Attacking the Tav-128 Hash function

Many RFID protocols use cryptographic hash functions for their security. The resource constrained nature of RFID systems forces the use of light weight cryptographic algorithms. Tav-128 is one such light weight hash function proposed by Peris-Lopez et al. for an RFID authentication protocol. In this article we show that Tav-128 is not collision resistant. We show a practical collision attack against Tav-128 and produce message pairs of arbitrary length which produce the same hash value under this hash function. We also study the constituent functions of Tav-128 and show that the concatenation of nonlinear functions A and B produces a 64-bit permutation from 32-bit messages. This could be a useful light weight primitive for future RFID protocols.