Cryptographic Accordion

Definition

A cryptographic accordion is a tweakable, variable-input-length strong pseudorandom permutation (VIL-SPRP) constructed from an underlying block cipher. Thus, an accordion serves simultaneously as 1) a mode of the underlying block cipher and 2) a tweakable block cipher on a range of input lengths.

A derived function is an input encoding that enables a specific functionality from an accordion, such as authenticated encryption with associated data (AEAD), tweakable encryption (e.g., for storage applications), or deterministic authenticated encryption (e.g., for key wrapping). The derived functions of efficient accordions can support enhanced security over currently approved modes.

Context

• 2025-06-06 NIST SP 800-197A PRE-DRAFT Call for Comments: NIST Launches Development of Cryptographic Accordions