ChaCha20-Blake3

Standard IETF ChaCha20-Poly1305 style construct with a cryptographically strong BLAKE3 hash instead, preventing key holders from crafting different messages that correspond to same tag or ciphertext.

The implementation follows standard practices, not the vastly modified KERKOUR ChaCha20-BLAKE3 implementation. Therefore we keep 12 byte nonce and 16 byte default tag length, so this remains a full drop-in replacement for ChaCha20-Poly1305, whereas they use 32 bytes for each, staged key/nonce derivation and a completely different authentication format.

Draft version 0.1.0: Implementation is still likely to change. Do not use in production.

Features

• Boxes: encrypt/decrypt and encrypt_into/decrypt_into — one-shot AEAD with appended random nonce, associated data, and MAC.
• Detached nonces: the standard AEAD construct using a provided nonce and does not attach it to the ciphertext; as opposed to random nonce attached in boxes
• Detached tags: tag — compute the BLAKE3 authentication tag separately, for use with external signature schemes over the tag.
• Channels: Sender/Receiver — ordered message encryption/decryption over a shared key using an incrementing counter nonce.
• CSPRNG: random(n) / random(buf) — fast ChaCha20-based random bytes, thread-safe, seeded from OS randomness.

Wire format: ciphertext mac [nonce]. The MAC is a keyed BLAKE3 over the associated data and ciphertext; the key stream is IETF ChaCha20.

Usage

import chab3

key = chab3.random(32)

ct = chab3.encrypt(b"hello", key, ad=b"metadata")
msg = chab3.decrypt(ct, key, ad=b"metadata")

s, r = chab3.Sender(key), chab3.Receiver(key)
assert r.decrypt(s.encrypt(b"in order")) == b"in order"

Using existing output buffer, in-place operation:

buf = bytearray(100)
out = chab3.encrypt_into(buf, b"attack at dawn", key)  # out is a sliced memoryview into buf
msg = chab3.decrypt_into(buf, out, key)  # memoryview into buf now showing b"hello"

Tampered ciphertext raises chab3.WireError; caller misuse (wrong buffer or key sizes) raises TypeError.