Controller Area Network (CAN) remains the leading protocol for networking automotive controllers. Access to CAN gives an attacker the ability to modify system operation, perform diagnostic actions, and disable the system. CAN is also used in SCADA networks and industrial control systems.Historically, software and hardware for CAN has been expensive and targeted at automotive OEMs. Last year, we launched CANtact, an open source hardware CAN bus tool for PCs. This provides a low cost solution for converting CAN to USB and getting on the bus.However, once connected to CAN, software is needed to make sense of traffic on the bus. CANtact is a new tool for this purpose. It allows the user to view CAN traffic, decode messages, and perform diagnostic actions in a graphical environment.Existing CAN software is focused on developing systems, CANtact is designed for breaking them. The tool has been designed with reverse engineering and fuzzing in mind.In this talk, we'll introduce the CANtact software, provide details about its design, and explain how it can be used to perform analysis on CAN systems. We'll also look into some of the analysis techinques that are useful for reverse engineering CAN systems.