Remove dead code.

[shekohex]

After making some code refactoring, i found that

curve25519-rs/src/lib.rs

Lines 1152 to 1156 in 540914f

	fn is_nonzero(&self) -> bool {
	let bs = self.to_bytes();
	let zero = [0; 32];
	!fixed_time_eq(bs.as_ref(), zero.as_ref())
	}

is only used here GeP3::from_bytes_negate_vartime

curve25519-rs/src/lib.rs

Line 1391 in 540914f

pub fn from_bytes_negate_vartime(s: &[u8]) -> Option<GeP3> {

...

curve25519-rs/src/lib.rs

Lines 1402 to 1412 in 540914f

	let mut x = uv7.pow25523() * v_raise_3 * u;
	let vxx = x.square() * v;
	let check = vxx - u;
	if check.is_nonzero() {
	let check2 = vxx + u;
	if check2.is_nonzero() {
	return None;
	}
	x = x * FE_SQRTM1;
	}

which the GeP3::from_bytes_negate_vartime is never used in the code.
so after removing it, we now can get rid of some other stuff like fixed_time_eq which is unsafe linked from other c code and written in asm.

[shekohex]

cc @jamesmunns could you review this ? thanks.

[jamesmunns]

Hey @shekohex, in general I am definitely not a crypto expert, and removing anything marked "fixed time" is something that would make me very nervous.

[shekohex]

@jamesmunns
oh, i know that maybe a bad thing, since i'm not a crypto expert too, but actually that code never have been referenced, so why we need it?

again, yesterday i was trying to port it to WASM using wasm-pack of course, but i got a linkage error from rust-lld, and guess what? the object causes the problem was that one from the cc compiler util_helpers.o.
which made me to search the full code, and i found that we never uses it.

and after removing that dead_code, it works perfectly in browser !

[jamesmunns]

Yeah, I would expect that this code would not work for targets other than x86[_64] or ARM, as the C code is only implemented for these targets. Additionally, I don't think it's possible to link in non-Rust code using the wasm32-unknown-unknown target (I think you need to use the emscripten one? I might be wrong about this)

[shekohex]

Ok, I'll create a new branch which i will remove c code from the base, and start to use rusty_wasm crate which i think would be nice to inline asm.
(but I'm not sure, if that could be a solution for compiling it to wasm target).