Elastic Block Ciphers in Practice: Constructions and Modes of Encryption

We demonstrate the general applicability of the elastic block cipher method by constructing examples from existing block ciphers: AES, Camellia, MISTY1 and RC6. An elastic block cipher is a variable-length block cipher created from an existing fixed-length block cipher. The elastic version supports any block size between one and two times that of the original block size. We compare the performance of the elastic versions to that of the original versions and evaluate the elastic versions using statistical tests measuring the randomness of the ciphertext. The benefit, in terms of an increased rate of encryption, of using an elastic block cipher varies based on the spe-cific block cipher and implementation. In most cases, there is an advantage to using an elastic block cipher to encrypt blocks that are a few bytes longer than the original block length. The sta-tistical test results indicate no obvious flaws in the method for constructing elastic block ciphers. We also use our examples to demonstrate the concept of a generic key schedule for block ciphers. In addition, we present ideas for new modes of encryption using the elastic block cipher construc- tion.