Chapter

Progress in Cryptology – Mycrypt 2005

Volume 3715 of the series Lecture Notes in Computer Science pp 244-262

Related-Key Differential Attacks on Cobra-S128, Cobra-F64a, and Cobra-F64b

  • Changhoon LeeAffiliated withCenter for Information Security Technologies(CIST), Korea University
  • , Jongsung KimAffiliated withKatholieke Universiteit Leuven, ESAT/SCD-COSIC
  • , Seokhie HongAffiliated withCenter for Information Security Technologies(CIST), Korea University
  • , Jaechul SungAffiliated withDepartment of Mathematics, University of Seoul
  • , Sangjin LeeAffiliated withCenter for Information Security Technologies(CIST), Korea University

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Abstract

Data-dependent permutations (DDPs) which are very suitable for cheap hardware implementations have been introduced as a cryptographic primitive. Cobra-S128 and Cobra-F64 (which is a generic name for Cobra-F64a and Cobra-F64b) are 128-bit and 64-bit iterated block ciphers with a 128-bit key size based on such DDPs, respectively. Unlike the predecessor DDP-based ciphers [16,5], Cobra-S128 is a software-oriented cipher and Cobra-F64 is a firmware-suitable cipher. In this paper, we derive several structural properties of Cobra-S128 and Cobra-F64 and then use them to devise key recovery attacks on Cobra-S128 and Cobra-F64. These works are the first known attacks on Cobra-S128 and Cobra-F64.

Keywords

Cobra-S128 Cobra-F64 Block Cipher Related-Key Attack Data-Dependent Permutation