AAD Explanation

[SalusaSecondus]

Do a deep dive into AAD explaining:

1. It is not secret
2. In general data can be decrypted without it (or with incorrect values). Thus it requires a trusted decryptor
3. Comes in two main types
4. Context (non-secret data that must have integrity, such as associated user IDs, etc.)
5. Parsing information (Describes the internal format for the encrypted data and thus how to parse and handle it. (Worth referencing Comparse for this one.)