wallet-core/node_modules/browserify-aes/modes/cfb.js

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

function encryptStart (self, data, decrypt) {
  var len = data.length
  var out = xor(data, self._cache)
  self._cache = self._cache.slice(len)
  self._prev = Buffer.concat([self._prev, decrypt ? data : out])
  return out
}

exports.encrypt = function (self, data, decrypt) {
  var out = Buffer.allocUnsafe(0)
  var len

  while (data.length) {
    if (self._cache.length === 0) {
      self._cache = self._cipher.encryptBlock(self._prev)
      self._prev = Buffer.allocUnsafe(0)
    }

    if (self._cache.length <= data.length) {
      len = self._cache.length
      out = Buffer.concat([out, encryptStart(self, data.slice(0, len), decrypt)])
      data = data.slice(len)
    } else {
      out = Buffer.concat([out, encryptStart(self, data, decrypt)])
      break
    }
  }

  return out
}