jedisct1/nonce-extension
Make AES-GCM safe to use with random nonces, for any practical number of messages.
AES-GCM is a very common choice of authenticated encryption algorithm.
Unfortunately, it has some pretty low usage limits.
Using it with a large amount of messages requires extra care to ensure that nonces never repeat, and that keys are frequently rotated.
The TLS protocol hides that complexity, but applications using AES-GCM directly need to be aware of these limitations in order to use AES-GCM safely.
Ideally, nonces should be large, allowing applications to safely generate them randomly, with a negligible collision probability. But AES-GCM, as commonly implemented and required by IETF protocols, is limited to 96-bit (12 bytes) nonces, which is not enough to avoid collisions. AES-GCM keys are also expected to be replaced way before 2^32 messages have been encrypted.
During the 2023 NIST Workshop on Block Ciphers, Shay Gueron presented a clever way to overcome these limitations, and extend a key lifetime to "forever": the Derive-Key-AES-GCM construction. This work has been formalized in the IETF draft specification.
This construction allows larger nonces to be used with AES-GCM, thus extending the key lifetime. With AES-256 and 192-bit nonces, a practically unlimited number of messages can be encrypted using a single key, and with nonces that can be randomly generated.
It significantly improves the safety of AES-GCM with minor overhead.
The Double-Nonce-Derive-Key
(DNDK) construction for AES-256
derives a fresh AES-256
encryption key from a root key and a nonce. The nonce can be either:
The derived encryption key is then used with AES-256-GCM
along with a static nonce (or the NTail portion from the specification), guaranteeing that keys will never repeat.
This repository contains implementations of the DNDK-GCM construction in multiple languages:
nonce-extension
: Core DNDK-GCM implementation for AES-256dndk_derive()
: Full implementation with optional key commitment as per IETF draft-gueron-cfrg-dndkgcm-03nonce_extension_aes256()
: Convenience function for key derivation without key commitmentxaes-gcm
: High-level wrapper providing XAes256Gcm
for easy useencryptWide
for optimal performanceISC License - See LICENSE file for details