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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 1.33 2001/04/05 10:42:50 markus Exp $");
#include <openssl/crypto.h>
#include "ssh2.h"
#include "xmalloc.h"
#include "buffer.h"
#include "bufaux.h"
#include "packet.h"
#include "compat.h"
#include "cipher.h"
#include "kex.h"
#include "key.h"
#include "log.h"
#include "mac.h"
#include "match.h"
#include "dispatch.h"
#define KEX_COOKIE_LEN 16
void kex_kexinit_finish(Kex *kex);
void kex_choose_conf(Kex *k);
/* put algorithm proposal into buffer */
void
kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
{
u_int32_t rand = 0;
int i;
buffer_clear(b);
for (i = 0; i < KEX_COOKIE_LEN; i++) {
if (i % 4 == 0)
rand = arc4random();
buffer_put_char(b, rand & 0xff);
rand >>= 8;
}
for (i = 0; i < PROPOSAL_MAX; i++)
buffer_put_cstring(b, proposal[i]);
buffer_put_char(b, 0); /* first_kex_packet_follows */
buffer_put_int(b, 0); /* uint32 reserved */
}
/* parse buffer and return algorithm proposal */
char **
kex_buf2prop(Buffer *raw)
{
Buffer b;
int i;
char **proposal;
proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
buffer_init(&b);
buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
/* skip cookie */
for (i = 0; i < KEX_COOKIE_LEN; i++)
buffer_get_char(&b);
/* extract kex init proposal strings */
for (i = 0; i < PROPOSAL_MAX; i++) {
proposal[i] = buffer_get_string(&b,NULL);
debug2("kex_parse_kexinit: %s", proposal[i]);
}
/* first kex follows / reserved */
i = buffer_get_char(&b);
debug2("kex_parse_kexinit: first_kex_follows %d ", i);
i = buffer_get_int(&b);
debug2("kex_parse_kexinit: reserved %d ", i);
buffer_free(&b);
return proposal;
}
void
kex_prop_free(char **proposal)
{
int i;
for (i = 0; i < PROPOSAL_MAX; i++)
xfree(proposal[i]);
xfree(proposal);
}
void
kex_protocol_error(int type, int plen, void *ctxt)
{
error("Hm, kex protocol error: type %d plen %d", type, plen);
}
void
kex_clear_dispatch(void)
{
int i;
/* Numbers 30-49 are used for kex packets */
for (i = 30; i <= 49; i++)
dispatch_set(i, &kex_protocol_error);
}
void
kex_finish(Kex *kex)
{
int plen;
kex_clear_dispatch();
packet_start(SSH2_MSG_NEWKEYS);
packet_send();
/* packet_write_wait(); */
debug("SSH2_MSG_NEWKEYS sent");
debug("waiting for SSH2_MSG_NEWKEYS");
packet_read_expect(&plen, SSH2_MSG_NEWKEYS);
debug("SSH2_MSG_NEWKEYS received");
kex->done = 1;
buffer_clear(&kex->peer);
/* buffer_clear(&kex->my); */
kex->flags &= ~KEX_INIT_SENT;
xfree(kex->name);
kex->name = NULL;
}
void
kex_send_kexinit(Kex *kex)
{
if (kex == NULL) {
error("kex_send_kexinit: no kex, cannot rekey");
return;
}
if (kex->flags & KEX_INIT_SENT) {
debug("KEX_INIT_SENT");
return;
}
kex->done = 0;
packet_start(SSH2_MSG_KEXINIT);
packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
packet_send();
debug("SSH2_MSG_KEXINIT sent");
kex->flags |= KEX_INIT_SENT;
}
void
kex_input_kexinit(int type, int plen, void *ctxt)
{
char *ptr;
int dlen;
int i;
Kex *kex = (Kex *)ctxt;
debug("SSH2_MSG_KEXINIT received");
if (kex == NULL)
fatal("kex_input_kexinit: no kex, cannot rekey");
ptr = packet_get_raw(&dlen);
buffer_append(&kex->peer, ptr, dlen);
/* discard packet */
for (i = 0; i < KEX_COOKIE_LEN; i++)
packet_get_char();
for (i = 0; i < PROPOSAL_MAX; i++)
xfree(packet_get_string(NULL));
packet_get_char();
packet_get_int();
packet_done();
kex_kexinit_finish(kex);
}
Kex *
kex_setup(char *proposal[PROPOSAL_MAX])
{
Kex *kex;
kex = xmalloc(sizeof(*kex));
memset(kex, 0, sizeof(*kex));
buffer_init(&kex->peer);
buffer_init(&kex->my);
kex_prop2buf(&kex->my, proposal);
kex->done = 0;
kex_send_kexinit(kex); /* we start */
kex_clear_dispatch();
dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
return kex;
}
void
kex_kexinit_finish(Kex *kex)
{
if (!(kex->flags & KEX_INIT_SENT))
kex_send_kexinit(kex);
kex_choose_conf(kex);
switch(kex->kex_type) {
case DH_GRP1_SHA1:
kexdh(kex);
break;
case DH_GEX_SHA1:
kexgex(kex);
break;
default:
fatal("Unsupported key exchange %d", kex->kex_type);
}
}
void
choose_enc(Enc *enc, char *client, char *server)
{
char *name = match_list(client, server, NULL);
if (name == NULL)
fatal("no matching cipher found: client %s server %s", client, server);
enc->cipher = cipher_by_name(name);
if (enc->cipher == NULL)
