Analysis and improvement of a pseudorandom number generator for EPC Gen2 tags

The EPC Gen2 is an international standard that proposes the use of Radio Frequency Identification (RFID) in the supply chain. It is designed to balance cost and functionality. The development of Gen2 tags faces, in fact, several challenging constraints such as cost, compatibility regulations, power consumption, and performance requirements. As a consequence, security on board of Gen2 tags is often minimal. It is, indeed, mainly based on the use of on board pseudorandomness. This pseudorandomness is used to blind the communication between readers and tags; and to acknowledge the proper execution of password-protected operations. Gen2 manufacturers are often reluctant to show the design of their pseudorandom generators. Security through obscurity has always been ineffective. Some open designs have also been proposed. Most of them fail, however, to prove their correctness. We analyze a recent proposal presented in the literature and demonstrate that it is, in fact, insecure. We propose an alternative mechanism that fits the Gen2 constraints and satisfies the security requirements.