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Simplify usage of DHM blinding

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This commit is contained in:
Manuel Pégourié-Gonnard
2013-09-17 11:34:11 +02:00
committed by Paul Bakker
parent c83e418149
commit 15d5de1969
8 changed files with 62 additions and 57 deletions
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68
library/dhm.c
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@ -273,51 +273,55 @@ static int dhm_update_blinding( dhm_context *ctx,
int ret, count;
/*
* If Vi is initialized, update it by squaring it
* Don't use any blinding the first time a particular X is used,
* but remember it to use blinding next time.
*/
if( ctx->Vi.p != NULL )
if( mpi_cmp_mpi( &ctx->X, &ctx->_X ) != 0 )
{
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 );
MPI_CHK( mpi_copy( &ctx->_X, &ctx->X ) );
MPI_CHK( mpi_lset( &ctx->Vi, 1 ) );
MPI_CHK( mpi_lset( &ctx->Vf, 1 ) );
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_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->P ) );
return( 0 );
}
/*
* Otherwise, compute Vf from scratch
* Ok, we need blinding. Can we re-use existing values?
* If yes, just update them by squaring them.
*/
if( mpi_cmp_int( &ctx->Vi, 1 ) != 0 )
{
MPI_CHK( mpi_mul_mpi( &ctx->Vi, &ctx->Vi, &ctx->Vi ) );
MPI_CHK( mpi_mod_mpi( &ctx->Vi, &ctx->Vi, &ctx->P ) );
MPI_CHK( mpi_mul_mpi( &ctx->Vf, &ctx->Vf, &ctx->Vf ) );
MPI_CHK( mpi_mod_mpi( &ctx->Vf, &ctx->Vf, &ctx->P ) );
return( 0 );
}
/*
* We need to generate blinding values 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 ) );
/* Remember secret associated with Vi and Vf */
MPI_CHK( mpi_copy( &ctx->_X, &ctx->X ) );;
cleanup:
return( ret );
}