mbedtls/library/dhm.c

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/*
* Diffie-Hellman-Merkle key exchange
*
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* Copyright (C) 2006-2010, Brainspark B.V.
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*
* This file is part of PolarSSL (http://www.polarssl.org)
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* Lead Maintainer: Paul Bakker <polarssl_maintainer at polarssl.org>
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*
* All rights reserved.
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*
* 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)
*/
#include "polarssl/config.h"
#if defined(POLARSSL_DHM_C)
#include "polarssl/dhm.h"
/*
* helper to validate the mpi size and import it
*/
static int dhm_read_bignum( mpi *X,
unsigned char **p,
const unsigned char *end )
{
int ret, n;
if( end - *p < 2 )
return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
n = ( (*p)[0] << 8 ) | (*p)[1];
(*p) += 2;
if( (int)( end - *p ) < n )
return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
if( ( ret = mpi_read_binary( X, *p, n ) ) != 0 )
return( POLARSSL_ERR_DHM_READ_PARAMS_FAILED + ret );
(*p) += n;
return( 0 );
}
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/*
* Verify sanity of parameter with regards to P
*
* Parameter should be: 2 <= public_param <= P - 2
*
* 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
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*/
static int dhm_check_range( const mpi *param, const mpi *P )
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{
mpi L, U;
int ret = POLARSSL_ERR_DHM_BAD_INPUT_DATA;
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mpi_init( &L ); mpi_init( &U );
mpi_lset( &L, 2 );
mpi_sub_int( &U, P, 2 );
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if( mpi_cmp_mpi( param, &L ) >= 0 &&
mpi_cmp_mpi( param, &U ) <= 0 )
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{
ret = 0;
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}
mpi_free( &L ); mpi_free( &U );
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return( ret );
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}
/*
* Parse the ServerKeyExchange parameters
*/
int dhm_read_params( dhm_context *ctx,
unsigned char **p,
const unsigned char *end )
{
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int ret;
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dhm_free( ctx );
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 );
if( ( ret = dhm_check_range( &ctx->GY, &ctx->P ) ) != 0 )
return( ret );
ctx->len = mpi_size( &ctx->P );
return( 0 );
}
/*
* Setup and write the ServerKeyExchange parameters
*/
int dhm_make_params( dhm_context *ctx, int x_size,
unsigned char *output, size_t *olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret, count = 0;
size_t n1, n2, n3;
unsigned char *p;
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if( mpi_cmp_int( &ctx->P, 0 ) == 0 )
return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
/*
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* Generate X as large as possible ( < P )
*/
do
{
mpi_fill_random( &ctx->X, x_size, f_rng, p_rng );
while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
mpi_shift_r( &ctx->X, 1 );
if( count++ > 10 )
return( POLARSSL_ERR_DHM_MAKE_PARAMS_FAILED );
}
while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
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/*
* Calculate GX = G^X mod P
*/
MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
&ctx->P , &ctx->RP ) );
if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 )
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return( ret );
/*
* 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 )
return( POLARSSL_ERR_DHM_MAKE_PARAMS_FAILED + ret );
return( 0 );
}
/*
* Import the peer's public value G^Y
*/
int dhm_read_public( dhm_context *ctx,
const unsigned char *input, size_t ilen )
{
int ret;
if( ctx == NULL || ilen < 1 || ilen > ctx->len )
return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
if( ( ret = mpi_read_binary( &ctx->GY, input, ilen ) ) != 0 )
return( POLARSSL_ERR_DHM_READ_PUBLIC_FAILED + ret );
return( 0 );
}
/*
* Create own private value X and export G^X
*/
int dhm_make_public( dhm_context *ctx, int x_size,
unsigned char *output, size_t olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret, count = 0;
if( ctx == NULL || olen < 1 || olen > ctx->len )
return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
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if( mpi_cmp_int( &ctx->P, 0 ) == 0 )
return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
/*
* generate X and calculate GX = G^X mod P
*/
do
{
mpi_fill_random( &ctx->X, x_size, f_rng, p_rng );
while( mpi_cmp_mpi( &ctx->X, &ctx->P ) >= 0 )
mpi_shift_r( &ctx->X, 1 );
if( count++ > 10 )
return( POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED );
}
while( dhm_check_range( &ctx->X, &ctx->P ) != 0 );
MPI_CHK( mpi_exp_mod( &ctx->GX, &ctx->G, &ctx->X,
&ctx->P , &ctx->RP ) );
if( ( ret = dhm_check_range( &ctx->GX, &ctx->P ) ) != 0 )
return( ret );
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MPI_CHK( mpi_write_binary( &ctx->GX, output, olen ) );
cleanup:
if( ret != 0 )
return( POLARSSL_ERR_DHM_MAKE_PUBLIC_FAILED + ret );
return( 0 );
}
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/*
* 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 CryptologyCRYPTO96. 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;
/*
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* If Vi is initialized, update it by squaring it
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*/
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if( ctx->Vi.p != NULL )
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{
MPI_CHK( mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &ctx->Vi ) );
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MPI_CHK( mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->P ) );
}
else
{
/* 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 )
mpi_shift_r( &ctx->Vi, 1 );
if( count++ > 10 )
return( POLARSSL_ERR_MPI_NOT_ACCEPTABLE );
}
while( mpi_cmp_int( &ctx->Vi, 1 ) <= 0 );
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}
/*
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* If X did not change, update Vf by squaring it too
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*/
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if( mpi_cmp_mpi( &ctx->X, &ctx->_X ) == 0 )
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{
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MPI_CHK( mpi_mul_mpi( &ctx->Vf, &ctx->Vf, &ctx->Vf ) );
MPI_CHK( mpi_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->P ) );
return( 0 );
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}
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/*
* Otherwise, compute Vf from scratch
*/
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/* 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 ) );
/* Remember secret associated with Vi and Vf */
MPI_CHK( mpi_copy( &ctx->_X, &ctx->X ) );;
cleanup:
return( ret );
}
/*
* Derive and export the shared secret (G^Y)^X mod P
*/
int dhm_calc_secret( dhm_context *ctx,
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unsigned char *output, size_t *olen,
int (*f_rng)(void *, unsigned char *, size_t),
void *p_rng )
{
int ret;
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mpi GYb;
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if( ctx == NULL || *olen < ctx->len )
return( POLARSSL_ERR_DHM_BAD_INPUT_DATA );
if( ( ret = dhm_check_range( &ctx->GY, &ctx->P ) ) != 0 )
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return( ret );
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mpi_init( &GYb );
/* Blind peer's value */
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if( f_rng != NULL )
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{
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 */
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if( f_rng != NULL )
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{
MPI_CHK( mpi_mul_mpi( &ctx->K, &ctx->K, &ctx->Vf ) );
MPI_CHK( mpi_mod_mpi( &ctx->K, &ctx->K, &ctx->P ) );
}
*olen = mpi_size( &ctx->K );
MPI_CHK( mpi_write_binary( &ctx->K, output, *olen ) );
cleanup:
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mpi_free( &GYb );
if( ret != 0 )
return( POLARSSL_ERR_DHM_CALC_SECRET_FAILED + ret );
return( 0 );
}
/*
* Free the components of a DHM key
*/
void dhm_free( dhm_context *ctx )
{
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mpi_free( &ctx->_X); mpi_free( &ctx->Vf ); mpi_free( &ctx->Vi );
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 );
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memset( ctx, 0, sizeof( dhm_context ) );
}
#if defined(POLARSSL_SELF_TEST)
/*
* Checkup routine
*/
int dhm_self_test( int verbose )
{
return( verbose++ );
}
#endif
#endif