Paper 2014/084

RECTANGLE: A Bit-slice Lightweight Block Cipher Suitable for Multiple Platforms

Wentao Zhang and Zhenzhen Bao and Dongdai Lin and Vincent Rijmen and Bohan Yang and Ingrid Verbauwhede

Abstract

In this paper, we propose a new lightweight block cipher named RECTANGLE. The main idea of the design of RECTANGLE is to allow lightweight and fast implementations using bit-slice techniques. RECTANGLE uses an SP-network. The substitution layer consists of 16 4 x 4 S-boxes in parallel. The permutation layer is composed of 3 rotations. As shown in this paper, RECTANGLE offers great performance in both hardware and software environment, which provides enough flexibility for different application scenario. The following are 3 main advantages of RECTANGLE. First, RECTANGLE is extremely hardware-friendly. For the 80-bit key version, a one-cycle-per-round parallel implementation only needs 1600 gates for a throughput of 246 Kbits/sec at 100 KHz clock and an energy efficiency of 3.0 pJ/bit. Second, RECTANGLE achieves a very competitive software speed among the existing lightweight block ciphers due to its bit-slice style. Using 128-bit SSE instructions, a bit-slice implementation of RECTANGLE reaches an average encryption speed of about 3.9 cycles/byte for messages around 3000 bytes. Last, but not least, we propose new design criteria for the RECTANGLE S-box. Due to our careful selection of the S-box and the asymmetric design of the permutation layer, RECTANGLE achieves a very good security-performance tradeoff. Our extensive and deep security analysis shows that the highest number of rounds that we can attack, is 18 (out of 25).

Note: We have presented the first version of RECTANGLE in Cryptology ePrint Archive in February 2014. In this new version, we have made two changes. Firstly, the S-box is changed to the inverse S-box of the first version, for a better software performance. Secondly, the key schedule is updated to improve its software performance and resistance against related-key attacks, at the cost of an acceptable increase in hardware area.