Ahmed Abdelkhalek

Meet-in-the-Middle Attacks on Round-Reduced Khudra

Khudra is a hardware-oriented lightweight block cipher that is designed to run efficiently on Field Programmable Gate Arrays. It employs an 18-rounds Generalized type-2 Feistel Structure with a 64-bit block length and an 80-bit key. In this paper, we present Meet-in-the-Middle MitM attacks on 13 and 14 round-reduced Khudra. These attacks are based on finding a distinguisher that is evaluated offline independently of the key. Then in an online phase, some rounds are appended before and after the distinguisher and the correct key candidates for these rounds are checked whether they verify the distinguisher property or not. Using this technique, we find two 6-round distinguishers and use them to attack 13 and 14 rounds of Khudra with time complexity of 266.11 and 266.19, respectively. Both attacks require the same data and memory complexities of 251 chosen plaintexts and 264.8 64-bit blocks, respectively.

Impossible Differential Cryptanalysis of Reduced-Round SKINNY

SKINNY is a new lightweight tweakable block cipher family proposed by Beierle et al. at CRYPTO 2016. SKINNY has 6 main variants where SKINNY-n-t is a block cipher that operates on n-bit blocks using t-bit tweakey (key and tweak) where \(n=64\) or 128 and \(t=n\), 2n, or 3n. In this paper, we present impossible differential attacks against reduced-round versions of all the 6 members of the SKINNY family in the single-tweakey model. More precisely, using an 11-round impossible differential distinguisher, we present impossible differential attacks against 18-round SKINNY-n-n, 20-round SKINNY-n-2n and 22-round SKINNY-n-3n (\(n=64\) or 128). To the best of our knowledge, these are the best attacks against these 6 variants in the single-tweakey model.

Meet-in-the-Middle Attacks on Reduced-Round Hierocrypt-3

Hierocrypt-3 is an SPN-based block cipher designed by Toshiba Corporation. It operates on 128-bit state using either 128, 192 or 256-bit key. In this paper, we present two meet-in-the-middle attacks in the single-key setting on the 4-round reduced Hierocrypt-3 with 256-bit key. The first attack is based on the differential enumeration approach where we propose a truncated differential characteristic in the first 2.5 rounds and match a multiset of state differences at its output. The other attack is based on the original meet-in-the-middle attack strategy proposed by Demirci and Selcuk at FSE 2008 to attack reduced versions of both AES-192 and AES-256. For our attack based on the differential enumeration, the master key is recovered with data complexity of

Meet-in-the-Middle Attacks on Reduced Round Piccolo

2^{113}

MILP Modeling for (Large) S-boxes to Optimize Probability of Differential Characteristics

2113 chosen plaintexts, time complexity of

Improved Linear Cryptanalysis of Round-Reduced ARIA

2^{238}