Standardize message hashing functions (#1424)

## Motivation
The goal of this PR is to standardize the message hashing functions.
Currently we have equivalent but inconsistent message hashing functions:
```solidity
function _hash(Any2EVMRampMessage memory original, bytes memory onRamp) internal pure returns (bytes32)
```
and 
```solidity
function _hash(EVM2AnyRampMessage memory original, bytes32 metadataHash) internal pure returns (bytes32)
```

## Solution
Standardize to `function _hash(message, metadataHash)` and consistently
encode dynamic fields.

---------

Co-authored-by: app-token-issuer-infra-releng[bot] <120227048+app-token-issuer-infra-releng[bot]@users.noreply.github.com>

contracts/src/v0.8/ccip/libraries/Internal.sol

@@ -187,30 +187,25 @@ library Internal {
   /// OnRamp hash(EVM2AnyMessage) != Any2EVMRampMessage.messageId
   /// OnRamp hash(EVM2AnyMessage) != OffRamp hash(Any2EVMRampMessage)
   /// @param original OffRamp message to hash
-  /// @param onRamp OnRamp to hash the message with - used to compute the metadataHash
+  /// @param metadataHash Hash preimage to ensure global uniqueness
   /// @return hashedMessage hashed message as a keccak256
-  function _hash(Any2EVMRampMessage memory original, bytes memory onRamp) internal pure returns (bytes32) {
+  function _hash(Any2EVMRampMessage memory original, bytes32 metadataHash) internal pure returns (bytes32) {
     // Fixed-size message fields are included in nested hash to reduce stack pressure.
     // This hashing scheme is also used by RMN. If changing it, please notify the RMN maintainers.
     return keccak256(
       abi.encode(
         MerkleMultiProof.LEAF_DOMAIN_SEPARATOR,
-        // Implicit metadata hash
-        keccak256(
-          abi.encode(
-            ANY_2_EVM_MESSAGE_HASH, original.header.sourceChainSelector, original.header.destChainSelector, onRamp
-          )
-        ),
+        metadataHash,
         keccak256(
           abi.encode(
             original.header.messageId,
-            original.sender,
             original.receiver,
             original.header.sequenceNumber,
             original.gasLimit,
             original.header.nonce
           )
         ),
+        keccak256(original.sender),
         keccak256(original.data),
         keccak256(abi.encode(original.tokenAmounts))
       )
@@ -227,13 +222,13 @@ library Internal {
         keccak256(
           abi.encode(
             original.sender,
-            original.receiver,
             original.header.sequenceNumber,
             original.header.nonce,
             original.feeToken,
             original.feeTokenAmount
           )
         ),
+        keccak256(original.receiver),
         keccak256(original.data),
         keccak256(abi.encode(original.tokenAmounts)),
         keccak256(original.extraArgs)

contracts/src/v0.8/ccip/offRamp/OffRamp.sol

@@ -393,7 +393,17 @@ contract OffRamp is ITypeAndVersion, MultiOCR3Base {
       // over the same data, which increases gas cost.
       // Hashing all of the message fields ensures that the message being executed is correct and not tampered with.
       // Including the known OnRamp ensures that the message originates from the correct on ramp version
-      hashedLeaves[i] = Internal._hash(message, onRamp);
+      hashedLeaves[i] = Internal._hash(
+        message,
+        keccak256(
+          abi.encode(
+            Internal.ANY_2_EVM_MESSAGE_HASH,
+            message.header.sourceChainSelector,
+            message.header.destChainSelector,
+            keccak256(onRamp)
+          )
+        )
+      );
     }
 
