Observations on the SIMON block cipher family

May 1, 2015·
Stefan Kölbl
Stefan Kölbl
,
Gregor Leander
,
Tyge Tiessen
· 0 min read
Abstract
In this paper we analyse the general class of functions underlying the Simon block cipher. In particular, we derive efficiently computable and easily implementable expressions for the exact differential and linear behaviour of Simon-like round functions. Following up on this, we use those expressions for a computer aided approach based on SAT/SMT solvers to find both optimal differential and linear characteristics for Simon. Furthermore, we are able to find all characteristics contributing to the probability of a differential for Simon32 and give better estimates for the probability for other variants. Finally, we investigate a large set of Simon variants using different rotation constants with respect to their resistance against differential and linear cryptanalysis. Interestingly, the default parameters seem to be not always optimal.
Type
Publication
publications
Block Cipher SIMON Cryptanalysis Differential Cryptanalysis
Stefan Kölbl
Authors
Stefan Kölbl
Staff Engineer, Tech Lead Manager

I am a Staff Engineer and Tech Lead Manager at Google, where I work in the Security Engineering team. My focus is on post-quantum cryptography and enabling developers at Google and across the internet to use cryptography safely and correctly.

I have a PhD in cryptography and an extensive background in the design and analysis of symmetric-key algorithms, post-quantum cryptography, and lightweight cryptography. I have contributed to several cryptographic standardization efforts, including the SKINNY cipher, which is part of the ISO/IEC 29192-2 standard. I also contributed to the SPHINCS+ signature scheme, which was standardized by NIST as FIPS 205. I currently represent Switzerland in the ISO/IEC JTC 1/SC 27/WG 2 committee for cryptography and security mechanisms.

Before joining Google, I was a Senior Technology Manager at Cybercrypt and a postdoctoral researcher at the Technical University of Denmark, working on the H2020 PQCRYPTO project.

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Authors
Gregor Leander
Authors
Tyge Tiessen