This is the sort of information we expect to receive from the receiver.
This might not be necessary if we agree on a format.
An object for decapsulating responses.
The only way to obtain one of these is through ClientRequest::encapsulate().
The key configuration of a server. This can be used by both client and server.
An important invariant of this structure is that it does not include
any combination of KEM, KDF, and AEAD that is not supported.
A server can handle multiple requests.
It holds a single key pair and can generate a configuration.
(A more complex server would have multiple key pairs. This is simple.)
An object for encapsulating responses.
The only way to obtain one of these is through Server::decapsulate().
A tuple of KDF and AEAD identifiers.