dhm.c 14.1 KB
Newer Older
1 2 3
/*
 *  Diffie-Hellman-Merkle key exchange
 *
Manuel Pégourié-Gonnard's avatar
Manuel Pégourié-Gonnard committed
4
 *  Copyright (C) 2006-2014, ARM Limited, All Rights Reserved
Paul Bakker's avatar
Paul Bakker committed
5
 *
Manuel Pégourié-Gonnard's avatar
Manuel Pégourié-Gonnard committed
6
 *  This file is part of mbed TLS (https://polarssl.org)
Paul Bakker's avatar
Paul Bakker committed
7
 *
8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27
 *  This program is free software; you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation; either version 2 of the License, or
 *  (at your option) any later version.
 *
 *  This program is distributed in the hope that it will be useful,
 *  but WITHOUT ANY WARRANTY; without even the implied warranty of
 *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *  GNU General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License along
 *  with this program; if not, write to the Free Software Foundation, Inc.,
 *  51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
/*
 *  Reference:
 *
 *  http://www.cacr.math.uwaterloo.ca/hac/ (chapter 12)
 */

28
#if !defined(POLARSSL_CONFIG_FILE)
29
#include "polarssl/config.h"
30 31 32
#else
#include POLARSSL_CONFIG_FILE
#endif
33

34
#if defined(POLARSSL_DHM_C)
35

36
#include "polarssl/dhm.h"
37

38 39
#include <string.h>

40
#if defined(POLARSSL_PEM_PARSE_C)
41 42 43 44 45 46 47
#include "polarssl/pem.h"
#endif

#if defined(POLARSSL_ASN1_PARSE_C)
#include "polarssl/asn1.h"
#endif

48 49
#if defined(POLARSSL_PLATFORM_C)
#include "polarssl/platform.h"
50 51
#else
#include <stdlib.h>
52
#define polarssl_printf     printf
53 54 55 56
#define polarssl_malloc     malloc
#define polarssl_free       free
#endif

57 58 59 60 61
/* Implementation that should never be optimized out by the compiler */
static void polarssl_zeroize( void *v, size_t n ) {
    volatile unsigned char *p = v; while( n-- ) *p++ = 0;
}

62 63 64 65 66
/*
 * helper to validate the mpi size and import it
 */
static int dhm_read_bignum( mpi *X,
                            unsigned char **p,
67
                            const unsigned char *end )
68 69 70 71
{
    int ret, n;

    if( end - *p < 2 )
72
        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
73 74 75 76 77

    n = ( (*p)[0] << 8 ) | (*p)[1];
    (*p) += 2;

    if( (int)( end - *p ) < n )
78
        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
79 80

    if( ( ret = mpi_read_binary( X, *p, n ) ) != 0 )
81
        return( POLARSSL_ERR_DHM_READ_PARAMS_FAILED + ret );
82 83 84 85 86 87

    (*p) += n;

    return( 0 );
}

Paul Bakker's avatar
Paul Bakker committed
88
/*
89
 * Verify sanity of parameter with regards to P
90
 *
91
 * Parameter should be: 2 <= public_param <= P - 2
92 93 94 95
 *
 * For more information on the attack, see:
 *  http://www.cl.cam.ac.uk/~rja14/Papers/psandqs.pdf
 *  http://web.nvd.nist.gov/view/vuln/detail?vulnId=CVE-2005-2643
Paul Bakker's avatar
Paul Bakker committed
96
 */
97
static int dhm_check_range( const mpi *param, const mpi *P )
Paul Bakker's avatar
Paul Bakker committed
98
{
99 100
    mpi L, U;
    int ret = POLARSSL_ERR_DHM_BAD_INPUT_DATA;
Paul Bakker's avatar
Paul Bakker committed
101

102
    mpi_init( &L ); mpi_init( &U );
103 104 105

    MPI_CHK( mpi_lset( &L, 2 ) );
    MPI_CHK( mpi_sub_int( &U, P, 2 ) );
Paul Bakker's avatar
Paul Bakker committed
106

107 108
    if( mpi_cmp_mpi( param, &L ) >= 0 &&
        mpi_cmp_mpi( param, &U ) <= 0 )
Paul Bakker's avatar
Paul Bakker committed
109
    {
110
        ret = 0;
Paul Bakker's avatar
Paul Bakker committed
111 112
    }

