Package ad is an abstract message type that composes the common elements of all ads - nonce ID, public key (identity), expiry and signature.

Package ont defines interfaces for the engine: Ngin and Onion coding.Codec subtypes, and some helpers that use the abstraction.

Package reg is a registry for message types that implement the coding.Codec interface.

Codec is a unit of data that can be read and written from a binary form.