Annotation of src/usr.bin/ssh/kexgex.c, Revision 1.1
1.1 ! markus 1: /*
! 2: * Copyright (c) 2000 Niels Provos. All rights reserved.
! 3: * Copyright (c) 2001 Markus Friedl. All rights reserved.
! 4: *
! 5: * Redistribution and use in source and binary forms, with or without
! 6: * modification, are permitted provided that the following conditions
! 7: * are met:
! 8: * 1. Redistributions of source code must retain the above copyright
! 9: * notice, this list of conditions and the following disclaimer.
! 10: * 2. Redistributions in binary form must reproduce the above copyright
! 11: * notice, this list of conditions and the following disclaimer in the
! 12: * documentation and/or other materials provided with the distribution.
! 13: *
! 14: * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
! 15: * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
! 16: * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
! 17: * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
! 18: * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
! 19: * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
! 20: * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
! 21: * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
! 22: * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
! 23: * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
! 24: */
! 25:
! 26: #include "includes.h"
! 27: RCSID("$OpenBSD: kex.c,v 1.24 2001/03/28 21:59:40 provos Exp $");
! 28:
! 29: #include <openssl/bn.h>
! 30:
! 31: #include "xmalloc.h"
! 32: #include "buffer.h"
! 33: #include "bufaux.h"
! 34: #include "key.h"
! 35: #include "kex.h"
! 36: #include "log.h"
! 37: #include "dispatch.h"
! 38: #include "packet.h"
! 39: #include "dh.h"
! 40: #include "ssh2.h"
! 41: #include "compat.h"
! 42:
! 43: extern u_char *session_id2;
! 44: extern int session_id2_len;
! 45:
! 46: typedef struct State State;
! 47: struct State {
! 48: DH *dh;
! 49: int min, nbits, max;
! 50: };
! 51:
! 52: dispatch_fn kexgex_input_request; /* C -> S */
! 53: dispatch_fn kexgex_input_group; /* S -> C */
! 54: dispatch_fn kexgex_input_init; /* C -> S */
! 55: dispatch_fn kexgex_input_reply; /* S -> C */
! 56:
! 57: u_char *
! 58: kexgex_hash(
! 59: char *client_version_string,
! 60: char *server_version_string,
! 61: char *ckexinit, int ckexinitlen,
! 62: char *skexinit, int skexinitlen,
! 63: char *serverhostkeyblob, int sbloblen,
! 64: int min, int wantbits, int max, BIGNUM *prime, BIGNUM *gen,
! 65: BIGNUM *client_dh_pub,
! 66: BIGNUM *server_dh_pub,
! 67: BIGNUM *shared_secret)
! 68: {
! 69: Buffer b;
! 70: static u_char digest[EVP_MAX_MD_SIZE];
! 71: EVP_MD *evp_md = EVP_sha1();
! 72: EVP_MD_CTX md;
! 73:
! 74: buffer_init(&b);
! 75: buffer_put_string(&b, client_version_string, strlen(client_version_string));
! 76: buffer_put_string(&b, server_version_string, strlen(server_version_string));
! 77:
! 78: /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
! 79: buffer_put_int(&b, ckexinitlen+1);
! 80: buffer_put_char(&b, SSH2_MSG_KEXINIT);
! 81: buffer_append(&b, ckexinit, ckexinitlen);
