crypto/dh/dh_key.c

   1 /*
   2  * Copyright 1995-2021 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         ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE);
  48         goto err;
  49     }
  50
  51     if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
  52         ERR_raise(ERR_LIB_DH, 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         ERR_raise(ERR_LIB_DH, 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         ERR_raise(ERR_LIB_DH, 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         ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB);
  86         goto err;
  87     }
  88
  89     /* return the padded key, i.e. same number of bytes as the modulus */
  90     ret = BN_bn2binpad(tmp, key, BN_num_bytes(dh->params.p));
  91  err:
  92     BN_CTX_end(ctx);
  93     BN_CTX_free(ctx);
  94     return ret;
  95 }
  96
  97 /*-
  98  * NB: This function is inherently not constant time due to the
  99  * RFC 5246 (8.1.2) padding style that strips leading zero bytes.
 100  */
 101 int DH_compute_key(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 102 {
 103     int ret = 0, i;
 104     volatile size_t npad = 0, mask = 1;
 105
 106     /* compute the key; ret is constant unless compute_key is external */
 107 #ifdef FIPS_MODULE
 108     ret = compute_key(key, pub_key, dh);
 109 #else
 110     ret = dh->meth->compute_key(key, pub_key, dh);
 111 #endif
 112     if (ret <= 0)
 113         return ret;
 114
 115     /* count leading zero bytes, yet still touch all bytes */
 116     for (i = 0; i < ret; i++) {
 117         mask &= !key[i];
 118         npad += mask;
 119     }
 120
 121     /* unpad key */
 122     ret -= npad;
 123     /* key-dependent memory access, potentially leaking npad / ret */
 124     memmove(key, key + npad, ret);
 125     /* key-dependent memory access, potentially leaking npad / ret */
 126     memset(key + ret, 0, npad);
 127
 128     return ret;
 129 }
 130
 131 int DH_compute_key_padded(unsigned char *key, const BIGNUM *pub_key, DH *dh)
 132 {
 133     int rv, pad;
 134
 135     /* rv is constant unless compute_key is external */
 136 #ifdef FIPS_MODULE
 137     rv = compute_key(key, pub_key, dh);
 138 #else
 139     rv = dh->meth->compute_key(key, pub_key, dh);
 140 #endif
 141     if (rv <= 0)
 142         return rv;
 143     pad = BN_num_bytes(dh->params.p) - rv;
 144     /* pad is constant (zero) unless compute_key is external */
 145     if (pad > 0) {
 146         memmove(key + pad, key, rv);
 147         memset(key, 0, pad);
 148     }
 149     return rv + pad;
 150 }
 151
 152 static DH_METHOD dh_ossl = {
 153     "OpenSSL DH Method",
 154     generate_key,
 155     compute_key,
 156     dh_bn_mod_exp,
 157     dh_init,
 158     dh_finish,
 159     DH_FLAG_FIPS_METHOD,
 160     NULL,
 161     NULL
 162 };
 163
 164 static const DH_METHOD *default_DH_method = &dh_ossl;
 165
 166 const DH_METHOD *DH_OpenSSL(void)
 167 {
 168     return &dh_ossl;
 169 }
 170
 171 const DH_METHOD *DH_get_default_method(void)
 172 {
 173     return default_DH_method;
 174 }
 175
 176 static int dh_bn_mod_exp(const DH *dh, BIGNUM *r,
 177                          const BIGNUM *a, const BIGNUM *p,
 178                          const BIGNUM *m, BN_CTX *ctx, BN_MONT_CTX *m_ctx)
 179 {
 180     return BN_mod_exp_mont(r, a, p, m, ctx, m_ctx);
 181 }
 182
 183 static int dh_init(DH *dh)
 184 {
 185     dh->flags |= DH_FLAG_CACHE_MONT_P;
 186     ossl_ffc_params_init(&dh->params);
 187     dh->dirty_cnt++;
 188     return 1;
 189 }
 190
 191 static int dh_finish(DH *dh)
 192 {
 193     BN_MONT_CTX_free(dh->method_mont_p);
 194     return 1;
 195 }
 196
 197 #ifndef FIPS_MODULE
 198 void DH_set_default_method(const DH_METHOD *meth)
 199 {
 200     default_DH_method = meth;
 201 }
 202 #endif /* FIPS_MODULE */
 203
 204 int DH_generate_key(DH *dh)
 205 {
 206 #ifdef FIPS_MODULE
 207     return generate_key(dh);
 208 #else
 209     return dh->meth->generate_key(dh);
 210 #endif
 211 }
 212
 213 int dh_generate_public_key(BN_CTX *ctx, const DH *dh, const BIGNUM *priv_key,
 214                            BIGNUM *pub_key)
 215 {
 216     int ret = 0;
 217     BIGNUM *prk = BN_new();
 218     BN_MONT_CTX *mont = NULL;
 219
 220     if (prk == NULL)
 221         return 0;
 222
 223     if (dh->flags & DH_FLAG_CACHE_MONT_P) {
 224         /*
 225          * We take the input DH as const, but we lie, because in some cases we
 226          * want to get a hold of its Montgomery context.
