{
  "slug": "checksum",
  "term": "Checksum",
  "aliases": [
    "Data checksum"
  ],
  "definition": "A checksum is a value computed from specified data and later compared with a reference value to detect changes.",
  "note": "A checksum names a checking role, not a security level: storage systems can use a CRC or a cryptographic digest in that role. Btrfs supports both categories. State the covered bytes, algorithm and location of the reference value; disagreement alone does not identify which copy is correct. [nist-checksum] [btrfs-checksumming]",
  "status": "shipping",
  "advantages": [],
  "limitations": [
    {
      "text": "CRC error-detection properties depend on the polynomial, message length and error model; CRC is not an authentication mechanism.",
      "citationIds": [
        "rfc3385"
      ]
    },
    {
      "text": "A valid checksum alone does not establish the requested address, committed generation or successful repair.",
      "citationIds": [
        "hesela-integrity"
      ]
    }
  ],
  "related": [
    "cryptographic-hash",
    "hash-collision",
    "data-scrubbing",
    "end-to-end-data-protection"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "nist-checksum",
      "title": "NIST CSRC glossary: checksum (definitions with source attribution)",
      "url": "https://csrc.nist.gov/glossary/term/checksum",
      "accessed": "2026-10-12"
    },
    {
      "id": "btrfs-checksumming",
      "title": "Btrfs documentation: Checksumming, algorithm choices and verification boundary",
      "url": "https://btrfs.readthedocs.io/en/latest/Checksumming.html",
      "accessed": "2026-10-12"
    },
    {
      "id": "rfc3385",
      "title": "RFC 3385: iSCSI CRC/Checksum Considerations, sections 1-2 and 10 (historical error-model analysis)",
      "url": "https://www.rfc-editor.org/rfc/rfc3385.html",
      "accessed": "2026-10-12"
    },
    {
      "id": "hesela-integrity",
      "title": "Hesela: Why a valid checksum can still return the wrong data",
      "url": "https://hesela.com/analyses/checksums-identity-and-lost-writes/",
      "accessed": "2026-10-12"
    }
  ],
  "updated": "2026-10-12"
}