A study on Rijndael-256 (a wider variant of Advanced Encryption Standard)

Abstract

This thesis explores the Rijndael-256 cipher, a wider variant of the Advanced Encryption Standard (AES), widely utilized in digital information security. AES always uses blocks of 128 bits, however, Rijndael-256 can handle blocks and keys that are 256 bits long, which makes it theoretically more secure. After a detailed analysis of AES, discussing design, key expansion, and wide usage, the thesis extends its focus to the Rijndael-256 implementation. The implementation involves complete key schedule construction, optimized T-tables, and verifying against official test vectors for correctness: NIST SP 800-38A and The Design of Rijndael for Rijndael-256. Performance is evaluated using high-precision, cycle-accurate RDTSC-based micro-benchmark on large buffers; block size and throughput versus computational efficiency are discussed. Finally, the practical use of Rijndael-256 is evaluated by comparing its stronger security with the extra computational and memory demands it introduces. This helps determine whether it offers any real benefit over standard AES in everyday cryptographic applications.