Hidden Bits Approach for Authentication in RFID Systems

We present an authentication scheme designed for tiny and strictly constrained devices like RFID-tags. Authentication is based on the symmetric key shared between a tag and a reader. While a tag needs to perform only simple operations in order to authenticate: to pick n/2+b random values and then to compute XORs of some values, a reader needs to try 2 possible values to check if a tag replied correctly (b is small). At the same time eavesdropping adversary after r executions of the protocol needs to solve a system of rk-multivariate quadratic equations over GF (2) with nk + rb variables. We present a security discussion of proposed solutions.