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Security Fundamentals & Crypto · Advanced

Stateful Hash-Based Signatures

Quantum-resistant signature schemes such as LMS and XMSS that require tracking which one-time keys have been used.

Definition

LMS (RFC 8554) and XMSS (RFC 8391) are approved in NIST SP 800-208 and required by CNSA 2.0 for firmware and software signing. Each one-time signing key may be used only once, so the signer must reliably maintain state; reusing state breaks security. They are best suited to infrequent signing in controlled environments such as HSMs.

Example

A router vendor signs firmware images with LMS keys held in an HSM that tracks the key index.

Exam tip

Stateful = never reuse a key index; contrast with stateless SLH-DSA.

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