Low-weight Pseudo Collision Attack on Shabal and Preimage Attack on Reduced Shabal-512

This paper studies two types of attacks on the hash function Shabal. The first attack is a low-weight pseudo collision attack on Shabal. Since a pseudo collision attack is trivial for Shabal, we focus on a low-weight pseudo collision attack. It means that only low-weight difference in a chaining value is considered. By analyzing the difference propagation in the underlying permutation, we can construct a low-weight (45-bits) pseudo collision attack on the full compression function with complexity of 2^84. The second attack is a preimage attack on variants of Shabal-512. We utilize a guess-and-determine technique, which is originally developed for a cryptanalysis of stream ciphers, and customize the technique for a preimage attack on Shabal-512. As a result, for the weakened variant of Shabal-512 using security parameters (p; r) = (2; 12), a preimage can be found with complexity of 2^497 and memory of 2^400. Moreover, for the Shabal-512 using security parameters (p; r) = (1:5; 8), a preimage can be found with complexity of 2^497 and memory of 2^272. To the best of our knowledge, these are best preimage attacks on Shabal variants and the second result is a first preimage attack on Shabal-512 with reduced security parameters

A MAC Mode for Lightweight Block Ciphers

status: accepte

On generalized Feistel structures using the diffusion switching mechanism

Abstract. We study a recently proposed design approach of Feistel structure which employs diffusion matrices in a switching way. At ASI-ACRYPT 2004, Shirai and Preneel have proved that large numbers of S-boxes are guaranteed to be active if a diffusion matrix used in a round function is selected among multiple matrices. However the optimality of matrices required by the proofs sometimes pose restriction to find matrices suitable for actual blockciphers. In this paper, we extend their theory by replacing the condition of optimal mappings with general-type mappings, consequently the restriction is eliminated. Moreover, by combining known lower bounds for usual Feistel structure, we establish a method to estimate the guaranteed number of active S-boxes for arbitrary round numbers. We also demonstrate how the generalization enables us to mount wide variety of diffusion mappings by showing concrete examples

Six Shades of AES

Recently there have been various attempts to construct light weight implementations of the AES-128 encryption and combined encryption/ decryption circuits. However no known lightweight circuit exists forAES-192 and AES-256, the variants of AES that use longer keys. Investing in lightweight implementations of these ciphers is important as we enter the post quantum era in which security is, by a rule of the thumb, scaled down to the square-root of the size of the keyspace. In this paper, we propose a single circuit that is able to offer functionalities of both encryption and decryption for AES-128/192/256. Our circuit operates on an 8-bit datapath and occupies around 3672 GE of area in silicon. We outline the challenges that presented themselves while performing the combinatorial optimization of circuit area and the methods we used to solve them