Explore changing the way secure channels are implemented in both key refresh protocols

[becgabri]

Key refresh in both the n/n and t/n settings require parties to send secret values to one another over a secure channel. In the original version of CGGMP this is done using Paillier encryption. In the updated version, this is done through establishing temporary pairwise DH keys and using them as a one time pad to transmit shares. This is more efficient, as the authors claim in their updated paper, and it makes the proof of security easier.

In the future, we should either look into incorporating the CGGMP change or adding an abstraction for a secure channel such that if two parties share a symmetric key they can simply use it to share these values instead.