Security Analysis of SKINNY under Related-Tweakey Settings

Denoting the variants of SKINNY as SKINNY-n-t, where n represents the block size and t represents the tweakey length, the design specifies t ∈ {n,2n,3n}. In this work, we evaluate the security of SKINNY against differential cryptanaly sis in the related-tweakey model.

First, we investigate truncated related-tweakey differential trails of SKINNY and search for the longest impossible and rectangle distinguishers where there is only one active cell in the input and the output. Based on the distinguishers obtained, 19, 23 and 27 rounds of SKINNY-n-n, SKINNY-n-2n and SKINNY-n-3n can be attacked respectively. Next, actual differential trails for SKINNY under related-tweakey model are explored and optimal differential trails of SKINNY-64 within certain number of rounds are searched with an indirect searching method based on Mixed-Integer Linear Programming.