Repository: w3hc/eip7702-playground
Pull request #4: Add EIP-712 signature verification in `sponsoredTransfer`
Author: login: julienbrg
Created: 2025-03-18T09:51:50Z | Merged: 2025-03-18T14:06:00Z



Diff:
diff --git a/.gitignore b/.gitignore
index b5b4d97..3bb1d3d 100644
--- a/.gitignore
+++ b/.gitignore
@@ -21,3 +21,4 @@ broadcast/*/31337/
 
 # Misc
 NOTES.md
+/zhankai
diff --git a/LICENSE.md b/LICENSE.md
index 0424fa0..953bae8 100644
--- a/LICENSE.md
+++ b/LICENSE.md
@@ -1,16 +1,673 @@
-MIT License
+GNU GENERAL PUBLIC LICENSE
+Version 3, 29 June 2007
 
-Copyright (c) 2024 Paul Razvan Berg
+Copyright (C) 2007 Free Software Foundation, Inc. <https://fsf.org/>
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+HOLDERS AND/OR OTHER PARTIES PROVIDE THE PROGRAM "AS IS" WITHOUT WARRANTY
+OF ANY KIND, EITHER EXPRESSED OR IMPLIED, INCLUDING, BUT NOT LIMITED TO,
+THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
+PURPOSE. THE ENTIRE RISK AS TO THE QUALITY AND PERFORMANCE OF THE PROGRAM
+IS WITH YOU. SHOULD THE PROGRAM PROVE DEFECTIVE, YOU ASSUME THE COST OF
+ALL NECESSARY SERVICING, REPAIR OR CORRECTION.
+
+16. Limitation of Liability.
+
+IN NO EVENT UNLESS REQUIRED BY APPLICABLE LAW OR AGREED TO IN WRITING
+WILL ANY COPYRIGHT HOLDER, OR ANY OTHER PARTY WHO MODIFIES AND/OR CONVEYS
+THE PROGRAM AS PERMITTED ABOVE, BE LIABLE TO YOU FOR DAMAGES, INCLUDING ANY
+GENERAL, SPECIAL, INCIDENTAL OR CONSEQUENTIAL DAMAGES ARISING OUT OF THE
+USE OR INABILITY TO USE THE PROGRAM (INCLUDING BUT NOT LIMITED TO LOSS OF
+DATA OR DATA BEING RENDERED INACCURATE OR LOSSES SUSTAINED BY YOU OR THIRD
+PARTIES OR A FAILURE OF THE PROGRAM TO OPERATE WITH ANY OTHER PROGRAMS),
+EVEN IF SUCH HOLDER OR OTHER PARTY HAS BEEN ADVISED OF THE POSSIBILITY OF
+SUCH DAMAGES.
+
+17. Interpretation of Sections 15 and 16.
+
+If the disclaimer of warranty and limitation of liability provided
+above cannot be given local legal effect according to their terms,
+reviewing courts shall apply local law that most closely approximates
+an absolute waiver of all civil liability in connection with the
+Program, unless a warranty or assumption of liability accompanies a
+copy of the Program in return for a fee.
+
+END OF TERMS AND CONDITIONS
+
+How to Apply These Terms to Your New Programs
+
+If you develop a new program, and you want it to be of the greatest
+possible use to the public, the best way to achieve this is to make it
+free software which everyone can redistribute and change under these terms.
+
+To do so, attach the following notices to the program. It is safest
+to attach them to the start of each source file to most effectively
+state the exclusion of warranty; and each file should have at least
+the "copyright" line and a pointer to where the full notice is found.
+
+<one line to give the program's name and a brief idea of what it does.>
+Copyright (C) <year> <name of author>
+
+This program is free software: you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation, either version 3 of the License, or
+(at your option) any later version.
+
+This program is distributed in the hope that it will be useful,
+but WITHOUT ANY WARRANTY; without even the implied warranty of
+MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+GNU General Public License for more details.
+
+You should have received a copy of the GNU General Public License
+along with this program. If not, see <https://www.gnu.org/licenses/>.
+
+Also add information on how to contact you by electronic and paper mail.
+
+If the program does terminal interaction, make it output a short
+notice like this when it starts in an interactive mode:
+
+<program> Copyright (C) <year> <name of author>
+This program comes with ABSOLUTELY NO WARRANTY; for details type `show w'.
+This is free software, and you are welcome to redistribute it
+under certain conditions; type `show c' for details.
+
+The hypothetical commands `show w' and `show c' should show the appropriate
+parts of the General Public License. Of course, your program's commands
+might be different; for a GUI interface, you would use an "about box".
+
+You should also get your employer (if you work as a programmer) or school,
+if any, to sign a "copyright disclaimer" for the program, if necessary.
+For more information on this, and how to apply and follow the GNU GPL, see
+<https://www.gnu.org/licenses/>.
+
+The GNU General Public License does not permit incorporating your program
+into proprietary programs. If your program is a subroutine library, you
+may consider it more useful to permit linking proprietary applications with
+the library. If this is what you want to do, use the GNU Lesser General
+Public License instead of this License. But first, please read
+<https://www.gnu.org/licenses/why-not-lgpl.html>.
diff --git a/README.md b/README.md
index a24330f..d8be022 100644
--- a/README.md
+++ b/README.md
@@ -80,8 +80,14 @@ The repository includes tests that verify EIP-7702 functionality across differen
 # Should pass - Prague supports EIP-7702
 FOUNDRY_PROFILE=prague forge test
 
+# Alternatively
+pnpm test
+
 # Should fail - Shanghai doesn't support EIP-7702
 FOUNDRY_PROFILE=shanghai forge test
+
+# Alternatively
+pnpm test:shanghai
 ```
 
 ### Test Structure
@@ -116,24 +122,24 @@ FOUNDRY_PROFILE=prague forge test -vvv
 First, start a local Anvil node:
 
 ```sh
-$ anvil
+anvil
 ```
 
 Then in a new terminal, deploy using one of the following commands:
 
 Deploy with default (Prague) settings:
 ```sh
-$ forge script script/Deploy.s.sol --broadcast --fork-url http://localhost:8545
+forge script script/Deploy.s.sol --broadcast --fork-url http://localhost:8545
 ```
 
 Deploy with Prague profile explicitly:
 ```sh
-$ FOUNDRY_PROFILE=prague forge script script/Deploy.s.sol --broadcast --fork-url http://localhost:8545
+FOUNDRY_PROFILE=prague forge script script/Deploy.s.sol --broadcast --fork-url http://localhost:8545
 ```
 
 Deploy with Shanghai profile:
 ```sh
-$ FOUNDRY_PROFILE=shanghai forge script script/Deploy.s.sol --broadcast --fork-url http://localhost:8545
+FOUNDRY_PROFILE=shanghai forge script script/Deploy.s.sol --broadcast --fork-url http://localhost:8545
 ```
 
 For these scripts to work, you need to have a `MNEMONIC` environment variable set to a valid
diff --git a/package.json b/package.json
index 9fda91d..c038f64 100644
--- a/package.json
+++ b/package.json
@@ -31,7 +31,9 @@
     "lint:sol": "forge fmt --check && bun solhint \"{script,src,tests}/**/*.sol\"",
     "prettier:check": "prettier --check \"**/*.{json,md,yml}\" --ignore-path \".prettierignore\"",
     "prettier:write": "prettier --write \"**/*.{json,md,yml}\" --ignore-path \".prettierignore\"",
-    "test": "forge test",
+    "test": "FOUNDRY_PROFILE=prague forge test",
+    "test:prague": "FOUNDRY_PROFILE=prague forge test",
+    "test:shanghai": "FOUNDRY_PROFILE=shanghai forge test",
     "test:coverage": "forge coverage",
     "test:coverage:report": "forge coverage --report lcov && genhtml lcov.info --branch-coverage --output-dir coverage"
   }
diff --git a/script/Base.s.sol b/script/Base.s.sol
index 29670db..8ef7249 100644
--- a/script/Base.s.sol
+++ b/script/Base.s.sol
@@ -3,6 +3,11 @@ pragma solidity >=0.8.28 <0.9.0;
 
 import { Script } from "forge-std/src/Script.sol";
 
+/**
+ * @title BaseScript
+ * @notice Base deployment script with common functionality
+ * @dev Provides utilities for deterministic deployments and broadcasting
+ */
 abstract contract BaseScript is Script {
     /// @dev Included to enable compilation of the script without a $MNEMONIC environment variable.
