Add ecp_mod_p255(): Curve25519 about 4x faster now

parent 357ff65a
......@@ -322,16 +322,29 @@ cleanup:
#if defined(POLARSSL_ECP_NIST_OPTIM)
/* Forward declarations */
#if defined(POLARSSL_ECP_DP_SECP192R1_ENABLED)
static int ecp_mod_p192( mpi * );
#endif
#if defined(POLARSSL_ECP_DP_SECP224R1_ENABLED)
static int ecp_mod_p224( mpi * );
#endif
#if defined(POLARSSL_ECP_DP_SECP256R1_ENABLED)
static int ecp_mod_p256( mpi * );
#endif
#if defined(POLARSSL_ECP_DP_SECP384R1_ENABLED)
static int ecp_mod_p384( mpi * );
#endif
#if defined(POLARSSL_ECP_DP_SECP521R1_ENABLED)
static int ecp_mod_p521( mpi * );
#endif
#if defined(POLARSSL_ECP_DP_M255_ENABLED)
static int ecp_mod_p255( mpi * );
#endif
#define NIST_MODP( P ) grp->modp = ecp_mod_ ## P;
#else
#define NIST_MODP( P )
#endif
#endif /* POLARSSL_ECP_NIST_OPTIM */
#define LOAD_GROUP( G ) ecp_group_read_binary( grp, \
G ## _p, sizeof( G ## _p ), \
......@@ -431,6 +444,7 @@ int ecp_use_known_dp( ecp_group *grp, ecp_group_id id )
#if defined(POLARSSL_ECP_DP_M255_ENABLED)
case POLARSSL_ECP_DP_M255:
grp->modp = ecp_mod_p255;
return( ecp_use_curve25519( grp ) );
#endif /* POLARSSL_ECP_DP_M255_ENABLED */
......@@ -843,4 +857,48 @@ cleanup:
#endif /* POLARSSL_ECP_NIST_OPTIM */
#if defined(POLARSSL_ECP_DP_M255_ENABLED)
/* Size of p255 in terms of t_uint */
#define P255_WIDTH ( 255 / 8 / sizeof( t_uint ) + 1 )
/*
* Fast quasi-reduction modulo p255 = 2^255 - 19
* Write N as A1 + 2^255 A1, return A0 + 19 * A1
*/
static int ecp_mod_p255( mpi *N )
{
int ret;
size_t i;
mpi M;
t_uint Mp[P255_WIDTH + 2];
if( N->n < P255_WIDTH )
return( 0 );
/* M = A1 */
M.s = 1;
M.n = N->n - ( P255_WIDTH - 1 );
if( M.n > P255_WIDTH + 1 )
M.n = P255_WIDTH + 1;
M.p = Mp;
memset( Mp, 0, sizeof Mp );
memcpy( Mp, N->p + P255_WIDTH - 1, M.n * sizeof( t_uint ) );
MPI_CHK( mpi_shift_r( &M, 255 % ( 8 * sizeof( t_uint ) ) ) );
M.n++; /* Make room for multiplication by 19 */
/* N = A0 */
mpi_set_bit( N, 255, 0 );
for( i = P255_WIDTH; i < N->n; i++ )
N->p[i] = 0;
/* N = A0 + 19 * A1 */
MPI_CHK( mpi_mul_int( &M, &M, 19 ) );
MPI_CHK( mpi_add_abs( N, N, &M ) );
cleanup:
return( ret );
}
#endif /* POLARSSL_ECP_DP_M255_ENABLED */
#endif
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