Remove Custom Metadata Signature Structure

To authorize the removeCustomMetadata operation within the MNS service, the user who currently owns the username must generate a cryptographic signature compliant with the EIP-191 standard.

This signature proves the current username owner's intent and authorization to remove a specific custom metadata entry (identified by its key/index _key) associated with their username (_username).

Signed Message Format

The signature verification uses the SignatureRecover.signatureVerification function with the following structure:

SignatureRecover.signatureVerification(
    Strings.toString(evvmID),                           // EVVM ID as string
    "removeCustomMetadata",                             // Action type
    string.concat(                                      // Concatenated parameters
        _username,
        ",",
        Strings.toString(_key),
        ",",
        Strings.toString(_nonce)
    ),
    signature,
    signer
);

Internal Message Construction

This results in a message format:

"{evvmID},removeCustomMetadata,{username},{key},{nonce}"

Message Components

1. EVVM ID (String):

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

2. Action Type (String):

• Fixed value: "removeCustomMetadata"
• Purpose: Identifies this as a remove custom metadata operation

3. Concatenated Parameters (String):

3.1. Target Username (String):

• The _username string itself
• Purpose: Specifies the username from which the custom metadata entry will be removed

3.2. Metadata Key/Index (String):

• The result of Strings.toString(_key)
• Purpose: The identifier for the specific metadata entry targeted for removal

3.3. Nonce (String):

• The result of Strings.toString(_nonce)
• Purpose: Provides replay protection for metadata removal operations

Example

Scenario: Owner wants to remove custom metadata from their username "alice"

Parameters:

• evvmID: 1
• _username: "alice"
• _key: 3 (metadata entry identifier)
• _nonce: 15

Signature verification call:

SignatureRecover.signatureVerification(
    "1",
    "removeCustomMetadata",
    "alice,3,15",
    signature,
    signer
);

Final message to be signed:

1,removeCustomMetadata,alice,3,15

EIP-191 formatted message hash:

keccak256(abi.encodePacked(
    "\x19Ethereum Signed Message:\n33",
    "1,removeCustomMetadata,alice,3,15"
))

Message Breakdown:

• 8adf3927: Function selector for remove custom metadata verification
• alice: The username from which the metadata will be removed
• 3: The key/index of the specific metadata entry to remove
• 15: The current username owner's nonce

This message would then be signed using EIP-191 standard, and the resulting signature would be used to verify the metadata removal request in the verifyMessageSignedForRemoveCustomMetadata function.

tip

• The function selector 8adf3927 is the first 4 bytes of the keccak256 hash of the function signature for verifyMessageSignedForRemoveCustomMetadata
• Strings.toString converts a number to a string (standard OpenZeppelin utility)
• The signature verification uses the EIP-191 standard for message signing
• Only the current owner of the username can remove custom metadata from their username
• The _key parameter identifies which specific metadata entry to remove by its index/identifier
• The _nonce parameter is the user's general nonce, not specifically the name service nonce