Improved Attacks on Full GOST

Abstract

Abstract. GOST is a well known block cipher which was developed in the Soviet Union during the 1970's as an alternative to the US-developed DES. In spite of considerable cryptanalytic effort, until very recently there were no published single key attacks against its full 32-round version which were faster than the 2 256 time complexity of exhaustive search. In February 2011, Isobe used in a novel way the previously discovered reflection property in order to develop the first such attack, which requires 2 32 data, 2 64 memory and 2 224 time. Shortly afterwards, Courtois and Misztal used a different technique to attack the full GOST using 2 64 data, 2 64 memory and 2 226 time. In this paper we introduce a new fixed point property and a better way to attack 8-round GOST in order to find improved attacks on full GOST: Given 2 32 data we can reduce the memory complexity from an impractical 2 64 to a practical 2 36 without changing the 2 224 time complexity, and given 2 64 data we can simultaneously reduce the time complexity to 2 192 and the memory complexity to 2 36 .

Complementing Feistel Ciphers

“…We note that the mentioned below complementation properties have been known and exploited in attacks on GOST [7,4]. However, to the best of our knowledge, all the attacks on GOST that recover the full key, are impractical.…”

“…Hence, in the case of former one has to try around 2 P different pairs of keys and encrypt one pair of plaintexts, while in the case of modular Feistels, for each of the 2 P pairs of related-key has to encrypt 2 Q pairs of plaintexts (2 −P , 2 −Q are the probabilities of the differential in the key schedule and in the state). 4 One of our anonymous reviewers has informed us that a similar idea was used against DESX in Kelsey et al [6]. 5 When r is odd, there are r 2 round keys with difference ∆1, and r 2 − 1 round keys with ∆2.…”

“…Thus we obtain the first analysis on the fullround Camellia without the F L, F L −1 in the hash mode -it requires around 2 112 encryptions. Complementation property of GOST has been known (see [7,4]), however all of the proposed key recovery attacks require impractical time complexity. We show that if one uses several similar complementation properties, an efficient key recovery attack on GOST exists.…”

Lightweight Cryptography. Part 1

“…Между тем LWC от-нюдь не является «простой». Аксель Пошманн, из-вестный специалист по Lightweight Cryptography, характеризует ее словами «As light as a feather, and as hard as dragon-scales» -«Легка, как пух и прочна как чешуя дракона» 7 .…”

“…Вопросы кибербезопасности №1 (9) 64 пар открытый текст-шифртекст, что делает предложенную ата-ку неосуществимой на практике [7]. Основным характеристиками реализации криптографического алгоритма являются слож-ность реализации и скорость работы.…”