How to sign data with app private key

mikecohen.id · October 31, 2018, 2:00pm

Hi, I have some user data and I want to be able to sign and verify with the users app private key. Very much welcome pointers on how to go about this. I’m trying for example…

var bitcoin = require('bitcoinjs-lib')
var bitcoinMessage = require('bitcoinjs-message')

const bytes = Buffer.from(appprivkey)
const privkeyBs58 = bs58.encode(bytes)
var keyPair = bitcoin.ECPair.fromWIF(privkeyBs58)
var privateKey = keyPair.privateKey
var signature = bitcoinMessage.sign(message, privkey, keyPair.compressed)

where this fails to get valid base 58 encoding of the private key - e.g.

var keyPair = bitcoin.ECPair.fromWIF(privkeyBs58)

throws ‘Invalid Checksum’

Is this close / a valid use case?

mikecohen.id · October 31, 2018, 2:05pm

Ah - think I just found the answer from bottom of this this post.

  var privKeyWith01 = account.appPrivateKey + '01'
  let privkey = hexStringToECPair(privKeyWith01).toWIF()

and then

var keyPair = bitcoin.ECPair.fromWIF(privkey)
var privateKey = keyPair.privateKey
var signature = bitcoinMessage.sign(message, privateKey, keyPair.compressed)

looks like it creates a valid signature but any general comments on this approach will be helpful?

nicktee · November 2, 2018, 4:39am

@mikecohen.id,

I implemented this in my dapp, Blockusign. I wanted to to prove a real person with a human identity signed a document hash ( preferable with attestations to twitter/facebook etc… ). I wanted it to link back to the users blockstack id, not just a public key. Then I wanted to persist this immutably forever via an anchor of that data to bitcoin using Blockstack subdomains ( $$$$ much cheaper) I anchor twice a day, costing only a few cents per day at the current BTC transaction cost!

code is here:

github.com

ntheile/blockusign/blob/master/BlockUSign.Ionic/src/pages/blockchain/blockchain.ts

import { Component, ViewChild } from '@angular/core';
import { IonicPage, NavController, NavParams, ToastController } from 'ionic-angular';
import { DocumentService } from './../../services/document.service';
import { BlockStepsComponent } from '../../components/block-steps/block-steps';
import { BitcoinService } from '../../services/bitcoin.service';
import { BlockStackService } from '../../services/blockstack.service';
import { EmailService } from '../../services/email.service';
import { Block } from 'bitcoinjs-lib';
import { AlertController } from 'ionic-angular';
import { LoadingComponent } from '../../components/loading/loading';
import { VideoComponent  } from '../../components/video/video';
declare let window: any; 
declare let blockstack: any;
declare let $:any;
declare let blast:any;
declare let parseZoneFile: any;

/**
 * Generated class for the SignPage page.
 *

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design thoughts here: https://github.com/ntheile/blockusign/issues/58

if you use the app there is a nice visual of it - https://blockusign.co/

mikecohen.id · November 2, 2018, 3:23pm

Thanks Nick - will take a deeper look - good to know about your project!

nicktee · November 2, 2018, 3:44pm

No prob mike. Also there is some helper code in the bitcoin service:

github.com

ntheile/blockusign/blob/master/BlockUSign.Ionic/src/services/bitcoin.service.ts

import { Injectable } from '@angular/core';
import 'rxjs/add/operator/toPromise';
import { Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';
import { AnonymousSubject } from 'rxjs/Subject';
import { map } from 'rxjs/operators';
import { of } from 'rxjs/observable/of';
import { delay } from 'rxjs/operator/delay';
import { Headers, RequestOptionsArgs, RequestOptions } from '@angular/http';
import { HttpHeaders } from '@angular/common/http';

declare let global: any;
//declare let bitcore: any;
declare let blockstack: any;
declare let bitcoin: any;
declare let window: any;
declare let parseZoneFile: any;

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and in the blockstack service

github.com

ntheile/blockusign/blob/master/BlockUSign.Ionic/src/services/blockstack.service.ts

import { Injectable } from '@angular/core';
import { Document, Log, Message } from './../models/models';
import 'rxjs/add/operator/toPromise';
import { Http, Response } from '@angular/http';
import { Observable } from 'rxjs/Observable';
import 'rxjs/add/operator/map';
import 'rxjs/add/operator/catch';
import { AnonymousSubject } from 'rxjs/Subject';
import { Events } from 'ionic-angular';
import { map } from 'rxjs/operators';
import { of } from 'rxjs/observable/of';
import { delay } from 'rxjs/operator/delay';
import { Headers, RequestOptionsArgs, RequestOptions } from '@angular/http';
import { HttpHeaders } from '@angular/common/http';
declare let blockstack: any;
declare let sjcl: any;

@Injectable()
export class BlockStackService {

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hank · November 2, 2018, 9:20pm

Thanks Nick for pointing out a live example!

It’s also a little easier to just use blockstack.js and not have to use the Bitcoin libs:

import { signECDSA, verifyECDSA } from 'blockstack/lib/encryption';
import { loadUserData } from 'blockstack/lib/auth/authApp';

// this returns an object like { signature: string, publicKey: string }
const sign = (message) => {
  const { appPrivateKey } = loadUserData();
  return signECDSA(appPrivateKey, message);
}

// returns true or false
const verify = (message, signedObject) => {
  return verifyECDSA(message, signedObject.publicKey, signedObject.signature);
}

const message = 'hello, world';
const signature = sign(message);
const valid = verify(messaged, signature);

nicktee · November 3, 2018, 1:04am

Thanks Hank. I was wondering where you guys put that in blockstack.js!