Reverse-Engineering a Cryptographic RFID Tag

The security of embedded devices often relies on the secrecy of proprietary cryptographic algorithms. These algorithms and their weaknesses are frequently disclosed through reverse-engineering software, but it is commonly thought to be too expensive to reconstruct designs from a hardware implementation alone. This paper challenges that belief by presenting an approach to reverse-engineering a cipher from a silicon implementation. Using this mostly automated approach, the paper reveals a cipher from an RFID tag that is not known to have a software or micro-code implementation. The paper reconstructs the cipher from the widely used Mifare Classic RFID tag by using a combination of image analysis of circuits and protocol analysis.