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Withdrawal Signature Structure

warning

Currently Not Implemented in SignatureUtils.sol

The withdrawal signature verification functionality is not currently implemented in the SignatureUtils.sol library. The current implementation only includes:

  • verifyMessageSignedForPay - for single payment operations
  • verifyMessageSignedForDispersePay - for disperse payment operations

This documentation is preserved for reference and will be updated when withdrawal signature verification is implemented.

To authorize withdrawal operations from the EVVM protocol, the user whose funds are being withdrawn (from) must generate a cryptographic signature compliant with the EIP-191 standard.

This signature proves the user's intent and authorization to withdraw a specific amount of a token to a designated external addressToReceive (if any), according to the parameters included in the signed message.

Expected Signed Message Format​

Based on the pattern established in the current SignatureUtils.sol implementation, withdrawal signature verification would likely follow this structure:

SignatureRecover.signatureVerification(
    Strings.toString(evvmID),        // EVVM ID as string
    "withdraw",                      // Action type (expected)
    string.concat(                   // Concatenated parameters
        AdvancedStrings.addressToString(addressToReceive),
        ",",
        AdvancedStrings.addressToString(_token),
        ",",
        Strings.toString(_amount),
        ",",
        Strings.toString(_priorityFee),
        ",",
        Strings.toString(_nonce),
        ",",
        _priorityFlag ? "true" : "false",
        ",",
        AdvancedStrings.addressToString(_executor)
    ),
    signature,
    signer
);

Expected Internal Message Construction​

Following the SignatureRecover pattern, the function would construct the final message by concatenating:

string.concat(evvmID, ",", functionName, ",", inputs)

This would result in a message format:

"{evvmID},withdraw,{addressToReceive},{token},{amount},{priorityFee},{nonce},{priorityFlag},{executor}"

Expected EIP-191 Message Hashing​

The message would be hashed according to EIP-191 standard:

bytes32 messageHash = keccak256(
    abi.encodePacked(
        "\x19Ethereum Signed Message:\n",
        Strings.toString(bytes(message).length),
        message
    )
);

Expected Message Components​

1. EVVM ID (String):

  • The result of Strings.toString(evvmID)
  • Purpose: Identifies the specific EVVM instance

2. Action Type (String):

  • Expected value: "withdraw"
  • Purpose: Identifies this as a withdrawal operation

3. Concatenated Parameters (String): The parameters would be concatenated with comma separators:

3.1. Recipient Address (String):

  • The result of AdvancedStrings.addressToString(addressToReceive)
  • Purpose: The destination address on the external network where the withdrawn tokens should be sent via the bridge

3.2. Token Address (String):

  • The result of AdvancedStrings.addressToString(_token)
  • Purpose: The ERC20 token contract address being withdrawn

3.3. Amount (String):

  • The result of Strings.toString(_amount)
  • Purpose: The quantity of the token the user authorizes to be withdrawn

3.4. Priority Fee (String):

  • The result of Strings.toString(_priorityFee)
  • Purpose: The fee included in the transaction authorization

3.5. Nonce (String):

  • The result of Strings.toString(_nonce)
  • Purpose: Provides replay protection for the transaction

3.6. Priority Flag (String):

  • "true": If _priorityFlag is true (asynchronous)
  • "false": If _priorityFlag is false (synchronous)
  • Purpose: Explicitly includes the execution mode in the signed message

3.7. Executor Address (String):

  • The result of AdvancedStrings.addressToString(_executor)
  • Purpose: Specifies the address authorized to submit this withdrawal request
Expected Technical Details

This structure is speculative and based on the pattern used in the implemented payment functions:

  • Expected Message Format: "{evvmID},{functionName},{parameters}"
  • Expected EIP-191 Compliance: Would use "\x19Ethereum Signed Message:\n" prefix with message length
  • Expected Hash Function: keccak256 would be used for the final message hash before signing
  • Expected Signature Recovery: Would use ecrecover to verify the signature against the expected signer
  • String Conversion:
    • AdvancedStrings.addressToString converts addresses to lowercase hex with "0x" prefix
    • Strings.toString converts numbers to decimal strings
  • Priority Flag: Would determine execution mode (async=true, sync=false)
  • EVVM ID: Would identify the specific EVVM instance for signature verification
  • Bridge Integration: addressToReceive would specify the destination on external network

Note: The actual implementation may differ from this expected structure when withdrawal functionality is added to SignatureUtils.sol.