Paper 2019/539

Iterated Truncated Differential for Internal Keyed Permutation of FlexAEAD

Mostafizar Rahman and Dhiman Saha and Goutam Paul

Abstract

In this draft, the internal keyed permutation of FlexAEAD has been analysed. In our analysis, we have first reported an iterated truncated differential for one round which holds with a probability of $2^{-7}$ and can penetrate same number of rounds as claimed by the designers with much less complexity which can be easily converted to a key-recovery attack. We have also reported a Super-Sbox construction in the internal permutation, which has been 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 64-bit and 256-bit internal permutation.