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openssh-portable
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openssh-portable/kex.c

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/*
* Copyright (c) 2000 Markus Friedl. All rights reserved.
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
*
* THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
* IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
* OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
* IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
* NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
* DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
* THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
* (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
* THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
*/
#include "includes.h"
RCSID("$OpenBSD: kex.c,v 1.10 2000/09/07 20:27:51 deraadt Exp $");
#include "ssh.h"
#include "ssh2.h"
#include "xmalloc.h"
#include "buffer.h"
#include "bufaux.h"
#include "packet.h"
#include "cipher.h"
#include "compat.h"
#include <openssl/bn.h>
#include <openssl/dh.h>
#include <openssl/crypto.h>
#include <openssl/bio.h>
#include <openssl/bn.h>
#include <openssl/dh.h>
#include <openssl/pem.h>
#include "kex.h"
#define KEX_COOKIE_LEN 16
Buffer *
kex_init(char *myproposal[PROPOSAL_MAX])
{
int first_kex_packet_follows = 0;
unsigned char cookie[KEX_COOKIE_LEN];
u_int32_t rand = 0;
int i;
Buffer *ki = xmalloc(sizeof(*ki));
for (i = 0; i < KEX_COOKIE_LEN; i++) {
if (i % 4 == 0)
rand = arc4random();
cookie[i] = rand & 0xff;
rand >>= 8;
}
buffer_init(ki);
buffer_append(ki, (char *)cookie, sizeof cookie);
for (i = 0; i < PROPOSAL_MAX; i++)
buffer_put_cstring(ki, myproposal[i]);
buffer_put_char(ki, first_kex_packet_follows);
buffer_put_int(ki, 0); /* uint32 reserved */
return ki;
}
/* send kexinit, parse and save reply */
void
kex_exchange_kexinit(
Buffer *my_kexinit, Buffer *peer_kexint,
char *peer_proposal[PROPOSAL_MAX])
{
int i;
char *ptr;
int plen;
debug("send KEXINIT");
packet_start(SSH2_MSG_KEXINIT);
packet_put_raw(buffer_ptr(my_kexinit), buffer_len(my_kexinit));
packet_send();
packet_write_wait();
debug("done");
/*
* read and save raw KEXINIT payload in buffer. this is used during
* computation of the session_id and the session keys.
*/
debug("wait KEXINIT");
packet_read_expect(&plen, SSH2_MSG_KEXINIT);
ptr = packet_get_raw(&plen);
buffer_append(peer_kexint, ptr, plen);
/* parse packet and save algorithm proposal */
/* skip cookie */
for (i = 0; i < KEX_COOKIE_LEN; i++)
packet_get_char();
/* extract kex init proposal strings */
for (i = 0; i < PROPOSAL_MAX; i++) {
peer_proposal[i] = packet_get_string(NULL);
debug("got kexinit: %s", peer_proposal[i]);
}
/* first kex follow / reserved */
i = packet_get_char();
debug("first kex follow: %d ", i);
i = packet_get_int();
debug("reserved: %d ", i);
packet_done();
debug("done");
}
/* diffie-hellman-group1-sha1 */
int
dh_pub_is_valid(DH *dh, BIGNUM *dh_pub)
{
int i;
int n = BN_num_bits(dh_pub);
int bits_set = 0;
/* we only accept g==2 */
if (!BN_is_word(dh->g, 2)) {
log("invalid DH base != 2");
return 0;
}
if (dh_pub->neg) {
log("invalid public DH value: negativ");
return 0;
}
for (i = 0; i <= n; i++)
if (BN_is_bit_set(dh_pub, i))
bits_set++;
debug("bits set: %d/%d", bits_set, BN_num_bits(dh->p));
/* if g==2 and bits_set==1 then computing log_g(dh_pub) is trivial */
if (bits_set > 1 && (BN_cmp(dh_pub, dh->p) == -1))
return 1;
log("invalid public DH value (%d/%d)", bits_set, BN_num_bits(dh->p));
return 0;
}
DH *
dh_new_group1()
{
static char *group1 =
"FFFFFFFF" "FFFFFFFF" "C90FDAA2" "2168C234" "C4C6628B" "80DC1CD1"
"29024E08" "8A67CC74" "020BBEA6" "3B139B22" "514A0879" "8E3404DD"
