LLLWBC: A New Low-Latency Light-Weight Block Cipher

Abstract

Lightweight cipher suitable for resource constrained environment is crucial to the security of applications such as RFID, Internet of Things, etc. Moreover, in recent years low-latency is becoming more important and highly desirable by some specific applications which need instant response and real-time security. In this paper, we propose a new low-latency block cipher named LLLWBC. Similar to other known low-latency block ciphers, LLLWBC preserves the important $\alpha$-reflection property, namely the decryption for a key K is equal to encryption with a key $K \oplus \alpha$ where $\alpha$ is a fixed constant. However, instead of the normally used SP-type construction, the core cipher employs a variant of generalized Feistel structure called extended GFS. It has 8 branches and employs byte-wise round function and nibble-wise round permutation iterated for 21 rounds. We choose the round permutations carefully together with a novel key schedule to guarantee the $\alpha$-reflection property. This allows an efficient fully unrolled implementation of LLLWBC in hardware and the overhead of decryption on top of encryption is negligible. Moreover, because of the involutory property of extended GFS, the inverse round function is not needed, which makes it possible to be implemented in round-based architecture with a competitive area cost. Furthermore, our security evaluation shows that LLLWBC can achieve enough security margin within the constraints of security claims. Finally, we evaluate the hardware and software performances of LLLWBC on various platforms and a brief comparison with other low-latency ciphers is also presented.

Appendix

Test vectors of LLLWBC (in hexadecimal).

• Plaintext: 01 23 45 67 89 ab cd ef

• Key: 01 23 45 67 89 ab cd ef fe dc ba 98 76 54 32 10

• Ciphertext: 4d ac 97 75 8b 96 f3 83