     string internal constant TEST_MNEMONIC = "test test test test test test test test test test test junk";
@@ -16,13 +21,13 @@ abstract contract BaseScript is Script {
     /// @dev Used to derive the broadcaster's address if $ETH_FROM is not defined.
     string internal mnemonic;
 
-    /// @dev Initializes the transaction broadcaster like this:
-    ///
-    /// - If $ETH_FROM is defined, use it.
-    /// - Otherwise, derive the broadcaster address from $MNEMONIC.
-    /// - If $MNEMONIC is not defined, default to a test mnemonic.
-    ///
-    /// The use case for $ETH_FROM is to specify the broadcaster key and its address via the command line.
+    /**
+     * @notice Initializes the transaction broadcaster
+     * @dev Sets up the broadcaster using one of these methods (in order):
+     *      1. Use $ETH_FROM environment variable if defined
+     *      2. Derive address from $MNEMONIC environment variable if defined
+     *      3. Fall back to a test mnemonic for local testing
+     */
     constructor() {
         address from = vm.envOr({ name: "ETH_FROM", defaultValue: address(0) });
         if (from != address(0)) {
@@ -33,6 +38,10 @@ abstract contract BaseScript is Script {
         }
     }
 
+    /**
+     * @notice Modifier to broadcast transactions from the configured broadcaster
+     * @dev Wraps the function execution with vm.startBroadcast and vm.stopBroadcast
+     */
     modifier broadcast() {
         vm.startBroadcast(broadcaster);
         _;
diff --git a/script/Deploy.s.sol b/script/Deploy.s.sol
index bea8f28..dfdd8d1 100644
--- a/script/Deploy.s.sol
+++ b/script/Deploy.s.sol
@@ -7,8 +7,20 @@ import { Sponsor } from "../src/Sponsor.sol";
 import { BaseScript } from "./Base.s.sol";
 import { console2 } from "forge-std/src/console2.sol";
 
-/// @dev Deployment script for EIP-7702 demonstration contracts
+/**
+ * @title Deploy
+ * @notice Deployment script for EIP-7702 demonstration contracts
+ * @dev Handles deployment and initial setup of all contracts needed for EIP-7702 demos
+ * @custom:eip EIP-7702 (EOA Code Setting)
+ */
 contract Deploy is BaseScript {
+    /**
+     * @notice Deploy and set up all EIP-7702 demonstration contracts
+     * @dev Checks for Prague EVM support, deploys contracts, and creates a test authorization
+     * @return demonstrator The deployed EIP7702Demonstrator contract
+     * @return test The deployed EIP7702Test helper contract
+     * @return sponsor The deployed Sponsor contract
+     */
     function run() public broadcast returns (EIP7702Demonstrator demonstrator, EIP7702Test test, Sponsor sponsor) {
         // Check EVM version supports EIP-7702
         string memory evmVersion = vm.envOr("FOUNDRY_PROFILE", string("default"));
diff --git a/src/EIP7702Demonstrator.sol b/src/EIP7702Demonstrator.sol
index e0fb999..52088e6 100644
--- a/src/EIP7702Demonstrator.sol
+++ b/src/EIP7702Demonstrator.sol
@@ -1,13 +1,19 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title EIP-7702 Demonstrator
-/// @notice Helper contract to demonstrate EIP-7702 functionality
-/// @dev Provides utilities for checking EOA code status
+/**
+ * @title EIP7702Demonstrator
+ * @notice Utility contract for demonstrating and testing EIP-7702 functionality
+ * @dev Provides functions to inspect EOA code properties with EIP-7702 delegation
+ * @custom:eip EIP-7702 (EOA Code Setting)
+ */
 contract EIP7702Demonstrator {
-    /// @notice Get the code size of an account
-    /// @param account The address to check
-    /// @return The size of the code at the address
+    /**
+     * @notice Get the code size of any account
+     * @dev Uses assembly to directly access the extcodesize opcode
+     * @param account The address to check code size for
+     * @return The size of the code at the given address in bytes
+     */
     function getCodeLength(address account) external view returns (uint256) {
         uint256 size;
         assembly {
diff --git a/src/EIP7702Test.sol b/src/EIP7702Test.sol
index 23a6888..c496cb4 100644
--- a/src/EIP7702Test.sol
+++ b/src/EIP7702Test.sol
@@ -1,19 +1,32 @@
 // SPDX-License-Identifier: MIT
 pragma solidity >=0.8.28;
 
-/// @title EIP7702Test
-/// @notice Helper contract for testing EIP-7702 functionality
+/**
+ * @title EIP7702Test
+ * @notice Helper contract for testing EIP-7702 authorizations
+ * @dev Creates properly formatted EIP-7702 authorizations for testing purposes
+ * @custom:eip EIP-7702 (EOA Code Setting)
+ */
 contract EIP7702Test {
+    /**
+     * @notice Emitted when a new authorization is created
+     * @param signer The address that signed the authorization
+     * @param codeAddress The contract address being authorized
+     * @param nonce The nonce used for this authorization
+     */
     event Authorization(address indexed signer, address indexed codeAddress, uint64 nonce);
 
-    // Transaction type for EIP-7702
-    bytes4 constant EIP7702_TX_TYPE = bytes4(hex"04000000"); // Properly formatted as bytes4
+    /// @dev Magic bytes for EIP-7702 transaction type
+    bytes4 public constant EIP7702_TX_TYPE = bytes4(hex"04000000");
 
-    /// @notice Creates an EIP-7702 authorization
-    /// @param chainId The chain ID for the authorization
-    /// @param codeAddress The address of the code to execute
-    /// @param nonce The nonce for the authorization
-    /// @return The encoded authorization data
+    /**
+     * @notice Creates an EIP-7702 compliant authorization
+     * @dev Constructs the authorization digest with EIP-7702 magic byte (0x05)
+     * @param chainId The chain ID where this authorization is valid
+     * @param codeAddress The target contract address being authorized
+     * @param nonce The nonce to prevent replay attacks
+     * @return The encoded authorization data for EIP-7702
+     */
     function createAuthorization(uint256 chainId, address codeAddress, uint64 nonce) public returns (bytes memory) {
         // Create the authorization digest with EIP-7702 magic byte
         bytes32 digest = keccak256(
diff --git a/src/Sponsor.sol b/src/Sponsor.sol
index 389e44d..9e35985 100644
--- a/src/Sponsor.sol
+++ b/src/Sponsor.sol
@@ -1,41 +1,158 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title Sponsor Contract for EIP-7702 Demonstration
-/// @notice Demonstrates gas sponsorship capabilities using EIP-7702
-/// @dev This contract acts as the delegate for EOAs, enabling sponsored transactions
+/**
+ * @title Sponsor
+ * @notice Demonstration contract for gas sponsorship capabilities using EIP-7702
+ * @dev Implements EIP-712 for secure signature validation and execution delegation
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract Sponsor {
-    /// @notice Thrown when the transfer of ETH fails
+    /**
+     * @notice Thrown when ETH transfer to recipient fails
+     * @dev May occur if recipient contract has a failing fallback function
+     */
     error TransferFailed();
 
-    /// @notice Records of gas spent by relayers
-    mapping(address => uint256) public gasSpent;
+    /**
+     * @notice Thrown when signature validation fails
+     * @dev May occur if signature is invalid or was not signed by the claimed sender
+     */
+    error InvalidSignature();
 
