EIP-721
Based on LooksRare
Last updated
Based on LooksRare
Last updated
EIP-712 aims to improve off-chain message signing
Currently, signed messages are an opaque hex string displayed to the user with little context about the items that make up the message.
EIP-712 aims to make these hex strings human readable.
An EIP-712 signature allows signers to see exactly what they are signing in a client wallet as the signed data is split into different fields.
It also prevents the reuse of signature - achieved by having a domain separator in the signature.
The domain separator prevents collision of otherwise identical structures.
The domainSeparator is a value unique to each domain that is ‘mixed in’ the signature. This helps to prevent a signature meant for one dApp from working in another.
The sellOrder hash contains all the necessary properties to be processed as a valid order, except the signature values.
EIP-712’s standard encoding prefix is \x19\x01, so the final digest is: bytes32 digest = keccak256(abi.encodePacked("\x19\x01", domainSeparator, hash));
The signature created by the seller is stored off-chain (v, r, s are the values for the transaction's signature).
Subsequently, when a prospective buyer wishes to make a purchase, he would do so with the buy function.
The buy function checks that the sellOrder struct submitted by the buyer lines up with the seller's signature that was previously stored off-chain.
ecrecover is used to verify the signature. ecrecover is simply recovering the public key (and from there the address) used to sign the digest.
ECDSA signatures consist of two numbers (integers): r and s. Ethereum uses an additional v (recovery identifier) variable.
r and s (ECDSA signature outputs), v (recovery identifier)
v is important because since we are working with elliptic curves, multiple points on the curve can be calculated from r and s alone. (two points of intersection) This would result in two different public keys (thus addresses) that can be recovered. The v simply indicates which one of these points to use.
To create a signature you need the message to sign and the private key to sign it with
The {r, s, v} signature can be combined into one 65-byte-long sequence: 32 bytes for r, 32 bytes for s, and one byte for v
In order to verify a message, we need the original message, the address of the private key it was signed with, and the signature {r, s, v} itself.
LooksRare uses exclusively EIP-712 signatures, for off-chain maker orders
A maker order is a passive order, which can be executed (if not cancelled!) against a taker order after it is signed.
Since the execution of a maker order is done once a taker order matches on-chain, network gas fees are never paid by the maker user.
A seller has to sign an EIP-712 signature of the order’s hash, which can then be later submitted on chain by the buyer.
