Some observations on HC-128

In this paper, we use linear approximations of the addition modulo 2n of three n-bit integers to identify linear approximations of g1, g2, 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. In a different note, 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 h1, h2 and present improved results.

• Type: Journal
• Year: 2011
• Where: DCC
• Authors: Subhamoy Maitra, Goutam Paul, Shashwat Raizada, Subhabrata Sen, Rudradev Sengupta
• Keywords: Complete 32-bit Word, Computer Graphics, DCC 2011, Keystream Output Generation, Linear Approximations