Key classification attack on block ciphers
This addresses security vulnerabilities in specific block ciphers, such as KASUMI, but appears incremental as it builds on known weaknesses.
The paper tackles the problem of key recovery in block ciphers with key length greater than block length by proposing an algorithm that exploits key classification, achieving a complexity of O(max(2^n, 2^{k-n})), and demonstrates it on the 2-round KASUMI cipher.
In this paper, security analysis of block ciphers with key length greater than block length is proposed. When key length is significantly greater than block length and the statistical distribution of cipher system is like a uniform distribution, there are more than one key which map fixed input to fixed output. If a block cipher designed sufficiently random, it is expected that the key space can be classified into same classes. Using such classes of keys, our proposed algorithm would be able to recover the key of block cipher with complexity O(max(2^n, 2^{k-n}) where n is block length and k is key length. We applied our algorithm to 2- round KASUMI block cipher as sample block cipher by using weakness of functions that used in KASUMI.