The Expeditious Cipher (X-cipher): A High Throughput Lightweight Cipher

Abstract: Pervasive computing utilizes devices with cost constraints and limited resources in terms of memory, processing speed, and battery supply. Furthermore, we are witnessing the phenomena of halving of the price for constant computing power in less than two years. RFID processes sensitive health-monitoring or biometric data. Accordingly there is a demand for specially-designed cryptographic primitives that are to be efficiently implemented. For these implementations and ciphers that are particularly suited for this purpose, we use the term “lightweight cipher”. The Expeditious Cipher (X-cipher) is a high throughput light-weight cipher with relatively simple design and hardware implementation. In this article, we discuss the cipher design rationale, its software and hardware implementations. The cipher security is based on the well-studied SHA-512 and Whirlpool 512 hash functions that are used to generate the cipher sub-keys. We appreciably enhance the cipher security by cascading the two hashes in a pseudo random manner that is user-key-dependent. The cipher employs a variable-size user key and we show that the encryption rate for its associated hardware implementation reaches 512 bits per cycle. The block size can be varied using other types of hash functions. 1