Iranian Society of Cryptology The ISC International Journal of Information Security 2008-2045 11 1 2019 01 30 Biclique Cryptanalysis of Block Ciphers LBlock and TWINE-80 with Practical Data Complexity 57 74 79989 10.22042/isecure.2018.138036.420 EN Siavash Ahmadi Department of Electrical Engineering Sharif University of Technology 0000-0002-8801-337X Zahra Ahmadian Shahid Beheshti University Javad Mohajeri Sharif University of Technology, Mohammad Reza Aref Department of Electrical Engineering Sharif University of Technology Journal Article 2018 06 30 In the biclique attack, a shorter biclique usually results in less data complexity, but at the expense of more computational complexity. The early abort technique can be used in partial matching part of the biclique attack in order to slightly reduce the computations. In this paper, we make use of this technique, but instead of slight improvement in the computational complexity, we keep the amount of this complexity the same and reduce the data complexity enormously by a shorter biclique.<br /> With this approach, we analysed full-round of LBlock, and also LBlock with modified key schedule (which was designed to resist biclique attack) both with data complexity 2^12, while the data complexity of the best biclique attack on the former was 2^52 and for the latter there is no attack on the full-round cipher, so far. Then we proposed a new key schedule that is more resistant against biclique cryptanalysis, though the low diffusion of the cipher makes it vulnerable to this attack regardless of the strength of the key schedule. Also using this method, we analyzed TWINE-80 with 2^12 data complexity. The lowest data complexity for the prior attack on the TWINE-80 was 2^60. In all the attacks presented in this paper, the computational complexities are slightly improved in comparison to the existing attacks. https://www.isecure-journal.com/article_79989_6ceed97c551abb399b4fbe5432af9197.pdf