Abstract
In April 2018, Beierle et al. launched the 3rd SKINNY cryptanalysis competition, a contest that aimed at motivating the analysis of their recent tweakable block cipher SKINNY . In contrary to the previous editions, the focus was made on practical attacks: contestants were asked to recover a 128-bit secret key from a given set of \(2^{20}\) plaintext blocks. The suggested SKINNY instances are 4- to 20-round reduced variants of SKINNY-64-128 and SKINNY-128-128. In this paper, we explain how to solve the challenges for 10-round SKINNY-128-128 and for 12-round SKINNY-64-128 in time equivalent to roughly \(2^{52}\) simple operations. Both techniques benefit from the highly biased sets of messages that are provided and that actually correspond to the encryption of various books in ECB mode.
Patrick Derbez was supported by the French Agence Nationale de la Recherche through the CryptAudit project under Contract ANR-17-CE39-0003. This work was initiated while Virginie Lallemand was with the Horst Görtz Institute for IT Security at the Ruhr-Universität Bochum. The work of Aleksei Udovenko was partially supported by the Fonds National de la Recherche, Luxembourg (project reference 9037104).
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Notes
- 1.
All the information on the competitions and on the cipher in general can be found on https://sites.google.com/site/skinnycipher/home.
- 2.
As seen previously, another possibility would have been to use the 76 pairs available for the same trail shifted by 2 columns, that are starting with only one nibble active at position 14 after 1 rounds and resulting into nibbles in position 2 and 14 that are equal at the end of round 7 (see Table 3).
- 3.
Sorting a table of n elements requires roughly \(n \log n\) operation so we consider that the complexity of this step is equal to \(28 \times 2^{28}\).
- 4.
Such distinguishers are also called integral distinguishers.
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Derbez, P., Lallemand, V., Udovenko, A. (2020). Cryptanalysis of SKINNY in the Framework of the SKINNY 2018–2019 Cryptanalysis Competition. In: Paterson, K., Stebila, D. (eds) Selected Areas in Cryptography – SAC 2019. SAC 2019. Lecture Notes in Computer Science(), vol 11959. Springer, Cham. https://doi.org/10.1007/978-3-030-38471-5_6
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