Abstract
SKINNY is a tweakable lightweight block cipher algorithm. In order to test its security, this paper performs optimal differential trail search analysis on all SKINNY-64 versions under single-key setting based on the MILP (Mixed Integer Linear Programming) algorithm. Firstly, SKINNY round function is abstracted equivalently by precise constraints, and the objective function is set as the minimum number of active S-box number to optimize SKINNY-64 MILP model. Experiments show the differential trail searched by this method is not necessarily optimal. In order to directly search for the optimal differential trail, the S-box differential probability coding information is added to the optimized SKINNY-64 MILP model, the S-box differential characteristic is reconstructed, and the objective function is set to the minimum value of the probability coding information, which improves the SKINNY-64 MILP model. The results of experimental show that the improved MILP model can directly search for the optimal differential trail, and the complexity is slightly increased, but the search efficiency is significantly improved. Under single-key setting, this method has obvious advantage in searching the optimal differential trails of SKINNY-64 with low round number.
Highlights
SKINNY is a SPN-structured tweakable lightweight block cipher algorithm proposed by Beierle [1] at AmericanCryptography Conference in 2016
Hong Dou [4] used the intermediate encounter technology to search out all 16 truncated impossible differential trails of the 11 rounds of the SKINNY encryption algorithm and used one of them to analyze 20 rounds of SKINNY-64-128 using the impossible differential technique under a single key setting
The results show that the probability of the optimal differential trail is much smaller than that obtained from the lower bound of the active S-boxes in SKINNY with the increase of the number of rounds
Summary
SKINNY is a SPN-structured tweakable lightweight block cipher algorithm proposed by Beierle [1] at American. Proposed a method to obtain stricter boundaries, verified whether the optimal differential trail using the maximum differential probability for all active S-boxes exists, and proposed the method of finding the optimal differential trail of the block cipher algorithm based on MILP. The results show that the probability of the optimal differential trail is much smaller than that obtained from the lower bound of the active S-boxes in SKINNY with the increase of the number of rounds. We analyze the differential propagation characteristics of all SKINNY-64 versions under the singlekey setting model by using MILP and obtain the optimal differential trails. The basic method is to establish the MILP model of SKINNY-64 under the single key setting and use the LPSolve optimizer to obtain an optimized solution with the objective function as the minimum number of active. Each difference cell can be expressed as Xj (x4j , x4j+1 , x4j+2 , x4j+3 )
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