code: function AESDecipher(key, iv, bits, mode) {
    if (!(this instanceof AESDecipher))
      return new AESDecipher(key, iv, mode);
  
    assert(mode === 'ecb' || mode === 'cbc', 'Unknown mode.');
  
    this.key = new AESKey(key, bits);
    this.mode = mode;
    this.prev = iv;
    this.waiting = null;
    this.lastBlock = null;
  }
docs: AES decipher.
  @constructor
  @ignore
  @param {Buffer} key
  @param {Buffer} iv
  @param {Number} bits
  @param {String} mode