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feat(ctb): introduces two step withdrawals #3677

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117 changes: 53 additions & 64 deletions packages/contracts-bedrock/.gas-snapshot
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110 changes: 90 additions & 20 deletions packages/contracts-bedrock/contracts/L1/OptimismPortal.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -19,6 +19,15 @@ import { Semver } from "../universal/Semver.sol";
* Users are encouraged to use the L1CrossDomainMessenger for a higher-level interface.
*/
contract OptimismPortal is Initializable, ResourceMetering, Semver {
/**
* @notice Data stored for proven withdrawals.
*/
struct ProvenWithdrawal {
uint256 timestamp;
uint256 l2BlockNumber;
bytes32 outputRoot;
}

/**
* @notice Version of the deposit event.
*/
Expand Down Expand Up @@ -58,6 +67,11 @@ contract OptimismPortal is Initializable, ResourceMetering, Semver {
*/
uint256 internal constant FINALIZE_GAS_BUFFER = 20_000;

/**
* @notice A list of withdrawal hashes which have been proven.
*/
mapping(bytes32 => ProvenWithdrawal) public provenWithdrawals;

/**
* @notice A list of withdrawal hashes which have been successfully finalized.
*/
Expand All @@ -79,6 +93,13 @@ contract OptimismPortal is Initializable, ResourceMetering, Semver {
bytes opaqueData
);

/**
* @notice Emitted when a withdrawal transaction is proven.
*
* @param withdrawalHash Hash of the withdrawal transaction.
*/
event WithdrawalProven(bytes32 indexed withdrawalHash);

/**
* @notice Emitted when a withdrawal transaction is finalized.
*
Expand Down Expand Up @@ -110,44 +131,30 @@ contract OptimismPortal is Initializable, ResourceMetering, Semver {
}

/**
* @notice Finalizes a withdrawal transaction.
* @notice Proves a withdrawal transaction.
*
* @param _tx Withdrawal transaction to finalize.
* @param _l2BlockNumber L2 block number of the outputRoot.
* @param _outputRootProof Inclusion proof of the L2ToL1MessagePasser contract's storage root.
* @param _withdrawalProof Inclusion proof of the withdrawal in L2ToL1MessagePasser contract.
*/
function finalizeWithdrawalTransaction(
function proveWithdrawalTransaction(
Types.WithdrawalTransaction memory _tx,
uint256 _l2BlockNumber,
Types.OutputRootProof calldata _outputRootProof,
bytes calldata _withdrawalProof
) external {
// Prevent nested withdrawals within withdrawals.
require(
l2Sender == DEFAULT_L2_SENDER,
"OptimismPortal: can only trigger one withdrawal per transaction"
);

// Prevent users from creating a deposit transaction where this address is the message
// sender on L2.
// In the context of the proxy delegate calling to this implementation,
// sender on L2. In the context of the proxy delegate calling to this implementation,
// address(this) will return the address of the proxy.
require(
_tx.target != address(this),
"OptimismPortal: you cannot send messages to the portal contract"
);

// Get the output root. This will fail if there is no
// output root for the given block number.
// Get the output root. This will fail if there is no output root for the given block.
Types.OutputProposal memory proposal = L2_ORACLE.getL2Output(_l2BlockNumber);

// Ensure that enough time has passed since the proposal was submitted before allowing a
// withdrawal. Under the assumption that the fault proof mechanism is operating correctly,
// we can infer that any withdrawal that has passed the finalization period must be valid
// and can therefore be operated on.
require(_isOutputFinalized(proposal), "OptimismPortal: proposal is not yet finalized");

// Verify that the output root can be generated with the elements in the proof.
require(
proposal.outputRoot == Hashing.hashOutputRootProof(_outputRootProof),
Expand All @@ -159,8 +166,8 @@ contract OptimismPortal is Initializable, ResourceMetering, Semver {
bytes32 withdrawalHash = Hashing.hashWithdrawal(_tx);

