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Optimize more common cases in ecp_muladd()

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This commit is contained in:
Manuel Pégourié-Gonnard 2015-10-23 15:50:37 +02:00
parent 241bf6717a
commit 00992d45c0
1 changed files with 33 additions and 10 deletions
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43
library/ecp.c
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@ -1667,8 +1667,39 @@ cleanup:
}
#endif /* ECP_SHORTWEIERSTRASS */
/*
* R = m * P with shortcuts for m == 1 and m == -1
* NOT constant-time - ONLY for short Weierstrass!
*/
static int mbedtls_ecp_mul_shortcuts( mbedtls_ecp_group *grp,
mbedtls_ecp_point *R,
const mbedtls_mpi *m,
const mbedtls_ecp_point *P )
{
int ret;
if( mbedtls_mpi_cmp_int( m, 1 ) == 0 )
{
MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) );
}
else if( mbedtls_mpi_cmp_int( m, -1 ) == 0 )
{
MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, P ) );
if( mbedtls_mpi_cmp_int( &R->Y, 0 ) != 0 )
MBEDTLS_MPI_CHK( mbedtls_mpi_sub_mpi( &R->Y, &grp->P, &R->Y ) );
}
else
{
MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, R, m, P, NULL, NULL ) );
}
cleanup:
return( ret );
}
/*
* Linear combination
* NOT constant-time
*/
int mbedtls_ecp_muladd( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
const mbedtls_mpi *m, const mbedtls_ecp_point *P,
@ -1682,16 +1713,8 @@ int mbedtls_ecp_muladd( mbedtls_ecp_group *grp, mbedtls_ecp_point *R,
mbedtls_ecp_point_init( &mP );
/* Optimize some simple special cases */
if( mbedtls_mpi_cmp_int( m, 1 ) == 0 )
MBEDTLS_MPI_CHK( mbedtls_ecp_copy( &mP, P ) );
else
MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, &mP, m, P, NULL, NULL ) );
if( mbedtls_mpi_cmp_int( n, 1 ) == 0 )
MBEDTLS_MPI_CHK( mbedtls_ecp_copy( R, Q ) );
else
MBEDTLS_MPI_CHK( mbedtls_ecp_mul( grp, R, n, Q, NULL, NULL ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_mul_shortcuts( grp, &mP, m, P ) );
MBEDTLS_MPI_CHK( mbedtls_ecp_mul_shortcuts( grp, R, n, Q ) );
MBEDTLS_MPI_CHK( ecp_add_mixed( grp, R, &mP, R ) );
MBEDTLS_MPI_CHK( ecp_normalize_jac( grp, R ) );