string,
198: char *server_version_string,
199: char *ckexinit, int ckexinitlen,
200: char *skexinit, int skexinitlen,
201: char *serverhostkeyblob, int sbloblen,
202: BIGNUM *client_dh_pub,
203: BIGNUM *server_dh_pub,
204: BIGNUM *shared_secret)
205: {
206: Buffer b;
207: static unsigned char digest[EVP_MAX_MD_SIZE];
208: EVP_MD *evp_md = EVP_sha1();
209: EVP_MD_CTX md;
210:
211: buffer_init(&b);
212: buffer_put_string(&b, client_version_string, strlen(client_version_string));
213: buffer_put_string(&b, server_version_string, strlen(server_version_string));
214:
215: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
216: buffer_put_int(&b, ckexinitlen+1);
217: buffer_put_char(&b, SSH2_MSG_KEXINIT);
218: buffer_append(&b, ckexinit, ckexinitlen);
219: buffer_put_int(&b, skexinitlen+1);
220: buffer_put_char(&b, SSH2_MSG_KEXINIT);
221: buffer_append(&b, skexinit, skexinitlen);
222:
223: buffer_put_string(&b, serverhostkeyblob, sbloblen);
224: buffer_put_bignum2(&b, client_dh_pub);
225: buffer_put_bignum2(&b, server_dh_pub);
226: buffer_put_bignum2(&b, shared_secret);
227:
228: #ifdef DEBUG_KEX
229: buffer_dump(&b);
230: #endif
231:
232: EVP_DigestInit(&md, evp_md);
233: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
234: EVP_DigestFinal(&md, digest, NULL);
235:
236: buffer_free(&b);
237:
238: #ifdef DEBUG_KEX
1.5 markus 239: dump_digest(digest, evp_md->md_size);
1.1 markus 240: #endif
241: return digest;
242: }
243:
244: unsigned char *
245: derive_key(int id, int need, char unsigned *hash, BIGNUM *shared_secret)
246: {
247: Buffer b;
248: EVP_MD *evp_md = EVP_sha1();
249: EVP_MD_CTX md;
250: char c = id;
251: int have;
252: int mdsz = evp_md->md_size;
253: unsigned char *digest = xmalloc(((need+mdsz-1)/mdsz)*mdsz);
254:
255: buffer_init(&b);
256: buffer_put_bignum2(&b, shared_secret);
257:
258: EVP_DigestInit(&md, evp_md);
259: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); /* shared_secret K */
260: EVP_DigestUpdate(&md, hash, mdsz); /* transport-06 */
261: EVP_DigestUpdate(&md, &c, 1); /* key id */
262: EVP_DigestUpdate(&md, hash, mdsz); /* session id */
263: EVP_DigestFinal(&md, digest, NULL);
264:
265: /* expand */
266: for (have = mdsz; need > have; have += mdsz) {
267: EVP_DigestInit(&md, evp_md);
268: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
269: EVP_DigestUpdate(&md, hash, mdsz);
270: EVP_DigestUpdate(&md, digest, have);
271: EVP_DigestFinal(&md, digest + have, NULL);
272: }
273: buffer_free(&b);
274: #ifdef DEBUG_KEX
275: fprintf(stderr, "Digest '%c'== ", c);
276: dump_digest(digest, need);
277: #endif
278: return digest;
279: }
280:
281: #define NKEYS 6
282:
283: #define MAX_PROP 20
284: #define SEP ","
285:
286: char *
287: get_match(char *client, char *server)
288: {
289: char *sproposals[MAX_PROP];
1.6.2.2 ! jason 290: char *c, *s, *p, *ret, *cp, *sp;
1.1 markus 291: int i, j, nproposals;
292:
1.6.2.2 ! jason 293: c = cp = xstrdup(client);
! 294: s = sp = xstrdup(server);
1.6.2.1 jason 295:
1.6.2.2 ! jason 296: for ((p = strsep(&sp, SEP)), i=0; p && *p != '\0';
! 297: (p = strsep(&sp, SEP)), i++) {
1.1 markus 298: if (i < MAX_PROP)
299: sproposals[i] = p;
300: else
301: break;
302: }
303: nproposals = i;
304:
1.6.2.2 ! jason 305: for ((p = strsep(&cp, SEP)), i=0; p && *p != '\0';
! 306: (p = strsep(&cp, SEP)), i++) {
1.6.2.1 jason 307: for (j = 0; j < nproposals; j++) {
308: if (strcmp(p, sproposals[j]) == 0) {
309: ret = xstrdup(p);
310: xfree(c);
311: xfree(s);
312: return ret;
313: }
314: }
1.1 markus 315: }
1.6.2.1 jason 316: xfree(c);
317: xfree(s);
1.1 markus 318: return NULL;
319: }
320: void
321: choose_enc(Enc *enc, char *client, char *server)
322: {
323: char *name = get_match(client, server);
324: if (name == NULL)
325: fatal("no matching cipher found: client %s server %s", client, server);
326: enc->type = cipher_number(name);
327:
328: switch (enc->type) {
329: case SSH_CIPHER_3DES_CBC:
330: enc->key_len = 24;
331: enc->iv_len = 8;
332: enc->block_size = 8;
333: break;
334: case SSH_CIPHER_BLOWFISH_CBC:
335: case SSH_CIPHER_CAST128_CBC:
336: enc->key_len = 16;
337: enc->iv_len = 8;
338: enc->block_size = 8;
