469 lines
12 KiB
C
469 lines
12 KiB
C
/*
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* Copyright (c) 2000 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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* 3. All advertising materials mentioning features or use of this software
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* must display the following acknowledgement:
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* This product includes software developed by Markus Friedl.
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* 4. The name of the author may not be used to endorse or promote products
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* derived from this software without specific prior written permission.
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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("$Id: kex.c,v 1.7 2000/05/25 20:45:20 markus Exp $");
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#include "ssh.h"
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#include "ssh2.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 "packet.h"
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#include "cipher.h"
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#include "compat.h"
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#include <openssl/bn.h>
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#include <openssl/dh.h>
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#include <openssl/crypto.h>
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#include <openssl/bio.h>
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#include <openssl/bn.h>
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#include <openssl/dh.h>
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#include <openssl/pem.h>
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#include "kex.h"
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#define KEX_COOKIE_LEN 16
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Buffer *
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kex_init(char *myproposal[PROPOSAL_MAX])
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{
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int first_kex_packet_follows = 0;
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unsigned char cookie[KEX_COOKIE_LEN];
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u_int32_t rand = 0;
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int i;
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Buffer *ki = xmalloc(sizeof(*ki));
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for (i = 0; i < KEX_COOKIE_LEN; i++) {
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if (i % 4 == 0)
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rand = arc4random();
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cookie[i] = rand & 0xff;
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rand >>= 8;
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}
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buffer_init(ki);
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buffer_append(ki, (char *)cookie, sizeof cookie);
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for (i = 0; i < PROPOSAL_MAX; i++)
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buffer_put_cstring(ki, myproposal[i]);
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buffer_put_char(ki, first_kex_packet_follows);
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buffer_put_int(ki, 0); /* uint32 reserved */
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return ki;
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}
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/* send kexinit, parse and save reply */
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void
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kex_exchange_kexinit(
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Buffer *my_kexinit, Buffer *peer_kexint,
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char *peer_proposal[PROPOSAL_MAX])
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{
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int i;
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char *ptr;
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int plen;
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debug("send KEXINIT");
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packet_start(SSH2_MSG_KEXINIT);
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packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
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packet_send();
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packet_write_wait();
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debug("done");
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/*
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* read and save raw KEXINIT payload in buffer. this is used during
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* computation of the session_id and the session keys.
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*/
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debug("wait KEXINIT");
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packet_read_expect(&plen, SSH2_MSG_KEXINIT);
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ptr = packet_get_raw(&plen);
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buffer_append(peer_kexint, ptr, plen);
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/* parse packet and save algorithm proposal */
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/* skip cookie */
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for (i = 0; i < KEX_COOKIE_LEN; i++)
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packet_get_char();
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/* extract kex init proposal strings */
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for (i = 0; i < PROPOSAL_MAX; i++) {
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peer_proposal[i] = packet_get_string(NULL);
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debug("got kexinit: %s", peer_proposal[i]);
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}
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/* first kex follow / reserved */
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i = packet_get_char();
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debug("first kex follow: %d ", i);
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i = packet_get_int();
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debug("reserved: %d ", i);
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packet_done();
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debug("done");
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}
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/* diffie-hellman-group1-sha1 */
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int
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dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
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{
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int i;
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int n = BN_num_bits(dh_pub);
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int bits_set = 0;
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/* we only accept g==2 */
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if (!BN_is_word(dh->g, 2)) {
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log("invalid DH base != 2");
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return 0;
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}
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if (dh_pub->neg) {
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log("invalid public DH value: negativ");
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return 0;
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}
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for (i = 0; i <= n; i++)
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if (BN_is_bit_set(dh_pub, i))
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bits_set++;
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debug("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
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/* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
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if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1))
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return 1;
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log("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
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return 0;
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}
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DH *
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dh_new_group1()
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{
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static char *group1 =
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"FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
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"29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
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"EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
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"E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
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"EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
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"FFFFFFFF" "FFFFFFFF";
