On the security of the LILI family of stream ciphers against algebraic attacks

Al-Hinai, Sultan Z., Dawson, Edward P., Henricksen, Matt, & Simpson, Leonie R. (2007) On the security of the LILI family of stream ciphers against algebraic attacks. In Pieprzyk, Josef, Ghodosi, Hossein, & Dawson, Edward P. (Eds.) 12th Australasian Conference, ACISP 2007: Information Security and Privacy, July 2-4, 2007, Townsville, Australia.

View at publisher


In this paper, we present an algebraic analysis of the LILI family of stream ciphers, and in particular LILI-II, and investigate the security provided against both standard and fast algebraic attacks. We show that the size of the two registers used, the difference between their lengths, the maximum number of times a register is clocked and the degree of the filter function all play important roles in providing resistance against algebraic attacks. Further, we show that the degree 10 filter function used in LILI-II has an algebraic immunity (AI) of 4. Using this, a fast algebraic attack can be performed on LILI-II that significantly reduces the attack complexity, although not to such a degree that it is more efficient than exhaustive key search. These algebraic attacks recover the internal state of the cipher rather than the key bits. We investigate the role of the initialization process in providing resistance to algebraic attacks aimed at key recovery. The investigation shows that, generally, for the LILI family of stream ciphers, the complexity of recovering key bits using algebraic attacks is much worse than exhaustive key search because of the very high degree equations generated during the initialization process.

Impact and interest:

10 citations in Scopus
7 citations in Web of Science®
Search Google Scholar™

Citation counts are sourced monthly from Scopus and Web of Science® citation databases.

These databases contain citations from different subsets of available publications and different time periods and thus the citation count from each is usually different. Some works are not in either database and no count is displayed. Scopus includes citations from articles published in 1996 onwards, and Web of Science® generally from 1980 onwards.

Citations counts from the Google Scholar™ indexing service can be viewed at the linked Google Scholar™ search.

Full-text downloads:

261 since deposited on 16 Oct 2008
7 in the past twelve months

Full-text downloads displays the total number of times this work’s files (e.g., a PDF) have been downloaded from QUT ePrints as well as the number of downloads in the previous 365 days. The count includes downloads for all files if a work has more than one.

ID Code: 15211
Item Type: Conference Paper
Refereed: Yes
Keywords: stream ciphers, algebraic attacks, filter function, clock, control, initialization
DOI: 10.1007/978-3-540-73458-1_2
ISBN: 9783540734574
ISSN: 1611-3349
Subjects: Australian and New Zealand Standard Research Classification > INFORMATION AND COMPUTING SCIENCES (080000) > DATA FORMAT (080400) > Data Encryption (080402)
Divisions: Past > QUT Faculties & Divisions > Faculty of Science and Technology
Past > Institutes > Information Security Institute
Copyright Owner: Copyright 2007 Springer
Copyright Statement: This is the author-version of the work. Conference proceedings published, by Springer Verlag, will be available via SpringerLink.
http://www.springer.de/comp/lncs/ Lecture Notes in Computer Science
Deposited On: 16 Oct 2008 00:00
Last Modified: 09 Feb 2015 04:20

Export: EndNote | Dublin Core | BibTeX

Repository Staff Only: item control page