Vote to Ballot

Prepare Election

The Election Authority:

• Decides the Registration Window (and the note filtering if used)
• States the Purpose (or Question) and Choices

The server:

• Generates a random seed phrase
• Derives an Orchard address per answer
• Builds the initial cmx & nf trees
• Monitors the Blockchain and update trees until the snapshot is reached. The setup is described in Server Setup

Optional:

• The Election Authority sets up a website for the election with information about the purpose, the candidates, etc.
• The URL of the voting server is published online. Alternatively, the URL is sent by email, etc.

Elector Registration

• Elector moves coins into Orchard or refreshes existing Orchard notes if necessary.

A wide window of registration reduces the need to move Orchard Notes but increases the reference data set that electors need to download and process.

Vote Preparation

• Voting app VA (or wallet with voting capabilities) downloads election definition from server
• VA downloads cmx and nf tree from either
  • server
  • lightwalletd, and process the raw block data to reconstruct the election data¹
  • get a bootstrap file from torrent or from ipfs
• VA caches the trees
• Once the snapshot height is reached, VA can compute the tree hashes and cache the result

Vote or Delegation

• User selects a candidate or candidates and a quantity of ZEC
• VA builds a voting transaction with 1 or many recipients
• VA adds a change output if needed
• VA computes ZKP for each action
• VA computes binding signature
• VA signs each input
• VA transmits transaction to Voting Server

Counting & Audit

Important Note about nf Tree

The nf tree is a non-inclusion tree. It is not an incremental merkle tree like the cmx and cannot be optimized because nullifier nodes are not only appended.

The client has to download and keep the complete set of nullifiers because the tree is sorted and new nullifiers can end up anywhere.

Every action has a nullifier and a note commitment. Some of them are dummies but there is no way to tell which ones.

Both nullifier nf and note commitment cmx take 32 bytes each. An action takes 64 bytes to download. The cmx does not need to be kept, but the nf does. Therefore it takes about 32 bytes of storage. It takes about N hash calculations to compute the Merkle Path when N is the number of leaves. We can compute the paths for multiple notes simultaneously. But when new leaves are added, the intermediate hashes must be recalculated². The nf tree has 2N leaves and the cmx tree has N leaves.