Commands and Messages

Command

A command represents an action that a user may take, such as casting a vote in a poll or changing their public key if bribed. It is made up of the following parameters:

Symbol	Name	Size	Description
$cm_i$	State index	50	State leaf index where the signing key is located
$cm_{p_{x}}$	Public key x-coordinate	253	If no change is necessary this parameter should reflect the current public key's x-coordinate
$cm_{p_{y}}$	Public key y-coordinate	253	If no change is necessary this parameter should reflect the current public key's y-coordinate
$cm_{i_{v}}$	Vote option index	50	Option state leaf index of preference to assign the vote for
$cm_w$	Voting weight	50	Voice credit balance allocation, this is an arbitrary value dependent on a user's available credits
$cm_n$	Nonce	50	State leaf's index of actions committed plus one
$cm_{id}$	Poll id	50	The poll's identifier to cast in regard to
$cm_s$	Salt	253	An entropy value to inhibit brute force attacks

Message

A message is an encrypted command using the shared key $k_s$ between the voter and the coordinator. The plaintext $t$ is computed as such:

$t = [p, cm_{p_{x}}, cm_{p_{y}}, cm_s, R8[0], R8[1], S]$

While the message can be computed with the formula below:

$M$ = ${poseidonEncrypt}(k_s[0], k_s[1], cm_n, 7, t)$

Decrypting a message

To decrypt a message using $k_s$ we have the following:

$[p, R8[0], R8[1], cm_s]$ = ${poseidonDecrypt}(M, k_s[0], k_s[1], cm_n, 7)$

To unpack $p$ to its original five parameters, it must be separated into 50 bit values from the parent 250 bit value. To extract 50 bits at byte $n$, we:

1. initialise 50 bits
2. shift left by $n$ bits
3. bitwise AND with $p$
4. shift right by $n$ bits