zstandard-dictionary-id · shipping · also Zstd dictionary identifier

Zstandard dictionary ID

A Zstandard dictionary ID is a numeric label used to select and check the external dictionary expected by a compressed frame.

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. [1] [2]

In 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. [3]

Relations

related

compression-dictionary, zstandard, backup-manifest, cryptographic-hash

Citations

1. RFC 8878, sections 3.1.1.1.3 and 5: dictionary identifiers and dictionary format (accessed 2026-10-17)
2. Zstandard v1.5.5 CLI manual: --dictID and --no-dictID (accessed 2026-10-17)
3. Hesela: formatted dictionary identity experiment (accessed 2026-10-17)

JSON: /data/terms/zstandard-dictionary-id.json