EIP712Domain missing chainId

[BlinkyStitt]

I'm trying to get an order hash from an order and noticed a difference between the official EIP712 example and what is in the spec here.

https://github.com/ethereum/EIPs/blob/master/assets/eip-712/Example.sol

struct EIP712Domain {
    string  name;
    string  version;
    uint256 chainId;
    address verifyingContract;
}

https://github.com/0xProject/0x-protocol-specification/blob/master/v2/v2-specification.md#eip712-usage

// Hash of the EIP712 Domain Separator Schema
bytes32 constant internal EIP712_DOMAIN_SEPARATOR_SCHEMA_HASH = keccak256(abi.encodePacked(
    "EIP712Domain(",
    "string name,",
    "string version,",
    "address verifyingContract",
    ")"
));

bytes32 EIP712_DOMAIN_HASH = keccak256(abi.encodePacked(
    EIP712_DOMAIN_SEPARATOR_SCHEMA_HASH,
    keccak256(bytes("0x Protocol")),
    keccak256(bytes("2")),
    bytes32(address(this))
));

The 0x spec is missing chainId. Is this intentional? It seems like it will be a problem.

Also, what address is the "this" referring to? The only place I see "verifyingContract" used in the spec is in the code I've pasted.

On a related note, are there any examples of valid orders and hashes so I can verify that what I'm doing matches what the protocol expects?

[fabioberger]

@wysenynja thanks for reaching out. The chainId is optional, and not security critical. Both signatures generated using eth_sign and eth_signTypedData already include the chainId in the signature (see: ethereum/EIPs#155).

[BlinkyStitt]

So does that mean this is only a documentation issue? If so that sounds great.

…

On Nov 9, 2018, at 2:51 PM, Fabio B ***@***.***> wrote: @wysenynja thanks for reaching out. The chainId is optional, and not security critical. Both signatures generated using eth_sign and eth_signTypedData already include the chainId in the signature (see: ethereum/EIPs#155). — You are receiving this because you were mentioned. Reply to this email directly, view it on GitHub, or mute the thread.

[fabioberger]

@wysenynja no, it means we do not include the chainId in the 0x EIP712 domain, but that is OK, because it is optional and not security critical.

[BlinkyStitt]

Ok. Thanks.

And what about verifyingContract? What address should that be?

And are there any example orders with valid hashes for testing my implementation?

[fabioberger]

Verifying contract should the 0x Exchange contract address. See: https://0xproject.com/wiki#Deployed-Addresses

I would just generate an order and hash it using @0x/order-utils. What exactly are you implementing?

[BlinkyStitt]

Thanks. I'm building an orderbook aggregator in Rust as a way to learn Rust. The Rust web3 library doesn't have any helpers for EIP712 though (tomusdrw/rust-web3#169)

[fabioberger]

😢 That's unfortunate. If you do end up implementing it, you should publish it for others to use! Good luck!