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openssh-portable/kex.c

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/* $OpenBSD: kex.c,v 1.95 2014/01/12 08:13:13 djm Exp $ */
/*
* Copyright (c) 2000, 2001 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"
#include <sys/param.h>
#include <signal.h>
#include <stdarg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <openssl/crypto.h>
#include "xmalloc.h"
#include "ssh2.h"
#include "buffer.h"
#include "packet.h"
#include "compat.h"
#include "cipher.h"
#include "key.h"
#include "kex.h"
#include "log.h"
#include "mac.h"
#include "match.h"
#include "dispatch.h"
#include "monitor.h"
#include "roaming.h"
#include "digest.h"
#if OPENSSL_VERSION_NUMBER >= 0x00907000L
# if defined(HAVE_EVP_SHA256)
# define evp_ssh_sha256 EVP_sha256
# else
extern const EVP_MD *evp_ssh_sha256(void);
# endif
#endif
/* prototype */
static void kex_kexinit_finish(Kex *);
static void kex_choose_conf(Kex *);
struct kexalg {
char *name;
int type;
int ec_nid;
int hash_alg;
};
static const struct kexalg kexalgs[] = {
{ KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
{ KEX_DH14, KEX_DH_GRP14_SHA1, 0, SSH_DIGEST_SHA1 },
{ KEX_DHGEX_SHA1, KEX_DH_GEX_SHA1, 0, SSH_DIGEST_SHA1 },
#ifdef HAVE_EVP_SHA256
{ KEX_DHGEX_SHA256, KEX_DH_GEX_SHA256, 0, SSH_DIGEST_SHA256 },
#endif
#ifdef OPENSSL_HAS_ECC
{ KEX_ECDH_SHA2_NISTP256, KEX_ECDH_SHA2,
NID_X9_62_prime256v1, SSH_DIGEST_SHA256 },
{ KEX_ECDH_SHA2_NISTP384, KEX_ECDH_SHA2, NID_secp384r1,
SSH_DIGEST_SHA384 },
# ifdef OPENSSL_HAS_NISTP521
{ KEX_ECDH_SHA2_NISTP521, KEX_ECDH_SHA2, NID_secp521r1,
SSH_DIGEST_SHA512 },
# endif
#endif
{ KEX_DH1, KEX_DH_GRP1_SHA1, 0, SSH_DIGEST_SHA1 },
#ifdef HAVE_EVP_SHA256
{ KEX_CURVE25519_SHA256, KEX_C25519_SHA256, 0, SSH_DIGEST_SHA256 },
#endif
{ NULL, -1, -1, -1},
};
char *
kex_alg_list(char sep)
{
char *ret = NULL;
size_t nlen, rlen = 0;
const struct kexalg *k;
for (k = kexalgs; k->name != NULL; k++) {
if (ret != NULL)
ret[rlen++] = sep;
nlen = strlen(k->name);
ret = xrealloc(ret, 1, rlen + nlen + 2);
memcpy(ret + rlen, k->name, nlen + 1);
rlen += nlen;
}
return ret;
}
static const struct kexalg *
kex_alg_by_name(const char *name)
{
const struct kexalg *k;
for (k = kexalgs; k->name != NULL; k++) {
if (strcmp(k->name, name) == 0)
return k;
}
return NULL;
}
/* Validate KEX method name list */
int
kex_names_valid(const char *names)
{
char *s, *cp, *p;
if (names == NULL || strcmp(names, "") == 0)
return 0;
s = cp = xstrdup(names);
for ((p = strsep(&cp, ",")); p && *p != '\0';
(p = strsep(&cp, ","))) {
if (kex_alg_by_name(p) == NULL) {
error("Unsupported KEX algorithm \"%.100s\"", p);
free(s);
return 0;
}
}
debug3("kex names ok: [%s]", names);
free(s);
return 1;
}
/* put algorithm proposal into buffer */
static void
kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
{
u_int i;
buffer_clear(b);
/*
* add a dummy cookie, the cookie will be overwritten by
* kex_send_kexinit(), each time a kexinit is set
*/
for (i = 0; i < KEX_COOKIE_LEN; i++)
buffer_put_char(b, 0);
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 */
static char **
kex_buf2prop(Buffer *raw, int *first_kex_follows)
{
Buffer b;
u_int i;
char **proposal;
proposal = xcalloc(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_cstring(&b,NULL);
debug2("kex_parse_kexinit: %s", proposal[i]);
}
/* first kex follows / reserved */
i = buffer_get_char(&b);
if (first_kex_follows != NULL)
*first_kex_follows = i;
debug2("kex_parse_kexinit: first_kex_follows %d ", i);
i = buffer_get_int(&b);
debug2("kex_parse_kexinit: reserved %u ", i);
buffer_free(&b);
return proposal;
}
static void
kex_prop_free(char **proposal)
{
u_int i;
for (i = 0; i < PROPOSAL_MAX; i++)
free(proposal[i]);
free(proposal);
}
/* ARGSUSED */
static void
kex_protocol_error(int type, u_int32_t seq, void *ctxt)
{
error("Hm, kex protocol error: type %d seq %u", type, seq);
}
static void
kex_reset_dispatch(void)
{
dispatch_range(SSH2_MSG_TRANSPORT_MIN,
SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
}
void
kex_finish(Kex *kex)
{
kex_reset_dispatch();
packet_start(SSH2_MSG_NEWKEYS);
packet_send();
/* packet_write_wait(); */
debug("SSH2_MSG_NEWKEYS sent");
debug("expecting SSH2_MSG_NEWKEYS");
packet_read_expect(SSH2_MSG_NEWKEYS);
packet_check_eom();
debug("SSH2_MSG_NEWKEYS received");
kex->done = 1;
buffer_clear(&kex->peer);
/* buffer_clear(&kex->my); */
kex->flags &= ~KEX_INIT_SENT;
free(kex->name);
kex->name = NULL;
}
void
kex_send_kexinit(Kex *kex)
{
u_int32_t rnd = 0;
u_char *cookie;
u_int i;
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;
/* generate a random cookie */
if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
fatal("kex_send_kexinit: kex proposal too short");
cookie = buffer_ptr(&kex->my);
for (i = 0; i < KEX_COOKIE_LEN; i++) {
if (i % 4 == 0)
rnd = arc4random();
cookie[i] = rnd;
rnd >>= 8;
}
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;
}
/* ARGSUSED */
void
kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
{
char *ptr;
u_int i, dlen;
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++)
free(packet_get_string(NULL));
/*
* XXX RFC4253 sec 7: "each side MAY guess" - currently no supported
* KEX method has the server move first, but a server might be using
* a custom method or one that we otherwise don't support. We should
* be prepared to remember first_kex_follows here so we can eat a
* packet later.
* XXX2 - RFC4253 is kind of ambiguous on what first_kex_follows means
* for cases where the server *doesn't* go first. I guess we should
* ignore it when it is set for these cases, which is what we do now.
