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Use constant-time conditional moves instead of byte slicing

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This commit is contained in:
Pieter Wuille
2014-12-02 20:20:13 +01:00
parent d220062ac2
commit efb7d4b299
7 changed files with 55 additions and 10 deletions
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15
src/field_5x52_impl.h
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@@ -276,4 +276,19 @@ static void secp256k1_fe_sqr(secp256k1_fe_t *r, const secp256k1_fe_t *a) {
#endif
}
static void secp256k1_fe_cmov(secp256k1_fe_t *r, const secp256k1_fe_t *a, int flag) {
uint64_t mask0 = flag + ~((uint64_t)0), mask1 = ~mask0;
r->n[0] = (r->n[0] & mask0) | (a->n[0] & mask1);
r->n[1] = (r->n[1] & mask0) | (a->n[1] & mask1);
r->n[2] = (r->n[2] & mask0) | (a->n[2] & mask1);
r->n[3] = (r->n[3] & mask0) | (a->n[3] & mask1);
r->n[4] = (r->n[4] & mask0) | (a->n[4] & mask1);
#ifdef VERIFY
if (flag) {
r->magnitude = a->magnitude;
r->normalized = a->normalized;
}
#endif
}
#endif