! 82: buffer_put_int(&b, skexinitlen+1);
! 83: buffer_put_char(&b, SSH2_MSG_KEXINIT);
! 84: buffer_append(&b, skexinit, skexinitlen);
! 85:
! 86: buffer_put_string(&b, serverhostkeyblob, sbloblen);
! 87: if (min == -1 || max == -1)
! 88: buffer_put_int(&b, wantbits);
! 89: else {
! 90: buffer_put_int(&b, min);
! 91: buffer_put_int(&b, wantbits);
! 92: buffer_put_int(&b, max);
! 93: }
! 94: buffer_put_bignum2(&b, prime);
! 95: buffer_put_bignum2(&b, gen);
! 96: buffer_put_bignum2(&b, client_dh_pub);
! 97: buffer_put_bignum2(&b, server_dh_pub);
! 98: buffer_put_bignum2(&b, shared_secret);
! 99:
! 100: #ifdef DEBUG_KEXDH
! 101: buffer_dump(&b);
! 102: #endif
! 103: EVP_DigestInit(&md, evp_md);
! 104: EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
! 105: EVP_DigestFinal(&md, digest, NULL);
! 106:
! 107: buffer_free(&b);
! 108:
! 109: #ifdef DEBUG_KEXDH
! 110: dump_digest("hash", digest, evp_md->md_size);
! 111: #endif
! 112: return digest;
! 113: }
! 114:
! 115: /* client */
! 116:
! 117: void
! 118: kexgex_client(Kex *kex)
! 119: {
! 120: State *state;
! 121:
! 122: dispatch_set(SSH2_MSG_KEX_DH_GEX_GROUP, &kexgex_input_group);
! 123:
! 124: state = xmalloc(sizeof(*state));
! 125: state->nbits = dh_estimate(kex->we_need * 8);
! 126: kex->state = state;
! 127:
! 128: if (datafellows & SSH_OLD_DHGEX) {
! 129: debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD sent");
! 130:
! 131: /* Old GEX request */
! 132: packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD);
! 133: packet_put_int(state->nbits);
! 134: state->min = DH_GRP_MIN;
! 135: state->max = DH_GRP_MAX;
! 136: } else {
! 137: debug("SSH2_MSG_KEX_DH_GEX_REQUEST sent");
! 138:
! 139: /* New GEX request */
! 140: state->min = DH_GRP_MIN;
! 141: state->max = DH_GRP_MAX;
! 142: packet_start(SSH2_MSG_KEX_DH_GEX_REQUEST);
! 143: packet_put_int(state->min);
! 144: packet_put_int(state->nbits);
! 145: packet_put_int(state->max);
! 146: }
! 147: #ifdef DEBUG_KEXDH
! 148: fprintf(stderr, "\nmin = %d, nbits = %d, max = %d\n",
! 149: state->min, state->nbits, state->max);
! 150: #endif
! 151: packet_send();
! 152: }
! 153:
! 154: void
! 155: kexgex_input_group(int type, int plen, void *ctxt)
! 156: {
! 157: DH *dh;
! 158: int dlen;
! 159: BIGNUM *p = 0, *g = 0;
! 160: Kex *kex = (Kex*) ctxt;
! 161: State *state = (State *) kex->state;
! 162:
! 163: debug("SSH2_MSG_KEX_DH_GEX_GROUP receivied");
! 164: dispatch_set(SSH2_MSG_KEX_DH_GEX_GROUP, &kex_protocol_error);
! 165: dispatch_set(SSH2_MSG_KEX_DH_GEX_REPLY, &kexgex_input_reply);
! 166:
! 167: if ((p = BN_new()) == NULL)
! 168: fatal("BN_new");
! 169: packet_get_bignum2(p, &dlen);
! 170: if ((g = BN_new()) == NULL)
! 171: fatal("BN_new");
! 172: packet_get_bignum2(g, &dlen);
! 173:
! 174: if (BN_num_bits(p) < state->min || BN_num_bits(p) > state->max)
! 175: fatal("DH_GEX group out of range: %d !< %d !< %d",
! 176: state->min, BN_num_bits(p), state->max);
! 177:
! 178: dh = dh_new_group(g, p);
! 179: dh_gen_key(dh, kex->we_need * 8);
! 180:
! 181: state->dh = dh;
! 182:
! 183: #ifdef DEBUG_KEXDH
! 184: DHparams_print_fp(stderr, dh);
! 185: fprintf(stderr, "pub= ");
