code: function(iv, output) {
        if(iv) {
          /* CBC mode */
          if(typeof iv === 'string') {
            iv = forge.util.createBuffer(iv);
          }
        }
  
        _finish = false;
        _input = forge.util.createBuffer();
        _output = output || new forge.util.createBuffer();
        _iv = iv;
  
        cipher.output = _output;
      }
docs: Starts or restarts the encryption or decryption process, whichever
  was previously configured.
  
  To use the cipher in CBC mode, iv may be given either as a string
  of bytes, or as a byte buffer.  For ECB mode, give null as iv.
  
  @param iv the initialization vector to use, null for ECB mode.
  @param output the output the buffer to write to, null to create one.