"EF9519B3" "CD3A431B" "302B0A6D" "F25F1437" "4FE1356D" "6D51C245"
"E485B576" "625E7EC6" "F44C42E9" "A637ED6B" "0BFF5CB6" "F406B7ED"
"EE386BFB" "5A899FA5" "AE9F2411" "7C4B1FE6" "49286651" "ECE65381"
"FFFFFFFF" "FFFFFFFF";
DH *dh;
int ret, tries = 0;
dh = DH_new();
if(dh == NULL)
fatal("DH_new");
ret = BN_hex2bn(&dh->p, group1);
if(ret<0)
fatal("BN_hex2bn");
dh->g = BN_new();
if(dh->g == NULL)
fatal("DH_new g");
BN_set_word(dh->g, 2);
do {
if (DH_generate_key(dh) == 0)
fatal("DH_generate_key");
if (tries++ > 10)
fatal("dh_new_group1: too many bad keys: giving up");
} while (!dh_pub_is_valid(dh, dh->pub_key));
return dh;
}
void
dump_digest(unsigned char *digest, int len)
{
int i;
for (i = 0; i< len; i++){
fprintf(stderr, "%02x", digest[i]);
if(i%2!=0)
fprintf(stderr, " ");
}
fprintf(stderr, "\n");
}
unsigned char *
kex_hash(
char *client_version_string,
char *server_version_string,
char *ckexinit, int ckexinitlen,
char *skexinit, int skexinitlen,
char *serverhostkeyblob, int sbloblen,
BIGNUM *client_dh_pub,
BIGNUM *server_dh_pub,
BIGNUM *shared_secret)
{
Buffer b;
static unsigned char digest[EVP_MAX_MD_SIZE];
EVP_MD *evp_md = EVP_sha1();
EVP_MD_CTX md;
buffer_init(&b);
buffer_put_string(&b, client_version_string, strlen(client_version_string));
buffer_put_string(&b, server_version_string, strlen(server_version_string));
/* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
buffer_put_int(&b, ckexinitlen+1);
buffer_put_char(&b, SSH2_MSG_KEXINIT);
buffer_append(&b, ckexinit, ckexinitlen);
buffer_put_int(&b, skexinitlen+1);
buffer_put_char(&b, SSH2_MSG_KEXINIT);
buffer_append(&b, skexinit, skexinitlen);
buffer_put_string(&b, serverhostkeyblob, sbloblen);
buffer_put_bignum2(&b, client_dh_pub);
buffer_put_bignum2(&b, server_dh_pub);
buffer_put_bignum2(&b, shared_secret);
#ifdef DEBUG_KEX
buffer_dump(&b);
#endif
EVP_DigestInit(&md, evp_md);
EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
EVP_DigestFinal(&md, digest, NULL);
buffer_free(&b);
#ifdef DEBUG_KEX
dump_digest(digest, evp_md->md_size);
#endif
return digest;
}
unsigned char *
derive_key(int id, int need, char unsigned *hash, BIGNUM *shared_secret)
{
Buffer b;
EVP_MD *evp_md = EVP_sha1();
EVP_MD_CTX md;
char c = id;
int have;
int mdsz = evp_md->md_size;
unsigned char *digest = xmalloc(((need+mdsz-1)/mdsz)*mdsz);
buffer_init(&b);
buffer_put_bignum2(&b, shared_secret);
EVP_DigestInit(&md, evp_md);
EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b)); /* shared_secret K */
EVP_DigestUpdate(&md, hash, mdsz); /* transport-06 */
EVP_DigestUpdate(&md, &c, 1); /* key id */
EVP_DigestUpdate(&md, hash, mdsz); /* session id */
EVP_DigestFinal(&md, digest, NULL);
/* expand */
for (have = mdsz; need > have; have += mdsz) {
EVP_DigestInit(&md, evp_md);
EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
EVP_DigestUpdate(&md, hash, mdsz);
EVP_DigestUpdate(&md, digest, have);
EVP_DigestFinal(&md, digest + have, NULL);
}
buffer_free(&b);
#ifdef DEBUG_KEX
fprintf(stderr, "Digest '%c'== ", c);
dump_digest(digest, need);
#endif
return digest;
}
#define NKEYS 6
#define MAX_PROP 20
#define SEP ","
char *
get_match(char *client, char *server)
{
char *sproposals[MAX_PROP];
char *c, *s, *p, *ret, *cp, *sp;
int i, j, nproposals;
c = cp = xstrdup(client);
s = sp = xstrdup(server);
for ((p = strsep(&sp, SEP)), i=0; p && *p != '\0';
(p = strsep(&sp, SEP)), i++) {
if (i < MAX_PROP)
sproposals[i] = p;
else
break;
}
nproposals = i;
for ((p = strsep(&cp, SEP)), i=0; p && *p != '\0';
(p = strsep(&cp, SEP)), i++) {
for (j = 0; j < nproposals; j++) {
if (strcmp(p, sproposals[j]) == 0) {
ret = xstrdup(p);
xfree(c);
xfree(s);
return ret;
}
}
}
xfree(c);
xfree(s);
return NULL;
}
void
choose_enc(Enc *enc, char *client, char *server)
{
char *name = get_match(client, server);
if (name == NULL)
