Support metamask signatures

[veqtor]

Using metamask ethereum accounts and signatures will be a good form of convenience to accelerate adoption. Metamask has created an arbitrary signature scheme for signing messages, the details are a bit fuzzy for me, but given a lotion light-client app embedded in a browser, it would be convenient to support signatures from metamask. Perhaps this should be a special account type

It seems the signature is a normal secp256k1 signature of the keccak256 hash of the message which is an array of parameters. This seems quite close to the current signature scheme, or?

Details:
https://medium.com/metamask/scaling-web3-with-signtypeddata-91d6efc8b290
https://medium.com/metamask/the-new-secure-way-to-sign-data-in-your-browser-6af9dd2a1527
ethereum/go-ethereum#2940

[veqtor]

With this scheme, signing a transfer would then be as simple as:

 var msgParams = [
  {
    type: 'string',
    name: 'Method',
    value: 'coins-transfer' //Here I'm thinking module name and function name
 },
 {   
   type: 'address',
      name: 'from',
      value: '0x0'
  },
 {   
   type: 'address',
      name: 'to',
      value: '0x1'
  },
 {   
   type: 'uint32',
      name: 'value',
      value: '10'
  },
 {   
   type: 'uint32',
      name: 'nonce',
      value: '3'
  },
 {   
    //IMPORTANT! Replay protection!
   type: 'bytes32',
      name: 'gci',
      value: APP_GCI
  }
]   

web3.eth.getAccounts(function (err, accounts) {
  if (!accounts) return
  signMsg(msgParams, accounts[0])
})
function signMsg(msgParams, from) {
  web3.currentProvider.sendAsync({
    method: 'eth_signTypedData',
    params: [msgParams, from],
    from: from,
  }, function (err, result) {
    if (err) return console.error(err)
    if (result.error) {
      return console.error(result.error.message)
    }
    const recovered = sigUtil.recoverTypedSignature({
      data: msgParams,
      sig: result.result 
    })
    if (recovered === from ) {
      alert('Recovered signer: ' + from)
    } else {
      alert('Failed to verify signer, got: ' + result)
    }
  })
}

Of course, this would be implemented as a coins.metamask_wallet function, so devs need not think about it

edit: probably the "from" field could be removed by using ecrecover to get the pubkey

[mappum]

It's been a long time since this issue was created, but I'm definitely interested in supporting this. I hadn't considered the way you suggest, which is interesting since the Metamask UI will display the data in a user-friendly way.

But I think I would lean toward using personal_sign so the user would just see the tx JSON in the prompt, then if this was widely adopted we could encourage the Metamask team to natively support our transaction formats.