crypto/openssh/kexc25519.c

   1 /* $OpenBSD: kexc25519.c,v 1.7 2014/05/02 03:27:54 djm Exp $ */
   2 /*
   3  * Copyright (c) 2001, 2013 Markus Friedl.  All rights reserved.
   4  * Copyright (c) 2010 Damien Miller.  All rights reserved.
   5  * Copyright (c) 2013 Aris Adamantiadis.  All rights reserved.
   6  *
   7  * Redistribution and use in source and binary forms, with or without
   8  * modification, are permitted provided that the following conditions
   9  * are met:
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  * 2. Redistributions in binary form must reproduce the above copyright
  13  *    notice, this list of conditions and the following disclaimer in the
  14  *    documentation and/or other materials provided with the distribution.
  15  *
  16  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  17  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  18  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  19  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  20  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  21  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  22  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  23  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  24  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  25  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  26  */
  27
  28 #include "includes.h"
  29
  30 #include <sys/types.h>
  31
  32 #include <signal.h>
  33 #include <string.h>
  34
  35 #include <openssl/bn.h>
  36 #include <openssl/evp.h>
  37
  38 #include "buffer.h"
  39 #include "ssh2.h"
  40 #include "key.h"
  41 #include "cipher.h"
  42 #include "kex.h"
  43 #include "log.h"
  44 #include "digest.h"
  45
  46 extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE],
  47     const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE])
  48         __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
  49         __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)))
  50         __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE)));
  51
  52 void
  53 kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
  54 {
  55         static const u_char basepoint[CURVE25519_SIZE] = {9};
  56
  57         arc4random_buf(key, CURVE25519_SIZE);
  58         crypto_scalarmult_curve25519(pub, key, basepoint);
  59 }
  60
  61 void
  62 kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
  63     const u_char pub[CURVE25519_SIZE], Buffer *out)
  64 {
  65         u_char shared_key[CURVE25519_SIZE];
  66
  67         crypto_scalarmult_curve25519(shared_key, key, pub);
  68 #ifdef DEBUG_KEXECDH
  69         dump_digest("shared secret", shared_key, CURVE25519_SIZE);
  70 #endif
  71         buffer_clear(out);
  72         buffer_put_bignum2_from_string(out, shared_key, CURVE25519_SIZE);
  73         explicit_bzero(shared_key, CURVE25519_SIZE);
  74 }
  75
  76 void
  77 kex_c25519_hash(
  78     int hash_alg,
  79     char *client_version_string,
  80     char *server_version_string,
  81     char *ckexinit, int ckexinitlen,
  82     char *skexinit, int skexinitlen,
  83     u_char *serverhostkeyblob, int sbloblen,
  84     const u_char client_dh_pub[CURVE25519_SIZE],
  85     const u_char server_dh_pub[CURVE25519_SIZE],
  86     const u_char *shared_secret, u_int secretlen,
  87     u_char **hash, u_int *hashlen)
  88 {
  89         Buffer b;
  90         static u_char digest[SSH_DIGEST_MAX_LENGTH];
  91
  92         buffer_init(&b);
  93         buffer_put_cstring(&b, client_version_string);
  94         buffer_put_cstring(&b, server_version_string);
  95
  96         /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
  97         buffer_put_int(&b, ckexinitlen+1);
  98         buffer_put_char(&b, SSH2_MSG_KEXINIT);
  99         buffer_append(&b, ckexinit, ckexinitlen);
 100         buffer_put_int(&b, skexinitlen+1);
 101         buffer_put_char(&b, SSH2_MSG_KEXINIT);
 102         buffer_append(&b, skexinit, skexinitlen);
 103
 104         buffer_put_string(&b, serverhostkeyblob, sbloblen);
 105         buffer_put_string(&b, client_dh_pub, CURVE25519_SIZE);
 106         buffer_put_string(&b, server_dh_pub, CURVE25519_SIZE);
 107         buffer_append(&b, shared_secret, secretlen);
 108
 109 #ifdef DEBUG_KEX
 110         buffer_dump(&b);
 111 #endif
 112         if (ssh_digest_buffer(hash_alg, &b, digest, sizeof(digest)) != 0)
 113                 fatal("%s: digest_buffer failed", __func__);
 114
 115         buffer_free(&b);
 116
 117 #ifdef DEBUG_KEX
 118         dump_digest("hash", digest, ssh_digest_bytes(hash_alg));
 119 #endif
 120         *hash = digest;
 121         *hashlen = ssh_digest_bytes(hash_alg);
 122 }