smartcontract: add CreateDefaultMultiSigRedeemScript

And use it where appropriate. Some of our code was just plain wrong (like the
one in GAS contract) and unification is always useful here.

pkg/core/helper_test.go

@@ -51,11 +51,7 @@ func (bc *Blockchain) newBlock(txs ...*transaction.Transaction) *block.Block {
 
 func newBlock(cfg config.ProtocolConfiguration, index uint32, prev util.Uint256, txs ...*transaction.Transaction) *block.Block {
 	validators, _ := validatorsFromConfig(cfg)
-	vlen := len(validators)
-	valScript, _ := smartcontract.CreateMultiSigRedeemScript(
-		vlen-(vlen-1)/3,
-		validators,
-	)
+	valScript, _ := smartcontract.CreateDefaultMultiSigRedeemScript(validators)
 	witness := transaction.Witness{
 		VerificationScript: valScript,
 	}
@@ -393,7 +389,7 @@ func addSigners(txs ...*transaction.Transaction) {
 
 func signTx(bc *Blockchain, txs ...*transaction.Transaction) error {
 	validators := bc.GetStandByValidators()
-	rawScript, err := smartcontract.CreateMultiSigRedeemScript(bc.config.ValidatorsCount/2+1, validators)
+	rawScript, err := smartcontract.CreateDefaultMultiSigRedeemScript(validators)
 	if err != nil {
 		return fmt.Errorf("failed to sign tx: %w", err)
 	}

pkg/core/native/native_gas.go

@@ -103,8 +103,7 @@ func (g *GAS) OnPersist(ic *interop.Context) error {
 }
 
 func getStandbyValidatorsHash(ic *interop.Context) (util.Uint160, error) {
-	vs := ic.Chain.GetStandByValidators()
-	s, err := smartcontract.CreateMultiSigRedeemScript(len(vs)/2+1, vs)
+	s, err := smartcontract.CreateDefaultMultiSigRedeemScript(ic.Chain.GetStandByValidators())
 	if err != nil {
 		return util.Uint160{}, err
 	}

pkg/core/util.go

@@ -118,11 +118,7 @@ func committeeFromConfig(cfg config.ProtocolConfiguration) ([]*keys.PublicKey, e
 }
 
 func getNextConsensusAddress(validators []*keys.PublicKey) (val util.Uint160, err error) {
-	vlen := len(validators)
-	raw, err := smartcontract.CreateMultiSigRedeemScript(
-		vlen-(vlen-1)/3,
-		validators,
-	)
+	raw, err := smartcontract.CreateDefaultMultiSigRedeemScript(validators)
 	if err != nil {
 		return val, err
 	}

pkg/internal/testchain/address.go

@@ -64,7 +64,7 @@ func MultisigVerificationScript() []byte {
 		pubs = append(pubs, priv.PublicKey())
 	}
 
-	script, err := smartcontract.CreateMultiSigRedeemScript(3, pubs)
+	script, err := smartcontract.CreateDefaultMultiSigRedeemScript(pubs)
 	if err != nil {
 		panic(err)
 	}

pkg/smartcontract/contract.go

@@ -10,7 +10,8 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/vm/opcode"
 )
 
-// CreateMultiSigRedeemScript creates a script runnable by the VM.
+// CreateMultiSigRedeemScript creates an "m out of n" type verification script
+// where n is the length of publicKeys.
 func CreateMultiSigRedeemScript(m int, publicKeys keys.PublicKeys) ([]byte, error) {
 	if m < 1 {
 		return nil, fmt.Errorf("param m cannot be smaller or equal to 1 got %d", m)
@@ -34,3 +35,11 @@ func CreateMultiSigRedeemScript(m int, publicKeys keys.PublicKeys) ([]byte, erro
 
 	return buf.Bytes(), nil
 }
+
+// CreateDefaultMultiSigRedeemScript creates an "m out of n" type verification script
+// using publicKeys length with the default BFT assumptions of (n - (n-1)/3) for m.
+func CreateDefaultMultiSigRedeemScript(publicKeys keys.PublicKeys) ([]byte, error) {
+	n := len(publicKeys)
+	m := n - (n-1)/3
+	return CreateMultiSigRedeemScript(m, publicKeys)
+}

pkg/smartcontract/contract_test.go

@@ -36,3 +36,50 @@ func TestCreateMultiSigRedeemScript(t *testing.T) {
 	assert.Equal(t, opcode.SYSCALL, opcode.Opcode(br.ReadB()))
 	assert.Equal(t, emit.InteropNameToID([]byte("Neo.Crypto.CheckMultisigWithECDsaSecp256r1")), br.ReadU32LE())
 }
+
+func TestCreateDefaultMultiSigRedeemScript(t *testing.T) {
+	var validators = make([]*keys.PublicKey, 0)
+
+	var addKey = func() {
+		key, err := keys.NewPrivateKey()
+		require.NoError(t, err)
+		validators = append(validators, key.PublicKey())
+	}
+	var checkM = func(m int) {
+		validScript, err := CreateMultiSigRedeemScript(m, validators)
+		require.NoError(t, err)
+		defaultScript, err := CreateDefaultMultiSigRedeemScript(validators)
+		require.NoError(t, err)
+		require.Equal(t, validScript, defaultScript)
+	}
+
+	// 1 out of 1
+	addKey()
+	checkM(1)
+
+	// 2 out of 2
+	addKey()
+	checkM(2)
+
+	// 3 out of 4
+	for i := 0; i < 2; i++ {
+		addKey()
+	}
+	checkM(3)
+
+	// 5 out of 6
+	for i := 0; i < 2; i++ {
+		addKey()
+	}
+	checkM(5)
+
+	// 5 out of 7
+	addKey()
+	checkM(5)
+
+	// 7 out of 10
+	for i := 0; i < 3; i++ {
+		addKey()
+	}
+	checkM(7)
+}