Usage

Made to work on common Linux (debian, fedora). Will not work on MacOS or Windows.
Make sure keygen, encaps and decaps are executable (chmod +x keygen encaps decaps)

Demo

$ ./keygen.py 
> 557538c0131e1bfa5051f99faf4f39c06d631ff11801abe69b16e002001b3844
$ ./encaps.py 557538c0131e1bfa5051f99faf4f39c06d631ff11801abe69b16e002001b3844
> af4384c742e640143152f8592edaf155f37c4f3571ca7f782e630a90d3254c77c8459e4fc0c0afab7a83a2078dcb9f7bc0e183a6b90f0c9f3a95cce5a4bab7f90533294462fd97700fa7c20ed5f9f2aa1d1cff408e0ac1152fee29a04f88febb
> 61a307e9753eef0843209cf9637e29fe
$ ./decaps.py pk.key af4384c742e640143152f8592edaf155f37c4f3571ca7f782e630a90d3254c77c8459e4fc0c0afab7a83a2078dcb9f7bc0e183a6b90f0c9f3a95cce5a4bab7f90533294462fd97700fa7c20ed5f9f2aa1d1cff408e0ac1152fee29a04f88febb
> 61a307e9753eef0843209cf9637e29fe

Requirements

You may use a python virtual environment if you wish. Using bash it may look like so :

python -m venv .venv; source .venv/bin/activate; pip install -r requirements.txt
./keygen sk.key
...
deactivate

Debug

Set DEBUG=True in lib/deps/KEM.py for debug messages.

Useful Info

Private key format

32 bytes for private key, followed by LS_bytes bytes for the extra randomness, followed by 32 bytes of public key and 32 bytes of public key hash, little endian for everything.

Symmetric encryption protocol

ChaCha20 is used here. Evidently, the symmetric encryption algorithm can be swapped with other ones (AES, Camellia, Blowfish, ...). To use Camellia for example, look at the comment in lib/deps/KEM.py. It is less trivial to make an example where the encapsulation is messed with using Camellia (decryption of message can fail to an error), hence ChaCha20 is used here.
SHAKE128 is used for all hashes. The size of the output differs each time (32, 64 and 16 bytes)

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