crypto/dh/dh_key.c

   1 /*
   2  * Copyright 1995-2020 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 /*
  11  * DH low level APIs are deprecated for public use, but still ok for
  12  * internal use.
  13  */
  14 #include "internal/deprecated.h"
  15
  16 #include <stdio.h>
  17 #include "internal/cryptlib.h"
  18 #include "dh_local.h"
  19 #include "crypto/bn.h"
  20 #include "crypto/dh.h"
  21
  22 #ifdef FIPS_MODE
  23 # define MIN_STRENGTH 112
  24 #else
  25 # define MIN_STRENGTH 80
  26 #endif
  27
  28 static int generate_key(DH *dh);
  29 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
  30                          const BIGNUM *a, const BIGNUM *p,
  31                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
  32 static int dh_init(DH *dh);
  33 static int dh_finish(DH *dh);
  34
  35 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  36 {
  37     BN_CTX *ctx = NULL;
  38     BN_MONT_CTX *mont = NULL;
  39     BIGNUM *tmp;
  40     int ret = -1;
  41 #ifndef FIPS_MODE
  42     int check_result;
  43 #endif
  44
  45     if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) {
  46         DHerr(0, DH_R_MODULUS_TOO_LARGE);
  47         goto err;
  48     }
  49
  50     if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
  51         DHerr(0, DH_R_MODULUS_TOO_SMALL);
  52         return 0;
  53     }
  54
  55     ctx = BN_CTX_new_ex(dh->libctx);
  56     if (ctx == NULL)
  57         goto err;
  58     BN_CTX_start(ctx);
  59     tmp = BN_CTX_get(ctx);
  60     if (tmp == NULL)
  61         goto err;
  62
  63     if (dh->priv_key == NULL) {
  64         DHerr(0, DH_R_NO_PRIVATE_VALUE);
  65         goto err;
  66     }
  67
  68     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
  69         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
  70                                       dh->lock, dh->params.p, ctx);
  71         BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
  72         if (!mont)
  73             goto err;
  74     }
  75 /* TODO(3.0) : Solve in a PR related to Key validation for DH */
  76 #ifndef FIPS_MODE
  77     if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
  78         DHerr(0, DH_R_INVALID_PUBKEY);
  79         goto err;
  80     }
  81 #endif
  82     if (!dh->meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->params.p, ctx,
  83                               mont)) {
  84         DHerr(0, ERR_R_BN_LIB);
  85         goto err;
  86     }
  87
  88     ret = BN_bn2bin(tmp, key);
  89  err:
  90     BN_CTX_end(ctx);
  91     BN_CTX_free(ctx);
  92     return ret;
  93 }
  94
  95 int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  96 {
  97 #ifdef FIPS_MODE
  98     return compute_key(key, pub_key, dh);
  99 #else
 100     return dh->meth->compute_key(key, pub_key, dh);
 101 #endif
 102 }
 103
 104 int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 105 {
 106     int rv, pad;
 107
 108 #ifdef FIPS_MODE
 109     rv = compute_key(key, pub_key, dh);
 110 #else
 111     rv = dh->meth->compute_key(key, pub_key, dh);
 112 #endif
 113     if (rv <= 0)
 114         return rv;
 115     pad = BN_num_bytes(dh->params.p) - rv;
 116     if (pad > 0) {
 117         memmove(key + pad, key, rv);
 118         memset(key, 0, pad);
 119     }
 120     return rv + pad;
 121 }
 122
 123 static DH_METHOD dh_ossl = {
 124     "OpenSSL DH Method",
 125     generate_key,
 126     compute_key,
 127     dh_bn_mod_exp,
 128     dh_init,
 129     dh_finish,