     // SECURITY CRITICAL CHECK

contracts/src/v0.8/ccip/test/NonceManager.t.sol

@@ -397,7 +397,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
       SOURCE_CHAIN_SELECTOR_1,
       messages[0].header.sequenceNumber,
       messages[0].header.messageId,
-      Internal._hash(messages[0], ON_RAMP_ADDRESS_1),
+      _hashMessage(messages[0], ON_RAMP_ADDRESS_1),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );
@@ -429,7 +429,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
       SOURCE_CHAIN_SELECTOR_3,
       messagesChain3[0].header.sequenceNumber,
       messagesChain3[0].header.messageId,
-      Internal._hash(messagesChain3[0], ON_RAMP_ADDRESS_3),
+      _hashMessage(messagesChain3[0], ON_RAMP_ADDRESS_3),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );
@@ -499,7 +499,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
       _generateSingleBasicMessage(SOURCE_CHAIN_SELECTOR_1, ON_RAMP_ADDRESS_1);
 
     messagesMultiRamp[0].header.nonce++;
-    messagesMultiRamp[0].header.messageId = Internal._hash(messagesMultiRamp[0], ON_RAMP_ADDRESS_1);
+    messagesMultiRamp[0].header.messageId = _hashMessage(messagesMultiRamp[0], ON_RAMP_ADDRESS_1);
 
     vm.recordLogs();
 
@@ -511,7 +511,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
       SOURCE_CHAIN_SELECTOR_1,
       messagesMultiRamp[0].header.sequenceNumber,
       messagesMultiRamp[0].header.messageId,
-      Internal._hash(messagesMultiRamp[0], ON_RAMP_ADDRESS_1),
+      _hashMessage(messagesMultiRamp[0], ON_RAMP_ADDRESS_1),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );
@@ -522,7 +522,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
 
     messagesMultiRamp[0].header.nonce++;
     messagesMultiRamp[0].header.sequenceNumber++;
-    messagesMultiRamp[0].header.messageId = Internal._hash(messagesMultiRamp[0], ON_RAMP_ADDRESS_1);
+    messagesMultiRamp[0].header.messageId = _hashMessage(messagesMultiRamp[0], ON_RAMP_ADDRESS_1);
 
     vm.recordLogs();
     s_offRamp.executeSingleReport(
@@ -532,7 +532,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
       SOURCE_CHAIN_SELECTOR_1,
       messagesMultiRamp[0].header.sequenceNumber,
       messagesMultiRamp[0].header.messageId,
-      Internal._hash(messagesMultiRamp[0], ON_RAMP_ADDRESS_1),
+      _hashMessage(messagesMultiRamp[0], ON_RAMP_ADDRESS_1),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );
@@ -555,7 +555,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
 
     bytes memory newSender = abi.encode(address(1234567));
     messagesMultiRamp[0].sender = newSender;
-    messagesMultiRamp[0].header.messageId = Internal._hash(messagesMultiRamp[0], ON_RAMP_ADDRESS_1);
+    messagesMultiRamp[0].header.messageId = _hashMessage(messagesMultiRamp[0], ON_RAMP_ADDRESS_1);
 
     // new sender nonce in new offramp should go from 0 -> 1
     assertEq(s_inboundNonceManager.getInboundNonce(SOURCE_CHAIN_SELECTOR_1, newSender), 0);
@@ -567,7 +567,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
       SOURCE_CHAIN_SELECTOR_1,
       messagesMultiRamp[0].header.sequenceNumber,
       messagesMultiRamp[0].header.messageId,
-      Internal._hash(messagesMultiRamp[0], ON_RAMP_ADDRESS_1),
+      _hashMessage(messagesMultiRamp[0], ON_RAMP_ADDRESS_1),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );
@@ -581,7 +581,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
     address newSender = address(1234567);
     messages[0].sender = abi.encode(newSender);
     messages[0].header.nonce = 2;
-    messages[0].header.messageId = Internal._hash(messages[0], ON_RAMP_ADDRESS_1);
+    messages[0].header.messageId = _hashMessage(messages[0], ON_RAMP_ADDRESS_1);
 
     uint64 startNonce = s_inboundNonceManager.getInboundNonce(SOURCE_CHAIN_SELECTOR_1, messages[0].sender);
 
