Single Key Recovery Attacks on 9-Round Kalyna-128/256 and Kalyna-256/512

Akshima, Donghoon Chang, Mohona Ghosh, Aarushi Goel, Somitra Kumar Sanadhya

Abstract: The Kalyna block cipher has recently been established as the Ukranian encryption standard in June, 2015. It was selected in a Ukrainian National Public Cryptographic Competition running from 2007 to 2010. Kalyna supports block sizes and key lengths of 128, 256 and 512 bits. Denoting variants of Kalyna as Kalyna-b / k, where b denotes the block size and k denotes the keylength, the design specifies \(k \in \{b, 2b\}\). In this work, we re-evaluate the security bound of some reduced round Kalyna variants, specifically Kalyna-128 / 256 and Kalyna-256 / 512 against key recovery attacks in the single key model. We first construct new 6-round distinguishers and then use these distinguishers to demonstrate 9-round attacks on these Kalyna variants. These attacks improve the previous best 7-round attacks on the same.