Related-key rectangle attacks on reduced AES-192 and AES-256

Abstract

This paper examines the security of AES-192 and AES-256 against a related-key rectangle attack. We find the following new attacks: 8-round reduced AES-192 with 2 related keys, 10-round reduced AES-192 with 64 or 256 related keys and 9-round reduced AES-256 with 4 related keys. Our attacks reduce the complexity of earlier attacks presented at FSE 2005 and Eurocrypt 2005: for reduced AES-192 with 8 rounds, we decrease the required number of related keys from 4 to 2 at the cost of a higher data and time complexity; we present the first shortcut attack on AES-192 reduced to 10 rounds; for reduced AES-256 with 9 rounds, we decrease the required number of related keys from 256 to 4 and both the data and time complexity at the cost of a smaller number of attacked rounds. Furthermore, we point out some flaw in the 9-round AES-192 attack presented at Eurocrypt 2005, show how to fix it and enhance the attack in terms of the number of related keys. © International Association for Cryptologic Research 2007.