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 #include "crypto/security_bits.h"
  22
  23 #ifdef FIPS_MODULE
  24 # define MIN_STRENGTH 112
  25 #else
  26 # define MIN_STRENGTH 80
  27 #endif
  28
  29 static int generate_key(DH *dh);
  30 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
  31                          const BIGNUM *a, const BIGNUM *p,
  32                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx);
  33 static int dh_init(DH *dh);
  34 static int dh_finish(DH *dh);
  35
  36 static int compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  37 {
  38     BN_CTX *ctx = NULL;
  39     BN_MONT_CTX *mont = NULL;
  40     BIGNUM *tmp;
  41     int ret = -1;
  42 #ifndef FIPS_MODULE
  43     int check_result;
  44 #endif
  45
  46     if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) {
  47         DHerr(0, DH_R_MODULUS_TOO_LARGE);
  48         goto err;
  49     }
  50
  51     if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
  52         DHerr(0, DH_R_MODULUS_TOO_SMALL);
  53         return 0;
  54     }
  55
  56     ctx = BN_CTX_new_ex(dh->libctx);
  57     if (ctx == NULL)
  58         goto err;
  59     BN_CTX_start(ctx);
  60     tmp = BN_CTX_get(ctx);
  61     if (tmp == NULL)
  62         goto err;
  63
  64     if (dh->priv_key == NULL) {
  65         DHerr(0, DH_R_NO_PRIVATE_VALUE);
  66         goto err;
  67     }
  68
  69     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
  70         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
  71                                       dh->lock, dh->params.p, ctx);
  72         BN_set_flags(dh->priv_key, BN_FLG_CONSTTIME);
  73         if (!mont)
  74             goto err;
  75     }
  76 /* TODO(3.0) : Solve in a PR related to Key validation for DH */
  77 #ifndef FIPS_MODULE
  78     if (!DH_check_pub_key(dh, pub_key, &check_result) || check_result) {
  79         DHerr(0, DH_R_INVALID_PUBKEY);
  80         goto err;
  81     }
  82 #endif
  83     if (!dh->meth->bn_mod_exp(dh, tmp, pub_key, dh->priv_key, dh->params.p, ctx,
  84                               mont)) {
  85         DHerr(0, ERR_R_BN_LIB);
  86         goto err;
  87     }
  88
  89     ret = BN_bn2bin(tmp, key);
  90  err:
  91     BN_CTX_end(ctx);
  92     BN_CTX_free(ctx);
  93     return ret;
  94 }
  95
  96 int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
  97 {
  98 #ifdef FIPS_MODULE
  99     return compute_key(key, pub_key, dh);
 100 #else
 101     return dh->meth->compute_key(key, pub_key, dh);
 102 #endif
 103 }
 104
 105 int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 106 {
 107     int rv, pad;
 108
 109 #ifdef FIPS_MODULE
 110     rv = compute_key(key, pub_key, dh);
 111 #else
 112     rv = dh->meth->compute_key(key, pub_key, dh);
 113 #endif
 114     if (rv <= 0)
 115         return rv;
 116     pad = BN_num_bytes(dh->params.p) - rv;
 117     if (pad > 0) {
 118         memmove(key + pad, key, rv);
 119         memset(key, 0, pad);
 120     }
 121     return rv + pad;
 122 }
 123
 124 static DH_METHOD dh_ossl = {
 125     "OpenSSL DH Method",
 126     generate_key,
 127     compute_key,
 128     dh_bn_mod_exp,
 129     dh_init,
 130     dh_finish,
 131     DH_FLAG_FIPS_METHOD,
 132     NULL,
 133     NULL
 134 };
 135
 136 static const DH_METHOD *default_DH_method = &dh_ossl;
 137
 138 const DH_METHOD *DH_OpenSSL(void)
 139 {
 140     return &dh_ossl;
 141 }
 142
 143 const DH_METHOD *DH_get_default_method(void)
 144 {
 145     return default_DH_method;
 146 }
 147
 148 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 149                          const BIGNUM *a, const BIGNUM *p,
 150                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 151 {
 152     return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 153 }
 154
 155 static int dh_init(DH *dh)
 156 {
 157     dh->flags |= DH_FLAG_CACHE_MONT_P;
 158     ossl_ffc_params_init(&dh->params);
 159     dh->dirty_cnt++;
 160     return 1;
 161 }
 162
 163 static int dh_finish(DH *dh)
 164 {
 165     BN_MONT_CTX_free(dh->method_mont_p);
 166     return 1;
 167 }
 168
 169 #ifndef FIPS_MODULE
 170 void DH_set_default_method(const DH_METHOD *meth)
 171 {
 172     default_DH_method = meth;
 173 }
 174 #endif /* FIPS_MODULE */
 175
 176 int DH_generate_key(DH *dh)
 177 {
 178 #ifdef FIPS_MODULE
 179     return generate_key(dh);
 180 #else
 181     return dh->meth->generate_key(dh);
 182 #endif
 183 }
 184
 185 int dh_generate_public_key(BN_CTX *ctx, const DH *dh, const BIGNUM *priv_key,
 186                            BIGNUM *pub_key)
 187 {
 188     int ret = 0;
 189     BIGNUM *prk = BN_new();
 190     BN_MONT_CTX *mont = NULL;
 191
 192     if (prk == NULL)
 193         return 0;
 194
 195     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 196         /*
 197          * We take the input DH as const, but we lie, because in some cases we
 198          * want to get a hold of its Montgomery context.