113
cleanup:
114
    mpi_free( &L ); mpi_free( &U );
115
    return( ret );
Paul Bakker's avatar
Paul Bakker committed
116 117
}

Paul Bakker's avatar
Paul Bakker committed
118 119 120 121 122
void dhm_init( dhm_context *ctx )
{
    memset( ctx, 0, sizeof( dhm_context ) );
}

123 124 125 126 127
/*
 * Parse the ServerKeyExchange parameters
 */
int dhm_read_params( dhm_context *ctx,
                     unsigned char **p,
128
                     const unsigned char *end )
129
{
Paul Bakker's avatar
Paul Bakker committed
130
    int ret;
131 132 133 134 135 136

    if( ( ret = dhm_read_bignum( &ctx->P,  p, end ) ) != 0 ||
        ( ret = dhm_read_bignum( &ctx->G,  p, end ) ) != 0 ||
        ( ret = dhm_read_bignum( &ctx->GY, p, end ) ) != 0 )
        return( ret );

137 138 139
    if( ( ret = dhm_check_range( &ctx->GY, &ctx->P ) ) != 0 )
        return( ret );

140 141 142 143 144 145 146 147 148
    ctx->len = mpi_size( &ctx->P );

    return( 0 );
}

/*
 * Setup and write the ServerKeyExchange parameters
 */
int dhm_make_params( dhm_context *ctx, int x_size,
149
                     unsigned char *output, size_t *olen,
150 151
                     int (*f_rng)(void *, unsigned char *, size_t),
                     void *p_rng )
152
{
153
    int ret, count = 0;
154
    size_t n1, n2, n3;
155 156
    unsigned char *p;

157 158 159
    if( mpi_cmp_int( &ctx->P, 0 ) == 0 )
        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );

160
    /*
161
     * Generate X as large as possible ( < P )
162
     */
163 164 165
    do
    {
        mpi_fill_random( &ctx->X, x_size, f_rng, p_rng );
166

167
        while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
168
            MPI_CHK( mpi_shift_r( &ctx->X, 1 ) );
169 170 171 172 173

        if( count++ > 10 )
            return( POLARSSL_ERR_DHM_MAKE_PARAMS_FAILED );
    }
    while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
174

175 176 177
    /*
     * Calculate GX = G^X mod P
     */
178 179 180
    MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
                          &ctx->P , &ctx->RP ) );

181
    if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 )
Paul Bakker's avatar
Paul Bakker committed
182 183
        return( ret );

184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207
    /*
     * export P, G, GX
     */
#define DHM_MPI_EXPORT(X,n)                     \
    MPI_CHK( mpi_write_binary( X, p + 2, n ) ); \
    *p++ = (unsigned char)( n >> 8 );           \
    *p++ = (unsigned char)( n      ); p += n;

    n1 = mpi_size( &ctx->P  );
    n2 = mpi_size( &ctx->G  );
    n3 = mpi_size( &ctx->GX );

    p = output;
    DHM_MPI_EXPORT( &ctx->P , n1 );
    DHM_MPI_EXPORT( &ctx->G , n2 );
    DHM_MPI_EXPORT( &ctx->GX, n3 );

    *olen  = p - output;

    ctx->len = n1;

cleanup:

    if( ret != 0 )
208
        return( POLARSSL_ERR_DHM_MAKE_PARAMS_FAILED + ret );
209 210 211 212 213 214 215 216

    return( 0 );
}

/*
 * Import the peer's public value G^Y
 */
int dhm_read_public( dhm_context *ctx,
217
                     const unsigned char *input, size_t ilen )
218 219 220 221
{
    int ret;

    if( ctx == NULL || ilen < 1 || ilen > ctx->len )
222
        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
223 224

    if( ( ret = mpi_read_binary( &ctx->GY, input, ilen ) ) != 0 )
225
        return( POLARSSL_ERR_DHM_READ_PUBLIC_FAILED + ret );
226 227 228 229 230 231 232 233

    return( 0 );
}

/*
 * Create own private value X and export G^X
 */
int dhm_make_public( dhm_context *ctx, int x_size,
234
                     unsigned char *output, size_t olen,
235 236
                     int (*f_rng)(void *, unsigned char *, size_t),
                     void *p_rng )
237
{
238
    int ret, count = 0;
239 240

    if( ctx == NULL || olen < 1 || olen > ctx->len )
241
        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
242