 130     DH_FLAG_FIPS_METHOD,
 131     NULL,
 132     NULL
 133 };
 134
 135 static const DH_METHOD *default_DH_method = &dh_ossl;
 136
 137 const DH_METHOD *DH_OpenSSL(void)
 138 {
 139     return &dh_ossl;
 140 }
 141
 142 const DH_METHOD *DH_get_default_method(void)
 143 {
 144     return default_DH_method;
 145 }
 146
 147 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 148                          const BIGNUM *a, const BIGNUM *p,
 149                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 150 {
 151     return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 152 }
 153
 154 static int dh_init(DH *dh)
 155 {
 156     dh->flags |= DH_FLAG_CACHE_MONT_P;
 157     ffc_params_init(&dh->params);
 158     dh->dirty_cnt++;
 159     return 1;
 160 }
 161
 162 static int dh_finish(DH *dh)
 163 {
 164     BN_MONT_CTX_free(dh->method_mont_p);
 165     return 1;
 166 }
 167
 168 #ifndef FIPS_MODE
 169 void DH_set_default_method(const DH_METHOD *meth)
 170 {
 171     default_DH_method = meth;
 172 }
 173 #endif /* FIPS_MODE */
 174
 175 int DH_generate_key(DH *dh)
 176 {
 177 #ifdef FIPS_MODE
 178     return generate_key(dh);
 179 #else
 180     return dh->meth->generate_key(dh);
 181 #endif
 182 }
 183
 184 int dh_generate_public_key(BN_CTX *ctx, DH *dh, const BIGNUM *priv_key,
 185                            BIGNUM *pub_key)
 186 {
 187     int ret = 0;
 188     BIGNUM *prk = BN_new();
 189     BN_MONT_CTX *mont = NULL;
 190
 191     if (prk == NULL)
 192         return 0;
 193
 194     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 195         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 196                                       dh->lock, dh->params.p, ctx);
 197         if (mont == NULL)
 198             goto err;
 199     }
 200     BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 201
 202     /* pub_key = g^priv_key mod p */
 203     if (!dh->meth->bn_mod_exp(dh, pub_key, dh->params.g, prk, dh->params.p,
 204                               ctx, mont))
 205         goto err;
 206     ret = 1;
 207 err:
 208     BN_clear_free(prk);
 209     return ret;
 210 }
 211
 212 static int generate_key(DH *dh)
 213 {
 214     int ok = 0;
 215     int generate_new_key = 0;
 216 #ifndef FIPS_MODE
 217     unsigned l;
 218 #endif
 219     BN_CTX *ctx = NULL;
 220     BIGNUM *pub_key = NULL, *priv_key = NULL;
 221
 222     if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 223         DHerr(0, DH_R_MODULUS_TOO_LARGE);
 224         return 0;
 225     }
 226
 227     if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
 228         DHerr(0, DH_R_MODULUS_TOO_SMALL);
 229         return 0;
 230     }
 231
 232     ctx = BN_CTX_new_ex(dh->libctx);
 233     if (ctx == NULL)
 234         goto err;
 235
 236     if (dh->priv_key == NULL) {
 237         priv_key = BN_secure_new();
 238         if (priv_key == NULL)
 239             goto err;
 240         generate_new_key = 1;
 241     } else {
 242         priv_key = dh->priv_key;
 243     }
 244
 245     if (dh->pub_key == NULL) {
 246         pub_key = BN_new();
 247         if (pub_key == NULL)
 248             goto err;
 249     } else {
 250         pub_key = dh->pub_key;
 251     }
 252     if (generate_new_key) {
 253         /* Is it an approved safe prime ?*/
 254         if (DH_get_nid(dh) != NID_undef) {
 255             /*
 256              * The safe prime group code sets N = 2*s
 257              * (where s = max security strength supported).
