exports.createSecureStream = function(clearStream, encryptedStream, credentials, is_server){
  var stream = new exports.SecureStream(credentials, is_server);

  // r/w cleartext data
  clearStream.pipe(stream._clear);
  stream._clear.pipe(clearStream);

  // r/w encrypted data
  stream._encrypted.pipe(encryptedStream);
  encryptedStream.pipe(stream._encrypted);
  return stream;
}

exports.SecureStream = function(){
  Stream.call(this);
}

...