243 244 245
    if( mpi_cmp_int( &ctx->P, 0 ) == 0 )
        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );

246 247 248
    /*
     * generate X and calculate GX = G^X mod P
     */
249 250 251
    do
    {
        mpi_fill_random( &ctx->X, x_size, f_rng, p_rng );
252

253
        while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
254
            MPI_CHK( mpi_shift_r( &ctx->X, 1 ) );
255 256 257 258 259

        if( count++ > 10 )
            return( POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED );
    }
    while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
260 261 262 263

    MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
                          &ctx->P , &ctx->RP ) );

264 265
    if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 )
        return( ret );
Paul Bakker's avatar
Paul Bakker committed
266

267 268 269 270 271
    MPI_CHK( mpi_write_binary( &ctx->GX, output, olen ) );

cleanup:

    if( ret != 0 )
272
        return( POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED + ret );
273 274 275 276

    return( 0 );
}

277 278 279 280 281 282 283 284 285 286 287 288
/*
 * Use the blinding method and optimisation suggested in section 10 of:
 *  KOCHER, Paul C. Timing attacks on implementations of Diffie-Hellman, RSA,
 *  DSS, and other systems. In : Advances in Cryptology—CRYPTO’96. Springer
 *  Berlin Heidelberg, 1996. p. 104-113.
 */
static int dhm_update_blinding( dhm_context *ctx,
                    int (*f_rng)(void *, unsigned char *, size_t), void *p_rng )
{
    int ret, count;

    /*
289 290
     * Don't use any blinding the first time a particular X is used,
     * but remember it to use blinding next time.
291
     */
292
    if( mpi_cmp_mpi( &ctx->X, &ctx->pX ) != 0 )
293
    {
294
        MPI_CHK( mpi_copy( &ctx->pX, &ctx->X ) );
295 296 297 298
        MPI_CHK( mpi_lset( &ctx->Vi, 1 ) );
        MPI_CHK( mpi_lset( &ctx->Vf, 1 ) );

        return( 0 );
299 300 301
    }

    /*
302 303
     * Ok, we need blinding. Can we re-use existing values?
     * If yes, just update them by squaring them.
304
     */
305
    if( mpi_cmp_int( &ctx->Vi, 1 ) != 0 )
306
    {
307 308 309
        MPI_CHK( mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &ctx->Vi ) );
        MPI_CHK( mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->P ) );

310 311
        MPI_CHK( mpi_mul_mpi( &ctx->Vf, &ctx->Vf, &ctx->Vf ) );
        MPI_CHK( mpi_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->P ) );
312

313
        return( 0 );
314
    }
315 316

    /*
317
     * We need to generate blinding values from scratch
318
     */
319

320 321 322 323 324 325 326
    /* Vi = random( 2, P-1 ) */
    count = 0;
    do
    {
        mpi_fill_random( &ctx->Vi, mpi_size( &ctx->P ), f_rng, p_rng );

        while( mpi_cmp_mpi( &ctx->Vi, &ctx->P ) >= 0 )
327
            MPI_CHK( mpi_shift_r( &ctx->Vi, 1 ) );
328 329 330 331 332 333

        if( count++ > 10 )
            return( POLARSSL_ERR_MPI_NOT_ACCEPTABLE );
    }
    while( mpi_cmp_int( &ctx->Vi, 1 ) <= 0 );

334 335 336 337 338 339 340 341
    /* Vf = Vi^-X mod P */
    MPI_CHK( mpi_inv_mod( &ctx->Vf, &ctx->Vi, &ctx->P ) );
    MPI_CHK( mpi_exp_mod( &ctx->Vf, &ctx->Vf, &ctx->X, &ctx->P, &ctx->RP ) );

cleanup:
    return( ret );
}

342 343 344 345
/*
 * Derive and export the shared secret (G^Y)^X mod P
 */
int dhm_calc_secret( dhm_context *ctx,
346 347 348
                     unsigned char *output, size_t *olen,
                     int (*f_rng)(void *, unsigned char *, size_t),
                     void *p_rng )
349 350
{
    int ret;
351
    mpi GYb;
352

353
    if( ctx == NULL || *olen < ctx->len )
354
        return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
355

