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Appendix

Signature Extraction

Data that are sent to TwoFactorBase contracts must strictly adhere to the following format.

Calldata Deadline Signature
dynamically-sized 32 bytes 65 bytes

Transaction data that are in compliance with the above format is then divided into three parts using the formula described below:

  • Deadline = Data [len-97 : len-65]

This is the given deadline of a transaction, which reverts at block.timestamp > deadline.

  • Signature = Data [-65]

The relayer signature can be simply extracting by slicing out the last 65-bytes of msg.data.

  • Calldata = Data [0 : len-97]

The actual calldata is the entire msg.data excluding the last 97-byte.

2FA Message

The message is a hash of the encoded structure, as defined by the following:

bytes32 hash = keccak256(
    abi.encode(
        uint256 chainId,
        uint256 walletNonce,
        bytes32 domain_name_hash,
        uint256 deadline,
        address primary,
        address target,
        bytes data
    )
)

An honest relayer may only sign this message if and only if the relayer is able to verify that the provided 2FA code from the primary wallet holder is valid.