@hydrogenplatform/raindrop/src/clientMessages.js

Convenience functions to integrate Raindrop authentication into your project.

const crypto = require('crypto')

function generateMessage () {
  return crypto.randomBytes ? generateMessageNode() : generateMessageBrowser()
}

function generateMessageBrowser () {
  var uints
  var challenges
  do {
    // using Uint32Array(1) won't work because bitwise operations convert to signed 32 bit ints, leading to overflows
    uints = new Uint16Array(2)
    window.crypto.getRandomValues(uints)
    // to get two csprns in [0, 1e3) they need 10 random bits each, so we get 10 = 16-6 bytes per uint16
    challenges = uints.map(u => { return u >> 6 })
  } while (!challenges.every(u => { return u < 1e3 })) // repeat if numbers >= 1e3, to maintain a uniform distribution

  return Array.from(challenges).map(u => { return u.toString().padStart(3, '0') }).join('')
}

function generateMessageNode () {
  var challenge
  do {
    // to get a csprn in [0, 1e6) we need 20 random bits, so we get 3 random bytes := 24 bits and shift off 4 bits
    challenge = crypto.randomBytes(3).readUIntBE(0, 3) >> 4
  } while (challenge >= 1e6) // repeat if number >= 1e6, to maintain a uniform distribution

  return challenge.toString().padStart(6, '0')
}

module.exports = {
  generateMessage: generateMessage
}