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