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 const DH_METHOD *DH_OpenSSL(void)
  60 {
  61     return &dh_ossl;
  62 }
  63
  64 static int generate_key(DH *dh)
  65 {
  66     int ok = 0;
  67     int generate_new_key = 0;
  68     unsigned l;
  69     BN_CTX *ctx;
  70     BN_MONT_CTX *mont = NULL;
  71     BIGNUM *pub_key = NULL, *priv_key = NULL;
  72
  73     ctx = BN_CTX_new();
  74     if (ctx == NULL)
  75         goto err;
  76
  77     if (dh->priv_key == NULL) {
  78         priv_key = BN_secure_new();
  79         if (priv_key == NULL)
  80             goto err;
  81         generate_new_key = 1;
  82     } else
  83         priv_key = dh->priv_key;
  84
  85     if (dh->pub_key == NULL) {
  86         pub_key = BN_new();
  87         if (pub_key == NULL)
  88             goto err;
  89     } else
  90         pub_key = dh->pub_key;
  91
  92     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
  93         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
  94                                       dh->lock, dh->p, ctx);
  95         if (!mont)
  96             goto err;
  97     }
  98
  99     if (generate_new_key) {
 100         if (dh->q) {
 101             do {
 102                 if (!BN_rand_range(priv_key, dh->q))
 103                     goto err;
 104             }
 105             while (BN_is_zero(priv_key) || BN_is_one(priv_key));
 106         } else {
 107             /* secret exponent length */
 108             l = dh->length ? dh->length : BN_num_bits(dh->p) - 1;
 109             if (!BN_rand(priv_key, l, 0, 0))
 110                 goto err;
 111         }
 112     }
 113
 114     {
 115         BIGNUM *prk = BN_new();
 116
 117         if (prk == NULL)
 118             goto err;
 119         BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 120
 121         if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {
 122             BN_free(prk);
 123             goto err;
 124         }
 125         /* We MUST free prk before any further use of priv_key */
 126         BN_free(prk);
 127     }
 128
 129     dh->pub_key = pub_key;
 130     dh->priv_key = priv_key;
 131     ok = 1;
 132  err:
 133     if (ok != 1)
 134         DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
 135
 136     if (pub_key != dh->pub_key)
 137         BN_free(pub_key);
 138     if (priv_key != dh->priv_key)
 139         BN_free(priv_key);
 140     BN_CTX_free(ctx);
 141     return (ok);
 142 }
 143
 144 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 145 {
 146     BN_CTX *ctx = NULL;
 147     BN_MONT_CTX *mont = NULL;
 148     BIGNUM *tmp;
 149     int ret = -1;
 150     int check_result;
 151
 152     if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 153         DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
 154         goto err;
 155     }
 156
 157     ctx = BN_CTX_new();
 158     if (ctx == NULL)
 159         goto err;
 160     BN_CTX_start(ctx);
 161     tmp = BN_CTX_get(ctx);
 162
 163     if (dh->priv_key == NULL) {
 164         DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
 165         goto err;
 166     }
 167
 168     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 169         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 170                                       dh->lock, dh->p, ctx);
 171         BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
 172         if (!mont)
 173             goto err;
 174     }
 175
 176     if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
 177         DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
 178         goto err;
 179     }
 180
 181     if (!dh->
 182         meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
 183         DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
 184         goto err;
 185     }
 186
 187     ret = BN_bn2bin(tmp, key);
 188  err:
 189     if (ctx != NULL) {
 190         BN_CTX_end(ctx);
 191         BN_CTX_free(ctx);
 192     }
 193     return (ret);
 194 }
 195
 196 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 197                          const BIGNUM *a, const BIGNUM *p,
 198                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 199 {
 200     return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 201 }
 202
 203 static int dh_init(DH *dh)
 204 {
 205     dh->flags |= DH_FLAG_CACHE_MONT_P;
 206     return (1);
 207 }
 208
 209 static int dh_finish(DH *dh)
 210 {
 211     BN_MONT_CTX_free(dh->method_mont_p);
 212     return (1);
 213 }