From 94a57fc82b3ef9babb11bfc4e7efa196970b171e Mon Sep 17 00:00:00 2001
From: chatton <cian@interchain.io>
Date: Thu, 12 Sep 2024 11:08:52 +0100
Subject: [PATCH] chore: adding commitV2 hash fn

---
 modules/core/04-channel/types/packet.go | 38 +++++++++++++++++++++++++
 1 file changed, 38 insertions(+)

diff --git a/modules/core/04-channel/types/packet.go b/modules/core/04-channel/types/packet.go
index 49b569af9b2..434d33df692 100644
--- a/modules/core/04-channel/types/packet.go
+++ b/modules/core/04-channel/types/packet.go
@@ -26,6 +26,7 @@ func CommitPacket(packet Packet) []byte {
 	case IBC_VERSION_UNSPECIFIED, IBC_VERSION_1:
 		return commitV1Packet(packet)
 	case IBC_VERSION_2:
+		// TODO: convert to PacketV2 and commit.
 		return commitV2Packet(packet)
 	default:
 		panic("unsupported version")
@@ -100,6 +101,43 @@ func commitV2Packet(packet Packet) []byte {
 	return hash[:]
 }
 
+// CommitPacketV2 returns the V2 packet commitment bytes. The commitment consists of:
+// sha256_hash(timeout) + sha256_hash(destinationID) + sha256_hash(packetData) from a given packet.
+// This results in a fixed length preimage.
+// NOTE: A fixed length preimage is ESSENTIAL to prevent relayers from being able
+// to malleate the packet fields and create a commitment hash that matches the original packet.
+func CommitPacketV2(packet PacketV2) []byte {
+	timeoutHash := sha256.Sum256([]byte(packet.Timeout))
+	buf := timeoutHash[:]
+
+	destIDHash := sha256.Sum256([]byte(packet.DestinationId))
+	buf = append(buf, destIDHash[:]...)
+
+	for _, data := range packet.Data {
+		buf = append(buf, hashPacketData(data)...)
+	}
+
+	hash := sha256.Sum256(buf)
+	return hash[:]
+}
+
+// hashPacketData returns the hash of the packet data.
+func hashPacketData(data PacketData) []byte {
+	var buf []byte
+	sourceHash := sha256.Sum256([]byte(data.SourcePort))
+	buf = append(buf, sourceHash[:]...)
+	destHash := sha256.Sum256([]byte(data.DestinationPort))
+	buf = append(buf, destHash[:]...)
+	payloadValueHash := sha256.Sum256(data.Payload.Value)
+	buf = append(buf, payloadValueHash[:]...)
+	payloadEncodingHash := sha256.Sum256([]byte(data.Payload.Encoding))
+	buf = append(buf, payloadEncodingHash[:]...)
+	payloadVersionHash := sha256.Sum256([]byte(data.Payload.Version))
+	buf = append(buf, payloadVersionHash[:]...)
+	hash := sha256.Sum256(buf)
+	return hash[:]
+}
+
 // CommitAcknowledgement returns the hash of commitment bytes
 func CommitAcknowledgement(data []byte) []byte {
 	hash := sha256.Sum256(data)