## Cryptology ePrint Archive: Report 2010/387

A Combinatorial Analysis of HC-128

Goutam Paul and Subhamoy Maitra and Shashwat Raizada

Abstract: We show that the knowledge of any one of the two internal state arrays of HC-128 along with the knowledge of 2048 keystream words is sufficient to construct the other state array completely in $2^{42}$ time complexity. Though our analysis does not lead to any attack on HC-128, it reveals a structural insight into the cipher. In the process, we theoretically establish certain combinatorial properties of HC-128 keystream generation algorithm. We also suggest a modification to HC-128 that takes care of the recently known cryptanalytic results with little reduction in speed.

Category / Keywords: secret-key cryptography / Cryptography, eSTREAM, HC-128, Keystream, State Recovery, Stream Cipher.

Publication Info: IWSEC 2011 (title: "A Theoretical Analysis of the Structure of HC-128")

Date: received 8 Jul 2010, last revised 16 Nov 2011

Contact author: subho at isical ac in

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