NIST recently unveiled the criteria for crafting a new block cipher mode of operation for AES called Accordion Cipher Mode. Simultaneously, they've announced Ascon as the Winner in the Lightweight Cryptography competition (LWC). This raises the question:

  1. What shortcomings does Ascon possess, prompting NIST to convene a workshop for further development?
  2. if new mode requirements are not supported by Ascon , why were not included in the LWC process?
  3. what are the intended applications of this mode?
  • 2
    $\begingroup$ This is the first I'm hearing of this so thanks for sharing. It's a tweakable, variable-input-length-strong pseudorandom permutation, which is completely different to Ascon. Why do you think this has anything to do with the LWC competition? The page you linked also lists applications of the mode (an AEAD with better properties than GCM, key wrapping better than KW/KWP, etc). $\endgroup$ Mar 16 at 11:17

1 Answer 1


This effort is separate from LWC. The main purpose of LWC is constrained environments. It's not really about shortcomings in the design of ASCON, it's a separate purpose.

NIST hosted a workshop in 2023 on Block Ciphers Modes of Operation, with the goal of addressing the limitations of existing NIST standardized modes. I recommend going through the submitted papers/presentations for the workshop, some talk about the existing areas of friction with existing modes, and others are about new constructions or security properties that community is highlighting to NIST.

The existing modes standardized by NIST, have really shown their age. See the report on block cipher modes from the SP 800-38 series by Nicky Mouha. As an example, there was a submission from AWS around the challenges of using AES-GCM at cloud scale securely.

  • $\begingroup$ Thanks for the answer. $\endgroup$
    – hardyrama
    Mar 21 at 20:18

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