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Constify the ladder

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This commit is contained in:
Frank Denis 2020-08-15 11:48:34 +02:00 committed by Andrew Kelley
parent d86cde5752
commit 5ab69633b7
2 changed files with 16 additions and 23 deletions
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35
lib/std/crypto/25519/curve25519.zig
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@ -43,28 +43,21 @@ pub const Curve25519 = struct {
var swap: u8 = 0;
var pos: usize = bits - 1;
while (true) : (pos -= 1) {
const b = (s[pos >> 3] >> @truncate(u3, pos)) & 1;
swap ^= b;
const bit = (s[pos >> 3] >> @truncate(u3, pos)) & 1;
swap ^= bit;
Fe.cSwap2(&x2, &x3, &z2, &z3, swap);
swap = b;
var tmp0 = x3.sub(z3);
var tmp1 = x2.sub(z2);
x2 = x2.add(z2);
z2 = x3.add(z3);
z3 = tmp0.mul(x2);
z2 = z2.mul(tmp1);
tmp0 = tmp1.sq();
tmp1 = x2.sq();
x3 = z3.add(z2);
z2 = z3.sub(z2);
x2 = tmp1.mul(tmp0);
tmp1 = tmp1.sub(tmp0);
z2 = z2.sq();
z3 = tmp1.mul32(121666);
x3 = x3.sq();
tmp0 = tmp0.add(z3);
z3 = x1.mul(z2);
z2 = tmp1.mul(tmp0);
swap = bit;
const a = x2.add(z2);
const b = x2.sub(z2);
const aa = a.sq();
const bb = b.sq();
x2 = aa.mul(bb);
const e = aa.sub(bb);
const da = x3.sub(z3).mul(a);
const cb = x3.add(z3).mul(b);
x3 = da.add(cb).sq();
z3 = x1.mul(da.sub(cb).sq());
z2 = e.mul(bb.add(e.mul32(121666)));
if (pos == 0) break;
}
Fe.cSwap2(&x2, &x3, &z2, &z3, swap);

4
lib/std/crypto/25519/edwards25519.zig
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@ -130,8 +130,8 @@ pub const Edwards25519 = struct {
var pos: usize = 252;
while (true) : (pos -= 4) {
q = q.dbl().dbl().dbl().dbl();
const b = (s[pos >> 3] >> @truncate(u3, pos)) & 0xf;
q = q.add(pcSelect(pc, b));
const bit = (s[pos >> 3] >> @truncate(u3, pos)) & 0xf;
q = q.add(pcSelect(pc, bit));
if (pos == 0) break;
}
try q.rejectIdentity();