@@ -611,7 +611,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
     );
 
     messages[0].header.nonce = 2;
-    messages[0].header.messageId = Internal._hash(messages[0], ON_RAMP_ADDRESS_1);
+    messages[0].header.messageId = _hashMessage(messages[0], ON_RAMP_ADDRESS_1);
 
     // new offramp is able to execute
     vm.recordLogs();
@@ -622,7 +622,7 @@ contract NonceManager_OffRampUpgrade is OffRampSetup {
       SOURCE_CHAIN_SELECTOR_1,
       messages[0].header.sequenceNumber,
       messages[0].header.messageId,
-      Internal._hash(messages[0], ON_RAMP_ADDRESS_1),
+      _hashMessage(messages[0], ON_RAMP_ADDRESS_1),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );

contracts/src/v0.8/ccip/test/e2e/MultiRampsEnd2End.sol

@@ -141,10 +141,10 @@ contract MultiRampsE2E is OnRampSetup, OffRampSetup {
     // Scoped to commit to reduce stack pressure
     {
       bytes32[] memory hashedMessages1 = new bytes32[](2);
-      hashedMessages1[0] = messages1[0]._hash(abi.encode(address(s_onRamp)));
-      hashedMessages1[1] = messages1[1]._hash(abi.encode(address(s_onRamp)));
+      hashedMessages1[0] = _hashMessage(messages1[0], abi.encode(address(s_onRamp)));
+      hashedMessages1[1] = _hashMessage(messages1[1], abi.encode(address(s_onRamp)));
       bytes32[] memory hashedMessages2 = new bytes32[](1);
-      hashedMessages2[0] = messages2[0]._hash(abi.encode(address(s_onRamp2)));
+      hashedMessages2[0] = _hashMessage(messages2[0], abi.encode(address(s_onRamp2)));
 
       merkleRoots[0] = MerkleHelper.getMerkleRoot(hashedMessages1);
       merkleRoots[1] = MerkleHelper.getMerkleRoot(hashedMessages2);
@@ -211,7 +211,7 @@ contract MultiRampsE2E is OnRampSetup, OffRampSetup {
       SOURCE_CHAIN_SELECTOR,
       messages1[0].header.sequenceNumber,
       messages1[0].header.messageId,
-      messages1[0]._hash(abi.encode(address(s_onRamp))),
+      _hashMessage(messages1[0], abi.encode(address(s_onRamp))),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );
@@ -220,7 +220,7 @@ contract MultiRampsE2E is OnRampSetup, OffRampSetup {
       SOURCE_CHAIN_SELECTOR,
       messages1[1].header.sequenceNumber,
       messages1[1].header.messageId,
-      messages1[1]._hash(abi.encode(address(s_onRamp))),
+      _hashMessage(messages1[1], abi.encode(address(s_onRamp))),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );
@@ -229,7 +229,7 @@ contract MultiRampsE2E is OnRampSetup, OffRampSetup {
       SOURCE_CHAIN_SELECTOR + 1,
       messages2[0].header.sequenceNumber,
       messages2[0].header.messageId,
-      messages2[0]._hash(abi.encode(address(s_onRamp2))),
+      _hashMessage(messages2[0], abi.encode(address(s_onRamp2))),
       Internal.MessageExecutionState.SUCCESS,
       ""
     );

contracts/src/v0.8/ccip/test/helpers/MessageHasher.sol

@@ -9,7 +9,14 @@ import {Internal} from "../../libraries/Internal.sol";
 /// @dev This is only deployed in tests and is not part of the production contracts.
 contract MessageHasher {
   function hash(Internal.Any2EVMRampMessage memory message, bytes memory onRamp) public pure returns (bytes32) {
-    return Internal._hash(message, onRamp);
+    return Internal._hash(
+      message,
+      keccak256(
+        abi.encode(
+          Internal.ANY_2_EVM_MESSAGE_HASH, message.header.sourceChainSelector, message.header.destChainSelector, onRamp
+        )
+      )
+    );
   }
 
   function encodeTokenAmountsHashPreimage(