Some observations on HC-128

  • Authors:
  • Subhamoy Maitra;Goutam Paul;Shashwat Raizada;Subhabrata Sen;Rudradev Sengupta

  • Affiliations:
  • Applied Statistics Unit, Indian Statistical Institute, Kolkata, India 700 108;Department of Computer Science and Engineering, Jadavpur University, Kolkata, India 700 032;Indian Statistical Institute, Kolkata, India 700 108;Indian Statistical Institute, Kolkata, India 700 108;Indian Statistical Institute, Kolkata, India 700 108

  • Venue:
  • Designs, Codes and Cryptography
  • Year:
  • 2011

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Abstract

In this paper, we study HC-128 in detail from cryptanalytic point of view. First, we use linear approximation of the addition modulo 2 n of three n-bit integers to identify linear approximations of g 1, g 2, the feedback functions of HC-128. This, in turn, shows that the process of keystream output generation of HC-128 can be well approximated by linear functions. In this direction, we show that the "least significant bit" based distinguisher (presented by the designer himself) of HC-128 works for the complete 32-bit word. Using the above linear approximations of g 1, g 2, we present a new distinguisher for HC-128 which is slightly weaker than Wu's distinguisher. Finally, in the line of Dunkelman's observation, we also study how HC-128 keystream words leak secret state information of the cipher due to the properties of the functions h 1, h 2 and present improved results.