Abstract
We apply McKay’s pseudo-linear approximation of addition modular 2n to lightweight ARX block ciphers with large words, specifically the Speck family. We demonstrate that a pseudo-linear approximation can be combined with a linear approximation using the meet-in-the-middle attack technique to recover several key bits. Thus we illustrate improvements to Speck linear distinguishers based solely on Cho–Pieprzyk approximations by combining them with pseudo-linear approximations, and propose key recovery attacks.
Highlights
We begin our work by implementing the pseudo-linear cryptanalysis on four rounds of S PECK 32/64, as a meet-in-the-middle attack with a four-bit window approximated by two rounds in the forward direction and two backward
We show that linear cryptanalysis relying on Cho–Pieprzyk approximations of modular addition is improved by replacing some rounds of linear approximation with pseudo-linear approximations
This paper presents a new cryptanalysis of the ARX block cipher Partly-Pseudo-Linear attack: combining linear and the pseudo-linear cryptanalysis
Summary
This paper presents a new approximation and corresponding key recovery attack, Partly-Pseudo-Linear attack, combining pseudo-linear approximation with linear cryptanalysis of addition modulo 2n using Cho and Pieprzyk’s property of modular addition [6,7]. Cryptography 2021, 5, 1 for more than a single bit of key, because its use requires nonlinear operations with some key bits Though they do not discuss this, the linear distinguishers of [9,10] could possibly be extended to key recovery attacks, bias permitting, by appending rounds of encryption and/or decryption. In this instance, our attack covers more rounds for the variants S PECK.
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