code: function decrypt (input, firstKey = 0xAB) {
    const buf = Buffer.from(input);
    let key = firstKey;
    let nextKey;
    for (let i = 0; i < buf.length; i++) {
      nextKey = buf[i];
      buf[i] = buf[i] ^ key;
      key = nextKey;
    }
    return buf;
  }
docs: Decrypts input where each byte is XOR'd with the previous encrypted byte.
  @alias  module:tplink-smarthome-crypto.decrypt
  @param  {Buffer} input           encrypted Buffer
  @param  {number} [firstKey=0xAB]
  @return {Buffer}                 decrypted buffer