*/
(void) packet_get_char(); /* first_kex_follows */
(void) packet_get_int(); /* reserved */
packet_check_eom();
kex_kexinit_finish(kex);
}
Kex *
kex_setup(char *proposal[PROPOSAL_MAX])
{
Kex *kex;
kex = xcalloc(1, 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_reset_dispatch();
return kex;
}
static void
kex_kexinit_finish(Kex *kex)
{
if (!(kex->flags & KEX_INIT_SENT))
kex_send_kexinit(kex);
kex_choose_conf(kex);
if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
kex->kex[kex->kex_type] != NULL) {
(kex->kex[kex->kex_type])(kex);
} else {
fatal("Unsupported key exchange %d", kex->kex_type);
}
}
static 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);
if ((enc->cipher = cipher_by_name(name)) == NULL)
fatal("matching cipher is not supported: %s", name);
enc->name = name;
enc->enabled = 0;
enc->iv = NULL;
enc->iv_len = cipher_ivlen(enc->cipher);
enc->key = NULL;
enc->key_len = cipher_keylen(enc->cipher);
enc->block_size = cipher_blocksize(enc->cipher);
}
static 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_setup(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;
}
static 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@openssh.com") == 0) {
comp->type = COMP_DELAYED;
} else if (strcmp(name, "zlib") == 0) {
comp->type = COMP_ZLIB;
} else if (strcmp(name, "none") == 0) {
comp->type = COMP_NONE;
} else {
fatal("unsupported comp %s", name);
}
comp->name = name;
}
static void
choose_kex(Kex *k, char *client, char *server)
{
const struct kexalg *kexalg;
k->name = match_list(client, server, NULL);
if (k->name == NULL)
fatal("Unable to negotiate a key exchange method");
if ((kexalg = kex_alg_by_name(k->name)) == NULL)
fatal("unsupported kex alg %s", k->name);
k->kex_type = kexalg->type;
k->hash_alg = kexalg->hash_alg;
k->ec_nid = kexalg->ec_nid;
}
static 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);
free(hostkeyalg);
}
static int
proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
{
static int check[] = {
PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
};
int *idx;
char *p;
for (idx = &check[0]; *idx != -1; idx++) {
if ((p = strchr(my[*idx], ',')) != NULL)
*p = '\0';
if ((p = strchr(peer[*idx], ',')) != NULL)
*p = '\0';
if (strcmp(my[*idx], peer[*idx]) != 0) {
debug2("proposal mismatch: my %s peer %s",
my[*idx], peer[*idx]);
return (0);
}
}
debug2("proposals match");
return (1);
}
static void
kex_choose_conf(Kex *kex)
{
Newkeys *newkeys;
char **my, **peer;
char **cprop, **sprop;
int nenc, nmac, ncomp;
u_int mode, ctos, need, authlen;
int first_kex_follows, type;
my = kex_buf2prop(&kex->my, NULL);
peer = kex_buf2prop(&kex->peer, &first_kex_follows);
if (kex->server) {
cprop=peer;
sprop=my;
} else {
cprop=my;
sprop=peer;
}
/* Check whether server offers roaming */
if (!kex->server) {
char *roaming;
roaming = match_list(KEX_RESUME, peer[PROPOSAL_KEX_ALGS], NULL);
if (roaming) {
kex->roaming = 1;
free(roaming);
}
}
/* Algorithm Negotiation */
for (mode = 0; mode < MODE_MAX; mode++) {
newkeys = xcalloc(1, 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]);
/* ignore mac for authenticated encryption */
authlen = cipher_authlen(newkeys->enc.cipher);
if (authlen == 0)
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,
authlen == 0 ? newkeys->mac.name : "<implicit>",
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.key_len)
need = newkeys->enc.key_len;
if (need < newkeys->enc.block_size)
need = newkeys->enc.block_size;
if (need < newkeys->enc.iv_len)
need = newkeys->enc.iv_len;
if (need < newkeys->mac.key_len)
need = newkeys->mac.key_len;
}
/* XXX need runden? */
kex->we_need = need;
/* ignore the next message if the proposals do not match */
if (first_kex_follows && !proposals_match(my, peer) &&
!(datafellows & SSH_BUG_FIRSTKEX)) {
