CHACHA20-POLY1305 is decribed in RFC 7539

AEAD_CHACHA20_POLY1305 is an Authenticated Encryption with Associated Data algorithm. The inputs to AEAD_CHACHA20_POLY1305 are:

  • A 256-bit key
  • A 96-bit nonce -- different for each invocation with the same key
  • An arbitrary length plaintext
  • Arbitrary length additional authenticated data (AAD)

Some protocols may have unique per-invocation inputs that are not 96 bits in length. For example, IPsec may specify a 64-bit nonce. In such a case, it is up to the protocol document to define how to transform the protocol nonce into a 96-bit nonce, for example, by concatenating a constant value.

The ChaCha20 and Poly1305 Cryptographic Primitives are combined into an Authenticated Encryption with Associated Data

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