Pattern-Free Block Encryption : Single-Key Camellia XEX with PRNG Tweaks and Permutation Diffusion

Abstract

Block ciphers in ECB mode, such as Camellia-ECB, offer high throughput but leak visual and structural patterns when encrypting images or other repetitive data. We show PRNG-XEX+Permutation, a stateless improvement that gets rid of repeating blocks that are the same while keeping performance close to baseline. A single Camellia call wrapped in an XOR-Encrypt-XOR (XEX) construction processes each 128-bit block, with tweaks produced from a one-time, key-seeded Xoroshiro128+ pseudorandom stream. A simple static byte permutation further strengthens intra-block diffusion. The scheme eliminates the need for chaining, padding, or external parameters beyond the master key, ensuring streamlined implementation while supporting full parallelism and random access; it also guarantees provable block uniqueness. Our tests show that PRNG-XEX + Permutation meets all of the randomness requirements set by NIST SP 800-22. It also restores full visual privacy in encrypted images while maintaining encryption speeds within a few percent of standard ECB mode. This demonstrates that strong pattern resistance can be attained without sacrificing cipher efficiency.