Cryptology ePrint Archive: Report 2019/539

Cryptanalysis of Internal Keyed Permutation of FlexAEAD

Mostafizar Rahman and Dhiman Saha and Goutam Paul

Abstract: In this paper, the internal keyed permutation of FlexAEAD is analysed. In our analysis, we report an iterated truncated differential for one round which holds with a probability of $2^{-7}$ and can penetrate the same number of rounds as claimed by the designers with much less complexity and can be easily converted to a key-recovery attack. We further report a Super-Sbox construction in the internal permutation, which is exploited using the Yoyo game to devise a 6-round deterministic distinguisher and a 7-round key recovery attack for 128-bit internal permutation. Similar attacks can be mounted for the 64-bit and 256-bit variants. Success probabilities of all the reported distinguishing attacks are shown to be high. All practical attacks are experimentally verified.

Category / Keywords: secret-key cryptography / Distinguisher, FlexAEAD, Iterated Differential, Key Recovery, NIST lightweight cryptography project, Yoyo

Date: received 20 May 2019, last revised 2 Aug 2019

Contact author: mrahman454 at gmail com, dhiman@iitbhilai ac in

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Version: 20190802:121405 (All versions of this report)

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