Abstract

This work studies the success probability of key recovery attacks based on using a single linear approximation. Previous works had analysed success probability under different hypotheses on the distributions of correlations for the right and wrong key choices. This work puts forward a unifying framework of general key randomisation hypotheses. All previously used key randomisation hypotheses as also zero correlation attacks can be seen as special cases of the general framework. Derivations of expressions for the success probability are carried out under both the settings of the plaintexts being sampled with and without replacements. Compared to previous analysis, we uncover several new cases which have not been considered in the literature. For most of the cases which have been considered earlier, we provide complete expressions for the respective success probabilities. Finally, the full picture of the dependence of the success probability on the data complexity is revealed. Compared to the extant literature, our work provides a deeper and more thorough understanding of the success probability of single linear cryptanalysis.

Highlights

  • A block cipher is a fundamental cryptographic primitive

  • The goal of cryptanalysis of a block cipher is to recover a portion of the secret key in time less than that required by a brute force algorithm to try out all possible keys

  • The expressions for the success probability obtained using the two different approaches are slightly different. They turn out to be equal if certain assumptions and approximations used by Selcuk in [26] are applied to the expression obtained from the order statistics based approach

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Summary

Introduction

A block cipher is a fundamental cryptographic primitive Such a primitive injectively maps an n-bit plaintext under the influence of a secret key to an n-bit ciphertext. It is required to first obtain an approximate linear relation between the input and the output of a block cipher. The goal of (linear) cryptanalysis of a block cipher is to recover a portion of the secret key in time less than that required by a brute force algorithm to try out all possible keys. It is required to obtain some data corresponding to the secret key. Such data consists of plaintext-ciphertext pairs (Pi, Ci), i = 1, . Bose Center for Cryptology and Security, Indian Statistical Institute, Kolkata, India

INTRODUCTION
Previous and Related Work
Background and Statistical Model
SUCCESS PROBABILITY IN LINEAR CRYPTANALYSIS
Success Probability in Linear Cryptanalysis
Order Statistics Based Analysis
Hypothesis Testing Based Analysis
GENERAL KEY RANDOMISATION HYPOTHESES
General Key Randomisation Hypotheses
Analysis of Success Probability
Success Probability under General Key Randomisation Hypotheses
Success Probability Under Standard Key Randomisation Hypotheses
Success Probability Under Adjusted Wrong Key Randomisation Hypothesis
Understanding Non-Monotonic Behaviour
Dependence of PS on N
Adjusted Wrong Key Randomisation Hypothesis
CONCLUSION
Conclusion
Order Statistics
Compound Normal
Hypergeometric Distribution

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