1. Hash-based Enhancement of Location Privacy for Radio- Frequency Identification Devices using Varying Identifiers Author ： Dirk Henrici and Paul Muller Presented by Li-yuan Lai March 20, 2007

2. Outline Introduction Scheme Normal Operation Example Conclusion

3. Introduction RFID may emerge as one of the most pervasive computing technologies in history. But products equipped with RFID tags enable tracking of persons by the tags they carry. This paper introduces a simple scheme relying on one-way hash functions that greatly enhances location privacy.

4. Scheme define y = h(x) as a cryptographic one-way hash function

5. - Database-identifier (“DB-ID”) read only, optionally writable - Current ID (“ID”) read/write - Transaction number (“TID”) read/write - Last successful transaction number (“LST”) read/write - Additional fields for user data or a master key are conceivable but not required at all - Hash of current ID (“HID”), acting as primary index of the table - Current ID (“ID”) - Last transaction number (“TID”) - Last successful transaction number (“LST”) - Associated DB entry (“AE”) - A reference to tag data / user data (“DATA”)

6. Normal Operation 1. tag ： h(ID) 2. When queried, TID+1 3. send ： h(ID), DB-ID, h(TID 。 ID), △ TID （ △ TID =TID - LST ） 4. database ： TID‘ ＝△ TID + LST, calculate h(TID’ 。 ID) 5. update ： create RND, generating ID’ （ ID‘= RND 。 ID ） 6. respond ： RND, h(RND 。 TID’ 。 ID) 7. receiver ： check hash, changing ID 、 TID

7. initial ： send ： H(14), tagdb, h(10), 1 ( h(10) = h(4 。 14) ) Suppose RND = 13, then ID’ = h(13 。 14) = h(3) respond ： 13, h(7) ( h(7) = h(13 。 4 。 14) ) final ： Suppose ID = 14, DB-ID = tagdb, TID = LST = 3 tagdb

8. Conclusion The main benefit of the proposed scheme is its simplicity: It only requires a hash function in the tag and data management at the back- end. it is enhancing location privacy greatly without restraining other applications.