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Faster scalarmult_ed25519()

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This commit is contained in:
Frank Denis
2017-12-06 15:13:18 +00:00
parent 99fa31a595
commit 715cb6ba33
1 changed files with 58 additions and 17 deletions
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src/libsodium/crypto_core/ed25519/ref10/ed25519_ref10.c
+58 -17
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@@ -553,6 +553,47 @@ ge25519_select(ge25519_precomp *t, const ge25519_precomp precomp[8], const signe
ge25519_cmov(t, &minust, bnegative);
}
static void
ge25519_cached_0(ge25519_cached *h)
{
fe25519_1(h->YplusX);
fe25519_1(h->YminusX);
fe25519_1(h->Z);
fe25519_0(h->T2d);
}
static void
ge25519_cmov_cached(ge25519_cached *t, const ge25519_cached *u, unsigned char b)
{
fe25519_cmov(t->YplusX, u->YplusX, b);
fe25519_cmov(t->YminusX, u->YminusX, b);
fe25519_cmov(t->Z, u->Z, b);
fe25519_cmov(t->T2d, u->T2d, b);
}
static void
ge25519_select_cached(ge25519_cached *t, const ge25519_cached cached[8], const signed char b)
{
ge25519_cached minust;
const unsigned char bnegative = negative(b);
const unsigned char babs = b - (((-bnegative) & b) * ((signed char) 1 << 1));
ge25519_cached_0(t);
ge25519_cmov_cached(t, &cached[0], equal(babs, 1));
ge25519_cmov_cached(t, &cached[1], equal(babs, 2));
ge25519_cmov_cached(t, &cached[2], equal(babs, 3));
ge25519_cmov_cached(t, &cached[3], equal(babs, 4));
ge25519_cmov_cached(t, &cached[4], equal(babs, 5));
ge25519_cmov_cached(t, &cached[5], equal(babs, 6));
ge25519_cmov_cached(t, &cached[6], equal(babs, 7));
ge25519_cmov_cached(t, &cached[7], equal(babs, 8));
fe25519_copy(minust.YplusX, t->YminusX);
fe25519_copy(minust.YminusX, t->YplusX);
fe25519_copy(minust.Z, t->Z);
fe25519_neg(minust.T2d, t->T2d);
ge25519_cmov_cached(t, &minust, bnegative);
}
static void
ge25519_select_base(ge25519_precomp *t, const int pos, const signed char b)
{
@@ -708,39 +749,39 @@ ge25519_scalarmult(ge25519_p3 *h, const unsigned char *a, const ge25519_p3 *p)
ge25519_p2 s;
ge25519_p1p1 t2, t3, t4, t5, t6, t7, t8;
ge25519_p3 p2, p3, p4, p5, p6, p7, p8;
ge25519_precomp pi[8];
ge25519_precomp t;
ge25519_cached pi[8];
ge25519_cached t;
int i;
ge25519_p3_to_precomp(&pi[1 - 1], p); /* p */
ge25519_p3_to_cached(&pi[1 - 1], p); /* p */
ge25519_p3_dbl(&t2, p);
ge25519_p1p1_to_p3(&p2, &t2);
ge25519_p3_to_precomp(&pi[2 - 1], &p2); /* 2p = 2*p */
ge25519_p3_to_cached(&pi[2 - 1], &p2); /* 2p = 2*p */
ge25519_madd(&t3, p, &pi[2 - 1]);
ge25519_add(&t3, p, &pi[2 - 1]);
ge25519_p1p1_to_p3(&p3, &t3);
ge25519_p3_to_precomp(&pi[3 - 1], &p3); /* 3p = 2p+p */
ge25519_p3_to_cached(&pi[3 - 1], &p3); /* 3p = 2p+p */
ge25519_p3_dbl(&t4, &p2);
ge25519_p1p1_to_p3(&p4, &t4);
ge25519_p3_to_precomp(&pi[4 - 1], &p4); /* 4p = 2*2p */
ge25519_p3_to_cached(&pi[4 - 1], &p4); /* 4p = 2*2p */
ge25519_madd(&t5, p, &pi[4 - 1]);
ge25519_add(&t5, p, &pi[4 - 1]);
ge25519_p1p1_to_p3(&p5, &t5);
ge25519_p3_to_precomp(&pi[5 - 1], &p5); /* 5p = 4p+p */
ge25519_p3_to_cached(&pi[5 - 1], &p5); /* 5p = 4p+p */
ge25519_p3_dbl(&t6, &p3);
ge25519_p1p1_to_p3(&p6, &t6);
ge25519_p3_to_precomp(&pi[6 - 1], &p6); /* 6p = 2*3p */
ge25519_p3_to_cached(&pi[6 - 1], &p6); /* 6p = 2*3p */
ge25519_madd(&t7, p, &pi[6 - 1]);
ge25519_add(&t7, p, &pi[6 - 1]);
ge25519_p1p1_to_p3(&p7, &t7);
ge25519_p3_to_precomp(&pi[7 - 1], &p7); /* 7p = 6p+p */
ge25519_p3_to_cached(&pi[7 - 1], &p7); /* 7p = 6p+p */
ge25519_p3_dbl(&t8, &p4);
ge25519_p1p1_to_p3(&p8, &t8);
ge25519_p3_to_precomp(&pi[8 - 1], &p8); /* 8p = 2*4p */
ge25519_p3_to_cached(&pi[8 - 1], &p8); /* 8p = 2*4p */
for (i = 0; i < 32; ++i) {
e[2 * i + 0] = (a[i] >> 0) & 15;
@@ -762,8 +803,8 @@ ge25519_scalarmult(ge25519_p3 *h, const unsigned char *a, const ge25519_p3 *p)
ge25519_p3_0(h);
for (i = 63; i != 0; i--) {
ge25519_select(&t, pi, e[i]);
ge25519_madd(&r, h, &t);
ge25519_select_cached(&t, pi, e[i]);
ge25519_add(&r, h, &t);
ge25519_p1p1_to_p2(&s, &r);
ge25519_p2_dbl(&r, &s);
@@ -776,8 +817,8 @@ ge25519_scalarmult(ge25519_p3 *h, const unsigned char *a, const ge25519_p3 *p)
ge25519_p1p1_to_p3(h, &r); /* *16 */
}
ge25519_select(&t, pi, e[i]);
ge25519_madd(&r, h, &t);
ge25519_select_cached(&t, pi, e[i]);
ge25519_add(&r, h, &t);
ge25519_p1p1_to_p3(h, &r);
}