Meet-in-the-Middle Attack on the 15-Round Variant of the Lightweight Block Cipher Shakey for Protection of IoT Devices

This paper applies Meet-in-the-Middle (MITM) attacks to Shakey [3]. Shakey is the lightweight block cipher for Internet of Things (IoT) applications proposed by Anushka Sivakumar et al. in 2023. It features a 128-bit secret key, 32 rounds of iterative function, and a 64-bit block size. The structure of Shakey is a Generalized Feistel Network (GFN) and Addition Rotation XOR (ARX) network. While the paper proposing Shakey assessed only differential attacks, no evaluation using MITM attacks, proposed by Diffie and Hellman in 1977 [6], has been conducted. This investigation applies MITM attacks on Shakey, demonstrating that the maximum number of attackable rounds is 15. The attack requires less than 2
¹²⁸
times of Shakey encryption operation –— specifically 2
^126.600
and 2
^126.596
times of an encryption operation–, three and sixty-five known plaintext-ciphertext pairs, respectively, and 2
¹²⁶
words of memory.