type = packet_read();
debug2("skipping next packet (type %u)", type);
}
kex_prop_free(my);
kex_prop_free(peer);
}
static u_char *
derive_key(Kex *kex, int id, u_int need, u_char *hash, u_int hashlen,
const u_char *shared_secret, u_int slen)
{
Buffer b;
struct ssh_digest_ctx *hashctx;
char c = id;
u_int have;
size_t mdsz;
u_char *digest;
if ((mdsz = ssh_digest_bytes(kex->hash_alg)) == 0)
fatal("bad kex md size %zu", mdsz);
digest = xmalloc(roundup(need, mdsz));
buffer_init(&b);
buffer_append(&b, shared_secret, slen);
/* K1 = HASH(K || H || "A" || session_id) */
if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
fatal("%s: ssh_digest_start failed", __func__);
if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
ssh_digest_update(hashctx, hash, hashlen) != 0 ||
ssh_digest_update(hashctx, &c, 1) != 0 ||
ssh_digest_update(hashctx, kex->session_id,
kex->session_id_len) != 0)
fatal("%s: ssh_digest_update failed", __func__);
if (ssh_digest_final(hashctx, digest, mdsz) != 0)
fatal("%s: ssh_digest_final failed", __func__);
ssh_digest_free(hashctx);
/*
* expand key:
* Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
* Key = K1 || K2 || ... || Kn
*/
for (have = mdsz; need > have; have += mdsz) {
if ((hashctx = ssh_digest_start(kex->hash_alg)) == NULL)
fatal("%s: ssh_digest_start failed", __func__);
if (ssh_digest_update_buffer(hashctx, &b) != 0 ||
ssh_digest_update(hashctx, hash, hashlen) != 0 ||
ssh_digest_update(hashctx, digest, have) != 0)
fatal("%s: ssh_digest_update failed", __func__);
if (ssh_digest_final(hashctx, digest + have, mdsz) != 0)
fatal("%s: ssh_digest_final failed", __func__);
ssh_digest_free(hashctx);
}
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, u_int hashlen,
const u_char *shared_secret, u_int slen)
{
u_char *keys[NKEYS];
u_int i, mode, ctos;
for (i = 0; i < NKEYS; i++) {
keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, hashlen,
shared_secret, slen);
}
debug2("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];
}
}
void
kex_derive_keys_bn(Kex *kex, u_char *hash, u_int hashlen, const BIGNUM *secret)
{
Buffer shared_secret;
buffer_init(&shared_secret);
buffer_put_bignum2(&shared_secret, secret);
kex_derive_keys(kex, hash, hashlen,
buffer_ptr(&shared_secret), buffer_len(&shared_secret));
buffer_free(&shared_secret);
}
Newkeys *
kex_get_newkeys(int mode)
{
Newkeys *ret;
ret = current_keys[mode];
current_keys[mode] = NULL;
return ret;
}
void
derive_ssh1_session_id(BIGNUM *host_modulus, BIGNUM *server_modulus,
u_int8_t cookie[8], u_int8_t id[16])
{
u_int8_t nbuf[2048], obuf[SSH_DIGEST_MAX_LENGTH];
int len;
struct ssh_digest_ctx *hashctx;
if ((hashctx = ssh_digest_start(SSH_DIGEST_MD5)) == NULL)
fatal("%s: ssh_digest_start", __func__);
len = BN_num_bytes(host_modulus);
if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
fatal("%s: bad host modulus (len %d)", __func__, len);
BN_bn2bin(host_modulus, nbuf);
if (ssh_digest_update(hashctx, nbuf, len) != 0)
fatal("%s: ssh_digest_update failed", __func__);
len = BN_num_bytes(server_modulus);
if (len < (512 / 8) || (u_int)len > sizeof(nbuf))
fatal("%s: bad server modulus (len %d)", __func__, len);
BN_bn2bin(server_modulus, nbuf);
if (ssh_digest_update(hashctx, nbuf, len) != 0 ||
ssh_digest_update(hashctx, cookie, 8) != 0)
fatal("%s: ssh_digest_update failed", __func__);
if (ssh_digest_final(hashctx, obuf, sizeof(obuf)) != 0)
fatal("%s: ssh_digest_final failed", __func__);
memcpy(id, obuf, ssh_digest_bytes(SSH_DIGEST_MD5));
memset(nbuf, 0, sizeof(nbuf));
memset(obuf, 0, sizeof(obuf));
}
#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH) || defined(DEBUG_KEXECDH)
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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