499 lines
12 KiB
C
499 lines
12 KiB
C
/*
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* Copyright (c) 2000, 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: kex.c,v 1.55 2003/04/01 10:31:26 markus Exp $");
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#include <openssl/crypto.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 "compat.h"
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#include "cipher.h"
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#include "kex.h"
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#include "key.h"
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#include "log.h"
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#include "mac.h"
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#include "match.h"
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#include "dispatch.h"
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#include "monitor.h"
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#define KEX_COOKIE_LEN 16
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/* prototype */
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static void kex_kexinit_finish(Kex *);
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static void kex_choose_conf(Kex *);
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/* put algorithm proposal into buffer */
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static void
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kex_prop2buf(Buffer *b, char *proposal[PROPOSAL_MAX])
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{
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int i;
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buffer_clear(b);
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/*
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* add a dummy cookie, the cookie will be overwritten by
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* kex_send_kexinit(), each time a kexinit is set
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*/
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for (i = 0; i < KEX_COOKIE_LEN; i++)
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buffer_put_char(b, 0);
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for (i = 0; i < PROPOSAL_MAX; i++)
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buffer_put_cstring(b, proposal[i]);
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buffer_put_char(b, 0); /* first_kex_packet_follows */
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buffer_put_int(b, 0); /* uint32 reserved */
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}
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/* parse buffer and return algorithm proposal */
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static char **
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kex_buf2prop(Buffer *raw, int *first_kex_follows)
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{
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Buffer b;
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int i;
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char **proposal;
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proposal = xmalloc(PROPOSAL_MAX * sizeof(char *));
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buffer_init(&b);
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buffer_append(&b, buffer_ptr(raw), buffer_len(raw));
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/* skip cookie */
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for (i = 0; i < KEX_COOKIE_LEN; i++)
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buffer_get_char(&b);
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/* extract kex init proposal strings */
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for (i = 0; i < PROPOSAL_MAX; i++) {
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proposal[i] = buffer_get_string(&b,NULL);
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debug2("kex_parse_kexinit: %s", proposal[i]);
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}
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/* first kex follows / reserved */
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i = buffer_get_char(&b);
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if (first_kex_follows != NULL)
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*first_kex_follows = i;
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debug2("kex_parse_kexinit: first_kex_follows %d ", i);
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i = buffer_get_int(&b);
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debug2("kex_parse_kexinit: reserved %d ", i);
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buffer_free(&b);
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return proposal;
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}
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static void
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kex_prop_free(char **proposal)
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{
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int i;
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for (i = 0; i < PROPOSAL_MAX; i++)
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xfree(proposal[i]);
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xfree(proposal);
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}
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static void
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kex_protocol_error(int type, u_int32_t seq, void *ctxt)
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{
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error("Hm, kex protocol error: type %d seq %u", type, seq);
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}
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static void
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kex_reset_dispatch(void)
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{
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dispatch_range(SSH2_MSG_TRANSPORT_MIN,
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SSH2_MSG_TRANSPORT_MAX, &kex_protocol_error);
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dispatch_set(SSH2_MSG_KEXINIT, &kex_input_kexinit);
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}
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void
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kex_finish(Kex *kex)
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{
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kex_reset_dispatch();
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packet_start(SSH2_MSG_NEWKEYS);
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packet_send();
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/* packet_write_wait(); */
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debug("SSH2_MSG_NEWKEYS sent");
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debug("expecting SSH2_MSG_NEWKEYS");
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packet_read_expect(SSH2_MSG_NEWKEYS);
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packet_check_eom();
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debug("SSH2_MSG_NEWKEYS received");
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kex->done = 1;
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buffer_clear(&kex->peer);
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/* buffer_clear(&kex->my); */
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kex->flags &= ~KEX_INIT_SENT;
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xfree(kex->name);
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kex->name = NULL;
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}
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void
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kex_send_kexinit(Kex *kex)
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{
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u_int32_t rand = 0;
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u_char *cookie;
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int i;
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if (kex == NULL) {
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error("kex_send_kexinit: no kex, cannot rekey");
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return;
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}
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if (kex->flags & KEX_INIT_SENT) {
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debug("KEX_INIT_SENT");
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return;
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}
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kex->done = 0;
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/* generate a random cookie */
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if (buffer_len(&kex->my) < KEX_COOKIE_LEN)
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fatal("kex_send_kexinit: kex proposal too short");
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cookie = buffer_ptr(&kex->my);
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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;
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rand >>= 8;
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}
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packet_start(SSH2_MSG_KEXINIT);
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packet_put_raw(buffer_ptr(&kex->my), buffer_len(&kex->my));
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packet_send();