fatal("no matching cipher found: client %s server %s", client, server);
enc->type = cipher_number(name);
switch (enc->type) {
case SSH_CIPHER_3DES_CBC:
enc->key_len = 24;
enc->iv_len = 8;
enc->block_size = 8;
break;
case SSH_CIPHER_BLOWFISH_CBC:
case SSH_CIPHER_CAST128_CBC:
enc->key_len = 16;
enc->iv_len = 8;
enc->block_size = 8;
break;
case SSH_CIPHER_ARCFOUR:
enc->key_len = 16;
enc->iv_len = 0;
enc->block_size = 8;
break;
default:
fatal("unsupported cipher %s", name);
}
enc->name = name;
enc->enabled = 0;
enc->iv = NULL;
enc->key = NULL;
}
void
choose_mac(Mac *mac, char *client, char *server)
{
char *name = get_match(client, server);
if (name == NULL)
fatal("no matching mac found: client %s server %s", client, server);
if (strcmp(name, "hmac-md5") == 0) {
mac->md = EVP_md5();
} else if (strcmp(name, "hmac-sha1") == 0) {
mac->md = EVP_sha1();
} else if (strcmp(name, "hmac-ripemd160@openssh.com") == 0) {
mac->md = EVP_ripemd160();
} else {
fatal("unsupported mac %s", name);
}
mac->name = name;
mac->mac_len = mac->md->md_size;
mac->key_len = (datafellows & SSH_BUG_HMAC) ? 16 : mac->mac_len;
mac->key = NULL;
mac->enabled = 0;
}
void
choose_comp(Comp *comp, char *client, char *server)
{
char *name = get_match(client, server);
if (name == NULL)
fatal("no matching comp found: client %s server %s", client, server);
if (strcmp(name, "zlib") == 0) {
comp->type = 1;
} else if (strcmp(name, "none") == 0) {
comp->type = 0;
} else {
fatal("unsupported comp %s", name);
}
comp->name = name;
}
void
choose_kex(Kex *k, char *client, char *server)
{
k->name = get_match(client, server);
if (k->name == NULL)
fatal("no kex alg");
if (strcmp(k->name, KEX_DH1) != 0)
fatal("bad kex alg %s", k->name);
}
void
choose_hostkeyalg(Kex *k, char *client, char *server)
{
k->hostkeyalg = get_match(client, server);
if (k->hostkeyalg == NULL)
fatal("no hostkey alg");
if (strcmp(k->hostkeyalg, KEX_DSS) != 0)
fatal("bad hostkey alg %s", k->hostkeyalg);
}
Kex *
kex_choose_conf(char *cprop[PROPOSAL_MAX], char *sprop[PROPOSAL_MAX], int server)
{
int mode;
int ctos; /* direction: if true client-to-server */
int need;
Kex *k;
k = xmalloc(sizeof(*k));
memset(k, 0, sizeof(*k));
k->server = server;
for (mode = 0; mode < MODE_MAX; mode++) {
int nenc, nmac, ncomp;
ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
nenc = ctos ? PROPOSAL_ENC_ALGS_CTOS : PROPOSAL_ENC_ALGS_STOC;
nmac = ctos ? PROPOSAL_MAC_ALGS_CTOS : PROPOSAL_MAC_ALGS_STOC;
ncomp = ctos ? PROPOSAL_COMP_ALGS_CTOS : PROPOSAL_COMP_ALGS_STOC;
choose_enc (&k->enc [mode], cprop[nenc], sprop[nenc]);
choose_mac (&k->mac [mode], cprop[nmac], sprop[nmac]);
choose_comp(&k->comp[mode], cprop[ncomp], sprop[ncomp]);
debug("kex: %s %s %s %s",
ctos ? "client->server" : "server->client",
k->enc[mode].name,
k->mac[mode].name,
k->comp[mode].name);
}
choose_kex(k, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
choose_hostkeyalg(k, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
need = 0;
for (mode = 0; mode < MODE_MAX; mode++) {
if (need < k->enc[mode].key_len)
need = k->enc[mode].key_len;
if (need < k->enc[mode].iv_len)
need = k->enc[mode].iv_len;
if (need < k->mac[mode].key_len)
need = k->mac[mode].key_len;
}
/* XXX need runden? */
k->we_need = need;
return k;
}
int
kex_derive_keys(Kex *k, unsigned char *hash, BIGNUM *shared_secret)
{
int i;
int mode;
int ctos;
unsigned char *keys[NKEYS];
for (i = 0; i < NKEYS; i++)
keys[i] = derive_key('A'+i, k->we_need, hash, shared_secret);
for (mode = 0; mode < MODE_MAX; mode++) {
ctos = (!k->server && mode == MODE_OUT) || (k->server && mode == MODE_IN);
k->enc[mode].iv = keys[ctos ? 0 : 1];
k->enc[mode].key = keys[ctos ? 2 : 3];
k->mac[mode].key = keys[ctos ? 4 : 5];
}
return 0;
}
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