From 0de447cd56c4eb2bb1a2a9a3af6ebc4883cf3177 Mon Sep 17 00:00:00 2001
From: Daniel Wang <dan@taiko.xyz>
Date: Mon, 22 Apr 2024 14:13:45 +0800
Subject: [PATCH 01/11] Delete ERC20 token adaptor

---
 .../contracts/tokenvault/BridgedERC20.sol     | 12 +--
 .../contracts/tokenvault/BridgedERC20Base.sol |  8 +-
 .../tokenvault/adapters/USDCAdapter.sol       | 55 ------------
 .../protocol/script/DeployUSDCAdapter.s.sol   | 83 -------------------
 4 files changed, 6 insertions(+), 152 deletions(-)
 delete mode 100644 packages/protocol/contracts/tokenvault/adapters/USDCAdapter.sol
 delete mode 100644 packages/protocol/script/DeployUSDCAdapter.s.sol

diff --git a/packages/protocol/contracts/tokenvault/BridgedERC20.sol b/packages/protocol/contracts/tokenvault/BridgedERC20.sol
index 10c15e1b960..65e9630c25f 100644
--- a/packages/protocol/contracts/tokenvault/BridgedERC20.sol
+++ b/packages/protocol/contracts/tokenvault/BridgedERC20.sol
@@ -145,14 +145,6 @@ contract BridgedERC20 is
         return (srcToken, srcChainId);
     }
 
-    function _mintToken(address _account, uint256 _amount) internal override {
-        return _mint(_account, _amount);
-    }
-
-    function _burnToken(address _from, uint256 _amount) internal override {
-        return _burn(_from, _amount);
-    }
-
     /// @dev For ERC20SnapshotUpgradeable and ERC20VotesUpgradeable, need to implement the following
     /// functions
     function _beforeTokenTransfer(
@@ -184,7 +176,7 @@ contract BridgedERC20 is
         uint256 _amount
     )
         internal
-        override(ERC20Upgradeable, ERC20VotesUpgradeable)
+        override(ERC20Upgradeable, ERC20VotesUpgradeable, BridgedERC20Base)
     {
         return super._mint(_to, _amount);
     }
@@ -194,7 +186,7 @@ contract BridgedERC20 is
         uint256 _amount
     )
         internal
-        override(ERC20Upgradeable, ERC20VotesUpgradeable)
+        override(ERC20Upgradeable, ERC20VotesUpgradeable, BridgedERC20Base)
     {
         return super._burn(_from, _amount);
     }
diff --git a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
index df7b834dfd2..e6324a6cabb 100644
--- a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
+++ b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
@@ -68,7 +68,7 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
             revert BB_PERMISSION_DENIED();
         }
 
-        _mintToken(_account, _amount);
+        _mint(_account, _amount);
     }
 
     /// @notice Burns tokens from the specified account.
@@ -87,7 +87,7 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
             revert RESOLVER_DENIED();
         }
 
-        _burnToken(_account, _amount);
+        _burn(_account, _amount);
     }
 
     /// @notice Returns the owner.
@@ -96,9 +96,9 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
         return super.owner();
     }
 
-    function _mintToken(address _account, uint256 _amount) internal virtual;
+    function _mint(address _account, uint256 _amount) internal virtual;
 
-    function _burnToken(address _from, uint256 _amount) internal virtual;
+    function _burn(address _from, uint256 _amount) internal virtual;
 
