subtle

Pure-Rust traits and utilities for constant-time cryptographic implementations.

Significant portions of this code are based upon Golang's "crypto/subtle" module, and this library aims to be that library's Rust equivalent¹, plus more.

¹ The only function in Golang's "crypto/subtle" module which we do not implement is ConstantTimeLessOrEq. This is for two reasons: first, that ConstantTimeLessOrEq, as far as this author knows, is only used to implement the RSA encryption padding scheme defined in the (now outdated) PKCS#1 v1.5 standard (superseded by the newer RSA-OAEP mode). Not only should use of this outdated mode cease to continue, it is known to be dangerous for encrypting anything other than a symmetric session key. Second, without other constant-time comparison functions (e.g. "greater or equal"), this author feels that providing solely ConstantTimeLessOrEq would provide a weird/incomplete API.

Warning

This code has not yet received sufficient peer review by other qualified cryptographers to be considered in any way, shape, or form, safe. Further, this library does not provide much in the way of assurance against deliberate misuse. Instead, it is a low-level library, mostly of bit-flipping tricks, intended for other cryptographers who would like to implement their own constant-time libraries. (For an example usage of this library, please see curve25519-dalek and ed25519-dalek.)

USE AT YOUR OWN RISK

Documentation

Extensive documentation is available here.

Installation

To install, add the following to the dependencies section of your project's Cargo.toml:

subtle = "^0.1"

Then, in your library or executable source, add:

extern crate subtle