nadeko

https://github.com/klutzy/nadeko is an example of doing this.

> As far as I know, it is currently not possible to implement constant-time functions using stable Rust. For those wondering, that's because asm! is not stabilised and the stabilisation path for it is unclear[0], there's also been a proposal for an alternative asm![1], Rust otherwise relies on LLVM and Brian Anderson reported[2] having > been told by LLVM folks that getting LLVM to do constant time code generation is essentially hopeless, and it should just be written in asm. Nadeko[3] aims to do exactly that, but because of the above only works on nightly. [0] an RFC was created then retracted[4] for discussions on internals[5] [1] https://github.com/rust-lang/rfcs/pull/129/files [2] http://rust-dev.1092773.n5.nabble.com/Rust-crypto-highlights... [3] https://github.com/klutzy/nadeko [4] https://github.com/rust-lang/rfcs/issues/1274 [5] h

Well, there is this: https://github.com/klutzy/nadeko

It is very probable that a sufficiently smart optimizer could see the assertion was always true and delete it. Then see no one reads "a" and delete it as well. In certain circumstances this can cause a secret to be leaked in, say a register, making our safe function unsafe. You need to be very careful writing secure code, and probably need to go down to the level of writing assembly to be sure the optimizer isn't turning your safe code into unsafe code. We actually have an interesting project in rust where someone is writing a syntax extension to take rust like code and generate assembly [0]. It's probably unsafe to use right now but if sufficiently well implemented it could be the foundation of a lot of interesting cryptography work. [0]: https://github.com/klutzy/nadeko

Rust has an asm! macro. You can implement the constant time operations in assembly. Here's a syntax extension that tries to use black magic to turn a subset of Rust code into corresponding asm! macros: https://github.com/klutzy/nadeko/blob/tmp/tests/rot13.rs Note it presently has no support for loops whatsoever.