! 186: BN_print_fp(stderr, dh->pub_key);
! 187: fprintf(stderr, "\n");
! 188: #endif
! 189:
! 190: debug("SSH2_MSG_KEX_DH_GEX_INIT sent");
! 191: /* generate and send 'e', client DH public key */
! 192: packet_start(SSH2_MSG_KEX_DH_GEX_INIT);
! 193: packet_put_bignum2(dh->pub_key);
! 194: packet_send();
! 195: }
! 196:
! 197: void
! 198: kexgex_input_reply(int type, int plen, void *ctxt)
! 199: {
! 200: BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
! 201: Key *server_host_key;
! 202: Kex *kex = (Kex*) ctxt;
! 203: State *state = (State *) kex->state;
! 204: DH *dh = state->dh;
! 205: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
! 206: u_int klen, kout, slen, sbloblen;
! 207: int dlen, min, max;
! 208:
! 209: debug("SSH2_MSG_KEX_DH_GEX_REPLY received");
! 210: dispatch_set(SSH2_MSG_KEX_DH_GEX_REPLY, &kex_protocol_error);
! 211:
! 212: /* key, cert */
! 213: server_host_key_blob = packet_get_string(&sbloblen);
! 214: server_host_key = key_from_blob(server_host_key_blob, sbloblen);
! 215: if (server_host_key == NULL)
! 216: fatal("cannot decode server_host_key_blob");
! 217:
! 218: if (kex->check_host_key == NULL)
! 219: fatal("cannot check server_host_key");
! 220: kex->check_host_key(server_host_key);
! 221:
! 222: /* DH paramter f, server public DH key */
! 223: dh_server_pub = BN_new();
! 224: if (dh_server_pub == NULL)
! 225: fatal("dh_server_pub == NULL");
! 226: packet_get_bignum2(dh_server_pub, &dlen);
! 227:
! 228: #ifdef DEBUG_KEXDH
! 229: fprintf(stderr, "dh_server_pub= ");
! 230: BN_print_fp(stderr, dh_server_pub);
! 231: fprintf(stderr, "\n");
! 232: debug("bits %d", BN_num_bits(dh_server_pub));
! 233: #endif
! 234:
! 235: /* signed H */
! 236: signature = packet_get_string(&slen);
! 237: packet_done();
! 238:
! 239: if (!dh_pub_is_valid(dh, dh_server_pub))
! 240: packet_disconnect("bad server public DH value");
! 241:
! 242: klen = DH_size(dh);
! 243: kbuf = xmalloc(klen);
! 244: kout = DH_compute_key(kbuf, dh_server_pub, dh);
! 245: #ifdef DEBUG_KEXDH
! 246: dump_digest("shared secret", kbuf, kout);
! 247: #endif
! 248: shared_secret = BN_new();
! 249: BN_bin2bn(kbuf, kout, shared_secret);
! 250: memset(kbuf, 0, klen);
! 251: xfree(kbuf);
! 252:
! 253: if (datafellows & SSH_OLD_DHGEX) {
! 254: min = max = -1;
! 255: } else {
! 256: min = state->min;
! 257: max = state->max;
! 258: }
! 259:
! 260: /* calc and verify H */
! 261: hash = kexgex_hash(
! 262: kex->client_version_string,
! 263: kex->server_version_string,
! 264: buffer_ptr(&kex->my), buffer_len(&kex->my),
! 265: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
! 266: server_host_key_blob, sbloblen,
! 267: min, state->nbits, max,
! 268: dh->p, dh->g,
! 269: dh->pub_key,
! 270: dh_server_pub,
! 271: shared_secret
! 272: );
! 273: xfree(server_host_key_blob);
! 274: BN_free(dh_server_pub);
! 275:
! 276: if (key_verify(server_host_key, (u_char *)signature, slen, hash, 20) != 1)
! 277: fatal("key_verify failed for server_host_key");
! 278: key_free(server_host_key);
! 279: xfree(signature);
! 280:
! 281: kex_derive_keys(kex, hash, shared_secret);
