lib/hcrypto/dh.c

   1 /*
   2  * Copyright (c) 2006 - 2007 Kungliga Tekniska Högskolan
   3  * (Royal Institute of Technology, Stockholm, Sweden).
   4  * All rights reserved.
   5  *
   6  * Redistribution and use in source and binary forms, with or without
   7  * modification, are permitted provided that the following conditions
   8  * are met:
   9  *
  10  * 1. Redistributions of source code must retain the above copyright
  11  *    notice, this list of conditions and the following disclaimer.
  12  *
  13  * 2. Redistributions in binary form must reproduce the above copyright
  14  *    notice, this list of conditions and the following disclaimer in the
  15  *    documentation and/or other materials provided with the distribution.
  16  *
  17  * 3. Neither the name of the Institute nor the names of its contributors
  18  *    may be used to endorse or promote products derived from this software
  19  *    without specific prior written permission.
  20  *
  21  * THIS SOFTWARE IS PROVIDED BY THE INSTITUTE AND CONTRIBUTORS ``AS IS'' AND
  22  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  23  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  24  * ARE DISCLAIMED.  IN NO EVENT SHALL THE INSTITUTE OR CONTRIBUTORS BE LIABLE
  25  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  26  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  27  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
  28  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  29  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  30  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  31  * SUCH DAMAGE.
  32  */
  33
  34 #ifdef HAVE_CONFIG_H
  35 #include <config.h>
  36 #endif
  37 #include <roken.h>
  38
  39 #include <krb5-types.h>
  40 #include <rfc2459_asn1.h>
  41
  42 #include <dh.h>
  43
  44 /**
  45  * @page page_dh DH - Diffie-Hellman key exchange
  46  *
  47  * Diffie-Hellman key exchange is a protocol that allows two parties
  48  * to establish a shared secret key.
  49  *
  50  * Include and example how to use DH_new() and friends here.
  51  *
  52  * See the library functions here: @ref hcrypto_dh
  53  */
  54
  55 /**
  56  * Create a new DH object using DH_new_method(NULL), see DH_new_method().
  57  *
  58  * @return a newly allocated DH object.
  59  *
  60  * @ingroup hcrypto_dh
  61  */
  62
  63 DH *
  64 DH_new(void)
  65 {
  66     return DH_new_method(NULL);
  67 }
  68
  69 /**
  70  * Create a new DH object from the given engine, if the NULL is used,
  71  * the default engine is used. Free the DH object with DH_free().
  72  *
  73  * @param engine The engine to use to allocate the DH object.
  74  *
  75  * @return a newly allocated DH object.
  76  *
  77  * @ingroup hcrypto_dh
  78  */
  79
  80 DH *
  81 DH_new_method(ENGINE *engine)
  82 {
  83     DH *dh;
  84
  85     dh = calloc(1, sizeof(*dh));
  86     if (dh == NULL)
  87         return NULL;
  88
  89     dh->references = 1;
  90
  91     if (engine) {
  92         ENGINE_up_ref(engine);
  93         dh->engine = engine;
  94     } else {
  95         dh->engine = ENGINE_get_default_DH();
  96     }
  97
  98     if (dh->engine) {
  99         dh->meth = ENGINE_get_DH(dh->engine);
 100         if (dh->meth == NULL) {
 101             ENGINE_finish(engine);
 102             free(dh);
 103             return 0;
 104         }
 105     }
 106
 107     if (dh->meth == NULL)
 108         dh->meth = DH_get_default_method();
 109
 110     (*dh->meth->init)(dh);
 111
 112     return dh;
 113 }
 114
 115 /**
 116  * Free a DH object and release related resources, like ENGINE, that
 117  * the object was using.
 118  *
 119  * @param dh object to be freed.
