Kiasu-BC is a recently proposed tweakable variant of the AES-128 block cipher. The designers of Kiasu-BC claim that no more than 7-round Meet-in-the-Middle (MitM) attack can be launched against it. In this letter, we present a MitM attack, utilizing the differential enumeration technique, on the 8-round reduced cipher. The attack has time complexity of 2116 encryptions, memory complexity of 286 128-bit blocks, and data complexity of 2116 plaintext-tweak combinations.

In this letter, we present a meet-in-the-middle attack on the 7-round reduced block cipher Kalyna-b/2b, which has been approved as the new encryption standard of Ukraine (DSTU 7624:2014) in 2015. According to its designers, the cipher provides strength to several cryptanalytic methods after the fifth and sixth rounds of the versions with block length of 128 and 256 bits, respectively. Our attack is based on the differential enumeration approach, where we carefully deploy a four-round distinguisher in the first four rounds to bypass the effect of the carry bits resulting from the prewhitening modular key addition. We also exploit the linear relation between consecutive odd and even indexed round keys, which enables us to attack seven rounds and recover all the round keys incrementally. The attack on Kalyna with 128-bit block has a data complexity of 289 chosen plaintexts, time complexity of 2230.2 and a memory complexity of 2202.64. The data, time and memory complexities of our attack on Kalyna with 256-bit block are 2233, 2502.2 and 2170, respectively.

In this letter, we present a meet-in-the-middle attack on the 5-round reduced Kuznyechik cipher which has been recently chosen to be standardized by the Russian federation. Our attack is based on the differential enumeration approach. However, the application of the exact approach is not successful on Kuznyechik due to its optimal round diffusion properties. Accordingly, we adopt an equivalent representation for the last round where we can efficiently filter ciphertext pairs and launch the attack in the chosen ciphertext setting. We also utilize partial sequence matching which further reduces the memory and time complexities. For the 5-round reduced cipher, the 256-bit master key is recovered with an online time complexity of 2140.3, a memory complexity of 2153.3, and a data complexity of 2113.