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DH *dh;
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int ret, tries = 0;
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dh = DH_new();
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if(dh == NULL)
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fatal("DH_new");
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ret = BN_hex2bn(&dh->p, group1);
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if(ret<0)
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fatal("BN_hex2bn");
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dh->g = BN_new();
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if(dh->g == NULL)
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fatal("DH_new g");
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BN_set_word(dh->g, 2);
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do {
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if (DH_generate_key(dh) == 0)
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fatal("DH_generate_key");
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if (tries++ > 10)
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fatal("dh_new_group1: too many bad keys: giving up");
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} while (!dh_pub_is_valid(dh, dh->pub_key));
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return dh;
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}
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void
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dump_digest(unsigned char *digest, int len)
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{
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int i;
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for (i = 0; i< len; i++){
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fprintf(stderr, "%02x", digest[i]);
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if(i%2!=0)
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fprintf(stderr, " ");
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}
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fprintf(stderr, "\n");
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}
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unsigned char *
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kex_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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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 unsigned char digest[EVP_MAX_MD_SIZE];
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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_string(&b, client_version_string, strlen(client_version_string));
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buffer_put_string(&b, server_version_string, strlen(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(digest, evp_md->md_size);
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#endif
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return digest;
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}
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unsigned char *
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derive_key(int id, int need, char unsigned *hash, BIGNUM *shared_secret)
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{
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Buffer b;
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EVP_MD *evp_md = EVP_sha1();
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EVP_MD_CTX md;
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char c = id;
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int have;
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int mdsz = evp_md->md_size;
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unsigned char *digest = xmalloc(((need+mdsz-1)/mdsz)*mdsz);
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buffer_init(&b);
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buffer_put_bignum2(&b, shared_secret);
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EVP_DigestInit(&md, evp_md);
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EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); /* shared_secret K */
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EVP_DigestUpdate(&md, hash, mdsz); /* transport-06 */
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EVP_DigestUpdate(&md, &c, 1); /* key id */
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EVP_DigestUpdate(&md, hash, mdsz); /* session id */
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EVP_DigestFinal(&md, digest, NULL);
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/* expand */
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for (have = mdsz; need > have; have += mdsz) {
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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_DigestUpdate(&md, hash, mdsz);
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EVP_DigestUpdate(&md, digest, have);
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EVP_DigestFinal(&md, digest + have, NULL);
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}
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buffer_free(&b);
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#ifdef DEBUG_KEX
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fprintf(stderr, "Digest '%c'== ", c);
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dump_digest(digest, need);
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#endif
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return digest;
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}
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#define NKEYS 6
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#define MAX_PROP 20
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#define SEP ","
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char *
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get_match(char *client, char *server)
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{
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char *sproposals[MAX_PROP];
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char *c, *s, *p, *ret;
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int i, j, nproposals;
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c = xstrdup(client);
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s = xstrdup(server);
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for ((p = strtok(s, SEP)), i=0; p; (p = strtok(NULL, SEP)), i++) {
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if (i < MAX_PROP)
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sproposals[i] = p;
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else
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break;
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}
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nproposals = i;
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for ((p = strtok(c, SEP)), i=0; p; (p = strtok(NULL, SEP)), i++) {
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for (j = 0; j < nproposals; j++) {
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if (strcmp(p, sproposals[j]) == 0) {
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ret = xstrdup(p);
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xfree(c);
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xfree(s);
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return ret;
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}
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}
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}
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xfree(c);
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xfree(s);
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return NULL;
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}
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void
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choose_enc(Enc *enc, char *client, char *server)
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{
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char *name = get_match(client, server);
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if (name == NULL)
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fatal("no matching cipher found: client %s server %s", client, server);
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enc->type = cipher_number(name);
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switch (enc->type) {
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case SSH_CIPHER_3DES_CBC:
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enc->key_len = 24;
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enc->iv_len = 8;
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enc->block_size = 8;
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break;
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case SSH_CIPHER_BLOWFISH_CBC:
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case SSH_CIPHER_CAST128_CBC:
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enc->key_len = 16;
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enc->iv_len = 8;
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enc->block_size = 8;
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break;
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case SSH_CIPHER_ARCFOUR:
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enc->key_len = 16;
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enc->iv_len = 0;
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enc->block_size = 8;