 258              * N = dh->length (N = maximum bit length of private key)
 259              */
 260             if (dh->params.q == NULL
 261                 || dh->length > BN_num_bits(dh->params.q))
 262                 goto err;
 263             if (!ffc_generate_private_key(ctx, &dh->params, dh->length,
 264                                           dh->length / 2, priv_key))
 265                 goto err;
 266         } else {
 267 #ifdef FIPS_MODE
 268             if (dh->params.q == NULL)
 269                 goto err;
 270 #else
 271             if (dh->params.q == NULL) {
 272                 /* secret exponent length */
 273                 l = dh->length ? dh->length : BN_num_bits(dh->params.p) - 1;
 274                 if (!BN_priv_rand_ex(priv_key, l, BN_RAND_TOP_ONE,
 275                                      BN_RAND_BOTTOM_ANY, ctx))
 276                     goto err;
 277                 /*
 278                  * We handle just one known case where g is a quadratic non-residue:
 279                  * for g = 2: p % 8 == 3
 280                  */
 281                 if (BN_is_word(dh->params.g, DH_GENERATOR_2)
 282                     && !BN_is_bit_set(dh->params.p, 2)) {
 283                     /* clear bit 0, since it won't be a secret anyway */
 284                     if (!BN_clear_bit(priv_key, 0))
 285                         goto err;
 286                 }
 287             } else
 288 #endif
 289             {
 290                 /*
 291                  * For FFC FIPS 186-4 keygen
 292                  * security strength s = 112,
 293                  * Max Private key size N = len(q)
 294                  */
 295                 if (!ffc_generate_private_key(ctx, &dh->params,
 296                                               BN_num_bits(dh->params.q),
 297                                               MIN_STRENGTH,
 298                                               priv_key))
 299                     goto err;
 300             }
 301         }
 302     }
 303
 304     if (!dh_generate_public_key(ctx, dh, priv_key, pub_key))
 305         goto err;
 306
 307     dh->pub_key = pub_key;
 308     dh->priv_key = priv_key;
 309     dh->dirty_cnt++;
 310     ok = 1;
 311  err:
 312     if (ok != 1)
 313         DHerr(0, ERR_R_BN_LIB);
 314
 315     if (pub_key != dh->pub_key)
 316         BN_free(pub_key);
 317     if (priv_key != dh->priv_key)
 318         BN_free(priv_key);
 319     BN_CTX_free(ctx);
 320     return ok;
 321 }
 322
 323 int dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
 324 {
 325     int err_reason = DH_R_BN_ERROR;
 326     BIGNUM *pubkey = NULL;
 327     const BIGNUM *p;
 328     size_t p_size;
 329
 330     if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
 331         goto err;
 332     DH_get0_pqg(dh, &p, NULL, NULL);
 333     if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
 334         err_reason = DH_R_NO_PARAMETERS_SET;
 335         goto err;
 336     }
 337     /*
 338      * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
 339      * public key is of size not equal to size of p
 340      */
 341     if (BN_is_zero(pubkey) || p_size != len) {
 342         err_reason = DH_R_INVALID_PUBKEY;
 343         goto err;
 344     }
 345     if (DH_set0_key(dh, pubkey, NULL) != 1)
 346         goto err;
 347     return 1;
 348 err:
 349     DHerr(DH_F_DH_BUF2KEY, err_reason);
 350     BN_free(pubkey);
 351     return 0;
 352 }
 353
 354 size_t dh_key2buf(const DH *dh, unsigned char **pbuf_out)
 355 {
 356     const BIGNUM *pubkey;
 357     unsigned char *pbuf;
 358     const BIGNUM *p;
 359     int p_size;
 360
 361     DH_get0_pqg(dh, &p, NULL, NULL);
 362     DH_get0_key(dh, &pubkey, NULL);
 363     if (p == NULL || pubkey == NULL
 364             || (p_size = BN_num_bytes(p)) == 0
 365             || BN_num_bytes(pubkey) == 0) {
 366         DHerr(DH_F_DH_KEY2BUF, DH_R_INVALID_PUBKEY);
 367         return 0;
 368     }
 369     if ((pbuf = OPENSSL_malloc(p_size)) == NULL) {
 370         DHerr(DH_F_DH_KEY2BUF, ERR_R_MALLOC_FAILURE);
 371         return 0;
 372     }
 373     /*
 374      * As per Section 4.2.8.1 of RFC 8446 left pad public
 375      * key with zeros to the size of p
 376      */
 377     if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) {
 378         OPENSSL_free(pbuf);
 379         DHerr(DH_F_DH_KEY2BUF, DH_R_BN_ERROR);
 380         return 0;
 381     }
 382     *pbuf_out = pbuf;
 383     return p_size;
 384 }