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Simplify DH blinding a bit

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This commit is contained in:
Manuel Pégourié-Gonnard 2013-09-04 16:39:03 +02:00
parent 143b5028a5
commit ed8a02bfae
3 changed files with 35 additions and 30 deletions
library
dhm.c

55
library/dhm.c
View file

@ -257,37 +257,44 @@ static int dhm_update_blinding( dhm_context *ctx,
int ret, count;
/*
* We can just update the previous values (by squaring them) if:
* - the values are initialized, and
* - our secret exponent did not change.
* If Vi is initialized, update it by squaring it
*/
if( ctx->Vi.p != NULL &&
mpi_cmp_mpi( &ctx->X, &ctx->_X ) == 0 )
if( ctx->Vi.p != NULL )
{
MPI_CHK( mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &ctx->Vi ) );
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 );
}
/*
* If X did not change, update Vf by squaring it too
*/
if( mpi_cmp_mpi( &ctx->X, &ctx->_X ) == 0 )
{
MPI_CHK( mpi_mul_mpi( &ctx->Vf, &ctx->Vf, &ctx->Vf ) );
MPI_CHK( mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &ctx->Vi ) );
MPI_CHK( mpi_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->P ) );
return( 0 );
}
/*
* Otherwise, we need to generate new values from scratch for this secret
* Otherwise, compute Vf from scratch
*/
/* 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 );
/* 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 ) );
@ -319,7 +326,7 @@ int dhm_calc_secret( dhm_context *ctx,
mpi_init( &GYb );
/* Blind peer's value */
if( f_rng != 0 )
if( f_rng != NULL )
{
MPI_CHK( dhm_update_blinding( ctx, f_rng, p_rng ) );
MPI_CHK( mpi_mul_mpi( &GYb, &ctx->GY, &ctx->Vi ) );
@ -333,7 +340,7 @@ int dhm_calc_secret( dhm_context *ctx,
&ctx->P, &ctx->RP ) );
/* Unblind secret value */
if( f_rng != 0 )
if( f_rng != NULL )
{
MPI_CHK( mpi_mul_mpi( &ctx->K, &ctx->K, &ctx->Vf ) );
MPI_CHK( mpi_mod_mpi( &ctx->K, &ctx->K, &ctx->P ) );