Status

This experiment is currently abandoned. If you want to use NaCl from Common Lisp, there are bindings for libsodium at https://github.com/Harleqin/foreign-sodium.

I might return to native implementation later, but that may or may not be based on the code in this repository.

Overview

This is a more-or-less direct translation of TweetNaCl, a version of the nacl.cr.yp.to library that was published in 100 tweets on Twitter in July 2013 by the NaCl main author, Daniel J. Bernstein. I watched his talk “The year in crypto” at the 30th Chaos Communication Congress in Hamburg, together with some fellow Lispers, and we half-jokingly agreed that this needed to be translated to a more useful language. ;-)

Note that this is not just a wrapper, but a complete reimplementation. I know that a wrapper is likely to be more useful, but I am doing this rather as a comparative linguistics experiment.

TweetNaCl is written in C, and condensed in almost code golf style to make it fit the 100 tweets. The C original is included in comments in the naclcl.lisp file (formatted to my own, not so fashionable tastes).

The translation is to Common Lisp. Current status: first pass, trying to get the bit fiddling translated one-to-one. This was mostly an exercise in Common Lisp’s bit manipulation features. The code compiles, but is otherwise untested. Current goal: Correct remaining mistakes, and a deeper understanding should lead to clearer Common Lisp code.

Some first impressions

• Common Lisp is just as useful for bit fiddling as C, with its elaborate set of bit manipulation functions.
• C-style “return parameters”, prevalent in the original, can be replaced by multiple-value semantics (although I currently have not yet refactored in this direction).
• C-style return of status codes can be replaced by conditions or additional return values. The original uses them frequently, and it is often not clear what meaning -1 or 0 are supposed to convey.
• The original often has pointers as parameters, which makes it unclear how big the underlying arrays/streams are supposed to be. Replacing these by Lisp vectors is useful to make these assumptions more explicit, and it also adds bounds checking. I am quite sure that I have made mistakes when extracting the intent from the C code.

Roadmap

• Add unit tests, understand each function for itself, add documentation to each, improve translation
• Add integration tests, understand the exported functions, separate into more files, add general documentation
• Understand the features outlined at http://nacl.cr.yp.to/features.html and try to support them as well
• Refactor! Fun! I especially want to get better parameter and return value handling and convert the stream operations to real stream handling.
• Optimize! More fun! Avoid consing, but keep an eye on constant running time to prevent side channel attacks (this should also be automatically tested).
• Compare the final result with both TweetNaCl and NaCl from nacl.cr.yp.to, by speed, clarity of code, and clarity of the API that a library user gets to see. Also include the C++ and Python wrapper APIs in this survey.
• Perhaps I will decide along the way to start afresh, this time based on the exported functions of the NaCl library from nacl.cr.yp.to and building from there.
• Brag a lot