From 7a52c0ecd54ee2db49b7fbf1309cf54ea912e5ca Mon Sep 17 00:00:00 2001
From: Ignotus Peverell <igno.peverell@protonmail.com>
Date: Sat, 22 Dec 2018 19:42:07 +0000
Subject: [PATCH] Revert "Verify features in one place; comment on needed
 Features enum type (#2191)"

This reverts commit 151aa1c842835c51a251e17d12751e3651a021e5.
---
 core/src/core/transaction.rs | 48 +++++++++++++++++++-----------------
 1 file changed, 25 insertions(+), 23 deletions(-)

diff --git a/core/src/core/transaction.rs b/core/src/core/transaction.rs
index 8bcc993c9..845116d90 100644
--- a/core/src/core/transaction.rs
+++ b/core/src/core/transaction.rs
@@ -36,14 +36,6 @@ use std::collections::HashSet;
 use std::sync::Arc;
 use std::{error, fmt};
 
-/// KernelFeatures needs to be a sumtype / tagged union as
-/// pub enum KernelFeatures {
-/// 	COINBASE,
-///	PLAIN { fee: u64 },
-///	HEIGHTLOCKED { fee: u64, lock_height: u64 },
-/// }
-/// Similarly for OutputFeatures
-///
 bitflags! {
 	/// Options for a kernel's structure or use
 	#[derive(Serialize, Deserialize)]
@@ -261,6 +253,10 @@ impl TxKernel {
 	/// as a public key and checking the signature verifies with the fee as
 	/// message.
 	pub fn verify(&self) -> Result<(), Error> {
+		if self.is_coinbase() && self.fee != 0 || !self.is_height_locked() && self.lock_height != 0
+		{
+			return Err(Error::InvalidKernelFeatures);
+		}
 		let secp = static_secp_instance();
 		let secp = secp.lock();
 		let sig = &self.excess_sig;
@@ -1353,30 +1349,36 @@ impl From<Output> for OutputIdentifier {
 }
 
 /// Construct msg from tx fee, lock_height and kernel features.
-/// msg = hash(features)                       for coinbase kernels
-///       hash(features || fee)                for plain kernels
-///       hash(features || fee || lock_height) for height locked kernels
+/// In testnet4 we did not include the kernel features in the message being signed.
+/// In mainnet we changed this to include features and we hash (fee || lock_height || features)
+/// to produce a 32 byte message to sign.
+///
+/// testnet4: msg = (fee || lock_height)
+/// mainnet:  msg = hash(features)                       for coinbase kernels
+///                 hash(features || fee)                for plain kernels
+///                 hash(features || fee || lock_height) for height locked kernels
 ///
 pub fn kernel_sig_msg(
 	fee: u64,
 	lock_height: u64,
 	features: KernelFeatures,
 ) -> Result<secp::Message, Error> {
-	let features_ok = match features {
-		KernelFeatures::COINBASE => fee == 0 && lock_height == 0,
-		KernelFeatures::PLAIN => lock_height == 0,
-		KernelFeatures::HEIGHT_LOCKED => true, 
-		_ => false
-	};
-	if !features_ok {
+	if features.is_coinbase() && fee != 0 || !features.is_height_locked() && lock_height != 0 {
 		return Err(Error::InvalidKernelFeatures);
 	}
-	let hash = match features {
-		KernelFeatures::COINBASE => features.hash(),
-		KernelFeatures::PLAIN => (features, fee).hash(),
-		_ => (features, fee, lock_height).hash(),
+	let msg = if global::is_testnet() {
+		let mut bytes = [0; 32];
+		BigEndian::write_u64(&mut bytes[16..24], fee);
+		BigEndian::write_u64(&mut bytes[24..], lock_height);
+		secp::Message::from_slice(&bytes)?
+	} else {
+		let hash = match features {
+			KernelFeatures::COINBASE => (features).hash(),
+			KernelFeatures::PLAIN => (features, fee).hash(),
+			_ => (features, fee, lock_height).hash(),
+		};
+		secp::Message::from_slice(&hash.as_bytes())?
 	};
-	let msg = secp::Message::from_slice(&hash.as_bytes())?;
 	Ok(msg)
 }