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debug("SSH2_MSG_KEXINIT sent");
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kex->flags |= KEX_INIT_SENT;
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}
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void
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kex_input_kexinit(int type, u_int32_t seq, void *ctxt)
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{
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char *ptr;
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int dlen;
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int i;
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Kex *kex = (Kex *)ctxt;
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debug("SSH2_MSG_KEXINIT received");
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if (kex == NULL)
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fatal("kex_input_kexinit: no kex, cannot rekey");
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ptr = packet_get_raw(&dlen);
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buffer_append(&kex->peer, ptr, dlen);
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/* discard packet */
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for (i = 0; i < KEX_COOKIE_LEN; i++)
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packet_get_char();
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for (i = 0; i < PROPOSAL_MAX; i++)
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xfree(packet_get_string(NULL));
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(void) packet_get_char();
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(void) packet_get_int();
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packet_check_eom();
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kex_kexinit_finish(kex);
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}
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Kex *
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kex_setup(char *proposal[PROPOSAL_MAX])
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{
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Kex *kex;
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kex = xmalloc(sizeof(*kex));
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memset(kex, 0, sizeof(*kex));
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buffer_init(&kex->peer);
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buffer_init(&kex->my);
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kex_prop2buf(&kex->my, proposal);
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kex->done = 0;
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kex_send_kexinit(kex); /* we start */
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kex_reset_dispatch();
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return kex;
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}
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static void
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kex_kexinit_finish(Kex *kex)
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{
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if (!(kex->flags & KEX_INIT_SENT))
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kex_send_kexinit(kex);
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kex_choose_conf(kex);
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if (kex->kex_type >= 0 && kex->kex_type < KEX_MAX &&
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kex->kex[kex->kex_type] != NULL) {
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(kex->kex[kex->kex_type])(kex);
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} else {
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fatal("Unsupported key exchange %d", kex->kex_type);
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}
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}
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static void
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choose_enc(Enc *enc, char *client, char *server)
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{
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char *name = match_list(client, server, NULL);
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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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if ((enc->cipher = cipher_by_name(name)) == NULL)
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fatal("matching cipher is not supported: %s", name);
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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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enc->key_len = cipher_keylen(enc->cipher);
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enc->block_size = cipher_blocksize(enc->cipher);
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}
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static void
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choose_mac(Mac *mac, char *client, char *server)
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{
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char *name = match_list(client, server, NULL);
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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 (mac_init(mac, name) < 0)
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fatal("unsupported mac %s", name);
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/* truncate the key */
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if (datafellows & SSH_BUG_HMAC)
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mac->key_len = 16;
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mac->name = name;
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mac->key = NULL;
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mac->enabled = 0;
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}
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static void
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choose_comp(Comp *comp, char *client, char *server)
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{
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char *name = match_list(client, server, NULL);
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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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static void
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choose_kex(Kex *k, char *client, char *server)
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{
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k->name = match_list(client, server, NULL);
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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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k->kex_type = KEX_DH_GRP1_SHA1;
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} else if (strcmp(k->name, KEX_DHGEX) == 0) {
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k->kex_type = KEX_DH_GEX_SHA1;
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} else
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fatal("bad kex alg %s", k->name);
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}
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static void
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choose_hostkeyalg(Kex *k, char *client, char *server)
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{
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char *hostkeyalg = match_list(client, server, NULL);
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if (hostkeyalg == NULL)
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fatal("no hostkey alg");
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k->hostkey_type = key_type_from_name(hostkeyalg);
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if (k->hostkey_type == KEY_UNSPEC)
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fatal("bad hostkey alg '%s'", hostkeyalg);
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xfree(hostkeyalg);
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}
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static int
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proposals_match(char *my[PROPOSAL_MAX], char *peer[PROPOSAL_MAX])
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{
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static int check[] = {
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PROPOSAL_KEX_ALGS, PROPOSAL_SERVER_HOST_KEY_ALGS, -1
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};
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int *idx;
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char *p;
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for (idx = &check[0]; *idx != -1; idx++) {
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if ((p = strchr(my[*idx], ',')) != NULL)
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*p = '\0';
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if ((p = strchr(peer[*idx], ',')) != NULL)
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*p = '\0';
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if (strcmp(my[*idx], peer[*idx]) != 0) {
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debug2("proposal mismatch: my %s peer %s",
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my[*idx], peer[*idx]);
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return (0);
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}
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}