     function _isMigratingOut() private view returns (bool) {
         return migratingAddress != address(0) && !migratingInbound;
diff --git a/packages/protocol/contracts/tokenvault/adapters/USDCAdapter.sol b/packages/protocol/contracts/tokenvault/adapters/USDCAdapter.sol
deleted file mode 100644
index 90726e700ea..00000000000
--- a/packages/protocol/contracts/tokenvault/adapters/USDCAdapter.sol
+++ /dev/null
@@ -1,55 +0,0 @@
-// SPDX-License-Identifier: MIT
-pragma solidity 0.8.24;
-
-import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
-import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
-import "../BridgedERC20Base.sol";
-
-/// @title IUSDC
-/// @custom:security-contact security@taiko.xyz
-interface IUSDC is IERC20 {
-    /// @notice Burns a specific amount of tokens.
-    /// @param _amount The amount of token to be burned.
-    function burn(uint256 _amount) external;
-
-    /// @notice Mints a specific amount of new tokens to an address.
-    /// @param _to The address that will receive the minted tokens.
-    /// @param _amount The amount of tokens to mint.
-    function mint(address _to, uint256 _amount) external;
-}
-
-/// @title USDCAdapter
-/// @custom:security-contact security@taiko.xyz
-contract USDCAdapter is BridgedERC20Base {
-    using SafeERC20 for IUSDC;
-
-    /// @notice The USDC instance.
-    /// @dev Slot 1.
-    IUSDC public usdc;
-    uint256[49] private __gap;
-
-    error INVALID_PARAM();
-
-    /// @notice Initializes the contract.
-    /// @param _owner The owner of this contract.
-    /// @param _addressManager The address of the {AddressManager} contract.
-    /// @param _usdc The USDC instance.
-    function init(address _owner, address _addressManager, IUSDC _usdc) external initializer {
-        if (address(_usdc) == address(0)) revert INVALID_PARAM();
-
-        __Essential_init(_owner, _addressManager);
-        usdc = _usdc;
-    }
-
-    function _mintToken(address _account, uint256 _amount) internal override {
-        usdc.mint(_account, _amount);
-    }
-
-    function _burnToken(address _from, uint256 _amount) internal override {
-        // We don't need to worry about
-        // https://github.com/crytic/slither/wiki/Detector-Documentation#arbitrary-from-in-transferfrom
-        // as switching from an old bridged token to a new one can only be performed by the owner.
-        usdc.safeTransferFrom(_from, address(this), _amount);
-        usdc.burn(_amount);
-    }
-}
diff --git a/packages/protocol/script/DeployUSDCAdapter.s.sol b/packages/protocol/script/DeployUSDCAdapter.s.sol
deleted file mode 100644
index 6dd53548f35..00000000000
--- a/packages/protocol/script/DeployUSDCAdapter.s.sol
+++ /dev/null
@@ -1,83 +0,0 @@
-// SPDX-License-Identifier: MIT
-pragma solidity 0.8.24;
-
-import "../contracts/tokenvault/adapters/USDCAdapter.sol";
-import "../contracts/tokenvault/ERC20Vault.sol";
-import "../test/DeployCapability.sol";
-
-/// @title DeployUSDCAdapter
-/// @notice This script deploys the adapter contract for USDC.
-contract DeployUSDCAdapter is DeployCapability {
-    address public usdcProxyL2 = vm.envAddress("NATIVE_USDC_PROXY_ON_L2");
-    address public usdcProxyL1 = vm.envAddress("NATIVE_USDC_PROXY_ON_L1");
-    address public l2SharedAddressManager = vm.envAddress("L2_SHARED_ADDRESS_MANAGER");
-    address public erc20Vault = vm.envAddress("ERC20_VAULT_ADDRESS");
-    address public erc20VaultOwner = vm.envAddress("ERC20_VAULT_OWNER");
-
-    uint256 public deployerPrivKey = vm.envUint("ADAPTOR_DEPLOYER_PRIVATE_KEY");
-    uint256 public masterMinterPrivKey = vm.envUint("MASTER_MINTER_PRIVATE_KEY");
-
-    uint256 public erc20VaultOwnerPrivKey = vm.envUint("ERC20_VAULT_OWNER_PRIVATE_KEY");
-
-    // Fixed, not changed. (From circle contracts)
-    // https://holesky.etherscan.io/tx/0xbfb68e7d92506498553e09ee22aba0adc23401108d508fc92f56da5e42ffc828
-    bytes4 public configureMinterSelector = 0x4e44d956;
-
-    error CANNOT_CONFIGURE_MINTER();
-    error CANNOT_CHANGE_BRIDGED_TOKEN();
-
-    function setUp() external { }
-
-    function run() external {
-        require(deployerPrivKey != 0, "invalid deplyoer priv key");
-        require(masterMinterPrivKey != 0, "invalid master minter priv key");
-        vm.startBroadcast(deployerPrivKey);
-        // Verify this contract after deployment (!)
-        address adapterProxy = deployProxy({
-            name: "usdc_adapter",
-            impl: address(new USDCAdapter()),
-            data: abi.encodeCall(
-                USDCAdapter.init, (address(0), l2SharedAddressManager, IUSDC(usdcProxyL2))
-                )
-        });
-
-        USDCAdapter(adapterProxy).transferOwnership(erc20VaultOwner);
-
-        vm.stopBroadcast();
-
-        // Grant the adapter the minter role by master minter
-        vm.startBroadcast(masterMinterPrivKey);
-        (bool success, bytes memory retVal) = address(usdcProxyL2).call(
-            abi.encodeWithSelector(configureMinterSelector, adapterProxy, type(uint256).max)
-        );
-
-        if (!success) {
-            console2.log("Error is:");
-            console2.logBytes(retVal);
-            revert CANNOT_CONFIGURE_MINTER();
-        }
-
-        vm.stopBroadcast();
-
-        vm.startBroadcast(erc20VaultOwnerPrivKey);
-        ERC20Vault.CanonicalERC20 memory canonicalToken = ERC20Vault.CanonicalERC20({
-            chainId: 17_000, // On mainnet, Ethereum chainID
-            addr: usdcProxyL1, // On mainnet, USDC contract address
-            decimals: 6,
-            symbol: "USDC",
-            name: "USD Coin"
-        });
-
-        (success, retVal) = erc20Vault.call(
-            abi.encodeCall(ERC20Vault.changeBridgedToken, (canonicalToken, adapterProxy))
-        );
-
-        if (!success) {
-            console2.log("Error is:");
-            console2.logBytes(retVal);
-            revert CANNOT_CHANGE_BRIDGED_TOKEN();
-        }
-
-        vm.stopBroadcast();
-    }
-}

