Secret Key Specification for a Variable-Length Cryptographic Cellular Automata Model

Reverse algorithm was previously evaluated as encryption method concluding that its simple adoption is unviable, since it does not assurance the pre-image existence. Variable-Length Encryption Method (VLE) was proposed where a alternative algorithm with extra bits is adopted when pre-image computation is not possible. If an adequate secret key is used with VLE it is expected that the final ciphertext length is close to plaintext size. Several CA static parameters were calculated for a set formed by all radius 2 right-toggle rules. A database was generated associating rules performance in VLE ciphering with its parameters. A genetic algorithm-based data mining was performed to discover an adequate key specification based on CA parameters. Using such specification, ciphertext length is short, encryption process returns high entropy and VLE has a good protection against differential cryptanalysis.