{
  "port": 37,
  "protocol": "both",
  "service": "Time",
  "oneLiner": "The Time Protocol — a 32-bit seconds-since-1900 count, returned as four raw bytes.",
  "whatItIs": "RFC 868 defines Time as a machine-readable counterpart to Daytime: connect, and the server returns a 32-bit big-endian count of seconds since 1 January 1900 UTC, then closes. NIST still answers on time.nist.gov and reports that only about 2% of its Internet Time Service traffic uses it, while urging users to move to NTP. The protocol has no authentication, no round-trip correction, and one-second resolution, and its 32-bit counter rolls over in 2036. It was an inetd built-in on classic UNIX and is off by default now.",
  "exposure": {
    "verdict": "careful",
    "note": "Only defensible as a deliberate public time service; the UDP form is spoofable and reflectable, and NTP replaces it for actually setting a clock."
  },
  "checkCommand": "nc -w 5 time.nist.gov 37 | xxd",
  "links": [
    {
      "title": "RFC 868 — Time Protocol",
      "url": "https://www.rfc-editor.org/rfc/rfc868.html",
      "kind": "spec"
    },
    {
      "title": "NIST Internet Time Service (ITS)",
      "url": "https://www.nist.gov/pml/time-and-frequency-division/time-distribution/internet-time-service-its",
      "kind": "official-docs"
    },
    {
      "title": "IANA Service Name and Transport Protocol Port Number Registry",
      "url": "https://www.iana.org/assignments/service-names-port-numbers/service-names-port-numbers.xhtml",
      "kind": "iana"
    }
  ]
}