OTFcreds: Activity 2.4 Write protocol specification

[jbonisteel]

We will write up a specification for the protocol and share it with domain experts to collect their feedback.

This activity will be led by the cryptographer and will be the primary output that they will produce. The specification needs to be detailed and complete enough to allow the OONI team to move into the implementation phase, which is why there is also a substantial amount of effort required from the CTO and research engineer.

Output: protocol specification document.