Improved Meet-in-the-Middle Distinguisher on Feistel Schemes

Improved meet-in-the-middle cryptanalysis with efficient tabulation technique has been shown to be a very powerful form of cryptanalysis against SPN block ciphers. However, few literatures show the effectiveness of this cryptanalysis against Balanced-Feistel-Networks (BFN) and Generalized-Feistel-Networks (GFN) ciphers due to the stagger of affected trail and special truncated differential trail. In this paper, we describe a versatile and powerful algorithm for searching the best improved meet-in-the-middle distinguisher with efficient tabulation technique on word-oriented BFN and GFN block ciphers, which is based on recursion and greedy algorithm. To demonstrate the usefulness of our approach, we show key recovery attacks on 14/16-round CLEFIA-192/256 which are the best attacks. We also propose key recovery attacks on 13/15-round Camellia-192/256 (without $FL/FL^{-1}$)

SoK: Security Evaluation of SBox-Based Block Ciphers

Cryptanalysis of block ciphers is an active and important research area with an extensive volume of literature. For this work, we focus on SBox-based ciphers, as they are widely used and cover a large class of block ciphers. While there have been prior works that have consolidated attacks on block ciphers, they usually focus on describing and listing the attacks. Moreover, the methods for evaluating a cipher\u27s security are often ad hoc, differing from cipher to cipher, as attacks and evaluation techniques are developed along the way. As such, we aim to organise the attack literature, as well as the work on security evaluation. In this work, we present a systematization of cryptanalysis of SBox-based block ciphers focusing on three main areas: (1) Evaluation of block ciphers against standard cryptanalytic attacks; (2) Organisation and relationships between various attacks; (3) Comparison of the evaluation and attacks on existing ciphers

Improved Integral and Zero-correlation Linear Cryptanalysis of Reduced-round CLEFIA Block Cipher

CLEFIA is a block cipher developed by Sony Corporation in 2007. It is a recommended cipher of CRYPTREC, and has been adopted as ISO/IEC international standard in lightweight cryptography. In this paper, some new 9-round zero-correlation linear distinguishers of CLEFIA are constructed with the input masks and output masks being independent, which allow multiple zero-correlation linear attacks on 14/15-rounds CLEAIA-192/256 with the partial sum technique. Furthermore, the relations between integral distinguishers and zero-correlation linear approximations are improved, and some new integral distinguishers over 9-round are deduced from zero-correlation linear approximations. By using these integral distinguishers and the partial sum technique, the previous integral results on CLEFIA are improved. The two results have either one more rounds or lower time complexity than previous attack results by means of integral and zero-correlation linear cryptanalysis

Automatic Search of Truncated Impossible Differentials for Word-Oriented Block Ciphers (Full Version)

Impossible differential cryptanalysis is a powerful technique to recover the secret key of block ciphers by exploiting the fact that in block ciphers specific input and output differences are not compatible. This paper introduces a novel tool to search truncated impossible differentials for word-oriented block ciphers with bijective Sboxes. Our tool generalizes the earlier $\mathcal{U}$-method and the UID-method. It allows to reduce the gap between the best impossible differentials found by these methods and the best known differentials found by ad hoc methods that rely on cryptanalytic insights. The time and space complexities of our tool in judging an $r$-round truncated impossible differential are about $O(c\cdot l^4\cdot r^4)$ and $O(c\u27\cdot l^2\cdot r^2)$ respectively, where $l$ is the number of words in the plaintext and $c$, $c\u27$ are constants depending on the machine and the block cipher. In order to demonstrate the strength of our tool, we show that it does not only allow to automatically rediscover the longest truncated impossible differentials of many word-oriented block ciphers, but also finds new results. It independently rediscovers all 72 known truncated impossible differentials on 9-round CLEFIA. In addition, finds new truncated impossible differentials for AES, ARIA, Camellia without FL and FL$^{-1}$ layers, E2, LBlock, MIBS and Piccolo. Although our tool does not improve the lengths of impossible differentials for existing block ciphers, it helps to close the gap between the best known results of previous tools and those of manual cryptanalysis

A Salad of Block Ciphers

This book is a survey on the state of the art in block cipher design and analysis. It is work in progress, and it has been for the good part of the last three years -- sadly, for various reasons no significant change has been made during the last twelve months. However, it is also in a self-contained, useable, and relatively polished state, and for this reason I have decided to release this \textit{snapshot} onto the public as a service to the cryptographic community, both in order to obtain feedback, and also as a means to give something back to the community from which I have learned much. At some point I will produce a final version -- whatever being a ``final version\u27\u27 means in the constantly evolving field of block cipher design -- and I will publish it. In the meantime I hope the material contained here will be useful to other people

Truncated Differential Analysis of Round-Reduced RoadRunneR Block Cipher

RoadRunneR is a small and fast bitslice lightweight block cipher for low cost 8-bit processors proposed by Adnan Baysal and Sa ̈hap S ̧ahin in the LightSec 2015 conference. While most software efficient lightweight block ciphers lacking a security proof, RoadRunneR’s security is provable against differential and linear attacks. RoadRunneR is a Feistel structure block cipher with 64-bit block size. RoadRunneR-80 is a vision with 80-bit key and 10 rounds, and RoadRunneR-128 is a vision with 128-bit key and 12 rounds. In this paper, we obtain 5-round truncated differentials of RoadRunneR-80 and RoadRunneR-128 with probability 2^{−56}. Using the truncated differentials, we give a truncated differential attack on 7-round RoadRunneR-128 without whitening keys with data complexity of 2^{55} chosen plaintexts, time complexity of 2^{121} encryptions and memory complexity of 2^{68}. This is first known attack on RoadRunneR block cipher

Partial Sums Meet FFT: Improved Attack on 6-Round AES

The partial sums cryptanalytic technique was introduced in 2000 by Ferguson et al., who used it to break 6-round AES with time complexity of $2^{52}$ S-box computations -- a record that has not been beaten ever since. In 2014, Todo and Aoki showed that for 6-round AES, partial sums can be replaced by a technique based on the Fast Fourier Transform (FFT), leading to an attack with a comparable complexity. In this paper we show that the partial sums technique can be combined with an FFT-based technique, to get the best of the two worlds. Using our combined technique, we obtain an attack on 6-round AES with complexity of about $2^{46.4}$ additions. We fully implemented the attack experimentally, along with the partial sums attack and the Todo-Aoki attack, and confirmed that our attack improves the best known attack on 6-round AES by a factor of more than 32. We expect that our technique can be used to significantly enhance numerous attacks that exploit the partial sums technique. To demonstrate this, we use our technique to improve the best known attack on 7-round Kuznyechik by a factor of more than 80, and to reduce the complexity of the best known attack on the full MISTY1 from $2^{69.5}$ to $2^{67}$