fix: fixing witness construction of slashing tx (#193)

CHANGELOG.md

@@ -44,6 +44,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ### Bug fixes
 
+* [#193](https://github.com/babylonlabs-io/babylon/pull/193) Fix witness construction of slashing tx
 * [#154](https://github.com/babylonlabs-io/babylon/pull/154) Fix "edit-finality-provider" cmd argument index
 * [#186](https://github.com/babylonlabs-io/babylon/pull/186) Do not panic on `nil`
 Proof when handling finality votes

x/btcstaking/types/btc_delegation.go

@@ -382,6 +382,7 @@ func (d *BTCDelegation) BuildSlashingTxWithWitness(bsParams *Params, btcNet *cha
 		d.StakingOutputIdx,
 		d.DelegatorSig,
 		covAdaptorSigs,
+		bsParams.CovenantQuorum,
 		slashingSpendInfo,
 	)
 	if err != nil {
@@ -433,6 +434,7 @@ func (d *BTCDelegation) BuildUnbondingSlashingTxWithWitness(bsParams *Params, bt
 		0,
 		d.BtcUndelegation.DelegatorSlashingSig,
 		covAdaptorSigs,
+		bsParams.CovenantQuorum,
 		slashingSpendInfo,
 	)
 	if err != nil {

x/btcstaking/types/btc_delegation_test.go

@@ -109,8 +109,7 @@ func FuzzBTCDelegation_SlashingTx(f *testing.F) {
 		slashingChangeLockTime := unbondingTime
 
 		// only the quorum of signers provided the signatures
-		covenantSigners := covenantSKs[:covenantQuorum]
-
+		covenantSigners := covenantSKs
 		// construct the BTC delegation with everything
 		btcDel, err := datagen.GenRandomBTCDelegation(
 			r,

x/btcstaking/types/btc_slashing_tx.go

@@ -274,6 +274,7 @@ func (tx *BTCSlashingTx) BuildSlashingTxWithWitness(
 	outputIdx uint32,
 	delegatorSig *bbn.BIP340Signature,
 	covenantSigs []*asig.AdaptorSignature,
+	covenantQuorum uint32,
 	slashingPathSpendInfo *btcstaking.SpendInfo,
 ) (*wire.MsgTx, error) {
 	/*
@@ -288,12 +289,21 @@ func (tx *BTCSlashingTx) BuildSlashingTxWithWitness(
 	}
 	// decrypt each covenant adaptor signature to Schnorr signature
 	covSigs := make([]*schnorr.Signature, len(covenantSigs))
+	numSigs := uint32(0)
 	for i, covenantSig := range covenantSigs {
 		if covenantSig != nil {
 			covSigs[i] = covenantSig.Decrypt(decKey)
+			numSigs++
 		} else {
 			covSigs[i] = nil
 		}
+		if numSigs == covenantQuorum {
+			break
+		}
+	}
+	// ensure the number of covenant signatures is at least the quorum number
+	if numSigs < covenantQuorum {
+		return nil, fmt.Errorf("not enough covenant signatures to reach quorum")
 	}
 
 	/*

x/btcstaking/types/btc_slashing_tx_test.go

@@ -194,7 +194,10 @@ func FuzzSlashingTxWithWitness(f *testing.F) {
 		delSig, err := slashingTx.Sign(stakingMsgTx, 0, slashingPkScriptPath, delSK)
 		require.NoError(t, err)
 
-		covenantSigners := covenantSKs[:covenantQuorum]
+		// ensure that event if all covenant members provide covenant signatures,
+		// BuildSlashingTxWithWitness will only take a quorum number of signatures
+		// to construct the witness
+		covenantSigners := covenantSKs
 		// get covenant Schnorr signatures
 		covenantSigs, err := datagen.GenCovenantAdaptorSigs(
 			covenantSigners,
@@ -235,7 +238,7 @@ func FuzzSlashingTxWithWitness(f *testing.F) {
 		}
 
 		// create slashing tx with witness
-		slashingMsgTxWithWitness, err := slashingTx.BuildSlashingTxWithWitness(fpSK, fpBTCPKs, stakingMsgTx, 0, delSig, covSigsForFP, slashingSpendInfo)
+		slashingMsgTxWithWitness, err := slashingTx.BuildSlashingTxWithWitness(fpSK, fpBTCPKs, stakingMsgTx, 0, delSig, covSigsForFP, covenantQuorum, slashingSpendInfo)
 		require.NoError(t, err)
 
 		// verify slashing tx with witness

x/btcstaking/types/btc_undelegation_test.go

@@ -47,7 +47,7 @@ func FuzzBTCUndelegation_SlashingTx(f *testing.F) {
 			CovenantPks:    bbn.NewBIP340PKsFromBTCPKs(covenantPKs),
 			CovenantQuorum: covenantQuorum,
 		}
-		covenantSigners := covenantSKs[:covenantQuorum]
+		covenantSigners := covenantSKs
 
 		stakingTimeBlocks := uint16(5)
 		stakingValue := int64(2 * 10e8)