356
    if( ( ret = dhm_check_range( &ctx->GY, &ctx->P ) ) != 0 )
Paul Bakker's avatar
Paul Bakker committed
357 358
        return( ret );

359 360 361
    mpi_init( &GYb );

    /* Blind peer's value */
362
    if( f_rng != NULL )
363 364 365 366 367 368 369 370 371 372 373 374 375
    {
        MPI_CHK( dhm_update_blinding( ctx, f_rng, p_rng ) );
        MPI_CHK( mpi_mul_mpi( &GYb, &ctx->GY, &ctx->Vi ) );
        MPI_CHK( mpi_mod_mpi( &GYb, &GYb, &ctx->P ) );
    }
    else
        MPI_CHK( mpi_copy( &GYb, &ctx->GY ) );

    /* Do modular exponentiation */
    MPI_CHK( mpi_exp_mod( &ctx->K, &GYb, &ctx->X,
                          &ctx->P, &ctx->RP ) );

    /* Unblind secret value */
376
    if( f_rng != NULL )
377 378 379 380 381
    {
        MPI_CHK( mpi_mul_mpi( &ctx->K, &ctx->K, &ctx->Vf ) );
        MPI_CHK( mpi_mod_mpi( &ctx->K, &ctx->K, &ctx->P ) );
    }

382 383 384 385 386
    *olen = mpi_size( &ctx->K );

    MPI_CHK( mpi_write_binary( &ctx->K, output, *olen ) );

cleanup:
387
    mpi_free( &GYb );
388 389

    if( ret != 0 )
390
        return( POLARSSL_ERR_DHM_CALC_SECRET_FAILED + ret );
391 392 393 394 395 396 397 398 399

    return( 0 );
}

/*
 * Free the components of a DHM key
 */
void dhm_free( dhm_context *ctx )
{
400
    mpi_free( &ctx->pX); mpi_free( &ctx->Vf ); mpi_free( &ctx->Vi );
401 402 403
    mpi_free( &ctx->RP ); mpi_free( &ctx->K ); mpi_free( &ctx->GY );
    mpi_free( &ctx->GX ); mpi_free( &ctx->X ); mpi_free( &ctx->G );
    mpi_free( &ctx->P );
404

405
    polarssl_zeroize( ctx, sizeof( dhm_context ) );
406 407
}

408 409 410 411
#if defined(POLARSSL_ASN1_PARSE_C)
/*
 * Parse DHM parameters
 */
412 413
int dhm_parse_dhm( dhm_context *dhm, const unsigned char *dhmin,
                   size_t dhminlen )
414 415 416 417
{
    int ret;
    size_t len;
    unsigned char *p, *end;
418
#if defined(POLARSSL_PEM_PARSE_C)
419 420 421 422 423 424 425 426 427 428 429 430 431 432 433 434 435 436 437 438 439 440
    pem_context pem;

    pem_init( &pem );

    ret = pem_read_buffer( &pem,
                           "-----BEGIN DH PARAMETERS-----",
                           "-----END DH PARAMETERS-----",
                           dhmin, NULL, 0, &dhminlen );

    if( ret == 0 )
    {
        /*
         * Was PEM encoded
         */
        dhminlen = pem.buflen;
    }
    else if( ret != POLARSSL_ERR_PEM_NO_HEADER_FOOTER_PRESENT )
        goto exit;

    p = ( ret == 0 ) ? pem.buf : (unsigned char *) dhmin;
#else
    p = (unsigned char *) dhmin;
441
#endif /* POLARSSL_PEM_PARSE_C */
442 443 444 445 446 447 448 449 450 451 452 453 454 455 456 457 458 459 460 461 462 463 464 465 466 467 468 469 470 471 472 473 474
    end = p + dhminlen;

    /*
     *  DHParams ::= SEQUENCE {
     *      prime            INTEGER,  -- P
     *      generator        INTEGER,  -- g
     *  }
     */
    if( ( ret = asn1_get_tag( &p, end, &len,
            ASN1_CONSTRUCTED | ASN1_SEQUENCE ) ) != 0 )
    {
        ret = POLARSSL_ERR_DHM_INVALID_FORMAT + ret;
        goto exit;
    }

    end = p + len;

    if( ( ret = asn1_get_mpi( &p, end, &dhm->P  ) ) != 0 ||
        ( ret = asn1_get_mpi( &p, end, &dhm->G ) ) != 0 )
    {
        ret = POLARSSL_ERR_DHM_INVALID_FORMAT + ret;
        goto exit;
    }

    if( p != end )
    {
        ret = POLARSSL_ERR_DHM_INVALID_FORMAT +
              POLARSSL_ERR_ASN1_LENGTH_MISMATCH;
        goto exit;
    }

    ret = 0;

