[Resource Topic] 2014/317: Analysis of NORX: Investigating Differential and Rotational Properties

Welcome to the resource topic for 2014/317

Title:
Analysis of NORX: Investigating Differential and Rotational Properties

Authors: Jean-Philippe Aumasson, Philipp Jovanovic, Samuel Neves

Abstract:

This paper presents a thorough analysis of the AEAD scheme NORX, focussing on differential and rotational properties. We first introduce mathematical models that describe differential propagation with respect to the non-linear operation of NORX. Afterwards, we adapt a framework previously proposed for ARX designs allowing us to automatise the search for differentials and characteristics. We give upper bounds on the differential probability for a small number of steps of the NORX core permutation. For example, in a scenario where an attacker can only modify the nonce during initialisation, we show that characteristics have probabilities of less than 2^{-60} (32-bit) and 2^{-53} (64-bit) after only one round. Furthermore, we describe how we found the best characteristics for four rounds, which have probabilities of 2^{-584} (32-bit) and 2^{-836} (64-bit), respectively. Finally, we discuss some rotational properties of the core permutation which yield some first, rough bounds and can be used as a basis for future studies.

ePrint: https://eprint.iacr.org/2014/317

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