Protocol: Private Message Delivery

[iAmMichaelConnor]

This is a tricky section, because it might end up being surprisingly small. I'm not sure how much of this is "in protocol" (which does belong in this spec), versus abstracted to be "whatever the app developer / user / wallet developer wants". We'll certainly be enshrining keys and the encryption scheme, but that info probably belongs in the separate 'Keys' section, which is already written.

There is still a big open question that need to be decided upon. We touched on it recently in London:

• Should constraining of encryption and tag computation be done in each app, or in each user's account contract?

To consider:

• Private Message Delivery
  • Is there anything that the protocol specifically needs to contain, to support delivery of note ciphertexts?
    • E.g. rigid encoding of ciphertexts, or special public inputs of circuits, or logs of arbitrary length?
    • Or is it all abstracted to be "whatever the app wants / whatever the wallet wants / whatever the user wants"?
  • Standardisation:
    • We should discuss the (hopeful) decision: "Constrain in apps or in account contracts?"
    • Standardisation of encodings for arbitrary tags, ciphertext headers, and ciphertexts
  • Encryption & decryption
    • (This is actually all already be covered in the 'keys' section... perhaps it should stay there, and this subsection can just link to the keys section?)