Cryptology ePrint Archive: Report 2021/238

Two Sides of The Same Coin: Weak-Keys and More Efficient Variants of CRAFT

Gregor Leander and Shahram Rasoolzadeh

Abstract: CRAFT is a lightweight tweakable Substitution-Permutation-Network (SPN) block cipher optimized for efficient protection of its implementations against Differential Fault Analysis (DFA) attacks. In this paper, we present an equivalent description of CRAFT up to a simple mapping on the plaintext, ciphertext and round tweakeys. We show that the new representation, for a sub-class of keys, leads to a new structure which is a Feistel network, i.e., with half state non-linear operation and half state key addition. This has two interesting consequences: First, it reveals a class of weak keys for which CRAFT is less resistant against differential and linear cryptanalyses. Second, on the constructive side, it suggests how a new version of the cipher with more efficient implementation can be built.

Category / Keywords: secret-key cryptography / CRAFT, partial key addition, partial non-linear layer

Date: received 1 Mar 2021, last revised 12 Jul 2021

Contact author: shahram rasoolzadeh at ru nl

Available format(s): PDF | BibTeX Citation

Version: 20210712:195830 (All versions of this report)

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