Collect F+1 instead of (N+F)/2+1 signatures in multisigcollector

pkg/availability/multisigcollector/internal/common/common.go

@@ -37,16 +37,7 @@ func DefaultModuleConfig() *ModuleConfig {
 type ModuleParams struct {
 	InstanceUID []byte     // unique identifier for this instance of BCB, used to prevent cross-instance replay attacks
 	AllNodes    []t.NodeID // the list of participating nodes
-}
-
-// N is the total number of replicas.
-func (params *ModuleParams) N() int {
-	return len(params.AllNodes)
-}
-
-// F is the maximum number of replicas that can be tolerated.
-func (params *ModuleParams) F() int {
-	return (params.N() - 1) / 3
+	F           int        // the maximum number of failures tolerated. Must be less than (len(AllNodes)-1) / 2
 }
 
 // State represents the common state used by all parts of the multisig collector implementation.

pkg/availability/multisigcollector/internal/parts/certcreation/certcreation.go

@@ -113,12 +113,12 @@ func IncludeCreatingCertificates(
 		return nil
 	})
 
-	// When a quorum (more than (N+F)/2) of signatures are collected, create and output a certificate.
+	// When F+1 signatures are collected, create and output a certificate.
 	dsl.UponCondition(m, func() error {
 		// Iterate over active outgoing requests.
 		//Most of the time, there is expected to be at most one active outgoing request.
 		for reqID, requestState := range state.RequestState {
-			if len(requestState.sigs) > (params.N()+params.F())/2 {
+			if len(requestState.sigs) > params.F+1 {
 				certNodes, certSigs := maputil.GetKeysAndValues(requestState.sigs)
 
 				requestingModule := t.ModuleID(requestState.ReqOrigin.Module)

pkg/availability/multisigcollector/internal/parts/certverification/certverification.go

@@ -67,7 +67,7 @@ func verifyCertificateStructure(params *common.ModuleParams, cert *apb.Cert) (*m
 	mscCert := mscCertWrapper.Msc
 
 	// Check that the certificate contains a sufficient number of signatures.
-	if len(mscCert.Signers) <= (params.N()+params.F())/2 {
+	if len(mscCert.Signers) <= params.F+1 {
 		return nil, fmt.Errorf("insuficient number of signatures")
 	}
 

pkg/availability/multisigcollector/multisigcollector.go

@@ -1,6 +1,8 @@
 package multisigcollector
 
 import (
+	"fmt"
+
 	"github.com/filecoin-project/mir/pkg/availability/multisigcollector/internal/common"
 	"github.com/filecoin-project/mir/pkg/availability/multisigcollector/internal/parts/batchreconstruction"
 	"github.com/filecoin-project/mir/pkg/availability/multisigcollector/internal/parts/certcreation"
@@ -18,9 +20,13 @@ type ModuleParams = common.ModuleParams
 // NewModule creates a new instance of the multisig collector module.
 // Multisig collector is the simplest implementation of the availability layer.
 // Whenever an availability certificate is requested, it pulls a batch from the mempool module,
-// sends it to all replicas and collects a quorum (i.e., more than (N+F)/2) of signatures confirming that
+// sends it to all replicas and collects params.F+1 signatures confirming that
 // other nodes have persistently stored the batch.
-func NewModule(mc *ModuleConfig, params *ModuleParams, nodeID t.NodeID) modules.PassiveModule {
+func NewModule(mc *ModuleConfig, params *ModuleParams, nodeID t.NodeID) (modules.PassiveModule, error) {
+	if 2*params.F+1 < len(params.AllNodes) {
+		return nil, fmt.Errorf("cannot tolerate %v / %v failures", params.F, len(params.AllNodes))
+	}
+
 	m := dsl.NewModule(mc.Self)
 
 	commonState := &common.State{
@@ -32,5 +38,5 @@ func NewModule(mc *ModuleConfig, params *ModuleParams, nodeID t.NodeID) modules.
 	certverification.IncludeVerificationOfCertificates(m, mc, params, nodeID, commonState)
 	batchreconstruction.IncludeBatchReconstruction(m, mc, params, nodeID, commonState)
 
-	return m
+	return m, nil
 }