ChaCha20-Poly1305 (RFC 8439)

1. ChaCha quarter round

   The ARX quarter round.

2. ChaCha20 block function

   20 rounds over a 512-bit state.

3. ChaCha20 encryption

   Counter mode keystream generation.

4. Poly1305 authenticator

   One-time MAC with 256-bit key.

5. AEAD construction

   Combining ChaCha20 and Poly1305 with associated data.

6. Security considerations

   Nonce uniqueness and key requirements.

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