International Association for Cryptologic Research

International Association
for Cryptologic Research

IACR News item: 18 July 2015

Stefan Kölbl, Arnab Roy
ePrint Report ePrint Report
Simeck is a new lightweight block cipher design based on

combining the Simon and Speck block cipher. While the design allows a

smaller and more efficient hardware implementation, its security margins are not well understood. The lack of design rationals of its predecessors further leaves some uncertainty on the security of Simeck.

In this work we give a short analysis of the impact of the design changes by comparing the lower bounds for differential and linear characteristics with Simon. We also give a comparison of the effort of finding those bounds, which surprisingly is significant less for Simeck while covering a larger number of rounds.

Furthermore, we provide new differentials for Simeck which can cover

more rounds compared to previous results on Simon. Based on this we

mount key recovery attacks on 19/26/33 rounds of Simeck32/48/64,

which also give insights on the reduced key guessing effort due to the

different set of rotation constants.

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