 120  *
 121  * @ingroup hcrypto_dh
 122  */
 123
 124 void
 125 DH_free(DH *dh)
 126 {
 127     if (dh->references <= 0)
 128         abort();
 129
 130     if (--dh->references > 0)
 131         return;
 132
 133     (*dh->meth->finish)(dh);
 134
 135     if (dh->engine)
 136         ENGINE_finish(dh->engine);
 137
 138 #define free_if(f) if (f) { BN_free(f); }
 139     free_if(dh->p);
 140     free_if(dh->g);
 141     free_if(dh->pub_key);
 142     free_if(dh->priv_key);
 143     free_if(dh->q);
 144     free_if(dh->j);
 145     free_if(dh->counter);
 146 #undef free_if
 147
 148     memset(dh, 0, sizeof(*dh));
 149     free(dh);
 150 }
 151
 152 /**
 153  * Add a reference to the DH object. The object should be free with
 154  * DH_free() to drop the reference.
 155  *
 156  * @param dh the object to increase the reference count too.
 157  *
 158  * @return the updated reference count, can't safely be used except
 159  * for debug printing.
 160  *
 161  * @ingroup hcrypto_dh
 162  */
 163
 164 int
 165 DH_up_ref(DH *dh)
 166 {
 167     return ++dh->references;
 168 }
 169
 170 /**
 171  * The maximum output size of the DH_compute_key() function.
 172  *
 173  * @param dh The DH object to get the size from.
 174  *
 175  * @return the maximum size in bytes of the out data.
 176  *
 177  * @ingroup hcrypto_dh
 178  */
 179
 180 int
 181 DH_size(const DH *dh)
 182 {
 183     return BN_num_bytes(dh->p);
 184 }
 185
 186 /**
 187  * Set the data index idx in the DH object to data.
 188  *
 189  * @param dh DH object.
 190  * @param idx index to set the data for.
 191  * @param data data to store for the index idx.
 192  *
 193  * @return 1 on success.
 194  *
 195  * @ingroup hcrypto_dh
 196  */
 197
 198 int
 199 DH_set_ex_data(DH *dh, int idx, void *data)
 200 {
 201     dh->ex_data.sk = data;
 202     return 1;
 203 }
 204
 205 /**
 206  * Get the data for index idx in the DH object.
 207  *
 208  * @param dh DH object.
 209  * @param idx index to get the data for.
 210  *
 211  * @return the object store in index idx
 212  *
 213  * @ingroup hcrypto_dh
 214  */
 215
 216 void *
 217 DH_get_ex_data(DH *dh, int idx)
 218 {
 219     return dh->ex_data.sk;
 220 }
 221
 222 /**
 223  * Generate DH parameters for the DH object give parameters.
 224  *
 225  * @param dh The DH object to generate parameters for.
 226  * @param prime_len length of the prime
 227  * @param generator generator, g
 228  * @param cb Callback parameters to show progress, can be NULL.
 229  *
 230  * @return the maximum size in bytes of the out data.
 231  *
 232  * @ingroup hcrypto_dh
 233  */
 234
 235 int
 236 DH_generate_parameters_ex(DH *dh, int prime_len, int generator, BN_GENCB *cb)
 237 {
 238     if (dh->meth->generate_params)
 239         return dh->meth->generate_params(dh, prime_len, generator, cb);
 240     return 0;
 241 }
 242
 243 /**
 244  * Check that the public key is sane.
 245  *
 246  * @param dh the local peer DH parameters.
 247  * @param pub_key the remote peer public key parameters.
 248  * @param codes return that the failures of the pub_key are.
 249  *
 250  * @return 1 on success, 0 on failure and *codes is set the the
 251  * combined fail check for the public key
 252  *
 253  * @ingroup hcrypto_dh
 254  */
 255
 256 int
 257 DH_check_pubkey(const DH *dh, const BIGNUM *pub_key, int *codes)
 258 {
 259     BIGNUM *bn = NULL, *sum = NULL;
 260     int ret = 0;
 261
 262     *codes = 0;
 263
 264     /**
 265      * Checks that the function performs are:
 266      * - pub_key is not negative
 267      */
 268
 269     if (BN_is_negative(pub_key))
 270         goto out;
 271
 272     /**
 273      * - pub_key > 1    and    pub_key < p - 1,
 274      *    to avoid small subgroups attack.
