Cross Chain Replay Protection (Sponsored Calls) (#3)

Adds `chainId` to the signature digest for cross chain replay
protection.

Thanks @schmanu for pointing this out!

Author: bh2smith

script/BatchCallAndSponsor.s.sol

@@ -97,7 +97,8 @@ contract BatchCallAndSponsorScript is Script {
         for (uint256 i = 0; i < calls.length; i++) {
             encodedCalls = abi.encodePacked(encodedCalls, calls[i].to, calls[i].value, calls[i].data);
         }
-        bytes32 digest = keccak256(abi.encodePacked(BatchCallAndSponsor(ALICE_ADDRESS).nonce(), encodedCalls));
+        bytes32 digest =
+            keccak256(abi.encodePacked(block.chainid, BatchCallAndSponsor(ALICE_ADDRESS).nonce(), encodedCalls));
         (uint8 v, bytes32 r, bytes32 s) = vm.sign(ALICE_PK, MessageHashUtils.toEthSignedMessageHash(digest));
         bytes memory signature = abi.encodePacked(r, s, v);
 

src/BatchCallAndSponsor.sol

@@ -18,6 +18,7 @@ import "@openzeppelin/contracts/utils/cryptography/MessageHashUtils.sol";
  * 2. Directly by the smart account: When the account itself (i.e. address(this)) calls the function, no signature is required.
  *
  * Replay protection is achieved by using a nonce that is included in the signed message.
+ * Cross chain replay protection is achieved by using the chainid in the signed message.
  */
 contract BatchCallAndSponsor {
     using ECDSA for bytes32;
@@ -51,7 +52,7 @@ contract BatchCallAndSponsor {
         for (uint256 i = 0; i < calls.length; i++) {
             encodedCalls = abi.encodePacked(encodedCalls, calls[i].to, calls[i].value, calls[i].data);
         }
-        bytes32 digest = keccak256(abi.encodePacked(nonce, encodedCalls));
+        bytes32 digest = keccak256(abi.encodePacked(block.chainid, nonce, encodedCalls));
 
         bytes32 ethSignedMessageHash = MessageHashUtils.toEthSignedMessageHash(digest);
 

test/BatchCallAndSponsor.t.sol

@@ -97,7 +97,8 @@ contract BatchCallAndSponsorTest is Test {
             encodedCalls = abi.encodePacked(encodedCalls, calls[i].to, calls[i].value, calls[i].data);
         }
 
-        bytes32 digest = keccak256(abi.encodePacked(BatchCallAndSponsor(ALICE_ADDRESS).nonce(), encodedCalls));
+        bytes32 digest =
+            keccak256(abi.encodePacked(block.chainid, BatchCallAndSponsor(ALICE_ADDRESS).nonce(), encodedCalls));
 
         (uint8 v, bytes32 r, bytes32 s) = vm.sign(ALICE_PK, MessageHashUtils.toEthSignedMessageHash(digest));
         bytes memory signature = abi.encodePacked(r, s, v);
@@ -171,7 +172,7 @@ contract BatchCallAndSponsorTest is Test {
         vm.attachDelegation(signedDelegation);
 
         uint256 nonceBefore = BatchCallAndSponsor(ALICE_ADDRESS).nonce();
-        bytes32 digest = keccak256(abi.encodePacked(nonceBefore, encodedCalls));
+        bytes32 digest = keccak256(abi.encodePacked(block.chainid, nonceBefore, encodedCalls));
         (uint8 v, bytes32 r, bytes32 s) = vm.sign(ALICE_PK, MessageHashUtils.toEthSignedMessageHash(digest));
         bytes memory signature = abi.encodePacked(r, s, v);