my-idlers/node_modules/browserify-aes/modes/cfb1.js

var Buffer = require('safe-buffer').Buffer

function encryptByte (self, byteParam, decrypt) {
  var pad
  var i = -1
  var len = 8
  var out = 0
  var bit, value
  while (++i < len) {
    pad = self._cipher.encryptBlock(self._prev)
    bit = (byteParam & (1 << (7 - i))) ? 0x80 : 0
    value = pad[0] ^ bit
    out += ((value & 0x80) >> (i % 8))
    self._prev = shiftIn(self._prev, decrypt ? bit : value)
  }
  return out
}

function shiftIn (buffer, value) {
  var len = buffer.length
  var i = -1
  var out = Buffer.allocUnsafe(buffer.length)
  buffer = Buffer.concat([buffer, Buffer.from([value])])

  while (++i < len) {
    out[i] = buffer[i] << 1 | buffer[i + 1] >> (7)
  }

  return out
}

exports.encrypt = function (self, chunk, decrypt) {
  var len = chunk.length
  var out = Buffer.allocUnsafe(len)
  var i = -1

  while (++i < len) {
    out[i] = encryptByte(self, chunk[i], decrypt)
  }

  return out
}