! 282: BN_clear_free(shared_secret);
! 283: packet_set_kex(kex);
! 284:
! 285: /* save session id */
! 286: session_id2_len = 20;
! 287: session_id2 = xmalloc(session_id2_len);
! 288: memcpy(session_id2, hash, session_id2_len);
! 289:
! 290: kex_send_newkeys();
! 291:
! 292: /* have keys, free DH */
! 293: DH_free(dh);
! 294: xfree(state);
! 295: kex->state = NULL;
! 296: }
! 297:
! 298: /* server */
! 299:
! 300: void
! 301: kexgex_server(Kex *kex)
! 302: {
! 303: State *state;
! 304:
! 305: state = xmalloc(sizeof(*state));
! 306: kex->state = state;
! 307:
! 308: dispatch_set(SSH2_MSG_KEX_DH_GEX_REQUEST, &kexgex_input_request);
! 309: dispatch_set(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD, &kexgex_input_request);
! 310: }
! 311:
! 312: void
! 313: kexgex_input_request(int type, int plen, void *ctxt)
! 314: {
! 315: Kex *kex = (Kex*) ctxt;
! 316: State *state = (State *) kex->state;
! 317: int min = -1, max = -1;
! 318:
! 319: dispatch_set(SSH2_MSG_KEX_DH_GEX_REQUEST, &kex_protocol_error);
! 320: dispatch_set(SSH2_MSG_KEX_DH_GEX_REQUEST_OLD, &kex_protocol_error);
! 321: dispatch_set(SSH2_MSG_KEX_DH_GEX_INIT, &kexgex_input_init);
! 322:
! 323: switch(type){
! 324: case SSH2_MSG_KEX_DH_GEX_REQUEST:
! 325: debug("SSH2_MSG_KEX_DH_GEX_REQUEST received");
! 326: min = packet_get_int();
! 327: state->nbits = packet_get_int();
! 328: max = packet_get_int();
! 329: min = MAX(DH_GRP_MIN, min);
! 330: max = MIN(DH_GRP_MAX, max);
! 331: state->min = min;
! 332: state->max = max;
! 333: break;
! 334: case SSH2_MSG_KEX_DH_GEX_REQUEST_OLD:
! 335: debug("SSH2_MSG_KEX_DH_GEX_REQUEST_OLD received");
! 336: state->nbits = packet_get_int();
! 337: min = DH_GRP_MIN;
! 338: max = DH_GRP_MAX;
! 339: /* unused for old GEX */
! 340: state->min = -1;
! 341: state->max = -1;
! 342: break;
! 343: }
! 344: packet_done();
! 345:
! 346: if (max < min || state->nbits < min || max < state->nbits)
! 347: fatal("DH_GEX_REQUEST, bad parameters: %d !< %d !< %d",
! 348: min, state->nbits, max);
! 349:
! 350: state->dh = choose_dh(min, state->nbits, max);
! 351: if (state->dh == NULL)
! 352: packet_disconnect("Protocol error: no matching DH grp found");
! 353:
! 354: debug("SSH2_MSG_KEX_DH_GEX_GROUP sent");
! 355: packet_start(SSH2_MSG_KEX_DH_GEX_GROUP);
! 356: packet_put_bignum2(state->dh->p);
! 357: packet_put_bignum2(state->dh->g);
! 358: packet_send();
! 359:
! 360: /* flush */
! 361: packet_write_wait();
! 362:
! 363: /* Compute our exchange value in parallel with the client */
! 364: dh_gen_key(state->dh, kex->we_need * 8);
! 365: }
! 366:
! 367: void
! 368: kexgex_input_init(int type, int plen, void *ctxt)
! 369: {
! 370: BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
! 371: Key *server_host_key;
! 372: Kex *kex = (Kex*) ctxt;
! 373: State *state = (State *) kex->state;
! 374: DH *dh = state->dh;
! 375: u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
! 376: u_int sbloblen, klen, kout;
! 377: int dlen, slen;
! 378:
! 379: if (kex->load_host_key == NULL)
! 380: fatal("Cannot load hostkey");
! 381: server_host_key = kex->load_host_key(kex->hostkey_type);
