tari-project / tari / 38896269154

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Build Type

push

github

Committed by web-flow

Commit Message

fix(sidechain): weigh quorum certificates by signer voting power (#8128)

Description
---
Quorum certificates in sidechain commit proofs are now weighed by voting
power instead of signature count.

- `CheckVnFunc` returns the signer's voting power (`u64`, 0 = not a
member) instead of `bool`.
- `validate_qc` sums the power of the distinct signers and rejects the
QC if that is below `quorum_threshold`. The threshold is now `u64`
voting power (was `usize` signer count). Batch verification is
all-or-nothing, so the sum is the power of the signers whose signatures
verify. The check runs before batch verification, so a QC short of
quorum is rejected without that cost.
- The duplicate-signer check, the `MAX_QC_SIGNATURES` cap and batch
verification are unchanged. A signer with power 0 is still rejected as
not in the active validator set.

Motivation and Context
---
A count threshold can't tell members apart by weight. In a weighted
committee, a QC signed by a supermajority of members can hold well under
a supermajority of the power, and the old check would still accept it.

This changes only the API, with no L1 fork. A caller that returns 1 for
each registered validator gets the old accept/reject behaviour. Nothing
in this repo outside `tari_sidechain` calls `validate_committed`, so the
existing tests are the only callers updated here (`Ok(true)` → `Ok(1)`,
`Ok(false)` → `Ok(0)`). Downstream users of `tari_sidechain` need the
same change.

How Has This Been Tested?
---
New `weighted_committee` tests in
`base_layer/sidechain/tests/commit_proof.rs`. The committee has 7
validators: 4 with power 1 and 3 with power 10, 34 in total, and the
threshold is 23.
- 5 of 7 signers holding 14 power: rejected.
- 3 of 7 signers holding 30 power: accepted.

Without this change, the old API can only express membership plus a
signer-count threshold (5 of 7). On `development`, using `|pk|
Ok(power_of(pk) > 0)` with threshold 5, the 14-power QC is **accepted**
(`unwrap_err()` on... (continued)

Coverage Stats

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1018 existing lines in 30 files now uncovered.

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