From 724962df67ee8cebace793777f03116bfa940eb1 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Keszey=20D=C3=A1niel?= <keszeyd@MacBook-Pro.local>
Date: Mon, 22 Apr 2024 11:40:10 +0200
Subject: [PATCH 02/11] modify ERC20Vault to work with custom token burns

---
 .../protocol/contracts/common/LibStrings.sol  |  3 ++
 .../contracts/tokenvault/ERC20Vault.sol       | 47 ++++++++++++++++++-
 2 files changed, 49 insertions(+), 1 deletion(-)

diff --git a/packages/protocol/contracts/common/LibStrings.sol b/packages/protocol/contracts/common/LibStrings.sol
index 16a05bf8826..689f829721e 100644
--- a/packages/protocol/contracts/common/LibStrings.sol
+++ b/packages/protocol/contracts/common/LibStrings.sol
@@ -34,6 +34,9 @@ library LibStrings {
     /// @notice bytes32 representation of the string "bridged_erc20".
     bytes32 internal constant B_BRIDGED_ERC20 = bytes32("bridged_erc20");
 
+    /// @notice bytes32 representation of the string "bridged_native_usdc".
+    bytes32 internal constant B_BRIDGED_NATIVE_USDC = bytes32("bridged_native_usdc");
+
     /// @notice bytes32 representation of the string "erc1155_vault".
     bytes32 internal constant B_ERC1155_VAULT = bytes32("erc1155_vault");
 
diff --git a/packages/protocol/contracts/tokenvault/ERC20Vault.sol b/packages/protocol/contracts/tokenvault/ERC20Vault.sol
index 35579106c1e..2ac626932d0 100644
--- a/packages/protocol/contracts/tokenvault/ERC20Vault.sol
+++ b/packages/protocol/contracts/tokenvault/ERC20Vault.sol
@@ -5,6 +5,7 @@ import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
 import "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";
 import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
 import "../libs/LibAddress.sol";
+import "../common/LibStrings.sol";
 import "./BridgedERC20.sol";
 import "./BaseVault.sol";
 
@@ -133,9 +134,11 @@ contract ERC20Vault is BaseVault {
 
     error VAULT_BTOKEN_BLACKLISTED();
     error VAULT_CTOKEN_MISMATCH();
+    error VAULT_ERROR_IN_SPECIAL_OPS();
     error VAULT_INVALID_TOKEN();
     error VAULT_INVALID_AMOUNT();
     error VAULT_INVALID_NEW_BTOKEN();
+    error VAULT_NOT_POSSIBLE_SPECIAL_OPERATION();
     error VAULT_INVALID_TO();
     error VAULT_NOT_SAME_OWNER();
 
@@ -328,6 +331,8 @@ contract ERC20Vault is BaseVault {
             IERC20(token_).safeTransfer(_to, _amount);
         } else {
             token_ = _getOrDeployBridgedToken(_ctoken);
+            //For native bridged tokens (like USDC), the mint() signature is the same, so no need to
+            // check.
             IBridgedERC20(token_).mint(_to, _amount);
         }
     }
@@ -355,7 +360,17 @@ contract ERC20Vault is BaseVault {
         // If it's a bridged token
         if (bridgedToCanonical[_token].addr != address(0)) {
             ctoken_ = bridgedToCanonical[_token];
-            IBridgedERC20(_token).burn(msg.sender, _amount);
+
+            bytes[] memory encodedCalls = _getBurnLowLevelCalls(_token, _user, _amount);
+            if (encodedCalls.length != 0) {
+                for (uint256 i; i < encodedCalls.length; ++i) {
+                    (bool result,) = _token.call(encodedCalls[i]);
+
+                    if (!result) revert VAULT_ERROR_IN_SPECIAL_OPS();
+                }
+            } else {
+                IBridgedERC20(_token).burn(msg.sender, _amount);
+            }
             balanceChange_ = _amount;
         } else {
             // If it's a canonical token
@@ -429,4 +444,34 @@ contract ERC20Vault is BaseVault {
             ctokenDecimal: ctoken.decimals
         });
     }
+
+    /// @dev If a token requires specific (e.g.: native USDC) operations to be burnt, then return
+    /// the low level calls.
+    /// @param toBeBurnt Token to be burnt.
+    /// @param user User trying to bridge.
+    /// @param amount Token amount to be burnt.
+    /// @return encodedCalls Address of the bridged token contract.
+    function _getBurnLowLevelCalls(
+        address toBeBurnt,
+        address user,
+        uint256 amount
+    )
+        private
+        returns (bytes[] memory encodedCalls)
+    {
+        if (toBeBurnt == resolve(LibStrings.B_BRIDGED_NATIVE_USDC, true)) {
+            // If this is a native USDC, then we need to:
+            // 1.transfer tokens from user to ERC20Vault
+            // 2. burn (supposing ERC20Vault has minterRole)
+            encodedCalls = new bytes[](2);
+            // 1. transfer to ERC20Vault
+            encodedCalls[0] = abi.encodeWithSignature(
+                "transferFrom(address,address,uint)", user, address(this), amount
+            );
+            // 2. burn
+            encodedCalls[1] = abi.encodeWithSignature("burn(uint)", amount);
+        }
+        // In case we will support other native tokens, custom logic can go here..
+        //else if() {...}
+    }
 }