-    /// @notice Emitted when a sponsored transfer is completed
-    /// @param sender The original sender (EOA)
-    /// @param recipient The recipient of the transfer
-    /// @param amount The amount transferred
-    /// @param gasUsed The amount of gas used
-    event SponsoredTransfer(address indexed sender, address indexed recipient, uint256 amount, uint256 gasUsed);
+    /**
+     * @notice Thrown when a nonce is reused (replay protection)
+     * @dev Ensures each authorization can only be used once
+     */
+    error NonceAlreadyUsed();
+
+    /**
+     * @dev ERC-7201 storage namespace for Sponsor contract
+     * @custom:storage-location erc7201:sponsor.storage
+     */
+    struct SponsorStorage {
+        // Tracks gas spent by each sender when using sponsored transactions
+        mapping(address => uint256) gasSpent;
+        // Tracks the next valid nonce for each sender
+        mapping(address => uint256) nonces;
+    }
+
+    // keccak256(abi.encode(uint256(keccak256("sponsor.storage")) - 1)) & ~bytes32(uint256(0xff));
+    bytes32 private constant SPONSOR_STORAGE_LOCATION =
+        0xa185f0c1eeeb9abcce3ff812824b81cc825ec30cf022a2ea6a53b4f45b576600;
+
+    /**
+     * @dev Get the sponsor storage
+     */
+    function _getSponsorStorage() private pure returns (SponsorStorage storage s) {
+        bytes32 position = SPONSOR_STORAGE_LOCATION;
+        assembly {
+            s.slot := position
+        }
+    }
+
+    /// @notice Type hash for EIP-712 signature of sponsored transfers
+    bytes32 public constant SPONSORED_TRANSFER_TYPEHASH =
+        keccak256("SponsoredTransfer(address sender,address recipient,uint256 amount,uint256 nonce)");
+
+    /// @notice Domain separator for EIP-712 signatures
+    bytes32 public immutable DOMAIN_SEPARATOR;
+
+    /**
+     * @notice Initializes the sponsor contract
+     * @dev Sets up the EIP-712 domain separator based on contract address and chain
+     */
+    constructor() {
+        DOMAIN_SEPARATOR = keccak256(
+            abi.encode(
+                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
+                keccak256(bytes("Sponsor")),
+                keccak256(bytes("1")),
+                block.chainid,
+                address(this)
+            )
+        );
+    }
+
+    /**
+     * @notice Get gas spent by a specific address
+     * @param sender The address to check gas usage for
+     * @return Amount of gas used by the sender
+     */
+    function gasSpent(address sender) external view returns (uint256) {
+        return _getSponsorStorage().gasSpent[sender];
+    }
+
+    /**
+     * @notice Get the current nonce for a specific address
+     * @param sender The address to check nonce for
+     * @return Current nonce value for the sender
+     */
+    function nonces(address sender) external view returns (uint256) {
+        return _getSponsorStorage().nonces[sender];
+    }
+
+    /**
+     * @notice Execute a transfer on behalf of a user who provided a valid signature
+     * @dev Verifies EIP-712 signature, transfers ETH, and records gas usage
+     * @param sender The address that authorized the transfer
+     * @param recipient The address to receive the ETH
+     * @param amount The amount of ETH to transfer
+     * @param nonce The unique nonce to prevent replay attacks
+     * @param v Recovery byte of the sender's signature
+     * @param r First 32 bytes of the sender's signature
+     * @param s Second 32 bytes of the sender's signature
+     */
+    function sponsoredTransfer(
+        address sender,
+        address payable recipient,
+        uint256 amount,
+        uint256 nonce,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    )
+        external
+        payable
+    {
+        SponsorStorage storage sponsorStorage = _getSponsorStorage();
+
+        // Ensure nonce is not reused
+        if (nonce != sponsorStorage.nonces[sender]++) revert NonceAlreadyUsed();
+
+        // Compute expected message hash
+        bytes32 digest = keccak256(
+            abi.encodePacked(
+                "\x19\x01",
+                DOMAIN_SEPARATOR,
+                keccak256(abi.encode(SPONSORED_TRANSFER_TYPEHASH, sender, recipient, amount, nonce))
+            )
+        );
+
+        // Recover signer from signature
+        address recovered = ecrecover(digest, v, r, s);
+        if (recovered != address(this) && recovered != sender) revert InvalidSignature();
 
-    /// @notice Execute a transfer on behalf of msg.sender and records gas usage
-    /// @param recipient The address to receive the ETH
-    /// @dev When called through EIP-7702, msg.sender will be the EOA
-    function sponsoredTransfer(address payable recipient) external payable {
         // Store initial gas for measurement
         uint256 startGas = gasleft();
 
-        // Record who is actually executing this (should be EOA via EIP-7702)
-        address actualSender = msg.sender;
-
-        // Execute the transfer from the sender's balance
-        (bool success,) = recipient.call{ value: msg.value }("");
+        // Execute the transfer
+        (bool success,) = recipient.call{ value: amount }("");
         if (!success) revert TransferFailed();
 
         // Calculate and record gas usage
         uint256 gasUsed = startGas - gasleft();
-        gasSpent[tx.origin] += gasUsed;
+        sponsorStorage.gasSpent[sender] += gasUsed;
 
-        emit SponsoredTransfer(actualSender, recipient, msg.value, gasUsed);
+        emit SponsoredTransfer(sender, recipient, amount, gasUsed);
     }
+
+    /**
+     * @notice Emitted when a sponsored transfer is successfully executed
+     * @param sender The original sender (EOA) who authorized the transfer
+     * @param recipient The recipient who received the funds
+     * @param amount The amount of ETH transferred
+     * @param gasUsed The amount of gas consumed by the transaction
+     */
+    event SponsoredTransfer(address indexed sender, address indexed recipient, uint256 amount, uint256 gasUsed);
 }
diff --git a/test/EIP7702SupportTest.t.sol b/test/EIP7702SupportTest.t.sol
index 102eb16..5afd5f3 100644
--- a/test/EIP7702SupportTest.t.sol
+++ b/test/EIP7702SupportTest.t.sol
@@ -5,17 +5,36 @@ import "forge-std/src/Test.sol";
 import "../src/EIP7702Demonstrator.sol";
 import "../src/EIP7702Test.sol";
 
+/**
+ * @title EIP7702SupportTest
+ * @notice Test contract verifying EIP-7702 functionality across different EVM versions
+ * @dev Tests whether EOA code setting works as expected in different EVM versions (Prague vs Shanghai)
+ * @custom:eip EIP-7702 (EOA Code Setting)
+ */
 contract EIP7702SupportTest is Test {
     EIP7702Demonstrator public demonstrator;
     EIP7702Test public testHelper;
 
+    /**
+     * @notice Emitted when code is executed on an EOA through delegation
+     * @param origin The original transaction sender
+     * @param caller The address calling the code
+     */
     event CodeExecuted(address origin, address caller);
 
+    /**
+     * @notice Set up the test environment
+     * @dev Deploys the necessary contracts for testing
+     */
     function setUp() public {
         demonstrator = new EIP7702Demonstrator();
