Key-Joined Block Ciphers with Input-Output Pseudorandom Shuffling Applied to Remotely Keyed Authenticated Encryption

After emphasizing the weaknesses of the basic Feistel network structure, we propose a more generalized structure, mainly with pre- (or post-) pseudorandom shuffling of the input (output) before (after, respectively) ciphering using two reversibly key-joined block ciphers, that is suitable for remotely keyed encryption/ authenticated encryption. The security robustness of the proposed structure is theoretically proved and three new efficient schemes 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 (with less complexity than the triple-DES and DEAL) and strengthening the security of the AES through stretching their key and block lengths. Since smart cards represent an effective tool for portable storage of secret-keys and critically needed processes in many recent applications, we finally introduce an extremely secure length increasing remotely keyed encryption/authenticated encryption protocol that effectively permits the use of a disposable key for reliable long-term security and is less complex, faster, and so more adequate for inexpensive secure smart cards than known protocols.