crypto/openssh/kexdh.c

   1 /* $OpenBSD: kexdh.c,v 1.34 2020/12/04 02:29:25 djm Exp $ */
   2 /*
   3  * Copyright (c) 2019 Markus Friedl.  All rights reserved.
   4  *
   5  * Redistribution and use in source and binary forms, with or without
   6  * modification, are permitted provided that the following conditions
   7  * are met:
   8  * 1. Redistributions of source code must retain the above copyright
   9  *    notice, this list of conditions and the following disclaimer.
  10  * 2. Redistributions in binary form must reproduce the above copyright
  11  *    notice, this list of conditions and the following disclaimer in the
  12  *    documentation and/or other materials provided with the distribution.
  13  *
  14  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
  15  * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
  16  * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
  17  * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
  18  * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
  19  * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
  20  * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
  21  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  22  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
  23  * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  24  */
  25
  26 #include "includes.h"
  27
  28 #ifdef WITH_OPENSSL
  29
  30 #include <sys/types.h>
  31
  32 #include <stdio.h>
  33 #include <string.h>
  34 #include <signal.h>
  35
  36 #include "openbsd-compat/openssl-compat.h"
  37 #include <openssl/dh.h>
  38
  39 #include "sshkey.h"
  40 #include "kex.h"
  41 #include "sshbuf.h"
  42 #include "digest.h"
  43 #include "ssherr.h"
  44 #include "dh.h"
  45 #include "log.h"
  46
  47 int
  48 kex_dh_keygen(struct kex *kex)
  49 {
  50         switch (kex->kex_type) {
  51         case KEX_DH_GRP1_SHA1:
  52                 kex->dh = dh_new_group1();
  53                 break;
  54         case KEX_DH_GRP14_SHA1:
  55         case KEX_DH_GRP14_SHA256:
  56                 kex->dh = dh_new_group14();
  57                 break;
  58         case KEX_DH_GRP16_SHA512:
  59                 kex->dh = dh_new_group16();
  60                 break;
  61         case KEX_DH_GRP18_SHA512:
  62                 kex->dh = dh_new_group18();
  63                 break;
  64         default:
  65                 return SSH_ERR_INVALID_ARGUMENT;
  66         }
  67         if (kex->dh == NULL)
  68                 return SSH_ERR_ALLOC_FAIL;
  69         return (dh_gen_key(kex->dh, kex->we_need * 8));
  70 }
  71
  72 int
  73 kex_dh_compute_key(struct kex *kex, BIGNUM *dh_pub, struct sshbuf *out)
  74 {
  75         BIGNUM *shared_secret = NULL;
  76         u_char *kbuf = NULL;
  77         size_t klen = 0;
  78         int kout, r;
  79
  80 #ifdef DEBUG_KEXDH
  81         fprintf(stderr, "dh_pub= ");
  82         BN_print_fp(stderr, dh_pub);
  83         fprintf(stderr, "\n");
  84         debug("bits %d", BN_num_bits(dh_pub));
  85         DHparams_print_fp(stderr, kex->dh);
  86         fprintf(stderr, "\n");
  87 #endif
  88
  89         if (!dh_pub_is_valid(kex->dh, dh_pub)) {
  90                 r = SSH_ERR_MESSAGE_INCOMPLETE;
  91                 goto out;
  92         }
  93         klen = DH_size(kex->dh);
  94         if ((kbuf = malloc(klen)) == NULL ||
  95             (shared_secret = BN_new()) == NULL) {
  96                 r = SSH_ERR_ALLOC_FAIL;
