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, 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         mont = BN_MONT_CTX_set_locked(&dh->method_mont_p,
 197                                       dh->lock, dh->params.p, ctx);
 198         if (mont == NULL)
 199             goto err;
 200     }
 201     BN_with_flags(prk, priv_key, BN_FLG_CONSTTIME);
 202
 203     /* pub_key = g^priv_key mod p */
 204     if (!dh->meth->bn_mod_exp(dh, pub_key, dh->params.g, prk, dh->params.p,
 205                               ctx, mont))
 206         goto err;
 207     ret = 1;
 208 err:
 209     BN_clear_free(prk);
 210     return ret;
 211 }
 212
 213 static int generate_key(DH *dh)
 214 {
 215     int ok = 0;
 216     int generate_new_key = 0;
 217 #ifndef FIPS_MODULE
 218     unsigned l;
 219 #endif
 220     BN_CTX *ctx = NULL;
 221     BIGNUM *pub_key = NULL, *priv_key = NULL;
 222
 223     if (BN_num_bits(dh->params.p) > OPENSSL_DH_MAX_MODULUS_BITS) {
 224         DHerr(0, DH_R_MODULUS_TOO_LARGE);
 225         return 0;
 226     }
 227
 228     if (BN_num_bits(dh->params.p) < DH_MIN_MODULUS_BITS) {
 229         DHerr(0, DH_R_MODULUS_TOO_SMALL);
 230         return 0;
 231     }
 232
 233     ctx = BN_CTX_new_ex(dh->libctx);
 234     if (ctx == NULL)
 235         goto err;
 236
 237     if (dh->priv_key == NULL) {
 238         priv_key = BN_secure_new();
 239         if (priv_key == NULL)
 240             goto err;
 241         generate_new_key = 1;
 242     } else {
 243         priv_key = dh->priv_key;
 244     }
 245
 246     if (dh->pub_key == NULL) {
 247         pub_key = BN_new();
 248         if (pub_key == NULL)
 249             goto err;
 250     } else {
 251         pub_key = dh->pub_key;
 252     }
 253     if (generate_new_key) {
 254         /* Is it an approved safe prime ?*/
 255         if (DH_get_nid(dh) != NID_undef) {
 256             int max_strength =
 257                     ifc_ffc_compute_security_bits(BN_num_bits(dh->params.p));
 258
 259             if (dh->params.q == NULL
 260                 || dh->length > BN_num_bits(dh->params.q))
 261                 goto err;
 262             /* dh->length = maximum bit length of generated private key */
 263             if (!ossl_ffc_generate_private_key(ctx, &dh->params, dh->length,
 264                                                max_strength, priv_key))
 265                 goto err;
 266         } else {
 267 #ifdef FIPS_MODULE
 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                 /* Do a partial check for invalid p, q, g */
 291                 if (!ossl_ffc_params_simple_validate(dh->libctx, &dh->params,
 292                                                      FFC_PARAM_TYPE_DH))
 293                     goto err;
 294                 /*
 295                  * For FFC FIPS 186-4 keygen
 296                  * security strength s = 112,
 297                  * Max Private key size N = len(q)
 298                  */
 299                 if (!ossl_ffc_generate_private_key(ctx, &dh->params,
 300                                                    BN_num_bits(dh->params.q),
 301                                                    MIN_STRENGTH,
 302                                                    priv_key))
 303                     goto err;
 304             }
 305         }
 306     }
 307
 308     if (!dh_generate_public_key(ctx, dh, priv_key, pub_key))
 309         goto err;
 310
 311     dh->pub_key = pub_key;
 312     dh->priv_key = priv_key;
 313     dh->dirty_cnt++;
 314     ok = 1;
 315  err:
 316     if (ok != 1)
 317         DHerr(0, ERR_R_BN_LIB);
 318
 319     if (pub_key != dh->pub_key)
 320         BN_free(pub_key);
 321     if (priv_key != dh->priv_key)
 322         BN_free(priv_key);
 323     BN_CTX_free(ctx);
 324     return ok;
 325 }
 326
 327 int dh_buf2key(DH *dh, const unsigned char *buf, size_t len)
 328 {
 329     int err_reason = DH_R_BN_ERROR;
 330     BIGNUM *pubkey = NULL;
 331     const BIGNUM *p;
 332     size_t p_size;
 333
 334     if ((pubkey = BN_bin2bn(buf, len, NULL)) == NULL)
 335         goto err;
 336     DH_get0_pqg(dh, &p, NULL, NULL);
 337     if (p == NULL || (p_size = BN_num_bytes(p)) == 0) {
 338         err_reason = DH_R_NO_PARAMETERS_SET;
 339         goto err;
 340     }
 341     /*
 342      * As per Section 4.2.8.1 of RFC 8446 fail if DHE's
 343      * public key is of size not equal to size of p
 344      */
 345     if (BN_is_zero(pubkey) || p_size != len) {
 346         err_reason = DH_R_INVALID_PUBKEY;
 347         goto err;
 348     }
 349     if (DH_set0_key(dh, pubkey, NULL) != 1)
 350         goto err;
 351     return 1;
 352 err:
 353     DHerr(DH_F_DH_BUF2KEY, err_reason);
 354     BN_free(pubkey);
 355     return 0;
 356 }
 357
 358 size_t dh_key2buf(const DH *dh, unsigned char **pbuf_out, size_t size, int alloc)
 359 {
 360     const BIGNUM *pubkey;
 361     unsigned char *pbuf = NULL;
 362     const BIGNUM *p;
 363     int p_size;
 364
 365     DH_get0_pqg(dh, &p, NULL, NULL);
 366     DH_get0_key(dh, &pubkey, NULL);
 367     if (p == NULL || pubkey == NULL
 368             || (p_size = BN_num_bytes(p)) == 0
 369             || BN_num_bytes(pubkey) == 0) {
 370         DHerr(DH_F_DH_KEY2BUF, DH_R_INVALID_PUBKEY);
 371         return 0;
 372     }
 373     if (pbuf_out != NULL && (alloc || *pbuf_out != NULL)) {
 374         if (!alloc) {
 375             if (size >= (size_t)p_size)
 376                 pbuf = *pbuf_out;
 377         } else {
 378             pbuf = OPENSSL_malloc(p_size);
 379         }
 380
 381         if (pbuf == NULL) {
 382             DHerr(DH_F_DH_KEY2BUF, ERR_R_MALLOC_FAILURE);
 383             return 0;
 384         }
 385         /*
 386          * As per Section 4.2.8.1 of RFC 8446 left pad public
 387          * key with zeros to the size of p
 388          */
 389         if (BN_bn2binpad(pubkey, pbuf, p_size) < 0) {
 390             if (alloc)
 391                 OPENSSL_free(pbuf);
 392             DHerr(DH_F_DH_KEY2BUF, DH_R_BN_ERROR);
 393             return 0;
 394         }
 395         *pbuf_out = pbuf;
 396     }
 397     return p_size;
 398 }