Square Attacks on Reduced-Round PES and IDEA Block Ciphers
Jorge Nakahara, Paulo S. L. M. Barreto, Bart Preneel, Joos P. L. Vandewalle, Hae Yong Kim · 2001
This paper reports on variants of the Square attack applied to reduced-round versions of the PES and IDEA block ciphers . Attacks on 2.5 rounds of IDEA require 32 chosen-plaintexts and recover 77 key bits with a time complexity of 2 . A new kind of attack, the related-key Square attack, is applied to 2.5 rounds of IDEA and recovers 32 key bits, with two chosen-plaintexts and 2 related keys with a time complexity of 2 . Similar results hold for 2.5 rounds of PES. Implementations of the attacks on 32-bit block mini-versions of both ciphers confirmed the expected computational complexity. Although our attacks do not improve on previous approaches, this report shows new variants of the Square attack on word-oriented block ciphers like IDEA and PES.