Partly-Pseudo-Linear Cryptanalysis of Reduced-Round S<span style="font-variant: small-caps">peck</span>

• Main Authors: Sarah A. Alzakari, Poorvi L. Vora
• Format: Article
• Language: English
• Published: MDPI AG 2021-12-01
• Series: Cryptography
• Subjects: S<span style="font-variant: small-caps">peck</span>; pseudo-linear cryptanalysis; linear cryptanalysis; partly-pseudo-linear attack
• Online Access: https://www.mdpi.com/2410-387X/5/1/1

We apply McKay’s pseudo-linear approximation of addition modular <inline-formula><math display="inline"><semantics><msup><mn>2</mn><mi>n</mi></msup></semantics></math></inline-formula> to lightweight ARX block ciphers with large words, specifically the S<span style="font-variant: small-caps;">peck</span> 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 S<span style="font-variant: small-caps;">peck</span> linear distinguishers based solely on Cho–Pieprzyk approximations by combining them with pseudo-linear approximations, and propose key recovery attacks.