Impossible differential cryptanalysis of reduced-round LBlock

Authors:
Ferhat Karakoç;Hüseyin Demirci;A. Emre Harmancı
Affiliations:
Tübitak BILGEM UEKAE, Gebze, Kocaeli, Turkey,Computer Engineering Department, Istanbul Technical University, Maslak, Istanbul, Turkey;Tübitak BILGEM UEKAE, Gebze, Kocaeli, Turkey;Computer Engineering Department, Istanbul Technical University, Maslak, Istanbul, Turkey
Venue:
WISTP'12 Proceedings of the 6th IFIP WG 11.2 international conference on Information Security Theory and Practice: security, privacy and trust in computing systems and ambient intelligent ecosystems
Year:
2012

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Abstract

In this paper, we improve the impossible differential attack on 20-round LBlock given in the design paper of the LBlock cipher. Using relations between the round keys we attack on 21-round and 22-round LBlock with a complexity of 269.5 and 279.28 encryptions respectively. We use the same 14-round impossible differential characteristic observed by the designers to attack on 21 rounds and another 14-round impossible differential characteristic to attack on 22 rounds of LBlock.