From 46033226da36cce3312ab69197d6041e8ab2add3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Keszey=20D=C3=A1niel?= <keszeyd@MacBook-Pro.local>
Date: Mon, 22 Apr 2024 11:41:10 +0200
Subject: [PATCH 03/11] fix resolve can return 0x0

---
 packages/protocol/contracts/tokenvault/ERC20Vault.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/protocol/contracts/tokenvault/ERC20Vault.sol b/packages/protocol/contracts/tokenvault/ERC20Vault.sol
index 2ac626932d0..77d9cac3ba1 100644
--- a/packages/protocol/contracts/tokenvault/ERC20Vault.sol
+++ b/packages/protocol/contracts/tokenvault/ERC20Vault.sol
@@ -459,7 +459,7 @@ contract ERC20Vault is BaseVault {
         private
         returns (bytes[] memory encodedCalls)
     {
-        if (toBeBurnt == resolve(LibStrings.B_BRIDGED_NATIVE_USDC, true)) {
+        if (toBeBurnt == resolve(LibStrings.B_BRIDGED_NATIVE_USDC, false)) {
             // If this is a native USDC, then we need to:
             // 1.transfer tokens from user to ERC20Vault
             // 2. burn (supposing ERC20Vault has minterRole)

From 4606c5f2c773196c052acba037e44619dfc1206c Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Keszey=20D=C3=A1niel?= <keszeyd@MacBook-Pro.local>
Date: Mon, 22 Apr 2024 13:38:25 +0200
Subject: [PATCH 04/11] change to transfer and mint pattern with BridgedERC20
 tokens

---
 .../contracts/tokenvault/BridgedERC20Base.sol | 16 +++++++
 .../contracts/tokenvault/ERC20Vault.sol       | 44 ++-----------------
 .../contracts/tokenvault/IBridgedERC20.sol    |  5 +++
 3 files changed, 25 insertions(+), 40 deletions(-)

diff --git a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
index e6324a6cabb..19792b00b27 100644
--- a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
+++ b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
@@ -29,6 +29,7 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
 
     error BB_PERMISSION_DENIED();
     error BB_INVALID_PARAMS();
+    error BB_INVALID_BURN_AMOUNT();
     error BB_MINT_DISALLOWED();
 
     /// @notice Start or stop migration to/from a specified contract.
@@ -90,6 +91,21 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
         _burn(_account, _amount);
     }
 
+    /// @notice Burns tokens from msg.sender, if this is the ERC20Vault. Otherwise do not allow
+    /// anyone to burn (e.g. USDC) or other coins, as it would be changing the supply (on other
+    /// chains too).
+    /// @param _amount The amount of tokens to burn.
+    function burn(uint256 _amount)
+        external
+        whenNotPaused
+        nonReentrant
+        onlyFromNamed(LibStrings.B_ERC20_VAULT)
+    {
+        if (_amount == 0) revert BB_INVALID_BURN_AMOUNT();
+        //All the necessary other checks (balance, etc.) are handled in the ERC20Upgradeable._burn()
+        _burn(msg.sender, _amount);
+    }
+
     /// @notice Returns the owner.
     /// @return The address of the owner.
     function owner() public view override(IBridgedERC20, OwnableUpgradeable) returns (address) {
diff --git a/packages/protocol/contracts/tokenvault/ERC20Vault.sol b/packages/protocol/contracts/tokenvault/ERC20Vault.sol
index 77d9cac3ba1..d54ab1b6a48 100644
--- a/packages/protocol/contracts/tokenvault/ERC20Vault.sol
+++ b/packages/protocol/contracts/tokenvault/ERC20Vault.sol
@@ -361,16 +361,10 @@ contract ERC20Vault is BaseVault {
         if (bridgedToCanonical[_token].addr != address(0)) {
             ctoken_ = bridgedToCanonical[_token];
 
