Key-linked block ciphers with input-output shuffling applied to remotely keyed encryption

We propose a more generalized Feistel network-like structure, with pre- (or post-) pseudorandom shuffling of the input (output) before (after, respectively) ciphering using two reversibly key-linked block ciphers, that is suitable for remotely keyed encryption. The security of the proposed structure is theoretically proved and new algorithms for the required pseudorandom shuffling stage are presented. Considering the many advantages of reusability, we apply this proposed universal ciphers merging structure for constructing practical new ciphers reviving the short-key DES and strengthening the security of the AES through stretching their key and block lengths. Since smart cards represent an effective tool for trustworthy portable storage of secret-keys and critical processes needed in many recent applications, we finally introduce an extremely secure length increasing remotely keyed encryption protocol allowing the use of a disposable (one-time) key for reliable long-term security.