Multidimensional Zero-Correlation Linear Cryptanalysis of the Block Cipher KASUMI

The block cipher KASUMI is widely used for security in many synchronous wireless standards. It was proposed by ETSI SAGE for usage in 3GPP (3rd Generation Partnership Project) ciphering algorthms in 2001. There are a great deal of cryptanalytic results on KASUMI, however, its security evaluation against the recent zero-correlation linear attacks is still lacking so far. In this paper, we select some special input masks to refine the general 5-round zero-correlation linear approximations combining with some observations on the $FL$ functions and then propose the 6-round zero-correlation linear attack on KASUMI. Moreover, zero-correlation linear attacks on the last 7-round KASUMI are also introduced under some weak keys conditions. These weak keys take $2^{-14}$ of the whole key space. The new zero-correlation linear attack on the 6-round needs about $2^{85}$ encryptions with $2^{62.8}$ known plaintexts. For the attack under weak keys conditions on the last 7 round, the data complexity is about $2^{62.1}$ known plaintexts and the time complexity $2^{110.5}$ encryptions

The (related-key) impossible boomerang attack and its application to the AES block cipher

The Advanced Encryption Standard (AES) is a 128-bit block cipher with a user key of 128, 192 or 256 bits, released by NIST in 2001 as the next-generation data encryption standard for use in the USA. It was adopted as an ISO international standard in 2005. Impossible differential cryptanalysis and the boomerang attack are powerful variants of differential cryptanalysis for analysing the security of a block cipher. In this paper, building on the notions of impossible differential cryptanalysis and the boomerang attack, we propose a new cryptanalytic technique, which we call the impossible boomerang attack, and then describe an extension of this attack which applies in a related-key attack scenario. Finally, we apply the impossible boomerang attack to break 6-round AES with 128 key bits and 7-round AES with 192/256 key bits, and using two related keys we apply the related-key impossible boomerang attack to break 8-round AES with 192 key bits and 9-round AES with 256 key bits. In the two-key related-key attack scenario, our results, which were the first to achieve this amount of attacked rounds, match the best currently known results for AES with 192/256 key bits in terms of the numbers of attacked rounds. The (related-key) impossible boomerang attack is a general cryptanalytic technique, and can potentially be used to cryptanalyse other block ciphers

Differential Cryptanalysis of Round-Reduced Sparx-64/128

Sparx is a family of ARX-based block ciphers designed according to the long-trail strategy (LTS) that were both introduced by Dinu et al. at ASIACRYPT'16. Similar to the wide-trail strategy, the LTS allows provable upper bounds on the length of differential characteristics and linear paths. Thus, the cipher is a highly interesting target for third-party cryptanalysis. However, the only third-party cryptanalysis on Sparx-64/128 to date was given by Abdelkhalek et al. at AFRICACRYPT'17 who proposed impossible-differential attacks on 15 and 16 (out of 24) rounds. In this paper, we present chosen-ciphertext differential attacks on 16 rounds of Sparx-64/128. First, we show a truncated-differential analysis that requires 232232 chosen ciphertexts and approximately 293293 encryptions. Second, we illustrate the effectiveness of boomerangs on Sparx by a rectangle attack that requires approximately 259.6259.6 chosen ciphertexts and about 2122.22122.2 encryption equivalents. Finally, we also considered a yoyo attack on 16 rounds that, however, requires the full codebook and approximately 21262126 encryption equivalents

Related-Key Impossible-Differential Attack on Reduced-Round Skinny

At CRYPTO’16, Beierle et al. presented SKINNY, a family of lightweight tweakable block ciphers intended to compete with the NSA designs SIMON and SPECK. SKINNY can be implemented efficiently in both soft- and hardware and supports block sizes of 64 and 128 bits as well as tweakey sizes of 64, 128, 192 and 128, 256, 384 bits respectively. This paper presents a related-tweakey impossible-differential attack on up to 23 (out of 36) rounds of SKINNY-64/128 for different tweak sizes. All our attacks can be trivially extended to SKINNY-128/128