 227          *
 228          * We cast to remove the const qualifier in this case, it should be
 229          * fine...
 230          */
 231         BN_MONT_CTX **pmont = (BN_MONT_CTX **)&dh->method_mont_p;
 232
 233         mont = BN_MONT_CTX_set_locked(pmont, dh->lock, dh->params.p, ctx);
 234         if (mont == NULL)
 235             goto err;
 236     }
 237     BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 238
 239     /* pub_key = g^priv_key mod p */
 240     if (!dh->meth->bn_mod_exp(dh, pub_key, dh->params.g, prk, dh->params.p,
 241                               ctx, mont))
 242         goto err;
 243     ret = 1;
 244 err:
 245     BN_clear_free(prk);
 246     return ret;
 247 }
 248
 249 static int generate_key(DH *dh)
 250 {
 251     int ok = 0;
 252     int generate_new_key = 0;
 253 #ifndef FIPS_MODULE
 254     unsigned l;
 255 #endif
 256     BN_CTX *ctx = NULL;
 257     BIGNUM *pub_key = NULL, *priv_key = NULL;
 258
 259     if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 260         ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_LARGE);
 261         return 0;
 262     }
 263
 264     if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
 265         ERR_raise(ERR_LIB_DH, DH_R_MODULUS_TOO_SMALL);
 266         return 0;
 267     }
 268
 269     ctx = BN_CTX_new_ex(dh->libctx);
 270     if (ctx == NULL)
 271         goto err;
 272
 273     if (dh->priv_key == NULL) {
 274         priv_key = BN_secure_new();
 275         if (priv_key == NULL)
 276             goto err;
 277         generate_new_key = 1;
 278     } else {
 279         priv_key = dh->priv_key;
 280     }
 281
 282     if (dh->pub_key == NULL) {
 283         pub_key = BN_new();
 284         if (pub_key == NULL)
 285             goto err;
 286     } else {
 287         pub_key = dh->pub_key;
 288     }
 289     if (generate_new_key) {
 290         /* Is it an approved safe prime ?*/
 291         if (DH_get_nid(dh) != NID_undef) {
 292             int max_strength =
 293                     ifc_ffc_compute_security_bits(BN_num_bits(dh->params.p));
 294
 295             if (dh->params.q == NULL
 296                 || dh->length > BN_num_bits(dh->params.q))
 297                 goto err;
 298             /* dh->length = maximum bit length of generated private key */
 299             if (!ossl_ffc_generate_private_key(ctx, &dh->params, dh->length,
 300                                                max_strength, priv_key))
 301                 goto err;
 302         } else {
 303 #ifdef FIPS_MODULE
 304             if (dh->params.q == NULL)
 305                 goto err;
 306 #else
 307             if (dh->params.q == NULL) {
 308                 /* secret exponent length, must satisfy 2^(l-1) <= p */
 309                 if (dh->length != 0
 310                     && dh->length >= BN_num_bits(dh->params.p))
 311                     goto err;
 312                 l = dh->length ? dh->length : BN_num_bits(dh->params.p) - 1;
 313                 if (!BN_priv_rand_ex(priv_key, l, BN_RAND_TOP_ONE,
 314                                      BN_RAND_BOTTOM_ANY, ctx))
 315                     goto err;
 316                 /*
 317                  * We handle just one known case where g is a quadratic non-residue:
 318                  * for g = 2: p % 8 == 3
 319                  */
 320                 if (BN_is_word(dh->params.g, DH_GENERATOR_2)
 321                     && !BN_is_bit_set(dh->params.p, 2)) {
 322                     /* clear bit 0, since it won't be a secret anyway */
 323                     if (!BN_clear_bit(priv_key, 0))
 324                         goto err;
 325                 }
 326             } else
 327 #endif
