Shadow: A Lightweight Block Cipher for IoT Nodes

The advancement of the Internet of Things (IoT) has promoted the rapid development of low-power and multifunctional sensors. However, it is seriously significant to ensure the security of data transmission of these nodes. Meanwhile, sensor nodes have the characteristics of converting analog signals into digital signals for operation processing in wireless sensor networks (WSNs). Given the particularity of Addition or AND, Rotation, and XOR (ARX) operations, its round function can only be based on the Feistel structure or generalized Feistel structure, otherwise, the process of decryption cannot be completed correctly. Furthermore, the existing ARX ciphers have the problems of only changing half of the plaintext block in one round and iterating for many rounds. In this article, a new logical combination method of generalized Feistel structure and ARX operations is proposed to improve the diffusion speed of ARX ciphers, called Shadow. Shadow overcomes the shortcomings of traditional ARX ciphers that only diffuse half of the block in one round. To ensure the efficiency of the encryption hardware circuit while ensuring the security of the physical-layer signal, we studied the round-based hardware architecture and the serial hardware architecture for Shadow cipher. Particularly, we conducted a series of performance tests on Shadow, including the avalanche effect, FPGA implementation, and ASIC implementation. Also, we conducted a security analysis of the Shadow. As shown by our experiments and comparisons, Shadow is compact in IoT nodes and is of high security against cryptanalysis.