From b641a4b8cc5b69a7ab293442bc0f3a02a4b88eb7 Mon Sep 17 00:00:00 2001 From: =?UTF-8?q?Niels=20M=C3=B6ller?= Date: Wed, 1 Jan 2020 20:22:21 +0100 Subject: [PATCH] Reduce scratch need for curve448 inverse and sqrt --- ChangeLog | 7 +++++++ ecc-448.c | 48 +++++++++++++++++++++++++++++------------------- 2 files changed, 36 insertions(+), 19 deletions(-) diff --git a/ChangeLog b/ChangeLog index c9895615..b7624be5 100644 --- a/ChangeLog +++ b/ChangeLog @@ -1,5 +1,12 @@ 2020-01-01 Niels Möller + * ecc-448.c (ecc_mod_pow_2kp1): New function. + (ecc_mod_pow_446m224m1): Reduce scratch usage from 6*n to 5*n, at + the cost of one copy operation. Also use ecc_mod_pow_2kp1 where + applicable. + (ECC_448_INV_ITCH): Reduce to 5*ECC_LIMB_SIZE. + (ECC_448_SQRT_ITCH): Reduce to 9*ECC_LIMB_SIZE. + * testsuite/eddsa-compress-test.c: Test also with curve448. 2019-12-30 Niels Möller diff --git a/ecc-448.c b/ecc-448.c index 6a957bb4..b32ad463 100644 --- a/ecc-448.c +++ b/ecc-448.c @@ -124,37 +124,48 @@ ecc_mod_pow_2k (const struct ecc_modulo *m, } } -/* Computes a^{(p-3)/4} = a^{2^446-2^222-1} mod m. Needs 6 * n scratch +static void +ecc_mod_pow_2kp1 (const struct ecc_modulo *m, + mp_limb_t *rp, const mp_limb_t *xp, + unsigned k, mp_limb_t *tp) +{ + ecc_mod_pow_2k (m, tp, xp, k, rp); + ecc_mod_mul (m, rp, tp, xp); +} + +/* Computes a^{(p-3)/4} = a^{2^446-2^222-1} mod m. Needs 5 * n scratch space. */ static void ecc_mod_pow_446m224m1 (const struct ecc_modulo *p, mp_limb_t *rp, const mp_limb_t *ap, mp_limb_t *scratch) { +/* Note overlap: operations writing to t0 clobber t1. */ #define t0 scratch -#define t1 (scratch + 2*ECC_LIMB_SIZE) -#define t2 (scratch + 4*ECC_LIMB_SIZE) +#define t1 (scratch + 1*ECC_LIMB_SIZE) +#define t2 (scratch + 3*ECC_LIMB_SIZE) ecc_mod_sqr (p, rp, ap); /* a^2 */ ecc_mod_mul (p, t0, ap, rp); /* a^3 */ ecc_mod_sqr (p, rp, t0); /* a^6 */ ecc_mod_mul (p, t0, ap, rp); /* a^{2^3-1} */ - ecc_mod_pow_2k (p, rp, t0, 3, t2); /* a^{2^6-2^3} */ - ecc_mod_mul (p, t1, t0, rp); /* a^{2^6-1} */ + + ecc_mod_pow_2kp1 (p, t1, t0, 3, rp); /* a^{2^6-1} */ ecc_mod_pow_2k (p, rp, t1, 3, t2); /* a^{2^9-2^3} */ - ecc_mod_mul (p, t1, t0, rp); /* a^{2^9-1} */ - ecc_mod_pow_2k (p, t0, t1, 9, t2); /* a^{2^18-2^9} */ - ecc_mod_mul (p, rp, t1, t0); /* a^{2^18-1} */ - ecc_mod_sqr (p, t1, rp); /* a^{2^19-2} */ - ecc_mod_mul (p, t0, ap, t1); /* a^{2^19-1} */ - ecc_mod_pow_2k (p, t1, t0, 18, t2); /* a^{2^37-2^18} */ - ecc_mod_mul (p, t0, rp, t1); /* a^{2^37-1} */ - ecc_mod_pow_2k (p, t1, t0, 37, t2); /* a^{2^74-2^37} */ - ecc_mod_mul (p, rp, t0, t1); /* a^{2^74-1} */ + ecc_mod_mul (p, t2, t0, rp); /* a^{2^9-1} */ + ecc_mod_pow_2kp1 (p, t0, t2, 9, rp); /* a^{2^18-1} */ + + ecc_mod_sqr (p, t1, t0); /* a^{2^19-2} */ + ecc_mod_mul (p, rp, ap, t1); /* a^{2^19-1} */ + ecc_mod_pow_2k (p, t1, rp, 18, t2); /* a^{2^37-2^18} */ + ecc_mod_mul (p, rp, t0, t1); /* a^{2^37-1} */ + mpn_copyi (t0, rp, p->size); + + ecc_mod_pow_2kp1 (p, rp, t0, 37, t2); /* a^{2^74-1} */ ecc_mod_pow_2k (p, t1, rp, 37, t2); /* a^{2^111-2^37} */ ecc_mod_mul (p, rp, t0, t1); /* a^{2^111-1} */ - ecc_mod_pow_2k (p, t1, rp, 111, t2); /* a^{2^222-2^111} */ - ecc_mod_mul (p, t0, rp, t1); /* a^{2^222-1} */ + ecc_mod_pow_2kp1 (p, t0, rp, 111, t2);/* a^{2^222-1} */ + ecc_mod_sqr (p, t1, t0); /* a^{2^223-2} */ ecc_mod_mul (p, rp, ap, t1); /* a^{2^223-1} */ ecc_mod_pow_2k (p, t1, rp, 223, t2); /* a^{2^446-2^223} */ @@ -164,8 +175,7 @@ ecc_mod_pow_446m224m1 (const struct ecc_modulo *p, #undef t2 } -/* Needs 6*ECC_LIMB_SIZE scratch space. */ -#define ECC_448_INV_ITCH (6*ECC_LIMB_SIZE) +#define ECC_448_INV_ITCH (5*ECC_LIMB_SIZE) static void ecc_448_inv (const struct ecc_modulo *p, mp_limb_t *rp, const mp_limb_t *ap, @@ -207,7 +217,7 @@ ecc_448_zero_p (const struct ecc_modulo *p, mp_limb_t *xp) */ /* Needs 4*n space + scratch for ecc_mod_pow_446m224m1. */ -#define ECC_448_SQRT_ITCH (10*ECC_LIMB_SIZE) +#define ECC_448_SQRT_ITCH (9*ECC_LIMB_SIZE) static int ecc_448_sqrt(const struct ecc_modulo *p, mp_limb_t *rp, -- GitLab