Ethereum: What is the use case for type hashes in EIP-712?
Ethereum Improvement Proposal (EIP) 712, also known as keccak-512, is a cryptographic hash function designed to sign messages. In Solidity, one of the most popular programming languages for building decentralized applications on the Ethereum blockchain, we can use this function to create robust and secure signature mechanisms. In this article, we will cover the use case for type hashes in EIP-712.
What is type hash?
Type hash, also known as keccak-512 or simply k256, is a cryptographic hash function that takes a string (in this case, the contract name) and generates a fixed-size hash. It is essentially a SHA-3-512 hash, the output of which is 32 bytes long.
EIP-712: Key Concept
The EIP-712 proposal introduced an additional field to contracts using keccak-512 signatures. This field is called “type” or “tag” that contains additional information about the contract. It is not related to the hash function itself, but serves as a way to provide context and metadata about the contract.
Use Case: Type Hashes in EIP-712
Type hashes play a key role in EIP-712, serving several purposes:
- Contract Metadata: The type hash is used to identify the contract at runtime. When an account calls a function in this contract, it can verify that it is executing code from this particular contract using the keccak-512 signature.
contract MyContract {
bytes32 private constant MY_TYPE_HASH = keccak256("MyContract");
// Contract metadata is stored here
}
- Proof of Existence: The type hash can be used to prove that the contract exists on the blockchain at runtime, making it more secure and less susceptible to deletion.
contract MyContract {
bytes32 private constant MY_TYPE_HASH = keccak256("MyContract");
// Contract metadata is stored here
}
- Audit: The type hash can be used to audit contracts for compliance with specific standards or regulations, making it easier to identify potential issues.
contract MyContract {
bytes32 private constant MY_TYPE_HASH = keccak256("MyContract");
function audit() public {
require(bytes32(0) == keccak256("MyContract"), "Contract is not valid");
}
}
- Security
: Type hashes can be used to add an extra layer of security to contracts, making it harder for attackers to reverse engineer the contract.
contract MyContract {
bytes32 private constant MY_TYPE_HASH = keccak256("MyContract");
function myFunction() public {
// Code here
}
}
In summary, type hashes in EIP-712 are a powerful tool that can be used to enhance the security, auditability, and metadata management of contracts. By storing additional context and contract information using keccak-512 signatures, developers can build more robust and secure decentralized applications.
It is important to note, however, that while type hashes provide these benefits, they also introduce additional complexity and requirements for contract development and implementation. Therefore, it is extremely important to carefully evaluate the use case for EIP-712 in a specific project before implementing them.