Improved Meet-in-the-Middle Cryptanalysis of KTANTAN
The authors 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, they identify techniques that can also be mounted on block ciphers, thus allowing one to improve the cryptanalysis of the block cipher KTANTAN family. The first and major contribution is that they spot errors in previous cryptanalysis, secondly they 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 the attacks.