This is a working implementation of RFC 8439: ChaCha20 and Poly1305 for IETF Protocols, written in Common Lisp. It passes the primary test vectors given in the RFC document.
The main functions mimick the RFC's pseudocode:
;; (aad: u8[], key: u8[32], iv: u8[8], constant: u8[4], plaintext: u8[]) => u8[], u8[16]
(chacha20-aead-encrypt aad key iv constant plaintext)
and
;; (aad: u8[], key: u8[32], iv: u8[8], constant: u8[4], ciphertext: u8[]) => u8[], u8[16]
(chacha20-aead-decrypt aad key iv constant ciphertext)
iv and constant get concatenated, forming a 96-bit nonce. The typical way
to use this cipher is to set said nonce to 1 and increase by 1 after each
message encrypted. A counter value MUST NOT ever be reused with the same key.
This was a fun little educational project, and hasn't been audited. Please don't use it for real software that affects people's lives. It also hasn't been optimized for speed.
AGPL-3.0