-            bytes[] memory encodedCalls = _getBurnLowLevelCalls(_token, _user, _amount);
-            if (encodedCalls.length != 0) {
-                for (uint256 i; i < encodedCalls.length; ++i) {
-                    (bool result,) = _token.call(encodedCalls[i]);
-
-                    if (!result) revert VAULT_ERROR_IN_SPECIAL_OPS();
-                }
-            } else {
-                IBridgedERC20(_token).burn(msg.sender, _amount);
-            }
+            // Following the "transfer and burn" pattern, as used by USDC
+            IERC20(_token).safeTransferFrom(_user, address(this), _amount);
+            IBridgedERC20(_token).burn(_amount);
+
             balanceChange_ = _amount;
         } else {
             // If it's a canonical token
@@ -444,34 +438,4 @@ contract ERC20Vault is BaseVault {
             ctokenDecimal: ctoken.decimals
         });
     }
-
-    /// @dev If a token requires specific (e.g.: native USDC) operations to be burnt, then return
-    /// the low level calls.
-    /// @param toBeBurnt Token to be burnt.
-    /// @param user User trying to bridge.
-    /// @param amount Token amount to be burnt.
-    /// @return encodedCalls Address of the bridged token contract.
-    function _getBurnLowLevelCalls(
-        address toBeBurnt,
-        address user,
-        uint256 amount
-    )
-        private
-        returns (bytes[] memory encodedCalls)
-    {
-        if (toBeBurnt == resolve(LibStrings.B_BRIDGED_NATIVE_USDC, false)) {
-            // If this is a native USDC, then we need to:
-            // 1.transfer tokens from user to ERC20Vault
-            // 2. burn (supposing ERC20Vault has minterRole)
-            encodedCalls = new bytes[](2);
-            // 1. transfer to ERC20Vault
-            encodedCalls[0] = abi.encodeWithSignature(
-                "transferFrom(address,address,uint)", user, address(this), amount
-            );
-            // 2. burn
-            encodedCalls[1] = abi.encodeWithSignature("burn(uint)", amount);
-        }
-        // In case we will support other native tokens, custom logic can go here..
-        //else if() {...}
-    }
 }
diff --git a/packages/protocol/contracts/tokenvault/IBridgedERC20.sol b/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
index 98b13cedcbd..f802c556f98 100644
--- a/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
+++ b/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
@@ -18,6 +18,11 @@ interface IBridgedERC20 {
     /// @param _amount The amount of tokens to burn.
     function burn(address _from, uint256 _amount) external;
 
+    /// @notice Burns `amount` tokens from the `msg.sender` address - if the caller is the
+    /// ERC20Vault.
+    /// @param _amount The amount of tokens to burn.
+    function burn(uint256 _amount) external;
+
     /// @notice Start or stop migration to/from a specified contract.
     /// @param _addr The address migrating 'to' or 'from'.
     /// @param _inbound If false then signals migrating 'from', true if migrating 'into'.

From 0e21f3cd5678a8a385f4d87b623dc3c1835f4c7f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Keszey=20D=C3=A1niel?= <keszeyd@MacBook-Pro.local>
Date: Mon, 22 Apr 2024 14:29:38 +0200
Subject: [PATCH 05/11] bridge cannot burn only if owns

---
 .../contracts/tokenvault/BridgedERC20Base.sol     |  7 ++++---
 .../protocol/test/tokenvault/BridgedERC20.t.sol   | 15 ++++++++++-----
 2 files changed, 14 insertions(+), 8 deletions(-)

diff --git a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
index 19792b00b27..4999ee05dca 100644
--- a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
+++ b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
@@ -83,9 +83,10 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
             emit MigratedTo(migratingAddress, _account, _amount);
             // Ask the new bridged token to mint token for the user.
             IBridgedERC20(migratingAddress).mint(_account, _amount);
-        } else if (msg.sender != resolve(LibStrings.B_ERC20_VAULT, true)) {
-            // Only the vault can burn tokens when not migrating out
-            revert RESOLVER_DENIED();
+        } else {
+            // When user wants to burn tokens only during 'migrating out' phase is possible. If
+            // ERC20Vault burns the tokens, that will go thru the burn(amount) function.
+            revert BB_MINT_DISALLOWED();
         }
 
         _burn(_account, _amount);
diff --git a/packages/protocol/test/tokenvault/BridgedERC20.t.sol b/packages/protocol/test/tokenvault/BridgedERC20.t.sol
index 7d9e24ddbd3..42c26bc646c 100644
--- a/packages/protocol/test/tokenvault/BridgedERC20.t.sol
+++ b/packages/protocol/test/tokenvault/BridgedERC20.t.sol
@@ -44,13 +44,17 @@ contract TestBridgedERC20 is TaikoTest {
         vm.stopPrank();
     }
 
-    function test_20Vault_migration___only_vault_can_min_burn_when_migration_off() public {
+    function test_20Vault_migration___only_vault_can_min__but_cannot_burn_when_migration_off()
+        public
+    {
         BridgedERC20 btoken = deployBridgedToken("BAR");
         // only erc20_vault can brun and mint
         vm.startPrank(vault);
         btoken.mint(Bob, 1000);
+        //Vault cannot burn only if it owns the tokens
+        vm.expectRevert();
         btoken.burn(Bob, 600);
-        assertEq(btoken.balanceOf(Bob), 400);
+        assertEq(btoken.balanceOf(Bob), 1000);
         vm.stopPrank();
 
         // Owner cannot burn/mint
@@ -131,9 +135,10 @@ contract TestBridgedERC20 is TaikoTest {
         vm.expectRevert();
         newToken.burn(Bob, 10);
 
-        vm.prank(vault);
-        newToken.burn(Bob, 25);
-        assertEq(newToken.balanceOf(Bob), 200);
+        // Vault cannot burn as itself only if owns the tokens.
+        // vm.prank(vault);
+        // newToken.burn(Bob, 25);
+        // assertEq(newToken.balanceOf(Bob), 200);
     }
 
     function deployBridgedToken(string memory name) internal returns (BridgedERC20) {

