SpeckEx is an Elixir version of block cipher Speck, developed by the NSA (
) in 2013 as a “lightweight” cipher. SpeckEx uses Rust crate “speck_cipher” as its base and is meant to be only a very thin wrapper around it. The main module only exposes CTR and AEAD modes (Speck-Poly1305) with 128-bits block sizes and provides guardrails with regards to nonce generation in particular. Submodules expose the raw block cipher, and CTR and AEAD modes with smaller (risky) block sizes. Extensive documentation including security guidelines is added.
The rationale behind the package is that I have a particular need for a modern cipher that operates on blocks of size 64 and 96, which are very thin on the ground indeed. OTP only offers DES, 3DES and Blowfish, which each have their issues (broken, slow, very slow with crypto_one_time), and nothing for 96-bits blocks. Speck seems like a good solution and supplements the OTP offerings. I figured that I might as well make it into a usable package.
Experimental state
The entire package should be considered experimental, and has not been reviewed or audited. I would welcome expert help, particularly with reviewing the Rust code where all of the magic happens, because I am by no means fluent in Rust (in fact Gemini wrote most of that 
). I did not implement any of the algorithms involved (neither Speck nor Poly1305), nor the CTR mode, but the combination of Speck and Poly1305 in the AEAD construction is implemented in SpeckEx itself, so that bit in particular qualifies as the prohibited “rolling your own” at this point. Hence the big warnings at the top of the documentation entrypoints. Since the Rust code is very small, hopefully this state of affairs can be improved with some help.
Package: speck_ex | Hex
Docs: SpeckEx — SpeckEx v0.0.1-beta5
