Learn how security researchers reverse-engineered and created the first open source implementation of HID SEOS, a proprietary RFID communication protocol used in corporate, educational, healthcare, and government access control systems. Discover the technical process behind analyzing this undocumented credential technology that serves as HID Global's leading access control solution. Explore the methodology used to understand the protocol's inner workings without publicly available documentation, and see how the resulting source code was integrated into the Proxmark3 project. Gain insights into the security implications of widely-deployed access control technologies and understand the challenges involved in reverse-engineering proprietary RFID protocols for security research purposes.