Privacy Analysis of Forward and Backward Untraceable RFID Authentication Schemes

In this paper, we analyze RFID authentication schemes designed to provide forward untraceability and backward untraceability: the L-K and S-M schemes. We show how to trace tags in the L-K scheme without corrupting tags. We also show that if a standard cryptographic pseudorandom bit generator (PRBG) is used in the SM scheme, then the scheme may fail to provide forward untraceability and backward untraceability. To achieve the desired untraceability features, the S-M scheme can use a robust PRBG which provides forward security and backward security.