{
  "id": "identifier/uuidv5",
  "family": "identifier",
  "slug": "uuidv5",
  "title": "UUID Version 5 (name-based, SHA-1)",
  "summary": "UUIDv5 is a name-based UUID derived deterministically by SHA-1-hashing a namespace UUID concatenated with a name, truncating to 128 bits, then overwriting the version (5) and variant bits. Like v3 it is stable — same namespace + name always yields the same UUID — but uses SHA-1 instead of MD5 and is the RFC 9562-recommended choice for name-based ids.",
  "kind": "identifier",
  "aliases": [
    "UUID v5",
    "name-based UUID (SHA-1)",
    "version 5 UUID"
  ],
  "status": "standard",
  "verification": "verified",
  "tier": "B",
  "source_url": "https://www.rfc-editor.org/rfc/rfc9562#section-5.5",
  "source_version": "RFC 9562 §5.5",
  "retrieved_date": "2026-05-29",
  "see_also": [
    "identifier/uuidv3",
    "identifier/uuidv4"
  ],
  "ext_type": "identifier@1",
  "ext": {
    "spec": "RFC 9562 §5.5",
    "example": "2ed6657d-e927-568b-95e1-2665a8aea6a2",
    "bit_layout": [
      {
        "field": "sha1_high",
        "bits": 48,
        "meaning": "High 48 bits of SHA-1(namespace_uuid || name) (digest truncated to 128 bits)."
      },
      {
        "field": "ver",
        "bits": 4,
        "meaning": "version = 0b0101 (5), overwriting hash bits."
      },
      {
        "field": "sha1_mid",
        "bits": 12,
        "meaning": "Next 12 bits of the truncated digest."
      },
      {
        "field": "var",
        "bits": 2,
        "meaning": "variant = 0b10, overwriting hash bits."
      },
      {
        "field": "sha1_low",
        "bits": 62,
        "meaning": "Remaining 62 bits of the truncated digest."
      }
    ],
    "length_bits": 128,
    "sortable": false,
    "encoding": "hex with dashes (8-4-4-4-12)",
    "notes": [
      "Deterministic: UUIDv5(namespace, name) = set_version_variant( SHA1( bytes(namespace) || bytes(name) )[0:16], 5 ). SHA-1 output is 160 bits, truncated to the leading 128.",
      "Example uses the DNS namespace (6ba7b810-9dad-11d1-80b4-00c04fd430c8) with name 'www.example.com', yielding 2ed6657d-e927-568b-95e1-2665a8aea6a2 (RFC 9562 Appendix).",
      "SHA-1 is used only for namespacing here, not as a security primitive; RFC 9562 recommends v5 over v3."
    ]
  },
  "updated": "2026-05-29T00:00:00Z"
}