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Analysis of Diagonal Constants in Salsa

  • Bhagwan N. Bathe
  • Bharti Hariramani
  • A. K. Bhattacharjee
  • S. V. Kulgod
Conference paper
Part of the Lecture Notes in Computer Science book series (LNCS, volume 10662)

Abstract

In this paper, we study the effect of diagonal constants in the software oriented stream ciphers Salsa and Chacha. So far, there has not been any clear justification why such constants are chosen. We concentrate on differential cryptanalysis to evaluate how different constants affect the biases after a few rounds in these ciphers. We are using Measure of Uniformity in bias as a measure for differentiating constants as good or bad constants w.r.t. original constant. We have observed that after 4 rounds of Salsa20, for an Input Differential (\(\mathcal {ID}\)) at Most Significant Bit (MSB) of the third word of quarterround function, the specific patterns in constant involved in that quarterround function leads to increase or decrease in Measure of Uniformity in bias. The location of specific patterns in those diagonal constants varies with the change in last two rotation constants. We did not observe any pattern for ChaCha after 3 rounds. We have also observed a slight increase and decrease in time and data complexity for good and bad constants respectively as compared to an original constant. The designer constants are a good constant however it can be even better with a slight change in constant \(c_0\) or \(c_3\).

Keywords

Constants Stream cipher ChaCha Salsa Bias Measure of Uniformity in bias ARX Cipher Input Differential Output differential Hamming distance 

Notes

Acknowledgements

The authors would like to thank anonymous reviewers for detailed comments. The authors are also thankful to Computer Division of Bhabha Atomic Research Centre for use of super computing facility.

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Copyright information

© Springer International Publishing AG 2017

Authors and Affiliations

  1. 1.Bhabha Atomic Research CentreMumbaiIndia
  2. 2.Bhabha Atomic Research Centre (CI)Homi Bhabha National InstituteMumbaiIndia

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