Mind the Gap - A Closer Look at the Security of Block Ciphers against Differential Cryptanalysis

Research output: Chapter in Book/Report/Conference proceedingArticle in proceedings – Annual report year: 2019Researchpeer-review

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Resistance against differential cryptanalysis is an important design criteria for any modern block cipher and most designs rely on finding some upper bound on probability of single differential characteristics. However, already at EUROCRYPT’91, Lai et al. comprehended that differential cryptanalysis rather uses differentials instead of single characteristics. In this paper, we consider exactly the gap between these two approaches and investigate this gap in the context of recent lightweight cryptographic primitives. This shows that for many recent designs like Midori, Skinny or Sparx one has to be careful as bounds from counting the number of active S-boxes only give an inaccurate evaluation of the best differential distinguishers. For several designs we found new differential distinguishers and show how this gap evolves. We found an 8-round differential distinguisher for Skinny-64 with a probability of, while the best single characteristic only suggests a probability of. Our approach is integrated into publicly available tools and can easily be used when developing new cryptographic primitives. Moreover, as differential cryptanalysis is critically dependent on the distribution over the keys for the probability of differentials, we provide experiments for some of these new differentials found, in order to confirm that our estimates for the probability are correct. While for Skinny-64 the distribution over the keys follows a Poisson distribution, as one would expect, we noticed that Speck-64 follows a bimodal distribution, and the distribution of Midori-64 suggests a large class of weak keys.
Original languageEnglish
Title of host publicationSelected Areas in Cryptography – SAC 2018
Publication date2019
ISBN (Print)9783030109691
Publication statusPublished - 2019
EventSAC 2018: Selected Areas in Cryptography - University of Calgary campus, Calgary, Canada
Duration: 15 Aug 201817 Aug 2018


ConferenceSAC 2018: Selected Areas in Cryptography
LocationUniversity of Calgary campus
SeriesLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
CitationsWeb of Science® Times Cited: No match on DOI

    Research areas

  • Symmetric-key cryptography, Twine, Light-weight cryptography, Symmetric key cryptography, Differential cryptanalysis, LBlock, Midori, Present, Prince, Rectangle, Simon, Skinny, Sparx, Speck

ID: 172636747