\input zb-basic \input zb-ioport \iteman{io-port 05488436} \itemau{Bogdanov, Andrey; Leander, Gregor; Paar, Christof; Poschmann, Axel; Robshaw, Matt J.B.; Seurin, Yannick} \itemti{Hash functions and RFID tags: mind the gap.} \itemso{Oswald, Elisabeth (ed.) et al., Cryptographic hardware and embedded systems -- CHES 2008. 10th international workshop, Washington, D.C., USA, August 10--13, 2008. Proceedings. Berlin: Springer (ISBN 978-3-540-85052-6/pbk). Lecture Notes in Computer Science 5154, 283-299 (2008).} \itemab Summary: The security challenges posed by RFID-tag deployments are well-known. In response there is a rich literature on new cryptographic protocols and an on-tag hash function is often assumed by protocol designers. Yet cheap tags pose severe implementation challenges and it is far from clear that a suitable hash function even exists. In this paper we consider the options available, including constructions based around compact block ciphers. While we describe the most compact hash functions available today, our work serves to highlight the difficulties in designing lightweight hash functions and we urge caution when routinely appealing to a hash function in an RFID-tag protocol. \itemrv{~} \itemcc{} \itemut{} \itemli{doi:10.1007/978-3-540-85053-3\_18} \end