{
  "slug": "lms-hss",
  "name": "LMS / HSS",
  "aka": "Leighton-Micali Signatures, Hierarchical Signature System",
  "kind": "Digital signature (stateful)",
  "family": "Hash-based (stateful)",
  "standard": "RFC 8554 and NIST SP 800-208",
  "standard_url": "https://csrc.nist.gov/pubs/sp/800/208/final",
  "body": "IETF / IRTF CFRG (RFC 8554) and NIST (SP 800-208)",
  "date": "RFC 8554: 2019-04; SP 800-208: 2020-10-30",
  "status": "Final",
  "summary": "LMS and its multi-tree variant HSS are stateful hash-based signatures specified in RFC 8554 (2019-04) and approved by NIST in SP 800-208 (2020-10). They are the signature schemes CNSA 2.0 requires for firmware and software signing, and are the first post-quantum signatures many hardware roots of trust support.",
  "parameter_sets": [
    {
      "name": "LMS_SHA256_M32_H10 (typical)",
      "category": 5,
      "pk": 60,
      "sk": "varies",
      "ct_or_sig": 1456
    },
    {
      "name": "HSS with 2 levels of H10 (typical)",
      "category": 5,
      "pk": 60,
      "sk": "varies",
      "ct_or_sig": 2964
    }
  ],
  "size_label": "Signature",
  "deployments": [
    "CNSA 2.0 firmware and software signing (exclusive use required by 2030)",
    "Hardware roots of trust, secure boot, HSM-backed code signing"
  ],
  "audit_focus": [
    "State management is the whole game: a one-time key reused once allows forgery. Audit state persistence, atomic updates, backups, HSM cloning, and crash recovery",
    "SP 800-208 restricts key generation and signing to hardware cryptographic modules for FIPS validation",
    "Parameter-set validation on the verifier, including the Winternitz parameter and tree height",
    "Domain separation constants and the exact hash-input layouts of RFC 8554"
  ],
  "references": [
    [
      "RFC 8554, Leighton-Micali Hash-Based Signatures",
      "https://datatracker.ietf.org/doc/rfc8554/"
    ],
    [
      "NIST SP 800-208, Recommendation for Stateful Hash-Based Signature Schemes",
      "https://csrc.nist.gov/pubs/sp/800/208/final"
    ]
  ],
  "url": "https://pqaudit.org/algorithms/lms-hss/",
  "updated": "2026-09-12"
}