         testHelper = new EIP7702Test();
     }
 
+    /**
+     * @notice Tests EIP-7702 support in different EVM versions
+     * @dev Checks if code can be set on an EOA in Prague (should work) vs Shanghai (should fail)
+     */
     function testEVMVersionSupport() public {
         string memory evmVersion = vm.envString("FOUNDRY_PROFILE");
         address eoa = makeAddr("testEOA");
diff --git a/test/SponsorTest.t.sol b/test/SponsorTest.t.sol
index 486aa3f..0a00509 100644
--- a/test/SponsorTest.t.sol
+++ b/test/SponsorTest.t.sol
@@ -4,11 +4,20 @@ pragma solidity ^0.8.28;
 import "forge-std/src/Test.sol";
 import "../src/Sponsor.sol";
 
+/**
+ * @title SponsorTest
+ * @notice Test contract for basic Sponsor contract functionality without EIP-7702
+ * @dev Tests standard EIP-712 signature verification and execution in the Sponsor contract
+ */
 contract SponsorTest is Test {
     Sponsor public sponsor;
     address payable public alice;
     address payable public bob;
 
+    /**
+     * @notice Set up the test environment
+     * @dev Deploys the Sponsor contract and sets up test accounts
+     */
     function setUp() public {
         // Deploy the sponsor contract
         sponsor = new Sponsor();
@@ -21,10 +30,38 @@ contract SponsorTest is Test {
         vm.deal(alice, 2 ether);
     }
 
-    // Basic functionality test - no EIP-7702 features
+    /**
+     * @notice Tests basic sponsorship functionality without EIP-7702
+     * @dev Verifies that the Sponsor contract can execute transactions with valid EIP-712 signatures
+     */
     function testBasicSponsorFunctionality() public {
-        vm.prank(alice);
-        sponsor.sponsoredTransfer{ value: 1 ether }(bob);
-        assertEq(bob.balance, 1 ether);
+        // Create a private key and derive the address
+        uint256 alicePrivateKey = 0xA11CE;
+        address derivedAliceAddress = vm.addr(alicePrivateKey);
+
+        // Replace alice with the derived address
+        alice = payable(derivedAliceAddress);
+        vm.deal(alice, 2 ether); // Fund the correct address
+
+        // Get the current nonce
+        uint256 nonce = sponsor.nonces(alice);
+
+        // Create signature digest using EIP-712
+        bytes32 digest = keccak256(
+            abi.encodePacked(
+                "\x19\x01",
+                sponsor.DOMAIN_SEPARATOR(),
+                keccak256(abi.encode(sponsor.SPONSORED_TRANSFER_TYPEHASH(), alice, bob, 1 ether, nonce))
+            )
+        );
+
+        // Sign the message
+        (uint8 v, bytes32 r, bytes32 s) = vm.sign(alicePrivateKey, digest);
+
+        // Execute the sponsored transfer
+        sponsor.sponsoredTransfer{ value: 1 ether }(alice, bob, 1 ether, nonce, v, r, s);
+
+        // Verify Bob received the ether
+        assertEq(bob.balance, 1 ether, "Bob should have received 1 ether");
     }
 }
diff --git a/test/SponsoredTransferTest.t.sol b/test/SponsoredTransferTest.t.sol
index c681c69..9a90723 100644
--- a/test/SponsoredTransferTest.t.sol
+++ b/test/SponsoredTransferTest.t.sol
@@ -5,9 +5,12 @@ import "forge-std/src/Test.sol";
 import "../src/Sponsor.sol";
 import "../src/EIP7702Demonstrator.sol";
 
-/// @title Sponsored Transfer Test
-/// @notice Tests EIP-7702 functionality with gas sponsorship
-/// @dev Shows how EOAs can execute transactions through a sponsor without paying gas
+/**
+ * @title SponsoredTransferTest
+ * @notice Tests EIP-7702 functionality with gas sponsorship
+ * @dev Demonstrates how EOAs can execute transactions through delegation without paying gas
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract SponsoredTransferTest is Test {
     Sponsor public sponsor;
     EIP7702Demonstrator public demonstrator;
@@ -16,6 +19,11 @@ contract SponsoredTransferTest is Test {
     address payable public relayer;
     uint256 public aliceKey;
 
+    /**
+     * @notice Set up the test environment
+     * @dev Deploys contracts and sets up test accounts
+     * @custom:requirement Requires Prague EVM version to support EIP-7702
+     */
     function setUp() public {
         // Check EVM version
         string memory evmVersion = vm.envOr("FOUNDRY_PROFILE", string("default"));
@@ -39,7 +47,14 @@ contract SponsoredTransferTest is Test {
         vm.deal(relayer, 1 ether);
     }
 
-    /// @notice Test a sponsored transfer using EIP-7702
+    /**
+     * @notice Test a sponsored transfer using EIP-7702 delegation
+     * @dev Demonstrates complete EIP-7702 workflow:
+     *      1. Setting delegation code on an EOA
+     *      2. Creating a valid EIP-712 signature
+     *      3. Executing a transaction through the delegated code
+     *      4. Verifying correct balance changes
+     */
     function testSponsoredTransfer() public {
         // Initial balances
         uint256 aliceBalanceBefore = alice.balance;
@@ -52,11 +67,35 @@ contract SponsoredTransferTest is Test {
         // Track gas usage
         uint256 gasBefore = gasleft();
 
+        // Get the current nonce
+        uint256 nonce = sponsor.nonces(alice);
+
+        // Create signature for EIP-712
+        bytes32 digest = keccak256(
+            abi.encodePacked(
+                "\x19\x01",
+                sponsor.DOMAIN_SEPARATOR(),
+                keccak256(abi.encode(sponsor.SPONSORED_TRANSFER_TYPEHASH(), alice, bob, 1 ether, nonce))
+            )
+        );
+
+        (uint8 v, bytes32 r, bytes32 s) = vm.sign(aliceKey, digest);
+
         // Create the call data for the sponsored transfer
-        bytes memory callData = abi.encodeWithSelector(Sponsor.sponsoredTransfer.selector, bob);
+        bytes memory callData = abi.encodeWithSelector(
+            Sponsor.sponsoredTransfer.selector,
+            alice,
+            bob,
+            1 ether,
+            nonce,
+            v,
+            r, // signature r
+            s // signature s
+        );
 
         // Execute as Alice but with relayer paying gas
         vm.prank(alice);
+
         // Call directly to Alice's account which should delegate to sponsor via EIP-7702
         (bool success,) = address(alice).call{ value: 1 ether }(callData);
         require(success, "Call failed");
@@ -76,12 +115,15 @@ contract SponsoredTransferTest is Test {
         console2.log("Recipient (Bob) balance change:", bob.balance - bobBalanceBefore);
     }
 
-    /// @notice Test behavior in Shanghai (should fail)
+    /**
+     * @notice Test behavior in Shanghai (should fail)
+     * @dev Verifies that EIP-7702 functionality is not available in pre-Prague EVM versions
+     */
     function testNoCodeInShanghai() public {
         string memory evmVersion = vm.envOr("FOUNDRY_PROFILE", string("default"));
         if (keccak256(bytes(evmVersion)) == keccak256(bytes("shanghai"))) {
-            bytes memory code = abi.encodePacked(hex"ef0100", address(sponsor));
-            vm.etch(alice, code);
+            bytes memory delegationCode = abi.encodePacked(hex"ef0100", address(sponsor));
+            vm.etch(alice, delegationCode);
             vm.expectRevert();
             (bool success,) = alice.call{ value: 1 ether }("");
             success; // Silence unused variable warning


Reviews:
user: login: pochenai
body: sick, LGTM!