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break;
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default:
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fatal("unsupported cipher %s", name);
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}
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enc->name = name;
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enc->enabled = 0;
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enc->iv = NULL;
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enc->key = NULL;
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}
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void
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choose_mac(Mac *mac, char *client, char *server)
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{
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char *name = get_match(client, server);
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if (name == NULL)
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fatal("no matching mac found: client %s server %s", client, server);
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if (strcmp(name, "hmac-md5") == 0) {
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mac->md = EVP_md5();
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} else if (strcmp(name, "hmac-sha1") == 0) {
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mac->md = EVP_sha1();
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} else if (strcmp(name, "hmac-ripemd160@openssh.com") == 0) {
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mac->md = EVP_ripemd160();
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} else {
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fatal("unsupported mac %s", name);
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}
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mac->name = name;
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mac->mac_len = mac->md->md_size;
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mac->key_len = (datafellows & SSH_BUG_HMAC) ? 16 : mac->mac_len;
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mac->key = NULL;
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mac->enabled = 0;
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}
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void
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choose_comp(Comp *comp, char *client, char *server)
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{
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char *name = get_match(client, server);
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if (name == NULL)
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fatal("no matching comp found: client %s server %s", client, server);
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if (strcmp(name, "zlib") == 0) {
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comp->type = 1;
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} else if (strcmp(name, "none") == 0) {
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comp->type = 0;
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} else {
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fatal("unsupported comp %s", name);
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}
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comp->name = name;
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}
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void
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choose_kex(Kex *k, char *client, char *server)
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{
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k->name = get_match(client, server);
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if (k->name == NULL)
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fatal("no kex alg");
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if (strcmp(k->name, KEX_DH1) != 0)
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fatal("bad kex alg %s", k->name);
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}
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void
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choose_hostkeyalg(Kex *k, char *client, char *server)
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{
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k->hostkeyalg = get_match(client, server);
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if (k->hostkeyalg == NULL)
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fatal("no hostkey alg");
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if (strcmp(k->hostkeyalg, KEX_DSS) != 0)
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fatal("bad hostkey alg %s", k->hostkeyalg);
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}
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Kex *
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kex_choose_conf(char *cprop[PROPOSAL_MAX], char *sprop[PROPOSAL_MAX], int server)
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{
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int mode;
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int ctos; /* direction: if true client-to-server */
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int need;
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Kex *k;
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k = xmalloc(sizeof(*k));
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memset(k, 0, sizeof(*k));
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k->server = server;
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for (mode = 0; mode < MODE_MAX; mode++) {
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int nenc, nmac, ncomp;
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ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
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nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
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nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
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ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
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choose_enc (&k->enc [mode], cprop[nenc], sprop[nenc]);
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choose_mac (&k->mac [mode], cprop[nmac], sprop[nmac]);
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choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
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debug("kex: %s %s %s %s",
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ctos ? "client->server" : "server->client",
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k->enc[mode].name,
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k->mac[mode].name,
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k->comp[mode].name);
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}
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choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
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choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
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sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
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need = 0;
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for (mode = 0; mode < MODE_MAX; mode++) {
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if (need < k->enc[mode].key_len)
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need = k->enc[mode].key_len;
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if (need < k->enc[mode].iv_len)
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need = k->enc[mode].iv_len;
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if (need < k->mac[mode].key_len)
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need = k->mac[mode].key_len;
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}
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/* XXX need runden? */
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k->we_need = need;
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return k;
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}
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int
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kex_derive_keys(Kex *k, unsigned char *hash, BIGNUM *shared_secret)
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{
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int i;
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int mode;
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int ctos;
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unsigned char *keys[NKEYS];
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for (i = 0; i < NKEYS; i++)
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keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);
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for (mode = 0; mode < MODE_MAX; mode++) {
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ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
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k->enc[mode].iv = keys[ctos ? 0 : 1];
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k->enc[mode].key = keys[ctos ? 2 : 3];
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k->mac[mode].key = keys[ctos ? 4 : 5];
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}
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return 0;
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}
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