 275      */
 276
 277     bn = BN_new();
 278     if (bn == NULL)
 279         goto out;
 280
 281     if (!BN_set_word(bn, 1))
 282         goto out;
 283
 284     if (BN_cmp(bn, pub_key) >= 0)
 285         *codes |= DH_CHECK_PUBKEY_TOO_SMALL;
 286
 287     sum = BN_new();
 288     if (sum == NULL)
 289         goto out;
 290
 291     BN_uadd(sum, pub_key, bn);
 292
 293     if (BN_cmp(sum, dh->p) >= 0)
 294         *codes |= DH_CHECK_PUBKEY_TOO_LARGE;
 295
 296     /**
 297      * - if g == 2, pub_key have more then one bit set,
 298      *   if bits set is 1, log_2(pub_key) is trival
 299      */
 300
 301     if (!BN_set_word(bn, 2))
 302         goto out;
 303
 304     if (BN_cmp(bn, dh->g) == 0) {
 305         unsigned i, n = BN_num_bits(pub_key);
 306         unsigned bits = 0;
 307
 308         for (i = 0; i <= n; i++)
 309             if (BN_is_bit_set(pub_key, i))
 310                 bits++;
 311
 312         if (bits < 2) {
 313             *codes |= DH_CHECK_PUBKEY_TOO_SMALL;
 314             goto out;
 315         }
 316     }
 317
 318     ret = 1;
 319 out:
 320     if (bn)
 321         BN_free(bn);
 322     if (sum)
 323         BN_free(sum);
 324
 325     return ret;
 326 }
 327
 328 /**
 329  * Generate a new DH private-public key pair. The dh parameter must be
 330  * allocted first with DH_new(). dh->p and dp->g must be set.
 331  *
 332  * @param dh dh parameter.
 333  *
 334  * @return 1 on success.
 335  *
 336  * @ingroup hcrypto_dh
 337  */
 338
 339 int
 340 DH_generate_key(DH *dh)
 341 {
 342     return dh->meth->generate_key(dh);
 343 }
 344
 345 /**
 346  * Complute the shared secret key.
 347  *
 348  * @param shared_key the resulting shared key, need to be at least
 349  * DH_size() large.
 350  * @param peer_pub_key the peer's public key.
 351  * @param dh the dh key pair.
 352  *
 353  * @return 1 on success.
 354  *
 355  * @ingroup hcrypto_dh
 356  */
 357
 358 int
 359 DH_compute_key(unsigned char *shared_key,
 360                const BIGNUM *peer_pub_key, DH *dh)
 361 {
 362     int codes;
 363
 364     /**
 365      * Checks that the pubkey passed in is valid using
 366      * DH_check_pubkey().
 367      */
 368
 369     if (!DH_check_pubkey(dh, peer_pub_key, &codes) || codes != 0)
 370         return -1;
 371
 372     return dh->meth->compute_key(shared_key, peer_pub_key, dh);
 373 }
 374
 375 /**
 376  * Set a new method for the DH keypair.
 377  *
 378  * @param dh dh parameter.
 379  * @param method the new method for the DH parameter.
 380  *
 381  * @return 1 on success.
