[docs] Compare function coverage to ethereumjs

[dawsbot]

ethereumjs has MANY functions, of which we should make a "checklist" of currently implemented equivalents in essential-eth.

A good starting-point would be the function here

import {
  hashPersonalMessage,
  toBuffer,
  fromRpcSig,
  ecrecover,
  publicToAddress,
  bufferToHex
} from 'ethereumjs-util';

[kesar]

after doing research, i think the only missing method to be implemented would be verifyMessage / recoverPublicKey :

https://docs.ethers.io/v4/api-utils.html#cryptographic-functions

utils . verifyMessage ( messageStringOrArrayish , signature ) => Address

everything else can be already implemented w eeth. I cloned web3-token repo and i was able to run test replacing all the other ethereumjs calls.

import Base64 from 'base-64'
import {
  toBuffer,
  ecrecover
} from 'ethereumjs-util';

import {
  hashMessage,
  computeAddress,
  splitSignature
} from 'essential-eth';

import { DecrypterResult } from '../interfaces';

const getVersion = (body: string): number => {
  // @ts-ignore
  const [ str ] = body.match(/Web3[\s-]+Token[\s-]+Version: \d/);

  return Number(str.replace(' ', '').split(':')[1]);
}

export const decrypt = (token: string): DecrypterResult => {
  if(!token || !token.length) {
    throw new Error('Token required.')
  }

  const base64_decoded = Base64.decode(token);

  if(!base64_decoded || !base64_decoded.length) {
    throw new Error('Token malformed (must be base64 encoded)')
  }

  let body: string, signature: string;

  try {
    ({ body, signature } = JSON.parse(base64_decoded));
  } catch (error) {
    throw new Error('Token malformed (unparsable JSON)')
  }

  if(!body || !body.length) {
    throw new Error('Token malformed (empty message)')
  }

  if(!signature || !signature.length) {
    throw new Error('Token malformed (empty signature)')
  }

  const msgHash = hashMessage(body);
  const signatureParams = splitSignature(signature);

  const publicKey = ecrecover(
    toBuffer(msgHash),
    signatureParams.v,
    toBuffer(signatureParams.r),
    toBuffer(signatureParams.s)
  );
  const address = computeAddress('0x04'+ publicKey.toString('hex')).toLowerCase();
  const version = getVersion(body);

  return {
    version,
    address,
    body,
    signature
  }
}