Improved meet-in-the-middle attacks on reduced-round Kalyna-128/256 and Kalyna-256/512

Kalyna is an SPN-based block cipher that was selected during Ukrainian National Public Cryptographic Competition (2007-2010) and its slight modification was approved as the new encryption standard of Ukraine. In this paper, we focus on the key-recovery attacks on reduced-round Kalyna-128/256 and Kalyna256/512 with meet-in-the-middle method. The differential enumeration technique and key-dependent sieve technique which are popular to analyze AES are used to attack them. Using the key-dependent sieve technique to improve the complexity is not an easy task, we should build some tables to achieve this. Since the encryption procedure of Kalyna employs a preand post-whitening operations using addition modulo 264 applied on the state columns independently, we carefully study the propagation of this operation and propose an addition plaintext structure to solve this. For Kalyna-128/256, we propose a 6-round distinguisher, and achieve a 9-round (out of total 14-round) attack. For Kalyna-256/512, we propose a 7-round distinguisher, then achieve an 11-round (out of total 18-round) attack. As far as we know, these are currently the best results on Kalyna-128/256 and Kalyna-256/512.