From 2a2b73b3b6e230acdf53fbcb936027a40e59785f Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Keszey=20D=C3=A1niel?= <keszeyd@MacBook-Pro.local>
Date: Mon, 22 Apr 2024 17:53:50 +0200
Subject: [PATCH 06/11] remove old burn interface

---
 .../contracts/tokenvault/BridgedERC20Base.sol | 31 +++--------
 .../contracts/tokenvault/IBridgedERC20.sol    | 10 ++--
 .../test/tokenvault/BridgedERC20.t.sol        | 54 ++++++++-----------
 3 files changed, 32 insertions(+), 63 deletions(-)

diff --git a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
index 4999ee05dca..8138b88a57e 100644
--- a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
+++ b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
@@ -72,38 +72,21 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
         _mint(_account, _amount);
     }
 
-    /// @notice Burns tokens from the specified account.
-    /// @param _account The address of the account to burn the tokens from.
+    /// @notice Burns tokens in case of 'migrating out' from msg.sender (EOA) or from teh ERC20Vault
+    /// if bridging back to canonical token.
     /// @param _amount The amount of tokens to burn.
-    function burn(address _account, uint256 _amount) external whenNotPaused nonReentrant {
+    function burn(uint256 _amount) external whenNotPaused nonReentrant {
         if (_isMigratingOut()) {
-            // Only the owner of the tokens himself can migrate out
-            if (msg.sender != _account) revert BB_PERMISSION_DENIED();
             // Outbound migration
-            emit MigratedTo(migratingAddress, _account, _amount);
+            emit MigratedTo(migratingAddress, msg.sender, _amount);
             // Ask the new bridged token to mint token for the user.
-            IBridgedERC20(migratingAddress).mint(_account, _amount);
-        } else {
+            IBridgedERC20(migratingAddress).mint(msg.sender, _amount);
+        } else if (msg.sender != resolve(LibStrings.B_ERC20_VAULT, true)) {
             // When user wants to burn tokens only during 'migrating out' phase is possible. If
             // ERC20Vault burns the tokens, that will go thru the burn(amount) function.
-            revert BB_MINT_DISALLOWED();
+            revert RESOLVER_DENIED();
         }
 
-        _burn(_account, _amount);
-    }
-
-    /// @notice Burns tokens from msg.sender, if this is the ERC20Vault. Otherwise do not allow
-    /// anyone to burn (e.g. USDC) or other coins, as it would be changing the supply (on other
-    /// chains too).
-    /// @param _amount The amount of tokens to burn.
-    function burn(uint256 _amount)
-        external
-        whenNotPaused
-        nonReentrant
-        onlyFromNamed(LibStrings.B_ERC20_VAULT)
-    {
-        if (_amount == 0) revert BB_INVALID_BURN_AMOUNT();
-        //All the necessary other checks (balance, etc.) are handled in the ERC20Upgradeable._burn()
         _burn(msg.sender, _amount);
     }
 
diff --git a/packages/protocol/contracts/tokenvault/IBridgedERC20.sol b/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
index f802c556f98..9d1ad319c5a 100644
--- a/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
+++ b/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
@@ -13,13 +13,9 @@ interface IBridgedERC20 {
     /// @param _amount The amount of tokens to mint.
     function mint(address _account, uint256 _amount) external;
 
-    /// @notice Burns `amount` tokens from the `from` address.
-    /// @param _from The account from which the tokens will be burned.
-    /// @param _amount The amount of tokens to burn.
-    function burn(address _from, uint256 _amount) external;
-
-    /// @notice Burns `amount` tokens from the `msg.sender` address - if the caller is the
-    /// ERC20Vault.
+    /// @notice Burns `amount` tokens from the `msg.sender` address - either if tokens are migrating
+    /// out to a new bridged token or if the caller is the or if the caller is ERC20Vault (during
+    /// "bridging back").
     /// @param _amount The amount of tokens to burn.
     function burn(uint256 _amount) external;
 
diff --git a/packages/protocol/test/tokenvault/BridgedERC20.t.sol b/packages/protocol/test/tokenvault/BridgedERC20.t.sol
index 42c26bc646c..689a995db40 100644
--- a/packages/protocol/test/tokenvault/BridgedERC20.t.sol
+++ b/packages/protocol/test/tokenvault/BridgedERC20.t.sol
@@ -49,21 +49,19 @@ contract TestBridgedERC20 is TaikoTest {
     {
         BridgedERC20 btoken = deployBridgedToken("BAR");
         // only erc20_vault can brun and mint
-        vm.startPrank(vault);
+        vm.prank(vault, vault);
         btoken.mint(Bob, 1000);
         //Vault cannot burn only if it owns the tokens
         vm.expectRevert();
-        btoken.burn(Bob, 600);
+        vm.prank(Bob, Bob);
+        btoken.burn(600);
         assertEq(btoken.balanceOf(Bob), 1000);
         vm.stopPrank();
 