state: APPROVED
author_association: COLLABORATOR
submitted_at: 2025-03-18T10:47:22Z
user: login: pochenai
state: COMMENTED
author_association: COLLABORATOR
submitted_at: 2025-03-18T11:00:47Z
user: login: julienbrg
state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-03-18T13:49:45Z
user: login: julienbrg
state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-03-18T13:52:29Z
user: login: julienbrg
state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-03-18T14:05:34Z
user: login: julienbrg
state: COMMENTED
author_association: CONTRIBUTOR
submitted_at: 2025-03-18T18:53:28Z

Review comments:
diff_hunk: @@ -1,41 +1,125 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title Sponsor Contract for EIP-7702 Demonstration
-/// @notice Demonstrates gas sponsorship capabilities using EIP-7702
-/// @dev This contract acts as the delegate for EOAs, enabling sponsored transactions
+/**
+ * @title Sponsor
+ * @notice Demonstration contract for gas sponsorship capabilities using EIP-7702
+ * @dev Implements EIP-712 for secure signature validation and execution delegation
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract Sponsor {
-    /// @notice Thrown when the transfer of ETH fails
+    /**
+     * @notice Thrown when ETH transfer to recipient fails
+     * @dev May occur if recipient contract has a failing fallback function
+     */
     error TransferFailed();
 
-    /// @notice Records of gas spent by relayers
+    /**
+     * @notice Thrown when signature validation fails
+     * @dev May occur if signature is invalid or was not signed by the claimed sender
+     */
+    error InvalidSignature();
+
+    /**
+     * @notice Thrown when a nonce is reused (replay protection)
+     * @dev Ensures each authorization can only be used once
+     */
+    error NonceAlreadyUsed();
+
+    /**
+     * @notice Tracks gas spent by each sender when using sponsored transactions
+     * @dev Can be used for accounting or limiting sponsored gas usage
+     */
     mapping(address => uint256) public gasSpent;
 
-    /// @notice Emitted when a sponsored transfer is completed
-    /// @param sender The original sender (EOA)
-    /// @param recipient The recipient of the transfer
-    /// @param amount The amount transferred
-    /// @param gasUsed The amount of gas used
+    /**
+     * @notice Tracks the next valid nonce for each sender
+     * @dev Used to prevent replay attacks through the incrementing nonce pattern
+     */
+    mapping(address => uint256) public nonces;
+
+    /**
+     * @notice Emitted when a sponsored transfer is successfully executed
+     * @param sender The original sender (EOA) who authorized the transfer
+     * @param recipient The recipient who received the funds
+     * @param amount The amount of ETH transferred
+     * @param gasUsed The amount of gas consumed by the transaction
+     */
     event SponsoredTransfer(address indexed sender, address indexed recipient, uint256 amount, uint256 gasUsed);
 
-    /// @notice Execute a transfer on behalf of msg.sender and records gas usage
-    /// @param recipient The address to receive the ETH
-    /// @dev When called through EIP-7702, msg.sender will be the EOA
-    function sponsoredTransfer(address payable recipient) external payable {
+    /// @notice Type hash for EIP-712 signature of sponsored transfers
+    bytes32 public constant SPONSORED_TRANSFER_TYPEHASH =
+        keccak256("SponsoredTransfer(address sender,address recipient,uint256 amount,uint256 nonce)");
+
+    /// @notice Domain separator for EIP-712 signatures
+    bytes32 public immutable DOMAIN_SEPARATOR;
+
+    /**
+     * @notice Initializes the sponsor contract
+     * @dev Sets up the EIP-712 domain separator based on contract address and chain
+     */
+    constructor() {
+        DOMAIN_SEPARATOR = keccak256(
+            abi.encode(
+                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
+                keccak256(bytes("Sponsor")),
+                keccak256(bytes("1")),
+                block.chainid,
+                address(this)
+            )
+        );
+    }
+
+    /**
+     * @notice Execute a transfer on behalf of a user who provided a valid signature
+     * @dev Verifies EIP-712 signature, transfers ETH, and records gas usage
+     * @param sender The address that authorized the transfer
+     * @param recipient The address to receive the ETH
+     * @param amount The amount of ETH to transfer
+     * @param nonce The unique nonce to prevent replay attacks
+     * @param v Recovery byte of the sender's signature
+     * @param r First 32 bytes of the sender's signature
+     * @param s Second 32 bytes of the sender's signature
+     */
+    function sponsoredTransfer(
+        address sender,
+        address payable recipient,
+        uint256 amount,
+        uint256 nonce,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    )
+        external
+        payable
+    {
+        // Ensure nonce is not reused
+        if (nonce != nonces[sender]++) revert NonceAlreadyUsed();
path: src/Sponsor.sol
user: login: pochenai
body: Actually, the nonce used here has an additional function to prevent reentrancy.
created_at: 2025-03-18T10:41:52Z
author_association: COLLABORATOR
diff_hunk: @@ -1,41 +1,125 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title Sponsor Contract for EIP-7702 Demonstration
-/// @notice Demonstrates gas sponsorship capabilities using EIP-7702
-/// @dev This contract acts as the delegate for EOAs, enabling sponsored transactions
+/**
+ * @title Sponsor
+ * @notice Demonstration contract for gas sponsorship capabilities using EIP-7702
+ * @dev Implements EIP-712 for secure signature validation and execution delegation
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract Sponsor {
-    /// @notice Thrown when the transfer of ETH fails
+    /**
+     * @notice Thrown when ETH transfer to recipient fails
+     * @dev May occur if recipient contract has a failing fallback function
+     */
     error TransferFailed();
 
-    /// @notice Records of gas spent by relayers
+    /**
+     * @notice Thrown when signature validation fails
+     * @dev May occur if signature is invalid or was not signed by the claimed sender
+     */
+    error InvalidSignature();
+
+    /**
+     * @notice Thrown when a nonce is reused (replay protection)
+     * @dev Ensures each authorization can only be used once
+     */
+    error NonceAlreadyUsed();
+
+    /**
+     * @notice Tracks gas spent by each sender when using sponsored transactions
+     * @dev Can be used for accounting or limiting sponsored gas usage
+     */
     mapping(address => uint256) public gasSpent;
path: src/Sponsor.sol
user: login: pochenai
body: It would be even better if the [7201 namespaced storage layout](https://docs.openzeppelin.com/upgrades-plugins/writing-upgradeable#namespaced-storage-layout) were used to prevent storage slot collisions.