  97                 goto out;
  98         }
  99         if ((kout = DH_compute_key(kbuf, dh_pub, kex->dh)) < 0 ||
 100             BN_bin2bn(kbuf, kout, shared_secret) == NULL) {
 101                 r = SSH_ERR_LIBCRYPTO_ERROR;
 102                 goto out;
 103         }
 104 #ifdef DEBUG_KEXDH
 105         dump_digest("shared secret", kbuf, kout);
 106 #endif
 107         r = sshbuf_put_bignum2(out, shared_secret);
 108  out:
 109         freezero(kbuf, klen);
 110         BN_clear_free(shared_secret);
 111         return r;
 112 }
 113
 114 int
 115 kex_dh_keypair(struct kex *kex)
 116 {
 117         const BIGNUM *pub_key;
 118         struct sshbuf *buf = NULL;
 119         int r;
 120
 121         if ((r = kex_dh_keygen(kex)) != 0)
 122                 return r;
 123         DH_get0_key(kex->dh, &pub_key, NULL);
 124         if ((buf = sshbuf_new()) == NULL)
 125                 return SSH_ERR_ALLOC_FAIL;
 126         if ((r = sshbuf_put_bignum2(buf, pub_key)) != 0 ||
 127             (r = sshbuf_get_u32(buf, NULL)) != 0)
 128                 goto out;
 129 #ifdef DEBUG_KEXDH
 130         DHparams_print_fp(stderr, kex->dh);
 131         fprintf(stderr, "pub= ");
 132         BN_print_fp(stderr, pub_key);
 133         fprintf(stderr, "\n");
 134 #endif
 135         kex->client_pub = buf;
 136         buf = NULL;
 137  out:
 138         sshbuf_free(buf);
 139         return r;
 140 }
 141
 142 int
 143 kex_dh_enc(struct kex *kex, const struct sshbuf *client_blob,
 144     struct sshbuf **server_blobp, struct sshbuf **shared_secretp)
 145 {
 146         const BIGNUM *pub_key;
 147         struct sshbuf *server_blob = NULL;
 148         int r;
 149
 150         *server_blobp = NULL;
 151         *shared_secretp = NULL;
 152
 153         if ((r = kex_dh_keygen(kex)) != 0)
 154                 goto out;
 155         DH_get0_key(kex->dh, &pub_key, NULL);
 156         if ((server_blob = sshbuf_new()) == NULL) {
 157                 r = SSH_ERR_ALLOC_FAIL;
 158                 goto out;
 159         }
 160         if ((r = sshbuf_put_bignum2(server_blob, pub_key)) != 0 ||
 161             (r = sshbuf_get_u32(server_blob, NULL)) != 0)
 162                 goto out;
 163         if ((r = kex_dh_dec(kex, client_blob, shared_secretp)) != 0)
 164                 goto out;
 165         *server_blobp = server_blob;
 166         server_blob = NULL;
 167  out:
 168         DH_free(kex->dh);
 169         kex->dh = NULL;
 170         sshbuf_free(server_blob);
 171         return r;
 172 }
 173
 174 int
 175 kex_dh_dec(struct kex *kex, const struct sshbuf *dh_blob,
 176     struct sshbuf **shared_secretp)
 177 {
 178         struct sshbuf *buf = NULL;
 179         BIGNUM *dh_pub = NULL;
 180         int r;
 181
 182         *shared_secretp = NULL;
 183
 184         if ((buf = sshbuf_new()) == NULL) {
 185                 r = SSH_ERR_ALLOC_FAIL;
 186                 goto out;
 187         }
 188         if ((r = sshbuf_put_stringb(buf, dh_blob)) != 0 ||
 189             (r = sshbuf_get_bignum2(buf, &dh_pub)) != 0)
 190                 goto out;
 191         sshbuf_reset(buf);
 192         if ((r = kex_dh_compute_key(kex, dh_pub, buf)) != 0)
 193                 goto out;
 194         *shared_secretp = buf;
 195         buf = NULL;
 196  out:
 197         BN_free(dh_pub);
 198         DH_free(kex->dh);
 199         kex->dh = NULL;
 200         sshbuf_free(buf);
 201         return r;
 202 }
 203 #endif /* WITH_OPENSSL */