A new attack on 6-round IDEA

Eli Biham, Orr Dunkelman, Nathan Keller

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review

22 Scopus citations


IDEA is a 64-bit block cipher with 128-bit keys introduced by Lai and Massey in 1991. IDEA is one of the most widely used block ciphers, due to its inclusion in several cryptographic packages, such as PGP. Since its introduction in 1991, IDEA has withstood extensive cryptanalytic effort, but no attack was found on the full (8.5-round) variant of the cipher. In this paper we present the first known attack on 6-round IDEA faster than exhaustive key search. The attack exploits the weak key-schedule algorithm of IDEA, and combines Square-like techniques with linear cryptanalysis to increase the number of rounds that can be attacked. The attack is the best known attack on IDEA. We also improve previous attacks on 5-round IDEA and introduce a 5-round attack which uses only 16 known plaintexts.

Original languageEnglish
Title of host publicationFast Software Encryption - 14th International Workshop, FSE 2007
PublisherSpringer Verlag
Number of pages14
ISBN (Print)354074617X, 9783540746171
StatePublished - 2007
Externally publishedYes
Event14th International Workshop on Fast Software Encryption, FSE 2007 - Luxembourg, Luxembourg
Duration: 26 Mar 200728 Mar 2007

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume4593 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference14th International Workshop on Fast Software Encryption, FSE 2007


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