! 382: if (server_host_key == NULL)
! 383: fatal("Unsupported hostkey type %d", kex->hostkey_type);
! 384:
! 385: dispatch_set(SSH2_MSG_KEX_DH_GEX_INIT, &kex_protocol_error);
! 386: debug("SSH2_MSG_KEX_DH_GEX_INIT received");
! 387:
! 388: /* key, cert */
! 389: dh_client_pub = BN_new();
! 390: if (dh_client_pub == NULL)
! 391: fatal("dh_client_pub == NULL");
! 392: packet_get_bignum2(dh_client_pub, &dlen);
! 393:
! 394: #ifdef DEBUG_KEXDH
! 395: fprintf(stderr, "dh_client_pub= ");
! 396: BN_print_fp(stderr, dh_client_pub);
! 397: fprintf(stderr, "\n");
! 398: debug("bits %d", BN_num_bits(dh_client_pub));
! 399: #endif
! 400:
! 401: #ifdef DEBUG_KEXDH
! 402: DHparams_print_fp(stderr, dh);
! 403: fprintf(stderr, "pub= ");
! 404: BN_print_fp(stderr, dh->pub_key);
! 405: fprintf(stderr, "\n");
! 406: #endif
! 407: if (!dh_pub_is_valid(dh, dh_client_pub))
! 408: packet_disconnect("bad client public DH value");
! 409:
! 410: klen = DH_size(dh);
! 411: kbuf = xmalloc(klen);
! 412: kout = DH_compute_key(kbuf, dh_client_pub, dh);
! 413: #ifdef DEBUG_KEXDH
! 414: dump_digest("shared secret", kbuf, kout);
! 415: #endif
! 416: shared_secret = BN_new();
! 417: BN_bin2bn(kbuf, kout, shared_secret);
! 418: memset(kbuf, 0, klen);
! 419: xfree(kbuf);
! 420:
! 421: key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
! 422:
! 423: /* calc H */ /* XXX depends on 'kex' */
! 424: hash = kexgex_hash(
! 425: kex->client_version_string,
! 426: kex->server_version_string,
! 427: buffer_ptr(&kex->peer), buffer_len(&kex->peer),
! 428: buffer_ptr(&kex->my), buffer_len(&kex->my),
! 429: (char *)server_host_key_blob, sbloblen,
! 430: state->min, state->nbits, state->max,
! 431: dh->p, dh->g,
! 432: dh_client_pub,
! 433: dh->pub_key,
! 434: shared_secret
! 435: );
! 436: BN_free(dh_client_pub);
! 437:
! 438: /* save session id := H */
! 439: /* XXX hashlen depends on KEX */
! 440: session_id2_len = 20;
! 441: session_id2 = xmalloc(session_id2_len);
! 442: memcpy(session_id2, hash, session_id2_len);
! 443:
! 444: /* sign H */
! 445: /* XXX hashlen depends on KEX */
! 446: key_sign(server_host_key, &signature, &slen, hash, 20);
! 447:
! 448: /* destroy_sensitive_data(); */
! 449:
! 450: /* send server hostkey, DH pubkey 'f' and singed H */
! 451: debug("SSH2_MSG_KEX_DH_GEX_REPLY sent");
! 452: packet_start(SSH2_MSG_KEX_DH_GEX_REPLY);
! 453: packet_put_string((char *)server_host_key_blob, sbloblen);
! 454: packet_put_bignum2(dh->pub_key); /* f */
! 455: packet_put_string((char *)signature, slen);
! 456: packet_send();
! 457: xfree(signature);
! 458: xfree(server_host_key_blob);
! 459: /* packet_write_wait(); */
! 460:
! 461: kex_derive_keys(kex, hash, shared_secret);
! 462: BN_clear_free(shared_secret);
! 463: packet_set_kex(kex);
! 464:
! 465: kex_send_newkeys();
! 466:
! 467: /* have keys, free DH */
! 468: DH_free(dh);
! 469: xfree(state);
! 470: kex->state = NULL;
! 471: }
! 472:
! 473: void
! 474: kexgex(Kex *kex)
! 475: {
! 476: if (kex->server)
! 477: kexgex_server(kex);
! 478: else
! 479: kexgex_client(kex);
! 480: }
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