crypto/dh/dh_key.c

   1 /*
   2  * Copyright 1995-2019 The OpenSSL Project Authors. All Rights Reserved.
   3  *
   4  * Licensed under the Apache License 2.0 (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              * We handle just one known case where g is a quadratic non-residue:
 130              * for g = 2: p % 8 == 3
 131              */
 132             if (BN_is_word(dh->g, DH_GENERATOR_2) && !BN_is_bit_set(dh->p, 2)) {
 133                 /* clear bit 0, since it won't be a secret anyway */
 134                 if (!BN_clear_bit(priv_key, 0))
 135                     goto err;
 136             }
 137         }
 138     }
 139
 140     {
 141         BIGNUM *prk = BN_new();
 142
 143         if (prk == NULL)
 144             goto err;
 145         BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 146
 147         if (!dh->meth->bn_mod_exp(dh, pub_key, dh->g, prk, dh->p, ctx, mont)) {
 148             BN_clear_free(prk);
 149             goto err;
 150         }
 151         /* We MUST free prk before any further use of priv_key */
 152         BN_clear_free(prk);
 153     }
 154
 155     dh->pub_key = pub_key;
 156     dh->priv_key = priv_key;
 157     dh->dirty_cnt++;
 158     ok = 1;
 159  err:
 160     if (ok != 1)
 161         DHerr(DH_F_GENERATE_KEY, ERR_R_BN_LIB);
 162
 163     if (pub_key != dh->pub_key)
 164         BN_free(pub_key);
 165     if (priv_key != dh->priv_key)
 166         BN_free(priv_key);
 167     BN_CTX_free(ctx);
 168     return ok;
 169 }
 170
 171 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 172 {
 173     BN_CTX *ctx = NULL;
 174     BN_MONT_CTX *mont = NULL;
 175     BIGNUM *tmp;
 176     int ret = -1;
 177     int check_result;
 178
 179     if (BN_num_bits(dh->p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 180         DHerr(DH_F_COMPUTE_KEY, DH_R_MODULUS_TOO_LARGE);
 181         goto err;
 182     }
 183
 184     ctx = BN_CTX_new();
 185     if (ctx == NULL)
 186         goto err;
 187     BN_CTX_start(ctx);
 188     tmp = BN_CTX_get(ctx);
 189     if (tmp == NULL)
 190         goto err;
 191
 192     if (dh->priv_key == NULL) {
 193         DHerr(DH_F_COMPUTE_KEY, DH_R_NO_PRIVATE_VALUE);
 194         goto err;
 195     }
 196
 197     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 198         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 199                                       dh->lock, dh->p, ctx);
 200         BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
 201         if (!mont)
 202             goto err;
 203     }
 204
 205     if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
 206         DHerr(DH_F_COMPUTE_KEY, DH_R_INVALID_PUBKEY);
 207         goto err;
 208     }
 209
 210     if (!dh->
 211         meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->p, ctx, mont)) {
 212         DHerr(DH_F_COMPUTE_KEY, ERR_R_BN_LIB);
 213         goto err;
 214     }
 215
 216     ret = BN_bn2bin(tmp, key);
 217  err:
 218     BN_CTX_end(ctx);
 219     BN_CTX_free(ctx);
 220     return ret;
 221 }
 222
 223 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 224                          const BIGNUM *a, const BIGNUM *p,
 225                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 226 {
 227     return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 228 }
 229
 230 static int dh_init(DH *dh)
 231 {
 232     dh->flags |= DH_FLAG_CACHE_MONT_P;
 233     return 1;
 234 }
 235
 236 static int dh_finish(DH *dh)
 237 {
 238     BN_MONT_CTX_free(dh->method_mont_p);
 239     return 1;
 240 }
 241
 242 int dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
 243 {
 244     int err_reason = DH_R_BN_ERROR;
 245     BIGNUM *pubkey = NULL;
 246     const BIGNUM *p;
 247     size_t p_size;
 248
 249     if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
 250         goto err;
 251     DH_get0_pqg(dh, &p, NULL, NULL);
 252     if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
 253         err_reason = DH_R_NO_PARAMETERS_SET;
 254         goto err;
 255     }
 256     /*
 257      * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
 258      * public key is of size not equal to size of p
 259      */
 260     if (BN_is_zero(pubkey) || p_size != len) {
 261         err_reason = DH_R_INVALID_PUBKEY;
 262         goto err;
 263     }
 264     if (DH_set0_key(dh, pubkey, NULL) != 1)
 265         goto err;
 266     return 1;
 267 err:
 268     DHerr(DH_F_DH_BUF2KEY, err_reason);
 269     BN_free(pubkey);
 270     return 0;
 271 }
 272
 273 size_t dh_key2buf(const DH *dh, unsigned char **pbuf_out)
 274 {
 275     const BIGNUM *pubkey;
 276     unsigned char *pbuf;
 277     const BIGNUM *p;
 278     int p_size;
 279
 280     DH_get0_pqg(dh, &p, NULL, NULL);
 281     DH_get0_key(dh, &pubkey, NULL);
 282     if (p == NULL || pubkey == NULL
 283             || (p_size = BN_num_bytes(p)) == 0
 284             || BN_num_bytes(pubkey) == 0) {
 285         DHerr(DH_F_DH_KEY2BUF, DH_R_INVALID_PUBKEY);
 286         return 0;
 287     }
 288     if ((pbuf = OPENSSL_malloc(p_size)) == NULL) {
 289         DHerr(DH_F_DH_KEY2BUF, ERR_R_MALLOC_FAILURE);
 290         return 0;
 291     }
 292     /*
 293      * As per Section 4.2.8.1 of RFC 8446 left pad public
 294      * key with zeros to the size of p
 295      */
 296     if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) {
 297         OPENSSL_free(pbuf);
 298         DHerr(DH_F_DH_KEY2BUF, DH_R_BN_ERROR);
 299         return 0;
 300     }
 301     *pbuf_out = pbuf;
 302     return p_size;
 303 }