Hardware implementations of the WG-5 cipher for passive RFID tags

Abstract

This paper presents two versions of a Welch-Gong cipher designed for use in passive RFID tags. The low-cost and low-power requirements for passive RFID tags impose stringent design constraints for the chips used in the tags. The WG5-80(x) cipher operates over the finite field F25, and has an 80-bit secret key and 80-bit initialization vector. WG5-80(x11) is the same as WG5-80(x), but includes a decimation function of x11, which increases the linear complexity at the cost of losing the 1-order resiliency property that is inherent in the WG-transform. Both ciphers can be implemented using parallel LFSRs to provide throughputs ranging from one to twenty-five bits per clock cycle. On a 130 nm fabrication process with a clockspeed of 100 kHz and a throughput of 100 kbps, WG5-80(x) has an area of 1229 GE (gate equivalents) and a power consumption of 0.78 μW. The linear complexity of the cipher is 217. The corresponding numbers for WG5-80(x11) are 1235GE, 0.79 μW, and 222. This paper presents results for a 130 nm and a 180 nm process, and data rates of 100 kbps and 200 kbps. The combined area and power results for the WG5 ciphers are approximately 5% better than previous results for low-data-rate ciphers. In addition, WG-ciphers offer mathematically guaranteed randomness and cryptographic properties not provided by other ciphers.