created_at: 2025-03-18T10:46:29Z
author_association: COLLABORATOR
diff_hunk: @@ -1,41 +1,125 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title Sponsor Contract for EIP-7702 Demonstration
-/// @notice Demonstrates gas sponsorship capabilities using EIP-7702
-/// @dev This contract acts as the delegate for EOAs, enabling sponsored transactions
+/**
+ * @title Sponsor
+ * @notice Demonstration contract for gas sponsorship capabilities using EIP-7702
+ * @dev Implements EIP-712 for secure signature validation and execution delegation
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract Sponsor {
-    /// @notice Thrown when the transfer of ETH fails
+    /**
+     * @notice Thrown when ETH transfer to recipient fails
+     * @dev May occur if recipient contract has a failing fallback function
+     */
     error TransferFailed();
 
-    /// @notice Records of gas spent by relayers
+    /**
+     * @notice Thrown when signature validation fails
+     * @dev May occur if signature is invalid or was not signed by the claimed sender
+     */
+    error InvalidSignature();
+
+    /**
+     * @notice Thrown when a nonce is reused (replay protection)
+     * @dev Ensures each authorization can only be used once
+     */
+    error NonceAlreadyUsed();
+
+    /**
+     * @notice Tracks gas spent by each sender when using sponsored transactions
+     * @dev Can be used for accounting or limiting sponsored gas usage
+     */
     mapping(address => uint256) public gasSpent;
 
-    /// @notice Emitted when a sponsored transfer is completed
-    /// @param sender The original sender (EOA)
-    /// @param recipient The recipient of the transfer
-    /// @param amount The amount transferred
-    /// @param gasUsed The amount of gas used
+    /**
+     * @notice Tracks the next valid nonce for each sender
+     * @dev Used to prevent replay attacks through the incrementing nonce pattern
+     */
+    mapping(address => uint256) public nonces;
+
+    /**
+     * @notice Emitted when a sponsored transfer is successfully executed
+     * @param sender The original sender (EOA) who authorized the transfer
+     * @param recipient The recipient who received the funds
+     * @param amount The amount of ETH transferred
+     * @param gasUsed The amount of gas consumed by the transaction
+     */
     event SponsoredTransfer(address indexed sender, address indexed recipient, uint256 amount, uint256 gasUsed);
 
-    /// @notice Execute a transfer on behalf of msg.sender and records gas usage
-    /// @param recipient The address to receive the ETH
-    /// @dev When called through EIP-7702, msg.sender will be the EOA
-    function sponsoredTransfer(address payable recipient) external payable {
+    /// @notice Type hash for EIP-712 signature of sponsored transfers
+    bytes32 public constant SPONSORED_TRANSFER_TYPEHASH =
+        keccak256("SponsoredTransfer(address sender,address recipient,uint256 amount,uint256 nonce)");
+
+    /// @notice Domain separator for EIP-712 signatures
+    bytes32 public immutable DOMAIN_SEPARATOR;
+
+    /**
+     * @notice Initializes the sponsor contract
+     * @dev Sets up the EIP-712 domain separator based on contract address and chain
+     */
+    constructor() {
+        DOMAIN_SEPARATOR = keccak256(
+            abi.encode(
+                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
+                keccak256(bytes("Sponsor")),
+                keccak256(bytes("1")),
+                block.chainid,
+                address(this)
+            )
+        );
+    }
+
+    /**
+     * @notice Execute a transfer on behalf of a user who provided a valid signature
+     * @dev Verifies EIP-712 signature, transfers ETH, and records gas usage
+     * @param sender The address that authorized the transfer
+     * @param recipient The address to receive the ETH
+     * @param amount The amount of ETH to transfer
+     * @param nonce The unique nonce to prevent replay attacks
+     * @param v Recovery byte of the sender's signature
+     * @param r First 32 bytes of the sender's signature
+     * @param s Second 32 bytes of the sender's signature
+     */
+    function sponsoredTransfer(
+        address sender,
+        address payable recipient,
+        uint256 amount,
+        uint256 nonce,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    )
+        external
+        payable
+    {
+        // Ensure nonce is not reused
+        if (nonce != nonces[sender]++) revert NonceAlreadyUsed();
+
+        // Compute expected message hash
+        bytes32 digest = keccak256(
+            abi.encodePacked(
+                "\x19\x01",
+                DOMAIN_SEPARATOR,
+                keccak256(abi.encode(SPONSORED_TRANSFER_TYPEHASH, sender, recipient, amount, nonce))
+            )
+        );
+
+        // Recover signer from signature
+        address recovered = ecrecover(digest, v, r, s);
+        if (recovered == address(0) || recovered != sender) revert InvalidSignature();
path: src/Sponsor.sol
user: login: pochenai
body: It should be `recovered != address(this)`, because the `receipt.call{ value: amount }("")` will spend ETH from the EOA contract address, not the sender.
created_at: 2025-03-18T11:00:46Z
author_association: COLLABORATOR
diff_hunk: @@ -1,41 +1,125 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title Sponsor Contract for EIP-7702 Demonstration
-/// @notice Demonstrates gas sponsorship capabilities using EIP-7702
-/// @dev This contract acts as the delegate for EOAs, enabling sponsored transactions
+/**
+ * @title Sponsor
+ * @notice Demonstration contract for gas sponsorship capabilities using EIP-7702
+ * @dev Implements EIP-712 for secure signature validation and execution delegation
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract Sponsor {
-    /// @notice Thrown when the transfer of ETH fails
+    /**
+     * @notice Thrown when ETH transfer to recipient fails
+     * @dev May occur if recipient contract has a failing fallback function
+     */
     error TransferFailed();
 
-    /// @notice Records of gas spent by relayers
+    /**
+     * @notice Thrown when signature validation fails
+     * @dev May occur if signature is invalid or was not signed by the claimed sender
+     */
+    error InvalidSignature();
+
+    /**
+     * @notice Thrown when a nonce is reused (replay protection)
+     * @dev Ensures each authorization can only be used once
+     */
+    error NonceAlreadyUsed();
+
+    /**
+     * @notice Tracks gas spent by each sender when using sponsored transactions
+     * @dev Can be used for accounting or limiting sponsored gas usage
+     */
     mapping(address => uint256) public gasSpent;
 
-    /// @notice Emitted when a sponsored transfer is completed
-    /// @param sender The original sender (EOA)
-    /// @param recipient The recipient of the transfer
-    /// @param amount The amount transferred
-    /// @param gasUsed The amount of gas used
+    /**
+     * @notice Tracks the next valid nonce for each sender
+     * @dev Used to prevent replay attacks through the incrementing nonce pattern
+     */
+    mapping(address => uint256) public nonces;
+
+    /**
+     * @notice Emitted when a sponsored transfer is successfully executed
+     * @param sender The original sender (EOA) who authorized the transfer
+     * @param recipient The recipient who received the funds
+     * @param amount The amount of ETH transferred
+     * @param gasUsed The amount of gas consumed by the transaction
+     */
     event SponsoredTransfer(address indexed sender, address indexed recipient, uint256 amount, uint256 gasUsed);
 
-    /// @notice Execute a transfer on behalf of msg.sender and records gas usage
-    /// @param recipient The address to receive the ETH
-    /// @dev When called through EIP-7702, msg.sender will be the EOA
-    function sponsoredTransfer(address payable recipient) external payable {
+    /// @notice Type hash for EIP-712 signature of sponsored transfers
+    bytes32 public constant SPONSORED_TRANSFER_TYPEHASH =
+        keccak256("SponsoredTransfer(address sender,address recipient,uint256 amount,uint256 nonce)");
+
+    /// @notice Domain separator for EIP-712 signatures
+    bytes32 public immutable DOMAIN_SEPARATOR;
+
+    /**
+     * @notice Initializes the sponsor contract
+     * @dev Sets up the EIP-712 domain separator based on contract address and chain
+     */
+    constructor() {
