Abstract: The security of ARIRANG encryption mode was revaluated with the method of related-key rectangle attack．First,some new high-probability related-key rectangle distinguishers of 38rounds and 39rounds were found．Based on these distinguishers,some improvements in them were made．The main idea is the use of modular subtraction and XOR differential instead of the only XOR differential．Also,outputs of the distinguishers chose a differential set instead of the only XOR differential．All kinds of results based on these new high-probability distinguishers are presented,and they are better than the previous results．The best result is the attack on full ARIRANG-256encryption mode with the data complexity and time complexity of 2220.79and 2155.60,respectively.

Key words: ARIRANG encryption mode,Related-key rectangle attack,Distinguisher,Modular subtraction differential,Differential set