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