Welcome to the resource topic for 2025/758
Title:
Blockcipher-Based Key Commitment for Nonce-Derived Schemes
Authors: Panos Kampanakis, Shai Halevi, Nevine Ebeid, Matt Campagna
Abstract:AES-GCM has been the status quo for efficient symmetric encryption for decades. As technology and cryptographic applications evolved over time, AES-GCM has posed some challenges to certain use-cases due to its default 96-bit nonce size, 128-bit block size, and lack of key commitment. Nonce-derived schemes are one way of addressing these challenges: Such schemes derive multiple keys from nonce values, then apply standard AES-GCM with the derived keys (and possibly another 96-bit nonce). The approach overcomes the nonce length and data limit issues since each derived key is only used to encrypt a few messages. By itself, the use of nonce-derived keys does not address key commitment, however. Some schemes chose to include a built-in key commitment mechanism, while others left it out of scope.
In this work, we explore efficient key commitment methods that can be added to any nonce-derived scheme in a black-box manner. Our focus is on options that use the underlying block cipher and no other primitive, are efficient, and only use standard primitives which are FIPS-approved. For concreteness we focus here specifically on adding key commitment to XAES-256-GCM, a nonce-scheme originally proposed by Filippo Valsorda, but these methods can be adapted to any other nonce-derived scheme. We propose an efficient CMAC-based key commitment solution, and prove its security in the ideal-cipher model. We argue that adding this solution yields a FIPS-compliant mode, quantify the data and message length limits of this mode and compare this combination to other nonce-derived modes. We also benchmark our key committing XAES-256-GCM performance.
ePrint: https://eprint.iacr.org/2025/758
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