Onion Salt
The onion salt source code is an encryption protocol that generates nested "onions" which can be used in an onion-like routing protocol. For more information, see the paper in the paper subdirectory.
The onion salt paper, in contrast, is copyrighted.
Building
To build onion salt, type make. This should build both the code and the paper. It also will incidentally build TweetNaCl. It does not, however, build a library. I recommend just including these C files into your project if you want to use onion salt.
However, I also recommend that you don't use onion salt unless you really understand what you are doing, and are qualified to review the code yourself.
Alternatively, if you have fac, then you can build by simply typing fac.
Running tests
You can run the test suite by running
python3 tests/harness.py
