WIP: Mixnet: Update spec for NomMix

[youngjoon-lee]

Reference: NomMix: Peer-to-Peer Mix Network over Gossip Channel

Now, the spec is much simpler.

• Deleted many files not necessary anymore
• Added the "Global Transmission Rate" (aka. GTR)
• Added the per-conn 0-hop noise
• No mixnode topology anymore.
  • Now we selects k nodes randomly from the membership table.
  • How the membership table will be disseminated is not determined yet. Maybe it will be gossiped through the network. Here, we assume that it is already disseminated completely to each node.
• No direct connection between mix nodes anymore.
  • All messages are gossiped. Only one node in the network can unwrap the Sphinx packet if he has a correct private key.

This spec will be used for the NomMix simulation. I'm already working on it.

TODO (Written as TODO commented in the source code):

• Temporal mixing
• Limiting the max length of mix route to make the size of Sphinx packet constant.

[youngjoon-lee]

I just opened a new PR #109 that moves the previous mixnet spec into a new deprecated/ directory to make the repo clean. Once the PR is merged, I will rebase this PR to the new master, so that this PR can add new spec files to the new mixnet/ directory. Until then, I am marking this PR as a draft.

[youngjoon-lee]

Closing this, as we discussed in Discord. The executable spec needs to be written with the technical spec, after the design is verified by simulations and PoC. Although I put only clear parts of the spec in this PR, which is not likely to change during further experiments, we are not sure right now. So, let's close this PR for now, and recreate a new PR once we are ready to write the technical spec.