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307 lines
8.4 KiB
C
307 lines
8.4 KiB
C
/*
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* Copyright (c) 2001 Markus Friedl. All rights reserved.
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in the
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* documentation and/or other materials provided with the distribution.
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*
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* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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*/
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#include "includes.h"
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RCSID("$OpenBSD: kexdh.c,v 1.17 2002/02/28 15:46:33 markus Exp $");
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#include <openssl/crypto.h>
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#include <openssl/bn.h>
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#include "xmalloc.h"
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#include "buffer.h"
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#include "bufaux.h"
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#include "key.h"
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#include "kex.h"
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#include "log.h"
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#include "packet.h"
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#include "dh.h"
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#include "ssh2.h"
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static u_char *
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kex_dh_hash(
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char *client_version_string,
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char *server_version_string,
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char *ckexinit, int ckexinitlen,
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char *skexinit, int skexinitlen,
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u_char *serverhostkeyblob, int sbloblen,
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BIGNUM *client_dh_pub,
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BIGNUM *server_dh_pub,
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BIGNUM *shared_secret)
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{
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Buffer b;
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static u_char digest[EVP_MAX_MD_SIZE];
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const EVP_MD *evp_md = EVP_sha1();
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EVP_MD_CTX md;
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buffer_init(&b);
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buffer_put_cstring(&b, client_version_string);
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buffer_put_cstring(&b, server_version_string);
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/* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
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buffer_put_int(&b, ckexinitlen+1);
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buffer_put_char(&b, SSH2_MSG_KEXINIT);
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buffer_append(&b, ckexinit, ckexinitlen);
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buffer_put_int(&b, skexinitlen+1);
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buffer_put_char(&b, SSH2_MSG_KEXINIT);
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buffer_append(&b, skexinit, skexinitlen);
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buffer_put_string(&b, serverhostkeyblob, sbloblen);
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buffer_put_bignum2(&b, client_dh_pub);
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buffer_put_bignum2(&b, server_dh_pub);
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buffer_put_bignum2(&b, shared_secret);
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#ifdef DEBUG_KEX
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buffer_dump(&b);
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#endif
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EVP_DigestInit(&md, evp_md);
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EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
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EVP_DigestFinal(&md, digest, NULL);
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buffer_free(&b);
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#ifdef DEBUG_KEX
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dump_digest("hash", digest, EVP_MD_size(evp_md));
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#endif
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return digest;
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}
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/* client */
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static void
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kexdh_client(Kex *kex)
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{
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BIGNUM *dh_server_pub = NULL, *shared_secret = NULL;
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DH *dh;
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Key *server_host_key;
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u_char *server_host_key_blob = NULL, *signature = NULL;
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u_char *kbuf, *hash;
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u_int klen, kout, slen, sbloblen;
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/* generate and send 'e', client DH public key */
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dh = dh_new_group1();
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dh_gen_key(dh, kex->we_need * 8);
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packet_start(SSH2_MSG_KEXDH_INIT);
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packet_put_bignum2(dh->pub_key);
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packet_send();
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debug("sending SSH2_MSG_KEXDH_INIT");
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#ifdef DEBUG_KEXDH
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DHparams_print_fp(stderr, dh);
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fprintf(stderr, "pub= ");
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BN_print_fp(stderr, dh->pub_key);
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fprintf(stderr, "\n");
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#endif
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debug("expecting SSH2_MSG_KEXDH_REPLY");
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packet_read_expect(SSH2_MSG_KEXDH_REPLY);
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/* key, cert */
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server_host_key_blob = packet_get_string(&sbloblen);
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server_host_key = key_from_blob(server_host_key_blob, sbloblen);
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if (server_host_key == NULL)
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fatal("cannot decode server_host_key_blob");
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if (server_host_key->type != kex->hostkey_type)
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fatal("type mismatch for decoded server_host_key_blob");
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if (kex->verify_host_key == NULL)
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fatal("cannot verify server_host_key");
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if (kex->verify_host_key(server_host_key) == -1)
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fatal("server_host_key verification failed");
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/* DH paramter f, server public DH key */
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if ((dh_server_pub = BN_new()) == NULL)
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fatal("dh_server_pub == NULL");
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packet_get_bignum2(dh_server_pub);
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#ifdef DEBUG_KEXDH
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fprintf(stderr, "dh_server_pub= ");
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BN_print_fp(stderr, dh_server_pub);
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fprintf(stderr, "\n");
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debug("bits %d", BN_num_bits(dh_server_pub));
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#endif
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/* signed H */
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signature = packet_get_string(&slen);
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packet_check_eom();
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if (!dh_pub_is_valid(dh, dh_server_pub))
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packet_disconnect("bad server public DH value");
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klen = DH_size(dh);
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kbuf = xmalloc(klen);
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kout = DH_compute_key(kbuf, dh_server_pub, dh);
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#ifdef DEBUG_KEXDH
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dump_digest("shared secret", kbuf, kout);
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#endif
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if ((shared_secret = BN_new()) == NULL)
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fatal("kexdh_client: BN_new failed");
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BN_bin2bn(kbuf, kout, shared_secret);
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memset(kbuf, 0, klen);
