Hard Binding
Definition
A content binding that stores SHA hashes of specific byte ranges of the media file inside the signed manifest. Any modification to those bytes produces a hash mismatch that is detectable during verification. Hard bindings break if the file is re-encoded or format-converted.
- Mechanism
- SHA hashes of specific media byte ranges in a signed manifest
- Detects
- Any modification to those bytes as a hash mismatch
- Weakness
- Breaks on re-encoding or format conversion
- Standard
- C2PA content credentials
Common questions
Why does a hard binding break when a file is simply re-encoded, even without tampering?+
Re-encoding recalculates the underlying byte stream even when the visible content is unchanged, so the stored hash no longer matches, which is why the standard also defines soft bindings that survive such transformations.
How does hard binding differ from soft binding in C2PA?+
Hard binding proves byte-exact integrity of the covered range and fails on any change at all, while soft binding uses more tolerant fingerprinting to survive re-encoding but gives weaker guarantees, so the two serve complementary needs.
What does a hard-binding failure actually tell an investigator?+
It flags that the file bytes differ from what the manifest was signed over, but it does not by itself distinguish malicious tampering from an innocent format conversion, so the surrounding provenance chain still needs review.
Related terms
- Assertion
- A single provenance statement inside a C2PA claim. Examples include the camera make and model, GPS coordinates at capture, an AI-training or...
- C2PA Manifest
- The structured provenance record embedded in or associated with a media file. Contains one or more signed claim blocks, each holding a...
- C2PA Trust List
- A curated list of trusted root certificate authorities whose chains can anchor a C2PA claim signature. Maintained by the C2PA organisation. A...
- Claim Signature
- An X.509-based digital signature over the hashes of all assertions in a claim plus the content binding hash. Produced by the signer's...
- Soft Binding
- A content binding using a perceptual fingerprint or watermark embedded in the signal rather than the file bytes. Designed to survive format...