Related-Key Cryptanalysis of RAIDEN

RAIDEN is a recent light-weight 128-bit block cipher. We report in this paper a critical weakness in its key schedule. Besides it reduces a 128-bit key down to 112-bit security, the weakness allows us to mount two related-key attacks. The best of the two attacks has a complexity of about 2
⁶⁵
. More precisely, the algorithm can be broken with one unknown plaintext, at most 33 unknown related keys, and about 2
⁶⁵
trial encryptions. This is the first successful attack on RAIDEN. We also suggest some changes for the key schedule so that our attacks are no more applicable.