Related-Key Attacks on DDP Based Ciphers: CIKS-128 and CIKS-128H

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CIKS-128 and CIKS-128H are 128-bit block ciphers with a 256-bit key sizes based on data-dependent operations, respectively. They are also fast hardware-oriented ciphers and improvements of block cipher CIKS-1 introduced in [14]. This paper presents related-key differential attacks on full-round CIKS-128 and CIKS-128H. In result, using full-round related-key differential characteristics with probability 2− − 36 and 2− − 35.4, these attacks can recover the partial subkey bits for CIKS-128 and CIKS-128H with about 240 plaintexts, respectively. These works suggests that the greatest possible care has to be taken when proposing improvements of the existing block ciphers.

This work was supported by the Ministry of Information & Communications, Korea, under the Information Technology Research Center (ITRC) Support Program.