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debug2("proposals match");
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return (1);
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}
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static void
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kex_choose_conf(Kex *kex)
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{
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Newkeys *newkeys;
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char **my, **peer;
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char **cprop, **sprop;
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int nenc, nmac, ncomp;
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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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int first_kex_follows, type;
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my = kex_buf2prop(&kex->my, NULL);
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peer = kex_buf2prop(&kex->peer, &first_kex_follows);
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if (kex->server) {
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cprop=peer;
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sprop=my;
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} else {
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cprop=my;
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sprop=peer;
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}
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/* Algorithm Negotiation */
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for (mode = 0; mode < MODE_MAX; mode++) {
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newkeys = xmalloc(sizeof(*newkeys));
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memset(newkeys, 0, sizeof(*newkeys));
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kex->newkeys[mode] = newkeys;
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ctos = (!kex->server && mode == MODE_OUT) || (kex->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 (&newkeys->enc, cprop[nenc], sprop[nenc]);
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choose_mac (&newkeys->mac, cprop[nmac], sprop[nmac]);
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choose_comp(&newkeys->comp, 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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newkeys->enc.name,
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newkeys->mac.name,
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newkeys->comp.name);
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}
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choose_kex(kex, cprop[PROPOSAL_KEX_ALGS], sprop[PROPOSAL_KEX_ALGS]);
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choose_hostkeyalg(kex, 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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newkeys = kex->newkeys[mode];
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if (need < newkeys->enc.key_len)
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need = newkeys->enc.key_len;
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if (need < newkeys->enc.block_size)
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need = newkeys->enc.block_size;
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if (need < newkeys->mac.key_len)
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need = newkeys->mac.key_len;
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}
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/* XXX need runden? */
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kex->we_need = need;
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/* ignore the next message if the proposals do not match */
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if (first_kex_follows && !proposals_match(my, peer) &&
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!(datafellows & SSH_BUG_FIRSTKEX)) {
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type = packet_read();
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debug2("skipping next packet (type %u)", type);
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}
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kex_prop_free(my);
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kex_prop_free(peer);
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}
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static u_char *
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derive_key(Kex *kex, int id, int need, u_char *hash, BIGNUM *shared_secret)
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{
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Buffer b;
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const 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_size(evp_md);
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u_char *digest = xmalloc(roundup(need, mdsz));
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buffer_init(&b);
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buffer_put_bignum2(&b, shared_secret);
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/* K1 = HASH(K || H || "A" || session_id) */
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EVP_DigestInit(&md, evp_md);
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if (!(datafellows & SSH_BUG_DERIVEKEY))
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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, &c, 1);
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EVP_DigestUpdate(&md, kex->session_id, kex->session_id_len);
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EVP_DigestFinal(&md, digest, NULL);
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/*
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* expand key:
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* Kn = HASH(K || H || K1 || K2 || ... || Kn-1)
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* Key = K1 || K2 || ... || Kn
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*/
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for (have = mdsz; need > have; have += mdsz) {
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EVP_DigestInit(&md, evp_md);
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if (!(datafellows & SSH_BUG_DERIVEKEY))
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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, "key '%c'== ", c);
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dump_digest("key", digest, need);
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#endif
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return digest;
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}
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Newkeys *current_keys[MODE_MAX];
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#define NKEYS 6
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void
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kex_derive_keys(Kex *kex, u_char *hash, BIGNUM *shared_secret)
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{
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u_char *keys[NKEYS];
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int i, mode, ctos;
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for (i = 0; i < NKEYS; i++)
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keys[i] = derive_key(kex, 'A'+i, kex->we_need, hash, shared_secret);
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debug2("kex_derive_keys");
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for (mode = 0; mode < MODE_MAX; mode++) {
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current_keys[mode] = kex->newkeys[mode];
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kex->newkeys[mode] = NULL;
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ctos = (!kex->server && mode == MODE_OUT) || (kex->server && mode == MODE_IN);
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current_keys[mode]->enc.iv = keys[ctos ? 0 : 1];
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current_keys[mode]->enc.key = keys[ctos ? 2 : 3];
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current_keys[mode]->mac.key = keys[ctos ? 4 : 5];
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}
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}
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Newkeys *
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kex_get_newkeys(int mode)
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{
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Newkeys *ret;
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ret = current_keys[mode];
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current_keys[mode] = NULL;
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return ret;
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}
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#if defined(DEBUG_KEX) || defined(DEBUG_KEXDH)
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void
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dump_digest(char *msg, u_char *digest, int len)
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{
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int i;
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fprintf(stderr, "%s\n", msg);
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for (i = 0; i< len; i++) {
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fprintf(stderr, "%02x", digest[i]);
|
|
if (i%32 == 31)
|
|
fprintf(stderr, "\n");
|
|
else if (i%8 == 7)
|
|
fprintf(stderr, " ");
|
|
}
|
|
fprintf(stderr, "\n");
|
|
}
|
|
#endif
|