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Withdraw Offer Signature Structure

To authorize the withdrawOffer operation within the MNS service, the user (the original offeror) must generate a cryptographic signature compliant with the EIP-191 standard.

This signature proves the offeror's intent and authorization to withdraw a specific, previously placed offer from a target username.

Signed Message Format​

The message is constructed by concatenating the following components as strings, separated by commas (,):

string.concat(
   "5761d8ed",
   ",",
   _username,
   ",",
   Strings.toString(_offerId),
   ",",
   Strings.toString(_nameServiceNonce)
)

1. MNS Withdraw Offer Identifier (Hex String):

  • Value: 5761d8ed
  • Purpose: A specific identifier used within the EIP-191 framework to distinguish MNS withdrawOffer messages from other types of signed messages.

2. Target Username (String):

  • Value: The _username string itself.
  • Purpose: Specifies the username associated with the offer that is being withdrawn.

3. Offer ID (String):

  • Value: The result of Strings.toString(_offerId).
  • Purpose: The string representation of the unique identifier (uint256) assigned to the specific offer when it was created via makeOffer. This identifies which offer to withdraw.

4. MNS Nonce (String):

  • Value: The result of Strings.toString(_nameServiceNonce).
  • Purpose: The string representation of the user's (original offeror's) nonce specific to the MNS contract for this withdrawOffer action. This prevents replay attacks.

Practical Example​

Let's say we want to withdraw an offer with the following parameters:

  • Target Username: "alice"
  • Offer ID: 42 (the unique identifier of the offer to withdraw)
  • Name Service Nonce: 7

The message would be constructed as:

"5761d8ed,alice,42,7"

Message Breakdown:

  • 5761d8ed: Function selector for withdraw offer verification
  • alice: The username associated with the offer being withdrawn
  • 42: The unique ID of the specific offer to withdraw
  • 7: The offeror's name service nonce

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

tip
  • The function selector 5761d8ed is the first 4 bytes of the keccak256 hash of the function signature for verifyMessageSignedForWithdrawOffer
  • Strings.toString converts a number to a string (standard OpenZeppelin utility)
  • The signature verification uses the EIP-191 standard for message signing
  • The _offerId must correspond to an existing offer that was previously made by the same user
  • Only the original offeror can withdraw their own offers