Abstract: In 1999, Mohammad Peyravian and Don Coppersmith from IBM proposed a structured symmetric key block cipher called CHAIN that supports variable block size, key size and number of rounds. In this paper, we initiate the study of CHAIN's security. More significantly, we show that CHAIN with various block sizes is insecure against impossible differential attack. To the best of our knowledge, this is the first known attack against CHAIN.
This research was not carried out under any specific funding.