475 476
    dhm->len = mpi_size( &dhm->P );

477
exit:
478
#if defined(POLARSSL_PEM_PARSE_C)
479 480 481 482 483 484 485 486 487 488 489 490 491 492 493 494 495 496 497 498 499 500 501 502 503 504 505 506 507 508 509 510 511 512 513 514 515 516 517 518 519 520 521 522 523 524 525 526 527 528 529 530 531 532 533 534 535 536 537 538
    pem_free( &pem );
#endif
    if( ret != 0 )
        dhm_free( dhm );

    return( ret );
}

#if defined(POLARSSL_FS_IO)
/*
 * Load all data from a file into a given buffer.
 */
static int load_file( const char *path, unsigned char **buf, size_t *n )
{
    FILE *f;
    long size;

    if( ( f = fopen( path, "rb" ) ) == NULL )
        return( POLARSSL_ERR_DHM_FILE_IO_ERROR );

    fseek( f, 0, SEEK_END );
    if( ( size = ftell( f ) ) == -1 )
    {
        fclose( f );
        return( POLARSSL_ERR_DHM_FILE_IO_ERROR );
    }
    fseek( f, 0, SEEK_SET );

    *n = (size_t) size;

    if( *n + 1 == 0 ||
        ( *buf = (unsigned char *) polarssl_malloc( *n + 1 ) ) == NULL )
    {
        fclose( f );
        return( POLARSSL_ERR_DHM_MALLOC_FAILED );
    }

    if( fread( *buf, 1, *n, f ) != *n )
    {
        fclose( f );
        polarssl_free( *buf );
        return( POLARSSL_ERR_DHM_FILE_IO_ERROR );
    }

    fclose( f );

    (*buf)[*n] = '\0';

    return( 0 );
}

/*
 * Load and parse DHM parameters
 */
int dhm_parse_dhmfile( dhm_context *dhm, const char *path )
{
    int ret;
    size_t n;
    unsigned char *buf;

539
    if( ( ret = load_file( path, &buf, &n ) ) != 0 )
540 541 542 543
        return( ret );

    ret = dhm_parse_dhm( dhm, buf, n );

544
    polarssl_zeroize( buf, n + 1 );
545 546 547 548 549 550 551
    polarssl_free( buf );

    return( ret );
}
#endif /* POLARSSL_FS_IO */
#endif /* POLARSSL_ASN1_PARSE_C */

552
#if defined(POLARSSL_SELF_TEST)
553

554 555
#include "polarssl/certs.h"

556 557 558 559 560
/*
 * Checkup routine
 */
int dhm_self_test( int verbose )
{
561 562 563 564
#if defined(POLARSSL_CERTS_C)
    int ret;
    dhm_context dhm;

Paul Bakker's avatar
Paul Bakker committed
565 566
    dhm_init( &dhm );

567
    if( verbose != 0 )
568
        polarssl_printf( "  DHM parameter load: " );
569 570 571 572 573

    if( ( ret = dhm_parse_dhm( &dhm, (const unsigned char *) test_dhm_params,
                               strlen( test_dhm_params ) ) ) != 0 )
    {
        if( verbose != 0 )
574
            polarssl_printf( "failed\n" );
575

576
        ret = 1;
Paul Bakker's avatar
Paul Bakker committed
577
        goto exit;
578 579 580
    }

    if( verbose != 0 )
581
        polarssl_printf( "passed\n\n" );
582

Paul Bakker's avatar
Paul Bakker committed
583
exit:
584 585
    dhm_free( &dhm );

Paul Bakker's avatar
Paul Bakker committed
586
    return( ret );
587
#else
588 589 590 591
    if( verbose != 0 )
        polarssl_printf( "  DHM parameter load: skipped\n" );

    return( 0 );
592
#endif /* POLARSSL_CERTS_C */
593 594
}

595
#endif /* POLARSSL_SELF_TEST */
596

597
#endif /* POLARSSL_DHM_C */