Improved Meet-in-the-Middle Cryptanalysis of KTANTAN

We revisit meet-in-the-middle attacks on block ciphers and recent developments in meet-in-the-middle preimage attacks on hash functions. Despite the presence of a secret key in the block cipher case, we identify techniques that can also be mounted on block ciphers, thus allowing us to improve the cryptanalysis of the block cipher KTANTAN family. The first and major contribution is that we spot errors in previous cryptanalysis, secondly we improve upon the corrected results. Especially, the technique indirect-partial-matching can be used to increase the number of matched bits significantly, as exemplified by our attacks. To the best of our knowledge, this is the first time that a splice-and-cut meet-in-the-middle attack is applied to block ciphers. When the splitting point is close to the start or the end of the cipher, the attack remains to be at very low data complexity. The secret key of the full cipher can be recovered faster than exhaustive search for all three block sizes in t...

• Type: Journal
• Year: 2011
• Where: IACR
• Authors: Lei Wei, Christian Rechberger, Jian Guo 0001, Hongjun Wu, Huaxiong Wang, San Ling
• Keywords: Block Ciphers, Hash Functions, IACR 2011, Time Complexity