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introduce ED25519_NO_PRECOMP flag to optimize ed25519 verify size

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This commit is contained in:
Pavol Rusnak 2017-03-29 00:18:56 +02:00
parent df2524e35b
commit c200ce121a
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GPG Key ID: 91F3B339B9A02A3D
1 changed files with 23 additions and 3 deletions
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26
ed25519-donna/ed25519-donna-impl-base.h
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@ -45,6 +45,7 @@ ge25519_double_p1p1(ge25519_p1p1 *r, const ge25519 *p) {
curve25519_sub_after_basic(r->t, c, r->z);
}
#ifndef ED25519_NO_PRECOMP
static void
ge25519_nielsadd2_p1p1(ge25519_p1p1 *r, const ge25519 *p, const ge25519_niels *q, unsigned char signbit) {
const bignum25519 *qb = (const bignum25519 *)q;
@ -63,6 +64,7 @@ ge25519_nielsadd2_p1p1(ge25519_p1p1 *r, const ge25519 *p, const ge25519_niels *q
curve25519_add(rb[2+signbit], rb[2+signbit], c); /* z for +, t for - */
curve25519_sub(rb[2+(signbit^1)], rb[2+(signbit^1)], c); /* t for +, z for - */
}
#endif
static void
ge25519_pnielsadd_p1p1(ge25519_p1p1 *r, const ge25519 *p, const ge25519_pniels *q, unsigned char signbit) {
@ -222,24 +224,38 @@ DONNA_INLINE static void ge25519_set_neutral(ge25519 *r)
#define S1_SWINDOWSIZE 5
#define S1_TABLE_SIZE (1<<(S1_SWINDOWSIZE-2))
#ifdef ED25519_NO_PRECOMP
#define S2_SWINDOWSIZE 5
#else
#define S2_SWINDOWSIZE 7
#endif
#define S2_TABLE_SIZE (1<<(S2_SWINDOWSIZE-2))
/* computes [s1]p1 + [s2]base */
static void ge25519_double_scalarmult_vartime(ge25519 *r, const ge25519 *p1, const bignum256modm s1, const bignum256modm s2) {
signed char slide1[256], slide2[256];
ge25519_pniels pre1[S1_TABLE_SIZE];
ge25519 d1;
#ifdef ED25519_NO_PRECOMP
ge25519_pniels pre2[S2_TABLE_SIZE];
#endif
ge25519 dp;
ge25519_p1p1 t;
int32_t i;
contract256_slidingwindow_modm(slide1, s1, S1_SWINDOWSIZE);
contract256_slidingwindow_modm(slide2, s2, S2_SWINDOWSIZE);
ge25519_double(&d1, p1);
ge25519_double(&dp, p1);
ge25519_full_to_pniels(pre1, p1);
for (i = 0; i < S1_TABLE_SIZE - 1; i++)
ge25519_pnielsadd(&pre1[i+1], &d1, &pre1[i]);
ge25519_pnielsadd(&pre1[i+1], &dp, &pre1[i]);
#ifdef ED25519_NO_PRECOMP
ge25519_double(&dp, &ge25519_basepoint);
ge25519_full_to_pniels(pre2, &ge25519_basepoint);
for (i = 0; i < S2_TABLE_SIZE - 1; i++)
ge25519_pnielsadd(&pre2[i+1], &dp, &pre2[i]);
#endif
ge25519_set_neutral(r);
@ -257,7 +273,11 @@ static void ge25519_double_scalarmult_vartime(ge25519 *r, const ge25519 *p1, con
if (slide2[i]) {
ge25519_p1p1_to_full(r, &t);
#ifdef ED25519_NO_PRECOMP
ge25519_pnielsadd_p1p1(&t, r, &pre2[abs(slide2[i]) / 2], (unsigned char)slide2[i] >> 7);
#else
ge25519_nielsadd2_p1p1(&t, r, &ge25519_niels_sliding_multiples[abs(slide2[i]) / 2], (unsigned char)slide2[i] >> 7);
#endif
}
ge25519_p1p1_to_partial(r, &t);