Verifying Signatures

Verifying Signatures with EIP-1271

Since contracts can’t generate signatures therefore ecrecoverwon’t work if the address is a contract, then the contract-based account needs to use the EIP1271 standard to verify signatures for contracts.

Verifying contract-based account signatures require calling the EIP1271 isValidSignature( data, signature) method on the account contract. Authereum, Dapper wallet, 0x, and a few others are already using EIP1271 to verify signatures where the "recovered address" is a contract address.

Here's an an example of how to verify Authereum dapp key signatures:

const Web3 = require('web3')
const provider = new Web3.providers.HttpProvider('https://kovan.infura.io')
const web3 = new Web3(provider)
const eip1271Abi = [
{
"constant": true,
"inputs": [
{
"name": "_messageHash",
"type": "bytes"
},
{
"name": "_signature",
"type": "bytes"
}
],
"name": "isValidSignature",
"outputs": [
{
"name": "magicValue",
"type": "bytes4"
}
],
"payable": false,
"stateMutability": "view",
"type": "function"
}
]
const account = '0x99bd0006D13542A0917Cf8F2F986Ca7667b84268'
const data = '0x47173285a8d7341e5e972fc677286384f802f8ef42a5ec5f03bbfa254cb01fad'
const signature = '0x0304494527023df3a811f5ad61aa35177a4455eb4bf098561f9380a574915f4c1ff4a5fc653afdfc086dcc9662848097703d18b82156618ccec1e5c9da7623e51b4760269d07f9a074dc2d6ab10cf52ff77852662e40fbb4b27289126a5bb538271e147c0952204161d710bb070a6e470b0b1ef65d11f1dc074e235e3dfaef00ae1b'
const magicValue = '0x20c13b0b'
const instance = await new web3.eth.Contract(eip1271Abi, account)
const result = await instance.methods.isValidSignature(data, signature).call()
const verified = (result === magicValue)
console.log(verified) // true

The isValidSignature method returns a magic which is computed from bytes4(keccak256("isValidSignature(bytes,bytes)"). The reason for returning a magic value to avoid accidentally returning true.

Using NPM package helper:

For convenience, there's the is-valid-signature NPM package you can use to validate signature for account contracts.

const validateContractSignature = require('is-valid-signature')
const Web3 = require('web3')
const provider = new Web3.providers.HttpProvider('https://kovan.infura.io')
const account = '0x99bd0006D13542A0917Cf8F2F986Ca7667b84268'
const data= '0x47173285a8d7341e5e972fc677286384f802f8ef42a5ec5f03bbfa254cb01fad'
const signature = '0x0304494527023df3a811f5ad61aa35177a4455eb4bf098561f9380a574915f4c1ff4a5fc653afdfc086dcc9662848097703d18b82156618ccec1e5c9da7623e51b4760269d07f9a074dc2d6ab10cf52ff77852662e40fbb4b27289126a5bb538271e147c0952204161d710bb070a6e470b0b1ef65d11f1dc074e235e3dfaef00ae1b'
const verified = await validateContractSignature(account, data, signature, provider)
console.log(verified) // true

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