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xfree(kbuf);
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/* calc and verify H */
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hash = kex_dh_hash(
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kex->client_version_string,
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kex->server_version_string,
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buffer_ptr(&kex->my), buffer_len(&kex->my),
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buffer_ptr(&kex->peer), buffer_len(&kex->peer),
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server_host_key_blob, sbloblen,
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dh->pub_key,
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dh_server_pub,
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shared_secret
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);
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xfree(server_host_key_blob);
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BN_clear_free(dh_server_pub);
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DH_free(dh);
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if (key_verify(server_host_key, signature, slen, hash, 20) != 1)
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fatal("key_verify failed for server_host_key");
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key_free(server_host_key);
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xfree(signature);
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/* save session id */
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if (kex->session_id == NULL) {
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kex->session_id_len = 20;
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kex->session_id = xmalloc(kex->session_id_len);
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memcpy(kex->session_id, hash, kex->session_id_len);
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}
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kex_derive_keys(kex, hash, shared_secret);
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BN_clear_free(shared_secret);
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kex_finish(kex);
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}
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/* server */
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static void
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kexdh_server(Kex *kex)
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{
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BIGNUM *shared_secret = NULL, *dh_client_pub = NULL;
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DH *dh;
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Key *server_host_key;
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u_char *kbuf, *hash, *signature = NULL, *server_host_key_blob = NULL;
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u_int sbloblen, klen, kout;
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u_int slen;
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/* generate server DH public key */
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dh = dh_new_group1();
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dh_gen_key(dh, kex->we_need * 8);
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debug("expecting SSH2_MSG_KEXDH_INIT");
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packet_read_expect(SSH2_MSG_KEXDH_INIT);
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if (kex->load_host_key == NULL)
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fatal("Cannot load hostkey");
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server_host_key = kex->load_host_key(kex->hostkey_type);
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if (server_host_key == NULL)
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fatal("Unsupported hostkey type %d", kex->hostkey_type);
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/* key, cert */
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if ((dh_client_pub = BN_new()) == NULL)
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fatal("dh_client_pub == NULL");
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packet_get_bignum2(dh_client_pub);
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packet_check_eom();
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#ifdef DEBUG_KEXDH
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fprintf(stderr, "dh_client_pub= ");
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BN_print_fp(stderr, dh_client_pub);
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fprintf(stderr, "\n");
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debug("bits %d", BN_num_bits(dh_client_pub));
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#endif
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#ifdef DEBUG_KEXDH
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DHparams_print_fp(stderr, dh);
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fprintf(stderr, "pub= ");
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BN_print_fp(stderr, dh->pub_key);
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fprintf(stderr, "\n");
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#endif
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if (!dh_pub_is_valid(dh, dh_client_pub))
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packet_disconnect("bad client public DH value");
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klen = DH_size(dh);
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kbuf = xmalloc(klen);
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kout = DH_compute_key(kbuf, dh_client_pub, dh);
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#ifdef DEBUG_KEXDH
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dump_digest("shared secret", kbuf, kout);
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#endif
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if ((shared_secret = BN_new()) == NULL)
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fatal("kexdh_server: BN_new failed");
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BN_bin2bn(kbuf, kout, shared_secret);
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memset(kbuf, 0, klen);
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xfree(kbuf);
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key_to_blob(server_host_key, &server_host_key_blob, &sbloblen);
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/* calc H */
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hash = kex_dh_hash(
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kex->client_version_string,
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kex->server_version_string,
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buffer_ptr(&kex->peer), buffer_len(&kex->peer),
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buffer_ptr(&kex->my), buffer_len(&kex->my),
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server_host_key_blob, sbloblen,
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dh_client_pub,
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dh->pub_key,
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shared_secret
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);
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BN_clear_free(dh_client_pub);
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/* save session id := H */
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/* XXX hashlen depends on KEX */
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if (kex->session_id == NULL) {
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kex->session_id_len = 20;
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kex->session_id = xmalloc(kex->session_id_len);
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memcpy(kex->session_id, hash, kex->session_id_len);
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}
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/* sign H */
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/* XXX hashlen depends on KEX */
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key_sign(server_host_key, &signature, &slen, hash, 20);
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/* destroy_sensitive_data(); */
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/* send server hostkey, DH pubkey 'f' and singed H */
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packet_start(SSH2_MSG_KEXDH_REPLY);
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packet_put_string(server_host_key_blob, sbloblen);
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packet_put_bignum2(dh->pub_key); /* f */
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packet_put_string(signature, slen);
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packet_send();
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xfree(signature);
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xfree(server_host_key_blob);
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/* have keys, free DH */
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DH_free(dh);
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kex_derive_keys(kex, hash, shared_secret);
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BN_clear_free(shared_secret);
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kex_finish(kex);
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}
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void
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kexdh(Kex *kex)
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{
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if (kex->server)
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kexdh_server(kex);
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else
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kexdh_client(kex);
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}
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