The University of Adelaide Use of the Shrinking Generator in Lightweight Cryptography for RFID

RFID tags have severe constraints in computing power and hence offer particular challenges in the provision of e-Security. Whatever is chosen to provide security in an RFID tag should have low computational overhead. New approaches, differing from the traditional cryptosystems based on RSA, Diffie-Hellman, et al. are required. The use of one time codes is particularly appropriate as they guarantee perfect security and offer simple implementation. Research, experimentation, and field deployment in RFID has been done using different types of algorithms including bit shift, xor operations, pseudorandom bit generators including linear feedback shift registers (LFSR). There are many different types of pseudorandom bit generators. Some use RSA, or discrete logarithm like arithmetic, but use the last bit of the generated sequence as the random bit. These are infeasible in RFID and other lightweight devices due to high computational loads arising from the complex arithmetic operations. Another approach to the generation of random sequences is to use a combination of LFSRs. These are used in portable devices such as the GSM mobile phones. They have lightweight computational loads, but are susceptible to attacks. Of the many ingenuous combinations of LFSRs, the Shrinking Generator, designed in 1993, seems to have withstood the challenges of attacks if the polynomial connection structure and the internal seeds are kept secret.