System Architecture

Components

Adder consists of the following separate components, which are designed to work together.

• The Main Server: It is written in C++ and uses the ACE networking library. It is responsible for recording the votes, maintaining the audit trail, running the tallying process, and coordinating the authorities. Its persistent data are stored in a MySQL database.
• libadder: This is the cryptographic library that accompanies the Adder system. It implements the threshold ElGamal encryption necessary for its operation. It is written in C++, and uses the GMP library for multiple precision arithmetic. The libadder library is used by both the browser plugin and the Main Server.
• Web Interface: Using the Web interface, a user interacts with the system. It consists of a set of pages generated by PHP, as well as PHP procedures that communicate with the Main Server. Currently, the PHP code runs on the Apache Web server.
• Browser Applet: This software is installed on each user's machine, and runs in a Java-enabled Web browser. It is responsible for performing all cryptographic operations on the client side. As a result, all major Web browsers are supported by our system.
• AdderGUI: For users who do not wish to use the Web interface, we provide a graphical client. This client, AdderGUI, is written in C++, and uses the Qt library, and so should work on most common platforms, including GNU/Linux, Microsoft Windows, MacOS X, and all major Unix variants. It includes all functionality provided by the Web interface, as well as additional auditing and administration utilities.

System Diagram

Here is a high-level diagram of the complete system: