diff --git a/include/polarssl/config.h b/include/polarssl/config.h index d98bdb34f..16643dcaf 100644 --- a/include/polarssl/config.h +++ b/include/polarssl/config.h @@ -1874,6 +1874,7 @@ // #define POLARSSL_ECP_MAX_BITS 521 /**< Maximum bit size of groups */ #define POLARSSL_ECP_WINDOW_SIZE 6 /**< Maximum window size used */ +#define POLARSSL_ECP_FIXED_POINT_OPTIM 1 /**< Enable fixed-point speed-up */ // Entropy options // diff --git a/include/polarssl/ecp.h b/include/polarssl/ecp.h index ff1072e0c..23351a742 100644 --- a/include/polarssl/ecp.h +++ b/include/polarssl/ecp.h @@ -178,11 +178,33 @@ ecp_keypair; * Minimum value: 2. Maximum value: 7. * * Result is an array of at most ( 1 << ( POLARSSL_ECP_WINDOW_SIZE - 1 ) ) - * points used for point multiplication. + * points used for point multiplication. This value is directly tied to EC + * peak memory usage, so decreasing it by one should roughly cut memory usage + * by two (if large curves are in use). * - * Reduction in size may reduce speed for big curves. + * Reduction in size may reduce speed, but larger curves are impacted first. + * Sample performances (in ECDHE handshakes/s, with FIXED_POINT_OPTIM = 1): + * w-size: 6 5 4 3 2 + * 521 145 141 135 120 97 + * 384 214 209 198 177 146 + * 256 320 320 303 262 226 + * 224 475 475 453 398 342 + * 192 640 640 633 587 476 */ #define POLARSSL_ECP_WINDOW_SIZE 6 /**< Maximum window size used */ + +/* + * Trade memory for speed on fixed-point multiplication. + * + * This speeds up repeated multiplication of the generator (that is, the + * multiplication in ECDSA signatures, and half of the multiplications in + * ECDSA verification and ECDHE) by a factor roughly 3 to 4. + * + * The cost is increasing EC peak memory usage by a factor roughly 2. + * + * Change this value to 0 to reduce peak memory usage. + */ +#define POLARSSL_ECP_FIXED_POINT_OPTIM 1 /**< Enable fixed-point speed-up */ #endif /* diff --git a/library/ecp.c b/library/ecp.c index c3397a4f8..58b5d752e 100644 --- a/library/ecp.c +++ b/library/ecp.c @@ -1315,12 +1315,17 @@ static int ecp_mul_comb( ecp_group *grp, ecp_point *R, /* * If P == G, pre-compute a bit more, since this may be re-used later. - * Just adding one ups the cost of the first mul by at most 3%. + * Just adding one avoids upping the cost of the first mul too much, + * and the memory cost too. */ +#if POLARSSL_ECP_FIXED_POINT_OPTIM == 1 p_eq_g = ( mpi_cmp_mpi( &P->Y, &grp->G.Y ) == 0 && mpi_cmp_mpi( &P->X, &grp->G.X ) == 0 ); if( p_eq_g ) w++; +#else + p_eq_g = 0; +#endif /* * Make sure w is within bounds.