From 51cebe9e4714996ffba61aec7d1a5e0912bf5d3c Mon Sep 17 00:00:00 2001
From: Evgenii Stratonikov <evgeniy@nspcc.ru>
Date: Fri, 21 Aug 2020 09:30:07 +0300
Subject: [PATCH] smartcontract: support creation of majority multisig scripts

---
 pkg/smartcontract/contract.go      |  8 ++++++
 pkg/smartcontract/contract_test.go | 45 ++++++++++++++++++++++++++++++
 2 files changed, 53 insertions(+)

diff --git a/pkg/smartcontract/contract.go b/pkg/smartcontract/contract.go
index 6a81896ae..6a88fe07b 100644
--- a/pkg/smartcontract/contract.go
+++ b/pkg/smartcontract/contract.go
@@ -44,3 +44,11 @@ func CreateDefaultMultiSigRedeemScript(publicKeys keys.PublicKeys) ([]byte, erro
 	m := n - (n-1)/3
 	return CreateMultiSigRedeemScript(m, publicKeys)
 }
+
+// CreateMajorityMultiSigRedeemScript creates an "m out of n" type verification script
+// using publicKeys length with m set to majority.
+func CreateMajorityMultiSigRedeemScript(publicKeys keys.PublicKeys) ([]byte, error) {
+	n := len(publicKeys)
+	m := n - (n-1)/2
+	return CreateMultiSigRedeemScript(m, publicKeys)
+}
diff --git a/pkg/smartcontract/contract_test.go b/pkg/smartcontract/contract_test.go
index abcd20c8a..0be9d2b58 100644
--- a/pkg/smartcontract/contract_test.go
+++ b/pkg/smartcontract/contract_test.go
@@ -83,3 +83,48 @@ func TestCreateDefaultMultiSigRedeemScript(t *testing.T) {
 	}
 	checkM(7)
 }
+
+func TestCreateMajorityMultiSigRedeemScript(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 := CreateMajorityMultiSigRedeemScript(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
+	addKey()
+	addKey()
+	checkM(3)
+
+	// 4 out of 6
+	addKey()
+	addKey()
+	checkM(4)
+
+	// 5 out of 8
+	addKey()
+	addKey()
+	checkM(5)
+
+	// 6 out of 10
+	addKey()
+	addKey()
+	checkM(6)
+}