crypto/openssh/kexc25519.c

   1 /* $OpenBSD: kexc25519.c,v 1.10 2016/05/02 08:49:03 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 "sshbuf.h"
  39 #include "ssh2.h"
  40 #include "sshkey.h"
  41 #include "cipher.h"
  42 #include "kex.h"
  43 #include "log.h"
  44 #include "digest.h"
  45 #include "ssherr.h"
  46
  47 extern int crypto_scalarmult_curve25519(u_char a[CURVE25519_SIZE],
  48     const u_char b[CURVE25519_SIZE], const u_char c[CURVE25519_SIZE])
  49         __attribute__((__bounded__(__minbytes__, 1, CURVE25519_SIZE)))
  50         __attribute__((__bounded__(__minbytes__, 2, CURVE25519_SIZE)))
  51         __attribute__((__bounded__(__minbytes__, 3, CURVE25519_SIZE)));
  52
  53 void
  54 kexc25519_keygen(u_char key[CURVE25519_SIZE], u_char pub[CURVE25519_SIZE])
  55 {
  56         static const u_char basepoint[CURVE25519_SIZE] = {9};
  57
  58         arc4random_buf(key, CURVE25519_SIZE);
  59         crypto_scalarmult_curve25519(pub, key, basepoint);
  60 }
  61
  62 int
  63 kexc25519_shared_key(const u_char key[CURVE25519_SIZE],
  64     const u_char pub[CURVE25519_SIZE], struct sshbuf *out)
  65 {
  66         u_char shared_key[CURVE25519_SIZE];
  67         int r;
  68
  69         /* Check for all-zero public key */
  70         explicit_bzero(shared_key, CURVE25519_SIZE);
  71         if (timingsafe_bcmp(pub, shared_key, CURVE25519_SIZE) == 0)
  72                 return SSH_ERR_KEY_INVALID_EC_VALUE;
  73
  74         crypto_scalarmult_curve25519(shared_key, key, pub);
  75 #ifdef DEBUG_KEXECDH
  76         dump_digest("shared secret", shared_key, CURVE25519_SIZE);
  77 #endif
  78         sshbuf_reset(out);
  79         r = sshbuf_put_bignum2_bytes(out, shared_key, CURVE25519_SIZE);
  80         explicit_bzero(shared_key, CURVE25519_SIZE);
  81         return r;
  82 }
  83
  84 int
  85 kex_c25519_hash(
  86     int hash_alg,
  87     const char *client_version_string,
  88     const char *server_version_string,
  89     const u_char *ckexinit, size_t ckexinitlen,
  90     const u_char *skexinit, size_t skexinitlen,
  91     const u_char *serverhostkeyblob, size_t sbloblen,
  92     const u_char client_dh_pub[CURVE25519_SIZE],
  93     const u_char server_dh_pub[CURVE25519_SIZE],
  94     const u_char *shared_secret, size_t secretlen,
  95     u_char *hash, size_t *hashlen)
  96 {
  97         struct sshbuf *b;
  98         int r;
  99
 100         if (*hashlen < ssh_digest_bytes(hash_alg))
 101                 return SSH_ERR_INVALID_ARGUMENT;
 102         if ((b = sshbuf_new()) == NULL)
 103                 return SSH_ERR_ALLOC_FAIL;
 104         if ((r = sshbuf_put_cstring(b, client_version_string)) < 0 ||
 105             (r = sshbuf_put_cstring(b, server_version_string)) < 0 ||
 106             /* kexinit messages: fake header: len+SSH2_MSG_KEXINIT */
 107             (r = sshbuf_put_u32(b, ckexinitlen+1)) < 0 ||
 108             (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
 109             (r = sshbuf_put(b, ckexinit, ckexinitlen)) < 0 ||
 110             (r = sshbuf_put_u32(b, skexinitlen+1)) < 0 ||
 111             (r = sshbuf_put_u8(b, SSH2_MSG_KEXINIT)) < 0 ||
 112             (r = sshbuf_put(b, skexinit, skexinitlen)) < 0 ||
 113             (r = sshbuf_put_string(b, serverhostkeyblob, sbloblen)) < 0 ||
 114             (r = sshbuf_put_string(b, client_dh_pub, CURVE25519_SIZE)) < 0 ||
 115             (r = sshbuf_put_string(b, server_dh_pub, CURVE25519_SIZE)) < 0 ||
 116             (r = sshbuf_put(b, shared_secret, secretlen)) < 0) {
 117                 sshbuf_free(b);
 118                 return r;
 119         }
 120 #ifdef DEBUG_KEX
 121         sshbuf_dump(b, stderr);
 122 #endif
 123         if (ssh_digest_buffer(hash_alg, b, hash, *hashlen) != 0) {
 124                 sshbuf_free(b);
 125                 return SSH_ERR_LIBCRYPTO_ERROR;
 126         }
 127         sshbuf_free(b);
 128         *hashlen = ssh_digest_bytes(hash_alg);
 129 #ifdef DEBUG_KEX
 130         dump_digest("hash", hash, *hashlen);
 131 #endif
 132         return 0;
 133 }