eip-712

This is a library for Node.js and web browsers with some utility functions that can help with signing and verifying EIP-712 based messages. It is fully written in TypeScript, and is currently only compatible with the latest specification of EIP-712 (eth_signTypedData_v4).

https://eips.ethereum.org/EIPS/eip-712

Note that this library currently does not handle the signing itself. For this, you can use something like Ethers.js or ethereumjs-util. For examples, please see the examples folder.

Installation

You can install this library with Yarn or NPM:

$ yarn add eip-712

$ npm install eip-712

There is a CommonJS version as well as an ES6 version available. Most tools should automatically pick the right version (e.g. Node.js, Webpack).

Getting Started

First, define your typed data as a JSON object, according to the JSON schema specified by EIP-712. For example:

{
  "types": {
    "EIP712Domain": [
      { "name": "name", "type": "string" },
      { "name": "version", "type": "string" },
      { "name": "chainId", "type": "uint256" },
      { "name": "verifyingContract", "type": "address" }
    ],
    "Person": [
      { "name": "name", "type": "string" },
      { "name": "wallet", "type": "address" }
    ],
    "Mail": [
      { "name": "from", "type": "Person" },
      { "name": "to", "type": "Person" },
      { "name": "contents", "type": "string" }
    ]
  },
  "primaryType": "Mail",
  "domain": {
    "name": "Ether Mail",
    "version": "1",
    "chainId": 1,
    "verifyingContract": "0xCcCCccccCCCCcCCCCCCcCcCccCcCCCcCcccccccC"
  },
  "message": {
    "from": {
      "name": "Cow",
      "wallet": "0xCD2a3d9F938E13CD947Ec05AbC7FE734Df8DD826"
    },
    "to": {
      "name": "Bob",
      "wallet": "0xbBbBBBBbbBBBbbbBbbBbbbbBBbBbbbbBbBbbBBbB"
    },
    "contents": "Hello, Bob!"
  }
}

Functions

Here is a brief description of the functions available in this library. For more detailed examples, you can refer to src/eip-712.test.ts, or to the examples in the examples folder.

getMessage(typedData, hash?)

This function will return the full EIP-191 encoded message to be signed as Buffer, for the typed data specified. If hash is enabled, the message will be hashed using Keccak256.

import { getMessage } from 'eip-712';

const typedData = { /*...*/ };
console.log(getMessage(typedData).toString('hex')); // 1901f2cee375fa42b42143804025fc449deafd50cc031ca257e0b194a650a912090fc52c0ee5d84264471806290a3f2c4cecfc5490626bf912d01f240d7a274b371e
console.log(getMessage(typedData, true).toString('hex')); // be609aee343fb3c4b28e1df9e632fca64fcfaede20f02e86244efddf30957bd2

asArray(typedData)

This function returns the typed data as an array. This can be useful for encoding typed data as ABI.

import { asArray } from 'eip-712';

const typedData = { /*...*/ };
console.log(asArray(typedData)); // [ ['Cow', '0xCD2a3d9F938E13CD947Ec05AbC7FE734Df8DD826'], ['Bob', '0xbBbBBBBbbBBBbbbBbbBbbbbBBbBbbbbBbBbbBBbB'], 'Hello, Bob!' ]

getStructHash(typedData, type, data)

This function returns a Keccak-256 hash for a single struct type (e.g. EIP712Domain, Person or Mail).

import { getStructHash } from 'eip-712';

const typedData = { /*...*/ };
console.log(getStructHash(typedData, 'EIP712Domain', typedData.domain).toString('hex')); // f2cee375fa42b42143804025fc449deafd50cc031ca257e0b194a650a912090f

encodeData(typedData, type, data)

This function returns the raw ABI encoded data for the struct type.

import { encodeData } from 'eip-712';

const typedData = { /*...*/ };
console.log(encodeData(typedData, 'EIP712Domain', typedData.domain).toString('hex')); // 8b73c3c69bb8fe3d512ecc4cf759cc79239f7b179b0ffacaa9a75d522b39400fc70ef06638535b4881fafcac8287e210e3769ff1a8e91f1b95d6246e61e4d3c6c89efdaa54c0f20c7adf612882df0950f5a951637e0307cdcb4c672f298b8bc60000000000000000000000000000000000000000000000000000000000000001000000000000000000000000cccccccccccccccccccccccccccccccccccccccc

getTypeHash(typedData, type)

This function returns the type hash for a struct type. This is the same as Keccak256(EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)), with optional sub-types automatically included too.

import { getTypeHash } from 'eip-712';

const typedData = { /*...*/ };
console.log(getTypeHash(typedData, 'EIP712Domain').toString('hex')); // 8b73c3c69bb8fe3d512ecc4cf759cc79239f7b179b0ffacaa9a75d522b39400f

encodeType(typedData, type)

This function returns the type before hashing it, e.g. EIP712Domain(string name,string version,uint256 chainId,address verifyingContract), with optional sub-types automatically included too.

import { encodeType } from 'eip-712';

const typedData = { /*...*/ };
console.log(encodeType(typedData, 'EIP712Domain')); // EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)

getDependencies(typedData, type)

This function returns all sub-types used by a struct as a string array. If the struct has no sub-types (like EIP712Domain), an array with only the type itself is returned.

import { getDependencies } from 'eip-712';

const typedData = { /*...*/ };
console.log(getDependencies(typedData, 'EIP712Domain')); // ['EIP712Domain']
console.log(getDependencies(typedData, 'Mail')); // ['Mail', 'Person']

Non-standard domains (e.g., CIP-23)

It's possible to use a custom domain format, like from the CIP-23 specification, or to disable verifying the domain format completely, if you want to use a custom implementation of EIP-712.

To do this, you can pass options to each function, as last parameter. For example, in order to get the message hash for a message, you can do the following:

import { getMessage } from 'eip-712';
import type { Options } from 'eip-712';

const typedData = { /*...*/ };
const options: Options = {
  // A custom domain identifier. Defaults to 'EIP712Domain'.
  domain: 'CIP23Domain',

  // Whether to verify the structure of the domain. Defaults to 'true'.
  verifyDomain: false
};

console.log(getMessage(typedData, true, options).toString('hex'));