lioness_blockcipher/README.md

Lioness large-block cipher with ChaCha20, Blake2b, and Turboshake.

Warning

This code has not been formally audited, Use at your own risk or ask a cryptographers before use.

Overview

Lioness is a large block cipher built from

• Stream cipher,
• Hash function,
• Key derivation function (KDF), although this can be remove if the input key is large enough to cover the four sub-keys used.

In here we use:

• Chacha20 from rustcrypto streamciphers
• Blake2b from rustcrypto hashes
• turboshake KDF from rustcrypto SHA3

The security of lioness reduce to the security of the underlying stream cipher or the hash function.
See the paper for more information.

How to use

Here is an example of how to use the Lioness_blockcipher create. Use a 32-byte master key and encrypt or decrypt a block in place:

use lioness_blockcipher::{Lioness, MasterKey};

fn main() -> anyhow::Result<()> {
    let mut key: MasterKey = [0x42; 32];

    let cipher = Lioness::new(&key);

    // Blocks must be at >32 bytes long
    let mut block = b"this is a long plaintext block and must stay a secret".to_vec();
    let original = block.clone();

    cipher.encrypt_in_place(&mut block)?;

    cipher.decrypt_in_place(&mut block)?;
    
    assert_eq!(block, original);

    Ok(())
}

Some notes:

• Encryption and decryption are both in-place for now.
• The block length need to be bigger than 32 bytes because Lioness splits the block into two where the left part is 32-byte, and the right part can't be empty. might support small blocks in the future, but for Sphinx use-case, this should work.
• If you need authenticity, make sure to prepend the plaintext with k zeros and check the zeros after decryption. This will be supported in the future... see integrity example

TODO

• Add more tests, examples, and benchmarks ...
• Make it generic for any compatible cipher, keyed_hash, and KDF.
• Compare with another implementation ... maybe with Haskel when available.
• Add a version with API which prepend the plaintext with k-zeros and checks authenticity after decryption.
• impl enc and dec to the API to work beside encrypt_in_place and decrypt_in_place.
• ...