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Add logic to amortize excess key shares, correcting is_bft

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This commit is contained in:
Luke Parker 2023-10-13 01:04:41 -04:00
parent 013a0cddfc
commit bb25baf3bc
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2 changed files with 33 additions and 3 deletions
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10
substrate/validator-sets/pallet/src/lib.rs
View file

@ -187,9 +187,12 @@ pub mod pallet {
fn is_bft(network: NetworkId) -> bool {
let allocation_per_key_share = AllocationPerKeyShare::<T>::get(network).unwrap().0;
let mut validators_len = 0;
let mut top = None;
let mut key_shares = 0;
for (_, amount) in SortedAllocationsIter::<T>::new(network) {
validators_len += 1;
key_shares += amount.0 / allocation_per_key_share;
if top.is_none() {
top = Some(key_shares);
@ -204,9 +207,10 @@ pub mod pallet {
// key_shares may be over MAX_KEY_SHARES_PER_SET, which will cause an off-chain reduction of
// each validator's key shares until their sum is MAX_KEY_SHARES_PER_SET
// That isn't modeled here, allowing an inaccuracy in an extreme edge case
// This may cause mis-reporting as BFT when not BFT (TODO: Investigate impact of this)
(top * 3) < key_shares
// post_amortization_key_shares_for_top_validator yields what the top validator's key shares
// would be after such a reduction, letting us evaluate this correctly
let top = post_amortization_key_shares_for_top_validator(validators_len, top, key_shares);
(top * 3) < key_shares.min(MAX_KEY_SHARES_PER_SET.into())
}
}

26
substrate/validator-sets/primitives/src/lib.rs
View file

@ -92,3 +92,29 @@ pub fn musig_key(set: ValidatorSet, set_keys: &[Public]) -> Public {
pub fn set_keys_message(set: &ValidatorSet, key_pair: &KeyPair) -> Vec<u8> {
[b"ValidatorSets-key_pair".as_ref(), &(set, key_pair).encode()].concat()
}
/// For a set of validators whose key shares may exceed the maximum, reduce until they equal the
/// maximum.
///
/// Reduction occurs by reducing each validator in a reverse round-robin.
pub fn amortize_excess_key_shares(validators: &mut [(Public, u64)]) {
let total_key_shares = validators.iter().map(|(_, shares)| shares).sum::<u64>();
for i in
0 .. usize::try_from(total_key_shares.saturating_sub(MAX_KEY_SHARES_PER_SET.into())).unwrap()
{
validators[validators.len() - ((i % validators.len()) + 1)].1 -= 1;
}
}
/// Returns the post-amortization key shares for the top validator.
///
/// Panics when `validators == 0`.
pub fn post_amortization_key_shares_for_top_validator(
validators: usize,
top: u64,
key_shares: u64,
) -> u64 {
top -
(key_shares.saturating_sub(MAX_KEY_SHARES_PER_SET.into()) /
u64::try_from(validators).unwrap())
}