339: break;
340: case SSH_CIPHER_ARCFOUR:
341: enc->key_len = 16;
342: enc->iv_len = 0;
343: enc->block_size = 8;
344: break;
345: default:
346: fatal("unsupported cipher %s", name);
347: }
348: enc->name = name;
349: enc->enabled = 0;
350: enc->iv = NULL;
351: enc->key = NULL;
352: }
353: void
354: choose_mac(Mac *mac, char *client, char *server)
355: {
356: char *name = get_match(client, server);
357: if (name == NULL)
358: fatal("no matching mac found: client %s server %s", client, server);
359: if (strcmp(name, "hmac-md5") == 0) {
360: mac->md = EVP_md5();
361: } else if (strcmp(name, "hmac-sha1") == 0) {
362: mac->md = EVP_sha1();
363: } else if (strcmp(name, "hmac-ripemd160@openssh.com") == 0) {
364: mac->md = EVP_ripemd160();
365: } else {
366: fatal("unsupported mac %s", name);
367: }
368: mac->name = name;
369: mac->mac_len = mac->md->md_size;
1.6 markus 370: mac->key_len = (datafellows & SSH_BUG_HMAC) ? 16 : mac->mac_len;
1.1 markus 371: mac->key = NULL;
372: mac->enabled = 0;
373: }
374: void
375: choose_comp(Comp *comp, char *client, char *server)
376: {
377: char *name = get_match(client, server);
378: if (name == NULL)
379: fatal("no matching comp found: client %s server %s", client, server);
380: if (strcmp(name, "zlib") == 0) {
381: comp->type = 1;
382: } else if (strcmp(name, "none") == 0) {
383: comp->type = 0;
384: } else {
385: fatal("unsupported comp %s", name);
386: }
387: comp->name = name;
388: }
389: void
390: choose_kex(Kex *k, char *client, char *server)
391: {
392: k->name = get_match(client, server);
393: if (k->name == NULL)
394: fatal("no kex alg");
1.5 markus 395: if (strcmp(k->name, KEX_DH1) != 0)
1.1 markus 396: fatal("bad kex alg %s", k->name);
397: }
398: void
399: choose_hostkeyalg(Kex *k, char *client, char *server)
400: {
401: k->hostkeyalg = get_match(client, server);
402: if (k->hostkeyalg == NULL)
403: fatal("no hostkey alg");
404: if (strcmp(k->hostkeyalg, KEX_DSS) != 0)
405: fatal("bad hostkey alg %s", k->hostkeyalg);
406: }
407:
408: Kex *
409: kex_choose_conf(char *cprop[PROPOSAL_MAX], char *sprop[PROPOSAL_MAX], int server)
410: {
411: int mode;
412: int ctos; /* direction: if true client-to-server */
413: int need;
414: Kex *k;
415:
416: k = xmalloc(sizeof(*k));
417: memset(k, 0, sizeof(*k));
418: k->server = server;
419:
420: for (mode = 0; mode < MODE_MAX; mode++) {
421: int nenc, nmac, ncomp;
422: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
423: nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
424: nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
425: ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
426: choose_enc (&k->enc [mode], cprop[nenc], sprop[nenc]);
427: choose_mac (&k->mac [mode], cprop[nmac], sprop[nmac]);
428: choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
1.2 markus 429: debug("kex: %s %s %s %s",
1.1 markus 430: ctos ? "client->server" : "server->client",
431: k->enc[mode].name,
432: k->mac[mode].name,
433: k->comp[mode].name);
434: }
435: choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
436: choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
437: sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
438: need = 0;
439: for (mode = 0; mode < MODE_MAX; mode++) {
440: if (need < k->enc[mode].key_len)
441: need = k->enc[mode].key_len;
442: if (need < k->enc[mode].iv_len)
443: need = k->enc[mode].iv_len;
444: if (need < k->mac[mode].key_len)
445: need = k->mac[mode].key_len;
446: }
1.6.2.1 jason 447: /* XXX need runden? */
1.1 markus 448: k->we_need = need;
449: return k;
450: }
451:
452: int
453: kex_derive_keys(Kex *k, unsigned char *hash, BIGNUM *shared_secret)
454: {
455: int i;
456: int mode;
457: int ctos;
458: unsigned char *keys[NKEYS];
459:
460: for (i = 0; i < NKEYS; i++)
461: keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);
462:
463: for (mode = 0; mode < MODE_MAX; mode++) {
464: ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
465: k->enc[mode].iv = keys[ctos ? 0 : 1];
466: k->enc[mode].key = keys[ctos ? 2 : 3];
467: k->mac[mode].key = keys[ctos ? 4 : 5];
468: }
469: return 0;
470: }
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