NIST Proposes Rijndael-256, Expanding AES Encryption for Larger Data Volumes

In response to the growing need for encryption mechanisms capable of efficiently processing vast amounts of data, the National Institute of Standards and Technology (NIST) has proposed standardizing a new variant of the Advanced Encryption Standard (AES) with a larger block size. This proposal aims to extend AES by adopting Rijndael-256, a variant of the Rijndael cipher with 256-bit blocks and a fixed 256-bit key size.

Why Rijndael-256?

The Advanced Encryption Standard (AES), currently the global encryption standard, uses a fixed 128-bit block size to secure sensitive data. While this configuration has proven highly effective since its adoption in 2001, advancements in data processing and the exponential growth of data volumes have revealed limitations in handling larger datasets efficiently. These concerns were highlighted in public comments during the review of NIST Special Publication (SP) 800-38A and reinforced in NIST Internal Report 8459, as well as during two public workshops focused on block cipher modes of operation.

Acknowledging this feedback, NIST announced its intention to explore Rijndael-256 as a viable alternative for modern cryptographic needs. The proposed variant uses larger blocks, which could mitigate data-handling bottlenecks in applications requiring high throughput and enhanced security.

NIST’s plan focuses on:

• Security analysis: Assessing potential cryptographic vulnerabilities or new cryptanalytic methods that may target Rijndael-256’s larger block size.
• Performance metrics: Evaluating the efficiency of Rijndael-256, particularly in hardware environments optimized for AES operations, to ensure practical applicability.

The shift to a 256-bit block size would represent a significant evolution in AES’s capabilities, potentially offering greater resilience against certain cryptographic attacks and improved scalability for applications in cloud computing, secure communications, and big data processing. Rijndael-256 would remain consistent with AES’s structure, ensuring a smoother transition for developers and organizations already familiar with the existing standard.

NIST plans to release a draft standard for Rijndael-256 in the next year, paving the way for further discussion and eventual adoption if the community deems it beneficial. Organizations leveraging encryption technologies are encouraged to participate in the public comment period to shape the future of this important cryptographic standard.

Public input is being sought to refine this proposal, with stakeholders invited to submit comments by June 25, 2025. Contributions should be emailed to ciphermodes@nist.gov with “Comments on Rijndael-256” as the subject line. Submitted feedback will be made public, excluding personal contact information, after the comment period ends.