Post-quantum cryptography

[DemiMarie]

This will require larger key+signature sizes, but that appears unavoidable.

[mikewest]

Indeed. We're starting with ed25519, but it does seem necessary to move beyond that in the future. The key sizes are a real problem, though, and it'll likely require a different distribution mechanism (perhaps one along the lines of the sketch in #43 (comment)).

Marking this as a future enhancement we'll want to look into.