 199          *
 200          * We cast to remove the const qualifier in this case, it should be
 201          * fine...
 202          */
 203         BN_MONT_CTX **pmont = (BN_MONT_CTX **)&dh->method_mont_p;
 204
 205         mont = BN_MONT_CTX_set_locked(pmont, dh->lock, dh->params.p, ctx);
 206         if (mont == NULL)
 207             goto err;
 208     }
 209     BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 210
 211     /* pub_key = g^priv_key mod p */
 212     if (!dh->meth->bn_mod_exp(dh, pub_key, dh->params.g, prk, dh->params.p,
 213                               ctx, mont))
 214         goto err;
 215     ret = 1;
 216 err:
 217     BN_clear_free(prk);
 218     return ret;
 219 }
 220
 221 static int generate_key(DH *dh)
 222 {
 223     int ok = 0;
 224     int generate_new_key = 0;
 225 #ifndef FIPS_MODULE
 226     unsigned l;
 227 #endif
 228     BN_CTX *ctx = NULL;
 229     BIGNUM *pub_key = NULL, *priv_key = NULL;
 230
 231     if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 232         DHerr(0, DH_R_MODULUS_TOO_LARGE);
 233         return 0;
 234     }
 235
 236     if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
 237         DHerr(0, DH_R_MODULUS_TOO_SMALL);
 238         return 0;
 239     }
 240
 241     ctx = BN_CTX_new_ex(dh->libctx);
 242     if (ctx == NULL)
 243         goto err;
 244
 245     if (dh->priv_key == NULL) {
 246         priv_key = BN_secure_new();
 247         if (priv_key == NULL)
 248             goto err;
 249         generate_new_key = 1;
 250     } else {
 251         priv_key = dh->priv_key;
 252     }
 253
 254     if (dh->pub_key == NULL) {
 255         pub_key = BN_new();
 256         if (pub_key == NULL)
 257             goto err;
 258     } else {
 259         pub_key = dh->pub_key;
 260     }
 261     if (generate_new_key) {
 262         /* Is it an approved safe prime ?*/
 263         if (DH_get_nid(dh) != NID_undef) {
 264             int max_strength =
 265                     ifc_ffc_compute_security_bits(BN_num_bits(dh->params.p));
 266
 267             if (dh->params.q == NULL
 268                 || dh->length > BN_num_bits(dh->params.q))
 269                 goto err;
 270             /* dh->length = maximum bit length of generated private key */
 271             if (!ossl_ffc_generate_private_key(ctx, &dh->params, dh->length,
 272                                                max_strength, priv_key))
 273                 goto err;
 274         } else {
 275 #ifdef FIPS_MODULE
 276             if (dh->params.q == NULL)
 277                 goto err;
 278 #else
 279             if (dh->params.q == NULL) {
 280                 /* secret exponent length, must satisfy 2^(l-1) <= p */
 281                 if (dh->length != 0
 282                     && dh->length >= BN_num_bits(dh->params.p))
 283                     goto err;
 284                 l = dh->length ? dh->length : BN_num_bits(dh->params.p) - 1;
 285                 if (!BN_priv_rand_ex(priv_key, l, BN_RAND_TOP_ONE,
 286                                      BN_RAND_BOTTOM_ANY, ctx))
 287                     goto err;
 288                 /*
 289                  * We handle just one known case where g is a quadratic non-residue:
 290                  * for g = 2: p % 8 == 3
 291                  */
 292                 if (BN_is_word(dh->params.g, DH_GENERATOR_2)
 293                     && !BN_is_bit_set(dh->params.p, 2)) {
 294                     /* clear bit 0, since it won't be a secret anyway */
 295                     if (!BN_clear_bit(priv_key, 0))
 296                         goto err;
 297                 }
 298             } else
 299 #endif
 300             {
