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Added a precompute() function for fast mult

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Manuel Pégourié-Gonnard 2012-11-21 10:00:45 +01:00 committed by Paul Bakker
parent 855560758c
commit 7652a593d6
1 changed files with 32 additions and 2 deletions
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34
library/ecp.c
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@ -727,8 +727,8 @@ cleanup:
* does. Finally, there is an off-by-one error in the reference: the * does. Finally, there is an off-by-one error in the reference: the
* last index should be k-1, not k. * last index should be k-1, not k.
*/ */
static int ecp_w_naf_fixed( signed char x[], size_t k, unsigned char w, static int ecp_w_naf_fixed( signed char x[], size_t k,
const mpi *m ) unsigned char w, const mpi *m )
{ {
int ret; int ret;
unsigned int i, u, mask, carry; unsigned int i, u, mask, carry;
@ -764,6 +764,36 @@ cleanup:
return( ret ); return( ret );
} }
/*
* Precompute odd multiples of P up to (2 * t_len - 1) P.
* The table is filled with T[i] = (2 * i + 1) P.
*/
static int ecp_precompute( ecp_point T[], size_t t_len,
const ecp_group *grp, const ecp_point *P )
{
int ret;
size_t i;
ecp_point PP;
ecp_point_init( &PP );
MPI_CHK( ecp_add( grp, &PP, P, P ) );
MPI_CHK( ecp_copy( &T[0], P ) );
/*
* TODO: use Montgomery's trick for less inversions
*/
for( i = 1; i < t_len; i++ )
MPI_CHK( ecp_add( grp, &T[i], &T[i-1], &PP ) );
cleanup:
ecp_point_free( &PP );
return( ret );
}
/* /*
* Integer multiplication: R = m * P (GECC 5.7, SPA-resistant) * Integer multiplication: R = m * P (GECC 5.7, SPA-resistant)
*/ */