+        DOMAIN_SEPARATOR = keccak256(
+            abi.encode(
+                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
+                keccak256(bytes("Sponsor")),
+                keccak256(bytes("1")),
+                block.chainid,
+                address(this)
+            )
+        );
+    }
+
+    /**
+     * @notice Execute a transfer on behalf of a user who provided a valid signature
+     * @dev Verifies EIP-712 signature, transfers ETH, and records gas usage
+     * @param sender The address that authorized the transfer
+     * @param recipient The address to receive the ETH
+     * @param amount The amount of ETH to transfer
+     * @param nonce The unique nonce to prevent replay attacks
+     * @param v Recovery byte of the sender's signature
+     * @param r First 32 bytes of the sender's signature
+     * @param s Second 32 bytes of the sender's signature
+     */
+    function sponsoredTransfer(
+        address sender,
+        address payable recipient,
+        uint256 amount,
+        uint256 nonce,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    )
+        external
+        payable
+    {
+        // Ensure nonce is not reused
+        if (nonce != nonces[sender]++) revert NonceAlreadyUsed();
+
+        // Compute expected message hash
+        bytes32 digest = keccak256(
+            abi.encodePacked(
+                "\x19\x01",
+                DOMAIN_SEPARATOR,
+                keccak256(abi.encode(SPONSORED_TRANSFER_TYPEHASH, sender, recipient, amount, nonce))
+            )
+        );
+
+        // Recover signer from signature
+        address recovered = ecrecover(digest, v, r, s);
+        if (recovered == address(0) || recovered != sender) revert InvalidSignature();
path: src/Sponsor.sol
user: login: julienbrg
body: Makes sense. Fixed here: https://github.com/w3hc/eip7702-playground/pull/4/commits/9730e0cc348f6b9b42b29150132cb396a89a65e6
created_at: 2025-03-18T13:49:45Z
author_association: CONTRIBUTOR
diff_hunk: @@ -1,41 +1,125 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title Sponsor Contract for EIP-7702 Demonstration
-/// @notice Demonstrates gas sponsorship capabilities using EIP-7702
-/// @dev This contract acts as the delegate for EOAs, enabling sponsored transactions
+/**
+ * @title Sponsor
+ * @notice Demonstration contract for gas sponsorship capabilities using EIP-7702
+ * @dev Implements EIP-712 for secure signature validation and execution delegation
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract Sponsor {
-    /// @notice Thrown when the transfer of ETH fails
+    /**
+     * @notice Thrown when ETH transfer to recipient fails
+     * @dev May occur if recipient contract has a failing fallback function
+     */
     error TransferFailed();
 
-    /// @notice Records of gas spent by relayers
+    /**
+     * @notice Thrown when signature validation fails
+     * @dev May occur if signature is invalid or was not signed by the claimed sender
+     */
+    error InvalidSignature();
+
+    /**
+     * @notice Thrown when a nonce is reused (replay protection)
+     * @dev Ensures each authorization can only be used once
+     */
+    error NonceAlreadyUsed();
+
+    /**
+     * @notice Tracks gas spent by each sender when using sponsored transactions
+     * @dev Can be used for accounting or limiting sponsored gas usage
+     */
     mapping(address => uint256) public gasSpent;
path: src/Sponsor.sol
user: login: julienbrg
body: 7201 namespaced storage layout will indeed prevent storage slot collisions: https://github.com/w3hc/eip7702-playground/pull/4/commits/ac87abc59a66449e8547efc05fd5dbadfbcaa570 
created_at: 2025-03-18T13:52:29Z
author_association: CONTRIBUTOR
diff_hunk: @@ -1,41 +1,125 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title Sponsor Contract for EIP-7702 Demonstration
-/// @notice Demonstrates gas sponsorship capabilities using EIP-7702
-/// @dev This contract acts as the delegate for EOAs, enabling sponsored transactions
+/**
+ * @title Sponsor
+ * @notice Demonstration contract for gas sponsorship capabilities using EIP-7702
+ * @dev Implements EIP-712 for secure signature validation and execution delegation
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract Sponsor {
-    /// @notice Thrown when the transfer of ETH fails
+    /**
+     * @notice Thrown when ETH transfer to recipient fails
+     * @dev May occur if recipient contract has a failing fallback function
+     */
     error TransferFailed();
 
-    /// @notice Records of gas spent by relayers
+    /**
+     * @notice Thrown when signature validation fails
+     * @dev May occur if signature is invalid or was not signed by the claimed sender
+     */
+    error InvalidSignature();
+
+    /**
+     * @notice Thrown when a nonce is reused (replay protection)
+     * @dev Ensures each authorization can only be used once
+     */
+    error NonceAlreadyUsed();
+
+    /**
+     * @notice Tracks gas spent by each sender when using sponsored transactions
+     * @dev Can be used for accounting or limiting sponsored gas usage
+     */
     mapping(address => uint256) public gasSpent;
 
-    /// @notice Emitted when a sponsored transfer is completed
-    /// @param sender The original sender (EOA)
-    /// @param recipient The recipient of the transfer
-    /// @param amount The amount transferred
-    /// @param gasUsed The amount of gas used
+    /**
+     * @notice Tracks the next valid nonce for each sender
+     * @dev Used to prevent replay attacks through the incrementing nonce pattern
+     */
+    mapping(address => uint256) public nonces;
+
+    /**
+     * @notice Emitted when a sponsored transfer is successfully executed
+     * @param sender The original sender (EOA) who authorized the transfer
+     * @param recipient The recipient who received the funds
+     * @param amount The amount of ETH transferred
+     * @param gasUsed The amount of gas consumed by the transaction
+     */
     event SponsoredTransfer(address indexed sender, address indexed recipient, uint256 amount, uint256 gasUsed);
 
-    /// @notice Execute a transfer on behalf of msg.sender and records gas usage
-    /// @param recipient The address to receive the ETH
-    /// @dev When called through EIP-7702, msg.sender will be the EOA
-    function sponsoredTransfer(address payable recipient) external payable {
+    /// @notice Type hash for EIP-712 signature of sponsored transfers
+    bytes32 public constant SPONSORED_TRANSFER_TYPEHASH =
+        keccak256("SponsoredTransfer(address sender,address recipient,uint256 amount,uint256 nonce)");
+
+    /// @notice Domain separator for EIP-712 signatures
+    bytes32 public immutable DOMAIN_SEPARATOR;
+
+    /**
+     * @notice Initializes the sponsor contract
+     * @dev Sets up the EIP-712 domain separator based on contract address and chain
+     */
+    constructor() {
+        DOMAIN_SEPARATOR = keccak256(
+            abi.encode(
+                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
+                keccak256(bytes("Sponsor")),
+                keccak256(bytes("1")),
+                block.chainid,
+                address(this)
+            )
+        );
+    }
+
+    /**
+     * @notice Execute a transfer on behalf of a user who provided a valid signature
+     * @dev Verifies EIP-712 signature, transfers ETH, and records gas usage
+     * @param sender The address that authorized the transfer
+     * @param recipient The address to receive the ETH
+     * @param amount The amount of ETH to transfer
+     * @param nonce The unique nonce to prevent replay attacks
+     * @param v Recovery byte of the sender's signature
+     * @param r First 32 bytes of the sender's signature
+     * @param s Second 32 bytes of the sender's signature
+     */
+    function sponsoredTransfer(
+        address sender,
+        address payable recipient,
+        uint256 amount,
+        uint256 nonce,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    )
+        external
+        payable
+    {
+        // Ensure nonce is not reused
+        if (nonce != nonces[sender]++) revert NonceAlreadyUsed();
path: src/Sponsor.sol
user: login: julienbrg
body: @dajuguan Yes, and maybe the use of OZ [Nonce.sol](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/Nonces.sol) or [EIP712.sol](https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/utils/cryptography/EIP712.sol) would make it more secure and readable.