fatal("matching cipher is not supported: %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 = match_list(client, server, NULL);
if (name == NULL)
fatal("no matching mac found: client %s server %s", client, server);
if (mac_init(mac, name) < 0)
fatal("unsupported mac %s", name);
/* truncate the key */
if (datafellows & SSH_BUG_HMAC)
mac->key_len = 16;
mac->name = name;
mac->key = NULL;
mac->enabled = 0;
}
void
choose_comp(Comp *comp, char *client, char *server)
{
char *name = match_list(client, server, NULL);
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 = match_list(client, server, NULL);
if (k->name == NULL)
fatal("no kex alg");
if (strcmp(k->name, KEX_DH1) == 0) {
k->kex_type = DH_GRP1_SHA1;
} else if (strcmp(k->name, KEX_DHGEX) == 0) {
k->kex_type = DH_GEX_SHA1;
} else
fatal("bad kex alg %s", k->name);
}
void
choose_hostkeyalg(Kex *k, char *client, char *server)
{
char *hostkeyalg = match_list(client, server, NULL);
if (hostkeyalg == NULL)
fatal("no hostkey alg");
k->hostkey_type = key_type_from_name(hostkeyalg);
if (k->hostkey_type == KEY_UNSPEC)
fatal("bad hostkey alg '%s'", hostkeyalg);
xfree(hostkeyalg);
}
void
kex_choose_conf(Kex *kex)
{
Newkeys *newkeys;
char **my, **peer;
char **cprop, **sprop;
int nenc, nmac, ncomp;
int mode;
int ctos; /* direction: if true client-to-server */
int need;
my = kex_buf2prop(&kex->my);
peer = kex_buf2prop(&kex->peer);
if (kex->server) {
cprop=peer;
sprop=my;
} else {
cprop=my;
sprop=peer;
}
/* Algorithm Negotiation */
for (mode = 0; mode < MODE_MAX; mode++) {
newkeys = xmalloc(sizeof(*newkeys));
memset(newkeys, 0, sizeof(*newkeys));
kex->newkeys[mode] = newkeys;
ctos = (!kex->server && mode == MODE_OUT) || (kex->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 (&newkeys->enc, cprop[nenc], sprop[nenc]);
choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
choose_comp(&newkeys->comp, cprop[ncomp], sprop[ncomp]);
debug("kex: %s %s %s %s",
ctos ? "client->server" : "server->client",
newkeys->enc.name,
newkeys->mac.name,
newkeys->comp.name);
}
choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
choose_hostkeyalg(kex, cprop[PROPOSAL_SERVER_HOST_KEY_ALGS],
sprop[PROPOSAL_SERVER_HOST_KEY_ALGS]);
need = 0;
for (mode = 0; mode < MODE_MAX; mode++) {
newkeys = kex->newkeys[mode];
if (need < newkeys->enc.cipher->key_len)
need = newkeys->enc.cipher->key_len;
if (need < newkeys->enc.cipher->block_size)
need = newkeys->enc.cipher->block_size;
if (need < newkeys->mac.key_len)
need = newkeys->mac.key_len;
}
/* XXX need runden? */
kex->we_need = need;
kex_prop_free(my);
kex_prop_free(peer);
}
u_char *
derive_key(Kex *kex, int id, int need, u_char *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;
u_char *digest = xmalloc(roundup(need, mdsz));
buffer_init(&b);
buffer_put_bignum2(&b, shared_secret);
/* K1 = HASH(K || H || "A" || session_id) */
EVP_DigestInit(&md, evp_md);
EVP_DigestUpdate(&md, buffer_ptr(&b), buffer_len(&b));
EVP_DigestUpdate(&md, hash, mdsz);
EVP_DigestUpdate(&md, &c, 1);
EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
EVP_DigestFinal(&md, digest, NULL);
/*
* expand key:
* Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
* Key = K1 || K2 || ... || Kn
*/
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, "key '%c'== ", c);
dump_digest("key", digest, need);
#endif
return digest;
}
Newkeys *current_keys[MODE_MAX];
#define NKEYS 6
void
kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
{
u_char *keys[NKEYS];
int i, mode, ctos;
for (i = 0; i < NKEYS; i++)
keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
debug("kex_derive_keys");
for (mode = 0; mode < MODE_MAX; mode++) {
current_keys[mode] = kex->newkeys[mode];
kex->newkeys[mode] = NULL;
ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
}
}
Newkeys *
kex_get_newkeys(int mode)
{
Newkeys *ret;
ret = current_keys[mode];
current_keys[mode] = NULL;
return ret;
}
#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
void
dump_digest(char *msg, u_char *digest, int len)
{
int i;
fprintf(stderr, "%s\n", msg);
for (i = 0; i< len; i++){
fprintf(stderr, "%02x", digest[i]);
if (i%32 == 31)
fprintf(stderr, "\n");
else if (i%8 == 7)
fprintf(stderr, " ");
}
fprintf(stderr, "\n");
}
#endif
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