Decrypt the given message using this [EstablishedEcies] session.
Encrypt the given plaintext using this [EstablishedEcies] session.
Get our [Curve25519PublicKey].
This public key needs to be sent to the other side so that it can complete the ECIES channel establishment.
Get the [
CheckCode] which uniquely identifies this [EstablishedEcies] session.This check code can be used to verify and confirm that both sides of the session are indeed using the same shared secret.