When the Controller Area Network (CAN) was designed, security was not a requirement. The primary usage of CAN was considered closed; possible intruders or attackers would simply not get physical or remote access to the network. However, today it is more and more common that devices connected to a CAN system also have connections to other networks, including the Internet. Recent car hacks have shown that attackers may get access to CAN systems. Without strong security features, an attacker automatically gains full access to everything connected, allowing active control commands to be recorded and replayed. In this book we examine which options developers of CAN based systems realistically can use to provide adequate security features. What can we do - without using heavy-weight security features? What can we do - to detect possibly injected messages? What can we do - without any hardware change? What can we do - with minimal software change? The CANcrypt protocol and software is introduced as a scalable security solution for the Controller Area Network. Free demo examples including C source code can be downloaded from ESAcademy's web pages. www.esacademy.com/cancrypt