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Changed ecp_mul() to always add the same point

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Manuel Pégourié-Gonnard 2012-11-08 18:24:10 +01:00 committed by Paul Bakker
parent d070f51224
commit 27b1ba8be0
1 changed files with 11 additions and 24 deletions
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35
library/ecp.c
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@ -434,55 +434,42 @@ int ecp_add( const ecp_group *grp, ecp_point *R,
/*
* Integer multiplication: R = m * P
* Using Montgomery's Ladder to avoid leaking information about m
* GECC 5.7 (SPA-resistant algorithm)
*/
int ecp_mul( const ecp_group *grp, ecp_point *R,
const mpi *m, const ecp_point *P )
{
int ret = 0;
size_t pos;
ecp_point A, B;
ecp_point Q[2];
ecp_point_init( &A ); ecp_point_init( &B );
ecp_point_init( &Q[0] ); ecp_point_init( &Q[1] );
/*
* The general method works only for m >= 2
* The general method works only for m >= 1
*/
if( mpi_cmp_int( m, 0 ) == 0 ) {
ecp_set_zero( R );
goto cleanup;
}
if( mpi_cmp_int( m, 1 ) == 0 ) {
MPI_CHK( ecp_copy( R, P ) );
goto cleanup;
}
ecp_set_zero( &Q[0] );
MPI_CHK( ecp_copy( &A, P ) );
MPI_CHK( ecp_add( grp, &B, P, P ) );
for( pos = mpi_msb( m ) - 2; ; pos-- )
for( pos = mpi_msb( m ) - 1; ; pos-- )
{
if( mpi_get_bit( m, pos ) == 0 )
{
MPI_CHK( ecp_add( grp, &B, &A, &B ) );
MPI_CHK( ecp_add( grp, &A, &A, &A ) ) ;
}
else
{
MPI_CHK( ecp_add( grp, &A, &A, &B ) );
MPI_CHK( ecp_add( grp, &B, &B, &B ) ) ;
}
MPI_CHK( ecp_add( grp, &Q[0], &Q[0], &Q[0] ) );
MPI_CHK( ecp_add( grp, &Q[1], &Q[0], P ) );
MPI_CHK( ecp_copy( &Q[0], &Q[ mpi_get_bit( m, pos ) ] ) );
if( pos == 0 )
break;
}
MPI_CHK( ecp_copy( R, &A ) );
MPI_CHK( ecp_copy( R, &Q[0] ) );
cleanup:
ecp_point_free( &A ); ecp_point_free( &B );
ecp_point_free( &Q[0] ); ecp_point_free( &Q[1] );
return( ret );
}