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Communication Dans Un Congrès Année : 2021

The Key-Dependent Message Security of Key-Alternating Feistel Ciphers

Résumé

Key-Alternating Feistel (KAF) ciphers are a popular variant of Feistel ciphers whereby the round functions are defined as x↦F(ki⊕x), where k_i are the round keys and F is a public random function. Most Feistel ciphers, such as DES, indeed have such a structure. However, the security of this construction has only been studied in the classical CPA/CCA models. We provide the first security analysis of KAF ciphers in the key-dependent message (KDM) attack model, where plaintexts can be related to the private key. This model is motivated by cryptographic schemes used within application scenarios such as full-disk encryption or anonymous credential systems. We show that the four-round KAF cipher, with a single function F reused across the rounds, provides KDM security for a non-trivial set of KDM functions. To do so, we develop a generic proof methodology, based on the H-coefficient technique, that can ease the analysis of other block ciphers in such strong models of security.
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Dates et versions

hal-03167663 , version 1 (12-03-2021)

Identifiants

  • HAL Id : hal-03167663 , version 1

Citer

Pooya Farshim, Louiza Khati, Yannick Seurin, Damien Vergnaud. The Key-Dependent Message Security of Key-Alternating Feistel Ciphers. Topics in Cryptology - CT-RSA 2021 - The Cryptographers' Track at the RSA Conference 2021, May 2021, San Francisco, CA, United States. ⟨hal-03167663⟩
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