Cryptanalysis of Reduced NORX

  • Nasour Bagheri
  • Tao Huang
  • Keting Jia
  • Florian Mendel
  • Yu Sasaki
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 9783)

Abstract

NORX is a second round candidate of the ongoing CAESAR competition for authenticated encryption. It is a nonce based authenticated encryption scheme based on the sponge construction. Its two variants denoted by NORX32 and NORX64 provide a security level of 128 and 256 bits, respectively. In this paper, we present a state/key recovery attack for both variants with the number of rounds of the core permutation reduced to 2 (out of 4) rounds. The time and data complexities of the attack for NORX32 are \(2^{119}\) and \( 2^{66} \) respectively, and for NORX64 are \( 2^{234} \) and \( 2^{132} \) respectively, while the memory complexity is negligible. Furthermore, we show a state recovery attack against NORX in the parallel mode using an internal differential attack for 2 rounds of the permutation. The data, time and memory complexities of the attack for NORX32 are \(2^{7.3}\), \(2^{124.3}\) and \(2^{115}\) respectively and for NORX64 are \(2^{6.2}\), \(2^{232.8}\) and \(2^{225}\) respectively. Finally, we present a practical distinguisher for the keystream of NORX64 based on two rounds of the permutation in the parallel mode using an internal differential-linear attack. To the best of our knowledge, our results are the best known results for NORX in nonce respecting manner.

Keywords

Authenticated encryption CAESAR NORX Guess and determine Internal differential attack State recovery Nonce respect 

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Copyright information

© International Association for Cryptologic Research 2016

Authors and Affiliations

  • Nasour Bagheri
    • 1
  • Tao Huang
    • 2
  • Keting Jia
    • 3
    • 4
  • Florian Mendel
    • 5
  • Yu Sasaki
    • 2
    • 6
  1. 1.SRTTU and IPMTehranIran
  2. 2.Nanyang Technological UniversitySingaporeSingapore
  3. 3.Department of Computer Science and TechnologyTsinghua UniversityBeijingChina
  4. 4.State Key Laboratory of CryptologyBeijingChina
  5. 5.Graz University of TechnologyGrazAustria
  6. 6.NTT Secure Platform LaboratoriesTokyoJapan

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