Cryptology ePrint Archive: Report 2010/011

Related Key Cryptanalysis of the LEX Stream Cipher

Mainack Mondal and Debdeep Mukhopadhyay

Abstract: LEX is a stream cipher proposed by Alex Biryukov. It was selected to phase 3 of the eSTREAM competition. LEX is based on the Advanced Encryption Standard (AES) block cipher and uses a methodology called "Leak Extraction", proposed by Biryukov himself.

In this paper, we cryptanalyze LEX using two related keys. We have mounted a key recovery attack on LEX, which using $2^{54. 3}$ key streams yields a complete round key with $2^{102}$ operations. This improves the existing best cryptanalysis of LEX which needs $2^{112}$ operations to ascertain the key.

Category / Keywords: secret-key cryptography /

Date: received 10 Jan 2010, withdrawn 19 Apr 2010

Contact author: mainack mondal at gmail com

Available format(s): (-- withdrawn --)

Note: We are withdrawing this paper due to technical errors in it. Please remove it from the achive.

Version: 20100419:061248 (All versions of this report)

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