// Verify that the hash of this withdrawal was stored in the L2toL1MessagePasser contract on
// L2. If this is true, then we know that this withdrawal was actually triggered on L2
// and can therefore be relayed on L1.
// L2. If this is true, then we know that this withdrawal was actually triggered on L2 and
// can therefore be relayed on L1.
require(
_verifyWithdrawalInclusion(
withdrawalHash,
Expand All @@ -170,6 +177,69 @@ contract OptimismPortal is Initializable, ResourceMetering, Semver {
"OptimismPortal: invalid withdrawal inclusion proof"
);

// Mark the withdrawal as proven and mark the timestamp at which the proof happened along
// with the outputRoot that was used to prove the withdrawal. It's fine for the same
// withdrawal to be proven twice, since we prevent replay attacks using the
// finalizedWithdrawals mapping and not the provenWithdrawals mapping. In some cases we
// need to prove the same withdrawal multiple times, for example if the original output
// root that was proven against was replaced with a different output root.
provenWithdrawals[withdrawalHash] = ProvenWithdrawal({
timestamp: block.timestamp,
l2BlockNumber: _l2BlockNumber,
outputRoot: proposal.outputRoot
});

// Tell the world that the withdrawal was proven.
emit WithdrawalProven(withdrawalHash);
}

/**
* @notice Finalizes a withdrawal transaction.
*
* @param _tx Withdrawal transaction to finalize.
*/
function finalizeWithdrawalTransaction(Types.WithdrawalTransaction memory _tx) external {
// Prevent nested withdrawals within withdrawals.
require(
l2Sender == DEFAULT_L2_SENDER,
"OptimismPortal: can only trigger one withdrawal per transaction"
);

// All withdrawals have a unique hash, we'll use this as the identifier for the withdrawal
// and to prevent replay attacks.
bytes32 withdrawalHash = Hashing.hashWithdrawal(_tx);

// Load up the withdrawal and check that it's been proven.
ProvenWithdrawal memory provenWithdrawal = provenWithdrawals[withdrawalHash];
require(
provenWithdrawal.timestamp != 0,
"OptimismPortal: withdrawal hash has not been proven"
);

// Check that the withdrawal has passed the finalization period.
require(
block.timestamp >= provenWithdrawal.timestamp + FINALIZATION_PERIOD_SECONDS,
"OptimismPortal: withdrawal finalization period has not elapsed"
);

// Check that the output proposal hasn't been updated.
Types.OutputProposal memory proposal = L2_ORACLE.getL2Output(
provenWithdrawal.l2BlockNumber
);
require(
proposal.outputRoot == provenWithdrawal.outputRoot,
"OptimismPortal: output root proven is not the same as current output root"
);

// Ensure that enough time has passed since the proposal was submitted before allowing a
// withdrawal. Under the assumption that the fault proof mechanism is operating correctly,
// we can infer that any withdrawal that has passed the finalization period must be valid
// and can therefore be operated on.
require(
_isOutputFinalized(proposal),
"OptimismPortal: proposal finalization period has not elapsed"
);

// Check that this withdrawal has not already been finalized, this is replay protection.
require(
finalizedWithdrawals[withdrawalHash] == false,
Expand Down
4 changes: 2 additions & 2 deletions packages/contracts-bedrock/contracts/test/CommonTest.t.sol
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Original file line number Diff line number Diff line change
Expand Up @@ -424,7 +424,7 @@ contract Bridge_Initializer is Messenger_Initializer {
}

contract FFIInterface is Test {
function getFinalizeWithdrawalTransactionInputs(Types.WithdrawalTransaction memory _tx)
function getProveWithdrawalTransactionInputs(Types.WithdrawalTransaction memory _tx)
external
returns (
bytes32,
Expand All @@ -437,7 +437,7 @@ contract FFIInterface is Test {
string[] memory cmds = new string[](9);
cmds[0] = "node";
cmds[1] = "dist/scripts/differential-testing.js";
cmds[2] = "getFinalizeWithdrawalTransactionInputs";
cmds[2] = "getProveWithdrawalTransactionInputs";
cmds[3] = vm.toString(_tx.nonce);
cmds[4] = vm.toString(_tx.sender);
cmds[5] = vm.toString(_tx.target);
Expand Down
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