         // Owner cannot burn/mint
-        vm.startPrank(owner);
         vm.expectRevert();
+        vm.prank(owner, owner);
         btoken.mint(Bob, 1000);
-        vm.expectRevert();
-        btoken.burn(Bob, 100);
-        vm.stopPrank();
     }
 
     function test_20Vault_migration__old_to_new() public {
@@ -92,23 +90,9 @@ contract TestBridgedERC20 is TaikoTest {
         vm.expectRevert();
         oldToken.mint(Bob, 10);
 
-        // 2. burning can NOT be done by anyone
-        vm.prank(randAddress());
-        vm.expectRevert();
-        oldToken.burn(Bob, 10);
-
-        // including the owners
-        vm.prank(oldToken.owner());
-        vm.expectRevert();
-        oldToken.burn(Bob, 10);
-
-        vm.prank(newToken.owner());
-        vm.expectRevert();
-        oldToken.burn(Bob, 10);
-
-        // but can be done by the token owner
+        // but can be done by the token owner - if migrating out phase
         vm.prank(Bob);
-        oldToken.burn(Bob, 10);
+        oldToken.burn(10);
         assertEq(oldToken.balanceOf(Bob), 90);
         assertEq(newToken.balanceOf(Bob), 210);
 
@@ -126,19 +110,25 @@ contract TestBridgedERC20 is TaikoTest {
         newToken.mint(Bob, 15);
         assertEq(newToken.balanceOf(Bob), 225);
 
-        // 2. Nobody can burn except the vault
-        vm.prank(Bob);
+        // Vault can only burn if it owns the tokens
+        vm.prank(vault);
         vm.expectRevert();
-        newToken.burn(Bob, 10);
+        newToken.burn(25);
+        assertEq(newToken.balanceOf(Bob), 225);
 
-        vm.prank(owner);
-        vm.expectRevert();
-        newToken.burn(Bob, 10);
+        // Imitate current bridge-back operation, as Bob gave approval (for bridging back) and then
+        // ERC20Vault does the "transfer and burn"
+        vm.prank(Bob);
+        newToken.approve(vault, 25);
+
+        // Following the "transfer and burn" pattern
+        vm.prank(vault);
+        newToken.transferFrom(Bob, vault, 25);
+
+        vm.prank(vault);
+        newToken.burn(25);
 
-        // Vault cannot burn as itself only if owns the tokens.
-        // vm.prank(vault);
-        // newToken.burn(Bob, 25);
-        // assertEq(newToken.balanceOf(Bob), 200);
+        assertEq(newToken.balanceOf(Bob), 200);
     }
 
     function deployBridgedToken(string memory name) internal returns (BridgedERC20) {

From 6782c8a039096dc30c2cd825f4a07b004ea1911b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Keszey=20D=C3=A1niel?= <keszeyd@MacBook-Pro.local>
Date: Mon, 22 Apr 2024 17:54:41 +0200
Subject: [PATCH 07/11] remove constant string

---
 packages/protocol/contracts/common/LibStrings.sol | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/packages/protocol/contracts/common/LibStrings.sol b/packages/protocol/contracts/common/LibStrings.sol
index 689f829721e..16a05bf8826 100644
--- a/packages/protocol/contracts/common/LibStrings.sol
+++ b/packages/protocol/contracts/common/LibStrings.sol
@@ -34,9 +34,6 @@ library LibStrings {
     /// @notice bytes32 representation of the string "bridged_erc20".
     bytes32 internal constant B_BRIDGED_ERC20 = bytes32("bridged_erc20");
 
-    /// @notice bytes32 representation of the string "bridged_native_usdc".
-    bytes32 internal constant B_BRIDGED_NATIVE_USDC = bytes32("bridged_native_usdc");
-
     /// @notice bytes32 representation of the string "erc1155_vault".
     bytes32 internal constant B_ERC1155_VAULT = bytes32("erc1155_vault");
 

From 1ec3a84f87cc71f37d69dd2f4b7789659aee2836 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Keszey=20D=C3=A1niel?= <keszeyd@MacBook-Pro.local>
Date: Mon, 22 Apr 2024 17:58:38 +0200
Subject: [PATCH 08/11] remove unnecessary leftover

---
 packages/protocol/contracts/tokenvault/BridgedERC20Base.sol | 1 -
 packages/protocol/contracts/tokenvault/ERC20Vault.sol       | 3 ---
 2 files changed, 4 deletions(-)

diff --git a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
index 8138b88a57e..134994c5325 100644
--- a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
+++ b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
@@ -29,7 +29,6 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
 
     error BB_PERMISSION_DENIED();
     error BB_INVALID_PARAMS();
-    error BB_INVALID_BURN_AMOUNT();
     error BB_MINT_DISALLOWED();
 