 382  *
 383  * @ingroup hcrypto_dh
 384  */
 385
 386 int
 387 DH_set_method(DH *dh, const DH_METHOD *method)
 388 {
 389     (*dh->meth->finish)(dh);
 390     if (dh->engine) {
 391         ENGINE_finish(dh->engine);
 392         dh->engine = NULL;
 393     }
 394     dh->meth = method;
 395     (*dh->meth->init)(dh);
 396     return 1;
 397 }
 398
 399 /*
 400  *
 401  */
 402
 403 static int
 404 dh_null_generate_key(DH *dh)
 405 {
 406     return 0;
 407 }
 408
 409 static int
 410 dh_null_compute_key(unsigned char *shared,const BIGNUM *pub, DH *dh)
 411 {
 412     return 0;
 413 }
 414
 415 static int
 416 dh_null_init(DH *dh)
 417 {
 418     return 1;
 419 }
 420
 421 static int
 422 dh_null_finish(DH *dh)
 423 {
 424     return 1;
 425 }
 426
 427 static int
 428 dh_null_generate_params(DH *dh, int prime_num, int len, BN_GENCB *cb)
 429 {
 430     return 0;
 431 }
 432
 433 static const DH_METHOD dh_null_method = {
 434     "hcrypto null DH",
 435     dh_null_generate_key,
 436     dh_null_compute_key,
 437     NULL,
 438     dh_null_init,
 439     dh_null_finish,
 440     0,
 441     NULL,
 442     dh_null_generate_params
 443 };
 444
 445 extern const DH_METHOD _hc_dh_ltm_method;
 446 static const DH_METHOD *dh_default_method = &_hc_dh_ltm_method;
 447
 448 /**
 449  * Return the dummy DH implementation.
 450  *
 451  * @return pointer to a DH_METHOD.
 452  *
 453  * @ingroup hcrypto_dh
 454  */
 455
 456 const DH_METHOD *
 457 DH_null_method(void)
 458 {
 459     return &dh_null_method;
 460 }
 461
 462 /**
 463  * Set the default DH implementation.
 464  *
 465  * @param meth pointer to a DH_METHOD.
 466  *
 467  * @ingroup hcrypto_dh
 468  */
 469
 470 void
 471 DH_set_default_method(const DH_METHOD *meth)
 472 {
 473     dh_default_method = meth;
 474 }
 475
 476 /**
 477  * Return the default DH implementation.
 478  *
 479  * @return pointer to a DH_METHOD.
 480  *
 481  * @ingroup hcrypto_dh
 482  */
 483
 484 const DH_METHOD *
 485 DH_get_default_method(void)
 486 {
 487     return dh_default_method;
 488 }
 489
 490 /*
 491  *
 492  */
 493
 494 static int
 495 bn2heim_int(BIGNUM *bn, heim_integer *integer)
 496 {
 497     integer->length = BN_num_bytes(bn);
 498     integer->data = malloc(integer->length);
 499     if (integer->data == NULL) {
 500         integer->length = 0;
 501         return ENOMEM;
 502     }
 503     BN_bn2bin(bn, integer->data);
 504     integer->negative = BN_is_negative(bn);
 505     return 0;
 506 }
 507
 508 /**
 509  *
 510  */
 511
 512 int
 513 i2d_DHparams(DH *dh, unsigned char **pp)
 514 {
 515     DHParameter data;
 516     size_t size;
 517     int ret;
 518
 519     memset(&data, 0, sizeof(data));
 520
 521     if (bn2heim_int(dh->p, &data.prime) ||
 522         bn2heim_int(dh->g, &data.base))
 523     {
 524         free_DHParameter(&data);
 525         return -1;
 526     }
 527
 528     if (pp == NULL) {
 529         size = length_DHParameter(&data);
 530         free_DHParameter(&data);
 531     } else {
 532         void *p;
 533         size_t len;
 534
 535         ASN1_MALLOC_ENCODE(DHParameter, p, len, &data, &size, ret);
 536         free_DHParameter(&data);
 537         if (ret)
 538             return -1;
 539         if (len != size) {
 540             abort();
 541             return -1;
 542         }
 543
 544         memcpy(*pp, p, size);
 545         free(p);
 546
 547         *pp += size;
 548     }
 549
 550     return size;
 551 }