{
  "status": "shipping",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-17",
  "slug": "zstandard-dictionary-id",
  "term": "Zstandard dictionary ID",
  "aliases": [
    "Zstd dictionary identifier"
  ],
  "definition": "A Zstandard dictionary ID is a numeric label used to select and check the external dictionary expected by a compressed frame.",
  "note": "The frame field is optional; a formatted dictionary stores its own identifier separately from its coding tables and content. The format does not specify how a reader obtains dictionary bytes. Dictionary managers must avoid assigning the same ID to distinct dictionaries in their scope. [rfc8878] [zstd-cli]\n\nIn a synthetic experiment, changing only the dictionary ID caused rejection, while retaining the ID and changing a content byte could return wrong bytes when no checksum was verified. This was deliberate mutation, not a naturally discovered collision. Preserve the exact dictionary and a trusted digest mapping across archive generations. [hesela-zstd]",
  "related": [
    "compression-dictionary",
    "zstandard",
    "backup-manifest",
    "cryptographic-hash"
  ],
  "citations": [
    {
      "id": "rfc8878",
      "title": "RFC 8878, sections 3.1.1.1.3 and 5: dictionary identifiers and dictionary format",
      "url": "https://www.rfc-editor.org/rfc/rfc8878.html#section-5",
      "accessed": "2026-10-17"
    },
    {
      "id": "zstd-cli",
      "title": "Zstandard v1.5.5 CLI manual: --dictID and --no-dictID",
      "url": "https://raw.githubusercontent.com/facebook/zstd/v1.5.5/programs/zstd.1.md",
      "accessed": "2026-10-17"
    },
    {
      "id": "hesela-zstd",
      "title": "Hesela: formatted dictionary identity experiment",
      "url": "https://hesela.com/analyses/compressed-archives-dictionary-dependencies/#dictionary-identity",
      "accessed": "2026-10-17"
    }
  ],
  "provenance": [
    "Format and CLI facts are distinct from Hesela's eight-case, single-build experiment; no codec vulnerability, collision probability or compression benchmark is claimed."
  ]
}