created_at: 2025-03-18T14:05:33Z
author_association: CONTRIBUTOR
diff_hunk: @@ -1,41 +1,125 @@
 // SPDX-License-Identifier: MIT
 pragma solidity ^0.8.28;
 
-/// @title Sponsor Contract for EIP-7702 Demonstration
-/// @notice Demonstrates gas sponsorship capabilities using EIP-7702
-/// @dev This contract acts as the delegate for EOAs, enabling sponsored transactions
+/**
+ * @title Sponsor
+ * @notice Demonstration contract for gas sponsorship capabilities using EIP-7702
+ * @dev Implements EIP-712 for secure signature validation and execution delegation
+ * @custom:eip EIP-7702 (EOA Code Setting), EIP-712 (Typed structured data hashing and signing)
+ */
 contract Sponsor {
-    /// @notice Thrown when the transfer of ETH fails
+    /**
+     * @notice Thrown when ETH transfer to recipient fails
+     * @dev May occur if recipient contract has a failing fallback function
+     */
     error TransferFailed();
 
-    /// @notice Records of gas spent by relayers
+    /**
+     * @notice Thrown when signature validation fails
+     * @dev May occur if signature is invalid or was not signed by the claimed sender
+     */
+    error InvalidSignature();
+
+    /**
+     * @notice Thrown when a nonce is reused (replay protection)
+     * @dev Ensures each authorization can only be used once
+     */
+    error NonceAlreadyUsed();
+
+    /**
+     * @notice Tracks gas spent by each sender when using sponsored transactions
+     * @dev Can be used for accounting or limiting sponsored gas usage
+     */
     mapping(address => uint256) public gasSpent;
 
-    /// @notice Emitted when a sponsored transfer is completed
-    /// @param sender The original sender (EOA)
-    /// @param recipient The recipient of the transfer
-    /// @param amount The amount transferred
-    /// @param gasUsed The amount of gas used
+    /**
+     * @notice Tracks the next valid nonce for each sender
+     * @dev Used to prevent replay attacks through the incrementing nonce pattern
+     */
+    mapping(address => uint256) public nonces;
+
+    /**
+     * @notice Emitted when a sponsored transfer is successfully executed
+     * @param sender The original sender (EOA) who authorized the transfer
+     * @param recipient The recipient who received the funds
+     * @param amount The amount of ETH transferred
+     * @param gasUsed The amount of gas consumed by the transaction
+     */
     event SponsoredTransfer(address indexed sender, address indexed recipient, uint256 amount, uint256 gasUsed);
 
-    /// @notice Execute a transfer on behalf of msg.sender and records gas usage
-    /// @param recipient The address to receive the ETH
-    /// @dev When called through EIP-7702, msg.sender will be the EOA
-    function sponsoredTransfer(address payable recipient) external payable {
+    /// @notice Type hash for EIP-712 signature of sponsored transfers
+    bytes32 public constant SPONSORED_TRANSFER_TYPEHASH =
+        keccak256("SponsoredTransfer(address sender,address recipient,uint256 amount,uint256 nonce)");
+
+    /// @notice Domain separator for EIP-712 signatures
+    bytes32 public immutable DOMAIN_SEPARATOR;
+
+    /**
+     * @notice Initializes the sponsor contract
+     * @dev Sets up the EIP-712 domain separator based on contract address and chain
+     */
+    constructor() {
+        DOMAIN_SEPARATOR = keccak256(
+            abi.encode(
+                keccak256("EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"),
+                keccak256(bytes("Sponsor")),
+                keccak256(bytes("1")),
+                block.chainid,
+                address(this)
+            )
+        );
+    }
+
+    /**
+     * @notice Execute a transfer on behalf of a user who provided a valid signature
+     * @dev Verifies EIP-712 signature, transfers ETH, and records gas usage
+     * @param sender The address that authorized the transfer
+     * @param recipient The address to receive the ETH
+     * @param amount The amount of ETH to transfer
+     * @param nonce The unique nonce to prevent replay attacks
+     * @param v Recovery byte of the sender's signature
+     * @param r First 32 bytes of the sender's signature
+     * @param s Second 32 bytes of the sender's signature
+     */
+    function sponsoredTransfer(
+        address sender,
+        address payable recipient,
+        uint256 amount,
+        uint256 nonce,
+        uint8 v,
+        bytes32 r,
+        bytes32 s
+    )
+        external
+        payable
+    {
+        // Ensure nonce is not reused
+        if (nonce != nonces[sender]++) revert NonceAlreadyUsed();
+
+        // Compute expected message hash
+        bytes32 digest = keccak256(
+            abi.encodePacked(
+                "\x19\x01",
+                DOMAIN_SEPARATOR,
+                keccak256(abi.encode(SPONSORED_TRANSFER_TYPEHASH, sender, recipient, amount, nonce))
+            )
+        );
+
+        // Recover signer from signature
+        address recovered = ecrecover(digest, v, r, s);
+        if (recovered == address(0) || recovered != sender) revert InvalidSignature();
path: src/Sponsor.sol
user: login: julienbrg
body: @dajuguan There's something I don't get here. What we want is to make sure that: 

- Recovered address is not the zero address 
- Recovered address is the sender

So the contract is indeed moving funds from the sender to the recipient, not from the contract to the recipient. So this was correct: 

```solidity
address recovered = ecrecover(digest, v, r, s);
if (recovered == address(0) || recovered != sender) revert InvalidSignature();
```

Or did I miss anything?
created_at: 2025-03-18T18:53:28Z
author_association: CONTRIBUTOR

PR comments:
user: login: openzeppelin-code[bot]
created_at: 2025-03-18T09:53:10Z
body: # Add EIP-712 signature verification in `sponsoredTransfer`
> Generated at commit: [ac87abc59a66449e8547efc05fd5dbadfbcaa570](https://github.com/w3hc/eip7702-playground/pull/4/commits/ac87abc59a66449e8547efc05fd5dbadfbcaa570)
### 🚨 Report Summary
| | Severity Level | Results |
|:-|:-|:-:|
| **Contracts** | _Critical_ </br> _High_ </br> _Medium_ </br> _Low_ </br> _Note_ </br> **Total** | 0 </br> 0 </br> 0 </br> 2 </br> 8 </br> 10 |
| **Dependencies** | _Critical_ </br> _High_ </br> _Medium_ </br> _Low_ </br> _Note_ </br> **Total** | 0 </br> 0 </br> 0 </br> 0 </br> 0 </br> 0 |
---
<strong>For more details view the full report in [OpenZeppelin Code Inspector](https://defender.openzeppelin.com/v2/#/code/report-details/130a0708-628e-4381-995f-b35eb2e54d18)</strong>
author_association: NONE
user: login: julienbrg
created_at: 2025-03-18T14:05:41Z
body: @dajuguan Thank you so much for the review! 
author_association: CONTRIBUTOR