     /// @notice Start or stop migration to/from a specified contract.
diff --git a/packages/protocol/contracts/tokenvault/ERC20Vault.sol b/packages/protocol/contracts/tokenvault/ERC20Vault.sol
index d54ab1b6a48..0af5fe89f35 100644
--- a/packages/protocol/contracts/tokenvault/ERC20Vault.sol
+++ b/packages/protocol/contracts/tokenvault/ERC20Vault.sol
@@ -5,7 +5,6 @@ import "@openzeppelin/contracts/token/ERC20/IERC20.sol";
 import "@openzeppelin/contracts/token/ERC20/extensions/IERC20Metadata.sol";
 import "@openzeppelin/contracts/token/ERC20/utils/SafeERC20.sol";
 import "../libs/LibAddress.sol";
-import "../common/LibStrings.sol";
 import "./BridgedERC20.sol";
 import "./BaseVault.sol";
 
@@ -134,11 +133,9 @@ contract ERC20Vault is BaseVault {
 
     error VAULT_BTOKEN_BLACKLISTED();
     error VAULT_CTOKEN_MISMATCH();
-    error VAULT_ERROR_IN_SPECIAL_OPS();
     error VAULT_INVALID_TOKEN();
     error VAULT_INVALID_AMOUNT();
     error VAULT_INVALID_NEW_BTOKEN();
-    error VAULT_NOT_POSSIBLE_SPECIAL_OPERATION();
     error VAULT_INVALID_TO();
     error VAULT_NOT_SAME_OWNER();
 

From ce32fecdc6f1fd337fa94adc6fa7a61f1284edf3 Mon Sep 17 00:00:00 2001
From: Daniel Wang <99078276+dantaik@users.noreply.github.com>
Date: Tue, 23 Apr 2024 11:41:27 +0800
Subject: [PATCH 09/11] Update
 packages/protocol/contracts/tokenvault/BridgedERC20Base.sol

---
 packages/protocol/contracts/tokenvault/BridgedERC20Base.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
index 134994c5325..e3a9fb82d37 100644
--- a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
+++ b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
@@ -71,7 +71,7 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
         _mint(_account, _amount);
     }
 
-    /// @notice Burns tokens in case of 'migrating out' from msg.sender (EOA) or from teh ERC20Vault
+    /// @notice Burns tokens in case of 'migrating out' from msg.sender (EOA) or from the ERC20Vault
     /// if bridging back to canonical token.
     /// @param _amount The amount of tokens to burn.
     function burn(uint256 _amount) external whenNotPaused nonReentrant {

From 879a78d923f16ac6fdfd822f9fadf8081c7743de Mon Sep 17 00:00:00 2001
From: Daniel Wang <dan@taiko.xyz>
Date: Tue, 23 Apr 2024 11:46:02 +0800
Subject: [PATCH 10/11] Update IBridgedERC20.sol

---
 packages/protocol/contracts/tokenvault/IBridgedERC20.sol | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/protocol/contracts/tokenvault/IBridgedERC20.sol b/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
index 9d1ad319c5a..1f85877570e 100644
--- a/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
+++ b/packages/protocol/contracts/tokenvault/IBridgedERC20.sol
@@ -13,13 +13,13 @@ interface IBridgedERC20 {
     /// @param _amount The amount of tokens to mint.
     function mint(address _account, uint256 _amount) external;
 
-    /// @notice Burns `amount` tokens from the `msg.sender` address - either if tokens are migrating
-    /// out to a new bridged token or if the caller is the or if the caller is ERC20Vault (during
-    /// "bridging back").
+    /// @notice Burns tokens from msg.sender. This is only allowed if:
+    /// - 1) tokens are migrating out to a new bridged token
+    /// - 2) The token is burned by ERC20Vault to bridge back to the canonical chain.
     /// @param _amount The amount of tokens to burn.
     function burn(uint256 _amount) external;
 
-    /// @notice Start or stop migration to/from a specified contract.
+    /// @notice Starts or stops migration to/from a specified contract.
     /// @param _addr The address migrating 'to' or 'from'.
     /// @param _inbound If false then signals migrating 'from', true if migrating 'into'.
     function changeMigrationStatus(address _addr, bool _inbound) external;

From 1235ccfddd8f52602b745e3b2f435b5ce90a81ca Mon Sep 17 00:00:00 2001
From: Daniel Wang <dan@taiko.xyz>
Date: Tue, 23 Apr 2024 11:46:49 +0800
Subject: [PATCH 11/11] Update BridgedERC20Base.sol

---
 packages/protocol/contracts/tokenvault/BridgedERC20Base.sol | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
index e3a9fb82d37..b5bccfbf293 100644
--- a/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
+++ b/packages/protocol/contracts/tokenvault/BridgedERC20Base.sol
@@ -82,7 +82,7 @@ abstract contract BridgedERC20Base is EssentialContract, IBridgedERC20 {
             IBridgedERC20(migratingAddress).mint(msg.sender, _amount);
         } else if (msg.sender != resolve(LibStrings.B_ERC20_VAULT, true)) {
             // When user wants to burn tokens only during 'migrating out' phase is possible. If
-            // ERC20Vault burns the tokens, that will go thru the burn(amount) function.
+            // ERC20Vault burns the tokens, that will go through the burn(amount) function.
             revert RESOLVER_DENIED();
         }