 328             {
 329                 /* Do a partial check for invalid p, q, g */
 330                 if (!ossl_ffc_params_simple_validate(dh->libctx, &dh->params,
 331                                                      FFC_PARAM_TYPE_DH, NULL))
 332                     goto err;
 333                 /*
 334                  * For FFC FIPS 186-4 keygen
 335                  * security strength s = 112,
 336                  * Max Private key size N = len(q)
 337                  */
 338                 if (!ossl_ffc_generate_private_key(ctx, &dh->params,
 339                                                    BN_num_bits(dh->params.q),
 340                                                    MIN_STRENGTH,
 341                                                    priv_key))
 342                     goto err;
 343             }
 344         }
 345     }
 346
 347     if (!dh_generate_public_key(ctx, dh, priv_key, pub_key))
 348         goto err;
 349
 350     dh->pub_key = pub_key;
 351     dh->priv_key = priv_key;
 352     dh->dirty_cnt++;
 353     ok = 1;
 354  err:
 355     if (ok != 1)
 356         ERR_raise(ERR_LIB_DH, ERR_R_BN_LIB);
 357
 358     if (pub_key != dh->pub_key)
 359         BN_free(pub_key);
 360     if (priv_key != dh->priv_key)
 361         BN_free(priv_key);
 362     BN_CTX_free(ctx);
 363     return ok;
 364 }
 365
 366 int dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
 367 {
 368     int err_reason = DH_R_BN_ERROR;
 369     BIGNUM *pubkey = NULL;
 370     const BIGNUM *p;
 371     size_t p_size;
 372
 373     if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
 374         goto err;
 375     DH_get0_pqg(dh, &p, NULL, NULL);
 376     if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
 377         err_reason = DH_R_NO_PARAMETERS_SET;
 378         goto err;
 379     }
 380     /*
 381      * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
 382      * public key is of size not equal to size of p
 383      */
 384     if (BN_is_zero(pubkey) || p_size != len) {
 385         err_reason = DH_R_INVALID_PUBKEY;
 386         goto err;
 387     }
 388     if (DH_set0_key(dh, pubkey, NULL) != 1)
 389         goto err;
 390     return 1;
 391 err:
 392     ERR_raise(ERR_LIB_DH, err_reason);
 393     BN_free(pubkey);
 394     return 0;
 395 }
 396
 397 size_t dh_key2buf(const DH *dh, unsigned char **pbuf_out, size_t size, int alloc)
 398 {
 399     const BIGNUM *pubkey;
 400     unsigned char *pbuf = NULL;
 401     const BIGNUM *p;
 402     int p_size;
 403
 404     DH_get0_pqg(dh, &p, NULL, NULL);
 405     DH_get0_key(dh, &pubkey, NULL);
 406     if (p == NULL || pubkey == NULL
 407             || (p_size = BN_num_bytes(p)) == 0
 408             || BN_num_bytes(pubkey) == 0) {
 409         ERR_raise(ERR_LIB_DH, DH_R_INVALID_PUBKEY);
 410         return 0;
 411     }
 412     if (pbuf_out != NULL && (alloc || *pbuf_out != NULL)) {
 413         if (!alloc) {
 414             if (size >= (size_t)p_size)
 415                 pbuf = *pbuf_out;
 416         } else {
 417             pbuf = OPENSSL_malloc(p_size);
 418         }
 419
 420         if (pbuf == NULL) {
 421             ERR_raise(ERR_LIB_DH, ERR_R_MALLOC_FAILURE);
 422             return 0;
 423         }
 424         /*
 425          * As per Section 4.2.8.1 of RFC 8446 left pad public
 426          * key with zeros to the size of p
 427          */
 428         if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) {
 429             if (alloc)
 430                 OPENSSL_free(pbuf);
 431             ERR_raise(ERR_LIB_DH, DH_R_BN_ERROR);
 432             return 0;
 433         }
 434         *pbuf_out = pbuf;
 435     }
 436     return p_size;
 437 }