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[ZKS-08][HackerOne-2289066] Make leader election tamper resistant #2378

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merged 2 commits into from Mar 8, 2024
Merged

[ZKS-08][HackerOne-2289066] Make leader election tamper resistant #2378

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911c3c3
Remove manipulatable elements from leader election
raychu86 Mar 3, 2024
2fdb843
Update sorted_members test
raychu86 Mar 3, 2024
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43 changes: 7 additions & 36 deletions ledger/committee/src/lib.rs
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Expand Up @@ -181,7 +181,7 @@ impl<N: Network> Committee<N> {
// Retrieve the total stake of the committee.
let total_stake = self.total_stake();
// Construct the round seed.
let seed = [self.starting_round, current_round, total_stake].map(Field::from_u64);
let seed = [current_round].map(Field::from_u64);
// Hash the round seed.
let hash = Literal::Field(N::hash_to_group_psd4(&seed)?.to_x_coordinate());
// Compute the stake index from the hash output.
Expand Down Expand Up @@ -211,17 +211,13 @@ impl<N: Network> Committee<N> {
Ok(leader.unwrap())
}

/// Returns the committee members sorted by stake in decreasing order.
/// For members with matching stakes, we further sort by their address' x-coordinate in decreasing order.
/// Returns the committee members sorted by their address' x-coordinate in decreasing order.
/// Note: This ensures the method returns a deterministic result that is SNARK-friendly.
fn sorted_members(&self) -> indexmap::map::IntoIter<Address<N>, (u64, bool)> {
let members = self.members.clone();
// Note: The use of 'sorted_unstable_by' is safe here because the addresses are guaranteed to be unique.
members.sorted_unstable_by(|address1, (stake1, _), address2, (stake2, _)| {
// Sort by stake in decreasing order.
let cmp = stake2.cmp(stake1);
// If the stakes are equal, sort by x-coordinate in decreasing order.
if cmp == Ordering::Equal { address2.to_x_coordinate().cmp(&address1.to_x_coordinate()) } else { cmp }
members.sorted_unstable_by(|address1, (_, _), address2, (_, _)| {
address2.to_x_coordinate().cmp(&address1.to_x_coordinate())
})
}
}
Expand Down Expand Up @@ -433,34 +429,9 @@ mod tests {
println!("sorted_members: {}ms", timer.elapsed().as_millis());
// Check that the members are sorted based on our sorting criteria.
for i in 0..sorted_members.len() - 1 {
let (address1, (stake1, _)) = sorted_members[i];
let (address2, (stake2, _)) = sorted_members[i + 1];
assert!(stake1 >= stake2);
if stake1 == stake2 {
assert!(address1.to_x_coordinate() > address2.to_x_coordinate());
}
}
}

#[test]
fn test_sorted_members_with_equal_stake() {
// Initialize the RNG.
let rng = &mut TestRng::default();
// Sample a committee.
let committee = crate::test_helpers::sample_committee_equal_stake_committee(200, rng);
// Start a timer.
let timer = std::time::Instant::now();
// Sort the members.
let sorted_members = committee.sorted_members().collect::<Vec<_>>();
println!("sorted_members: {}ms", timer.elapsed().as_millis());
// Check that the members are sorted based on our sorting criteria.
for i in 0..sorted_members.len() - 1 {
let (address1, (stake1, _)) = sorted_members[i];
let (address2, (stake2, _)) = sorted_members[i + 1];
assert!(stake1 >= stake2);
if stake1 == stake2 {
assert!(address1.to_x_coordinate() > address2.to_x_coordinate());
}
let (address1, (_, _)) = sorted_members[i];
let (address2, (_, _)) = sorted_members[i + 1];
assert!(address1.to_x_coordinate() > address2.to_x_coordinate());
}
}

Expand Down