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 "dh_locl.h"
  13 #include "internal/bn_int.h"
  14
  15 static int generate_key(DH *dh);
  16 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh);
  17 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
  18                          const BIGNUM *a, const BIGNUM *p,
  19                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
  20 static int dh_init(DH *dh);
  21 static int dh_finish(DH *dh);
  22
  23 int DH_generate_key(DH *dh)
  24 {
  25     return dh->meth->generate_key(dh);
  26 }
  27
  28 int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  29 {
  30     return dh->meth->compute_key(key, pub_key, dh);
  31 }
  32
  33 int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  34 {
  35     int rv, pad;
  36     rv = dh->meth->compute_key(key, pub_key, dh);
  37     if (rv <= 0)
  38         return rv;
  39     pad = BN_num_bytes(dh->p) - rv;
  40     if (pad > 0) {
  41         memmove(key + pad, key, rv);
  42         memset(key, 0, pad);
  43     }
  44     return rv + pad;
  45 }
  46
  47 static DH_METHOD dh_ossl = {
  48     "OpenSSL DH Method",
  49     generate_key,
  50     compute_key,
  51     dh_bn_mod_exp,
  52     dh_init,
  53     dh_finish,
  54     DH_FLAG_FIPS_METHOD,
  55     NULL,
  56     NULL
  57 };
  58
  59 static const DH_METHOD *default_DH_method = &dh_ossl;
  60
  61 const DH_METHOD *DH_OpenSSL(void)
  62 {
  63     return &dh_ossl;
  64 }
  65
  66 void DH_set_default_method(const DH_METHOD *meth)
  67 {
  68     default_DH_method = meth;
  69 }
  70
  71 const DH_METHOD *DH_get_default_method(void)
  72 {
  73     return default_DH_method;
  74 }
  75
  76 static int generate_key(DH *dh)
  77 {
  78     int ok = 0;
  79     int generate_new_key = 0;
  80     unsigned l;
  81     BN_CTX *ctx = NULL;
  82     BN_MONT_CTX *mont = NULL;
  83     BIGNUM *pub_key = NULL, *priv_key = NULL;
  84
  85     if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
  86         DHerr(DH_F_GENERATE_KEY, DH_R_MODULUS_TOO_LARGE);
  87         return 0;
  88     }
  89
  90     ctx = BN_CTX_new();
  91     if (ctx == NULL)
  92         goto err;
  93
  94     if (dh->priv_key == NULL) {
  95         priv_key = BN_secure_new();
  96         if (priv_key == NULL)
  97             goto err;
  98         generate_new_key = 1;
  99     } else
 100         priv_key = dh->priv_key;
 101
 102     if (dh->pub_key == NULL) {
 103         pub_key = BN_new();
 104         if (pub_key == NULL)
 105             goto err;
 106     } else
 107         pub_key = dh->pub_key;
 108
 109     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 110         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 111                                       dh->lock, dh->p, ctx);
 112         if (!mont)
 113             goto err;
 114     }
 115
 116     if (generate_new_key) {
 117         if (dh->q) {
 118             do {
 119                 if (!BN_priv_rand_range(priv_key, dh->q))
 120                     goto err;
 121             }
 122             while (BN_is_zero(priv_key) || BN_is_one(priv_key));
 123         } else {
 124             /* secret exponent length */
 125             l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
 126             if (!BN_priv_rand(priv_key, l, BN_RAND_TOP_ONE, BN_RAND_BOTTOM_ANY))
 127                 goto err;
 128         }
 129     }
 130
 131     {
 132         BIGNUM *prk = BN_new();
 133
 134         if (prk == NULL)
 135             goto err;
 136         BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 137
 138         if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {
 139             BN_free(prk);
 140             goto err;
 141         }
 142         /* We MUST free prk before any further use of priv_key */
 143         BN_free(prk);
 144     }
 145
 146     dh->pub_key = pub_key;
 147     dh->priv_key = priv_key;
 148     ok = 1;
 149  err:
 150     if (ok != 1)
 151         DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
 152
 153     if (pub_key != dh->pub_key)
 154         BN_free(pub_key);
 155     if (priv_key != dh->priv_key)
 156         BN_free(priv_key);
 157     BN_CTX_free(ctx);
 158     return ok;
 159 }
 160
 161 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 162 {
 163     BN_CTX *ctx = NULL;
 164     BN_MONT_CTX *mont = NULL;
 165     BIGNUM *tmp;
 166     int ret = -1;
 167     int check_result;
 168
 169     if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 170         DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
 171         goto err;
 172     }
 173
 174     ctx = BN_CTX_new();
 175     if (ctx == NULL)
 176         goto err;
 177     BN_CTX_start(ctx);
 178     tmp = BN_CTX_get(ctx);
 179     if (tmp == NULL)
 180         goto err;
 181
 182     if (dh->priv_key == NULL) {
 183         DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
 184         goto err;
 185     }
 186
 187     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 188         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 189                                       dh->lock, dh->p, ctx);
 190         BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
 191         if (!mont)
 192             goto err;
 193     }
 194
 195     if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
 196         DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
 197         goto err;
 198     }
 199
 200     if (!dh->
 201         meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
 202         DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
 203         goto err;
 204     }
 205
 206     ret = BN_bn2bin(tmp, key);
 207  err:
 208     if (ctx != NULL) {
 209         BN_CTX_end(ctx);
 210         BN_CTX_free(ctx);
 211     }
 212     return ret;
 213 }
 214
 215 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 216                          const BIGNUM *a, const BIGNUM *p,
 217                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 218 {
 219     return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 220 }
 221
 222 static int dh_init(DH *dh)
 223 {
 224     dh->flags |= DH_FLAG_CACHE_MONT_P;
 225     return 1;
 226 }
 227
 228 static int dh_finish(DH *dh)
 229 {
 230     BN_MONT_CTX_free(dh->method_mont_p);
 231     return 1;
 232 }