crypto/dh/dh_key.c

   1 /*
   2  * Copyright 1995-2016 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the OpenSSL license (the "License").  You may not use
   5  * this file except in compliance with the License.  You can obtain a copy
   6  * in the file LICENSE in the source distribution or at
   7  * https://www.openssl.org/source/license.html
   8  */
   9
  10 #include <stdio.h>
  11 #include "internal/cryptlib.h"
  12 #include <openssl/rand.h>
  13 #include "dh_locl.h"
  14 #include "internal/bn_int.h"
  15
  16 static int generate_key(DH *dh);
  17 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
  18 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
  19                          const BIGNUM *a, const BIGNUM *p,
  20                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
  21 static int dh_init(DH *dh);
  22 static int dh_finish(DH *dh);
  23
  24 int DH_generate_key(DH *dh)
  25 {
  26     return dh->meth->generate_key(dh);
  27 }
  28
  29 int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  30 {
  31     return dh->meth->compute_key(key, pub_key, dh);
  32 }
  33
  34 int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  35 {
  36     int rv, pad;
  37     rv = dh->meth->compute_key(key, pub_key, dh);
  38     if (rv <= 0)
  39         return rv;
  40     pad = BN_num_bytes(dh->p) - rv;
  41     if (pad > 0) {
  42         memmove(key + pad, key, rv);
  43         memset(key, 0, pad);
  44     }
  45     return rv + pad;
  46 }
  47
  48 static DH_METHOD dh_ossl = {
  49     "OpenSSL DH Method",
  50     generate_key,
  51     compute_key,
  52     dh_bn_mod_exp,
  53     dh_init,
  54     dh_finish,
  55     DH_FLAG_FIPS_METHOD,
  56     NULL,
  57     NULL
  58 };
  59
  60 const DH_METHOD *DH_OpenSSL(void)
  61 {
  62     return &dh_ossl;
  63 }
  64
  65 static int generate_key(DH *dh)
  66 {
  67     int ok = 0;
  68     int generate_new_key = 0;
  69     unsigned l;
  70     BN_CTX *ctx;
  71     BN_MONT_CTX *mont = NULL;
  72     BIGNUM *pub_key = NULL, *priv_key = NULL;
  73
  74     ctx = BN_CTX_new();
  75     if (ctx == NULL)
  76         goto err;
  77
  78     if (dh->priv_key == NULL) {
  79         priv_key = BN_secure_new();
  80         if (priv_key == NULL)
  81             goto err;
  82         generate_new_key = 1;
  83     } else
  84         priv_key = dh->priv_key;
  85
  86     if (dh->pub_key == NULL) {
  87         pub_key = BN_new();
  88         if (pub_key == NULL)
  89             goto err;
  90     } else
  91         pub_key = dh->pub_key;
  92
  93     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
  94         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
  95                                       dh->lock, dh->p, ctx);
  96         if (!mont)
  97             goto err;
  98     }
  99
 100     if (generate_new_key) {
 101         if (dh->q) {
 102             do {
 103                 if (!BN_rand_range(priv_key, dh->q))
 104                     goto err;
 105             }
 106             while (BN_is_zero(priv_key) || BN_is_one(priv_key));
 107         } else {
 108             /* secret exponent length */
 109             l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
 110             if (!BN_rand(priv_key, l, 0, 0))
 111                 goto err;
 112         }
 113     }
 114
 115     {
 116         BIGNUM *local_prk = NULL;
 117         BIGNUM *prk;
 118
 119         if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0) {
 120             local_prk = prk = BN_new();
 121             if (local_prk == NULL)
 122                 goto err;
 123             BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 124         } else {
 125             prk = priv_key;
 126         }
 127
 128         if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {
 129             BN_free(local_prk);
 130             goto err;
 131         }
 132         /* We MUST free local_prk before any further use of priv_key */
 133         BN_free(local_prk);
 134     }
 135
 136     dh->pub_key = pub_key;
 137     dh->priv_key = priv_key;
 138     ok = 1;
 139  err:
 140     if (ok != 1)
 141         DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
 142
 143     if (pub_key != dh->pub_key)
 144         BN_free(pub_key);
 145     if (priv_key != dh->priv_key)
 146         BN_free(priv_key);
 147     BN_CTX_free(ctx);
 148     return (ok);
 149 }
 150
 151 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 152 {
 153     BN_CTX *ctx = NULL;
 154     BN_MONT_CTX *mont = NULL;
 155     BIGNUM *tmp;
 156     int ret = -1;
 157     int check_result;
 158
 159     if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 160         DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
 161         goto err;
 162     }
 163
 164     ctx = BN_CTX_new();
 165     if (ctx == NULL)
 166         goto err;
 167     BN_CTX_start(ctx);
 168     tmp = BN_CTX_get(ctx);
 169
 170     if (dh->priv_key == NULL) {
 171         DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
 172         goto err;
 173     }
 174
 175     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 176         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 177                                       dh->lock, dh->p, ctx);
 178         if ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) == 0) {
 179             /* XXX */
 180             BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
 181         }
 182         if (!mont)
 183             goto err;
 184     }
 185
 186     if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
 187         DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
 188         goto err;
 189     }
 190
 191     if (!dh->
 192         meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
 193         DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
 194         goto err;
 195     }
 196
 197     ret = BN_bn2bin(tmp, key);
 198  err:
 199     if (ctx != NULL) {
 200         BN_CTX_end(ctx);
 201         BN_CTX_free(ctx);
 202     }
 203     return (ret);
 204 }
 205
 206 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 207                          const BIGNUM *a, const BIGNUM *p,
 208                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 209 {
 210     /*
 211      * If a is only one word long and constant time is false, use the faster
 212      * exponentiation function.
 213      */
 214     if (bn_get_top(a) == 1 && ((dh->flags & DH_FLAG_NO_EXP_CONSTTIME) != 0)) {
 215         BN_ULONG A = bn_get_words(a)[0];
 216         return BN_mod_exp_mont_word(r, A, p, m, ctx, m_ctx);
 217     } else
 218         return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 219 }
 220
 221 static int dh_init(DH *dh)
 222 {
 223     dh->flags |= DH_FLAG_CACHE_MONT_P;
 224     return (1);
 225 }
 226
 227 static int dh_finish(DH *dh)
 228 {
 229     BN_MONT_CTX_free(dh->method_mont_p);
 230     return (1);
 231 }