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Withdraw Offer Signature Structure

To authorize the withdrawOffer operation within the Name Service, the user (the original offeror) must generate a cryptographic signature compliant with the EIP-191 standard using the Ethereum Signed Message format.

The signature verification process uses the SignatureRecover library. This signature proves the offeror's intent and authorization to withdraw a specific, previously placed offer from a target 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
    "withdrawOffer",                                    // Action type
    string.concat(                                      // Concatenated parameters
        _username,
        ",",
        Strings.toString(_offerId),
        ",",
        Strings.toString(_nameServiceNonce)
    ),
    signature,
    signer
);

Internal Message Construction​

This results in a message format:

"{evvmID},withdrawOffer,{username},{offerId},{nameServiceNonce}"

Message Components​

1. EVVM ID (String):

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

2. Action Type (String):

  • Fixed value: "withdrawOffer"
  • Purpose: Identifies this as a withdraw offer operation

3. Concatenated Parameters (String):

3.1. Target Username (String):

  • The _username string itself
  • Purpose: Specifies the username associated with the offer being withdrawn

3.2. Offer ID (String):

  • The result of Strings.toString(_offerId)
  • Purpose: The unique identifier assigned to the specific offer when created

3.3. Name Service Nonce (String):

  • The result of Strings.toString(_nameServiceNonce)
  • Purpose: Provides replay protection for withdraw offer actions

Example​

Scenario: User wants to withdraw their offer on username "alice"

Parameters:

  • evvmID: 1
  • _username: "alice"
  • _offerId: 42
  • _nameServiceNonce: 7

Signature verification call:

SignatureRecover.signatureVerification(
    "1",
    "withdrawOffer",
    "alice,42,7",
    signature,
    signer
);

Final message to be signed:

1,withdrawOffer,alice,42,7

EIP-191 formatted message hash:

keccak256(abi.encodePacked(
    "\x19Ethereum Signed Message:\n27",
    "1,withdrawOffer,alice,42,7"
))
Technical Details
  • Message Format: "{evvmID},{functionName},{parameters}"
  • EIP-191 Compliance: Uses "\x19Ethereum Signed Message:\n" prefix with message length
  • Offer ID Validation: _offerId must correspond to an existing offer made by the same user
  • Authorization: Only the original offeror can withdraw their own offers
  • Replay Protection: _nameServiceNonce prevents replay attacks
  • EVVM ID: Identifies the specific EVVM instance for signature verification