Commit 3a64c5a7 authored by Niels Möller's avatar Niels Möller

Added curve25519 special case in ecc_set_point.

parent d583973e
2014-08-25 Niels Möller <nisse@lysator.liu.se>
* ecc-point.c (ecc_point_set): Handle curve25519 as a special
case, when checking if the point is on the curve.
2014-08-24 Niels Möller <nisse@lysator.liu.se>
* testsuite/ecdh-test.c: Test ecc_point_mul and ecc_point_mul_g,
......
......@@ -68,12 +68,26 @@ ecc_point_set (struct ecc_point *p, const mpz_t x, const mpz_t y)
mpz_init (lhs);
mpz_init (rhs);
/* Check that y^2 = x^3 - 3*x + b (mod p) */
if (p->ecc->bit_size == 255)
{
/* curve25519 special case. FIXME: Do in some cleaner way? */
/* Check that y^2 = x^3 + 486662 x^2 + x (mod p)*/
mpz_mul (lhs, x, x); /* Reuse lhs as a temporary */
mpz_add_ui (rhs, x, 486662);
mpz_mul (rhs, rhs, lhs);
mpz_add (rhs, rhs, x);
}
else
{
/* Check that y^2 = x^3 - 3*x + b (mod p) */
mpz_mul (rhs, x, x);
mpz_sub_ui (rhs, rhs, 3);
mpz_mul (rhs, rhs, x);
mpz_add (rhs, rhs, mpz_roinit_n (t, p->ecc->b, size));
}
mpz_mul (lhs, y, y);
mpz_mul (rhs, x, x);
mpz_sub_ui (rhs, rhs, 3);
mpz_mul (rhs, rhs, x);
mpz_add (rhs, rhs, mpz_roinit_n (t, p->ecc->b, size));
res = mpz_congruent_p (lhs, rhs, mpz_roinit_n (t, p->ecc->p, size));
......
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