 301                 /* Do a partial check for invalid p, q, g */
 302                 if (!ossl_ffc_params_simple_validate(dh->libctx, &dh->params,
 303                                                      FFC_PARAM_TYPE_DH))
 304                     goto err;
 305                 /*
 306                  * For FFC FIPS 186-4 keygen
 307                  * security strength s = 112,
 308                  * Max Private key size N = len(q)
 309                  */
 310                 if (!ossl_ffc_generate_private_key(ctx, &dh->params,
 311                                                    BN_num_bits(dh->params.q),
 312                                                    MIN_STRENGTH,
 313                                                    priv_key))
 314                     goto err;
 315             }
 316         }
 317     }
 318
 319     if (!dh_generate_public_key(ctx, dh, priv_key, pub_key))
 320         goto err;
 321
 322     dh->pub_key = pub_key;
 323     dh->priv_key = priv_key;
 324     dh->dirty_cnt++;
 325     ok = 1;
 326  err:
 327     if (ok != 1)
 328         DHerr(0, ERR_R_BN_LIB);
 329
 330     if (pub_key != dh->pub_key)
 331         BN_free(pub_key);
 332     if (priv_key != dh->priv_key)
 333         BN_free(priv_key);
 334     BN_CTX_free(ctx);
 335     return ok;
 336 }
 337
 338 int dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
 339 {
 340     int err_reason = DH_R_BN_ERROR;
 341     BIGNUM *pubkey = NULL;
 342     const BIGNUM *p;
 343     size_t p_size;
 344
 345     if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
 346         goto err;
 347     DH_get0_pqg(dh, &p, NULL, NULL);
 348     if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
 349         err_reason = DH_R_NO_PARAMETERS_SET;
 350         goto err;
 351     }
 352     /*
 353      * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
 354      * public key is of size not equal to size of p
 355      */
 356     if (BN_is_zero(pubkey) || p_size != len) {
 357         err_reason = DH_R_INVALID_PUBKEY;
 358         goto err;
 359     }
 360     if (DH_set0_key(dh, pubkey, NULL) != 1)
 361         goto err;
 362     return 1;
 363 err:
 364     DHerr(DH_F_DH_BUF2KEY, err_reason);
 365     BN_free(pubkey);
 366     return 0;
 367 }
 368
 369 size_t dh_key2buf(const DH *dh, unsigned char **pbuf_out, size_t size, int alloc)
 370 {
 371     const BIGNUM *pubkey;
 372     unsigned char *pbuf = NULL;
 373     const BIGNUM *p;
 374     int p_size;
 375
 376     DH_get0_pqg(dh, &p, NULL, NULL);
 377     DH_get0_key(dh, &pubkey, NULL);
 378     if (p == NULL || pubkey == NULL
 379             || (p_size = BN_num_bytes(p)) == 0
 380             || BN_num_bytes(pubkey) == 0) {
 381         DHerr(DH_F_DH_KEY2BUF, DH_R_INVALID_PUBKEY);
 382         return 0;
 383     }
 384     if (pbuf_out != NULL && (alloc || *pbuf_out != NULL)) {
 385         if (!alloc) {
 386             if (size >= (size_t)p_size)
 387                 pbuf = *pbuf_out;
 388         } else {
 389             pbuf = OPENSSL_malloc(p_size);
 390         }
 391
 392         if (pbuf == NULL) {
 393             DHerr(DH_F_DH_KEY2BUF, ERR_R_MALLOC_FAILURE);
 394             return 0;
 395         }
 396         /*
 397          * As per Section 4.2.8.1 of RFC 8446 left pad public
 398          * key with zeros to the size of p
 399          */
 400         if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) {
 401             if (alloc)
 402                 OPENSSL_free(pbuf);
 403             DHerr(DH_F_DH_KEY2BUF, DH_R_BN_ERROR);
 404             return 0;
 405         }
 406         *pbuf_out = pbuf;
 407     }
 408     return p_size;
 409 }