NIST Workshop on the Requirements for an Accordion Cipher Mode 2024

NIST hosted a workshop on the development of a new block cipher mode of operation on June 20–21, 2024, at the National Cybersecurity Center of Excellence in Rockville, Maryland. 

NIST plans to develop a new mode of the AES that is a tweakable, variable-input-length-strong pseudorandom permutation (VIL-SPRP) with a reduction proof to the security of the underlying block cipher.

The term “accordion cipher mode” (or “accordion mode,” for short) is introduced to indicate that the mode would act as a cipher, not only on a single block but on a range of input sizes. A well-designed accordion mode could potentially provide significant advantages over most of the block cipher modes that NIST currently approves. For example, an accordion mode could provide better resistance to cut-and-paste attacks than CBC, or it could be adapted to provide authenticated encryption with associated data (AEAD) with better properties than GCM, such as resistance to nonce misuse, support for short tags, nonce hiding, and key commitment. An accordion mode could also be adapted to provide key wrapping that is more efficient than KW and KWP.

• Parameter lengths for the accordion mode: keys, tweaks, data input
• Whether the accordion mode should support an underlying block cipher with 256-bit blocks
• Formal security goals for the accordion mode
• Requirements and features for the main use cases (e.g., AEAD )
• Potential design strategies
• Performance targets
• Implementation considerations
• The development and standardization process.

Updates and additional information will be posted to the workshop website and ciphermodes-forum email distribution list. Instructions for subscribing to the email forum can be found at https://csrc.nist.gov/Projects/block-cipher-techniques/email-list-ciphermodes-forum.

Workshop Announcement/Call for Abstracts (PDF)

Inquiries:  ciphermodes@nist.gov