Cryptanalysis Of IDEA And ARIA Block Cipher

The block cipher is the most important basic to ensure modern information security. For example, IDEA has been widely used in commercial environment and ARIA is established as a Korean standard block cipher algorithm. Both algorithms have withstood all kinds of cryptographical attacks, and no efficient attack exists so far. Consequently, the study on cryptanalysis of IDEA and ARIA is very significant for academic research and practical application.This dissertation focuses on studying of the key schedule algorithm and round function of IDEA and the differential property of ARIA. Three results are presented: a related-key attack on IDEA, a meet-in-the-middle attack on IDEA and a differential enumeration attack on ARIA. The main works are as follows.1. Utilizing the characteristic of the key schedule algorithm of IDEA, especially for the 5-round subkey, and combining the properties of IDEA, a related-key differential attack on 5-round IDEA is presented by choosing proper plaintext pair. This attack uses 223.2 plaintexts and has a complexity of 270.55-round IDEA encryptions.2. Based on newly proposed properties of the round function of IDEA, a meet-in-the-middle attack on 5-round IDEA is developed, which requires only 27 chosen plaintexts and 2120 5-round IDEA encryptions.3. Extending the principle of meet-in-the-middle attack, differential enumeration attack is proposed. By this proposed scheme, based on newly given differential property of 4-round ARIA, differential enumeration attacks on 7-round and 8-round ARIA-256 are presented, both of which need 256 chosen plaintexts. The preprocessing and processing phase of attack on 7-round ARIA require 2238.2, 2124.2 7-round ARIA encryptions, respectively. And the attack on 8-round ARIA has a time complexity of 2238, 2253.6 8-round ARIA encryptions in the preprocessing and processing phase respectively.