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SFNT content provenance

Content provenanceContent provenance: The record of where a piece of content came from and how it changed, carried with the content itself. for SFNT files is a signed C2PA manifestC2PA manifest: The signed label itself: a small package inside a file that records who signed it, what they declared and how to check it. inside the file. Anyone can check who signed it and whether it changed, for free.

Start signing freeCheck a SFNT file
A file holds a signed label in four layers: who signed it, what they declared including AI use, a fingerprint of the content, and a signature that seals them together.
The label sits inside the file. It names the signer, carries what they declared, fingerprints the content, and is sealed by a signature.
File
.sfnt, MIME typeMIME type: The standard name for a file format, such as image/jpeg or audio/wav, that software uses to decide how to read a file. font/sfnt
Where the label sits
Inside the file, in its own table, one of the named sections a font file is built from.
Standard
C2PAC2PA: The Coalition for Content Provenance and Authenticity: the group that publishes the open standard for content labels., the open standard for content labels.
Made for
Font tooling, Font pipelines, Mixed OTF and TTF libraries

What Encypher supports for SFNT

  • SignSupported

    Encypher signs SFNT files under C2PA 2.2 and 2.4.

  • CheckSupported

    Free in the browser checker, with no account.

  • Formal conformanceNot yet

    Not in our formal conformance record. That record is a narrower test than signing and checking.

How to check a SFNT file

  1. Open the free checker.

    It runs in your browser. No account needed.

    Open the checker

  2. Add your SFNT file.

    Drop it in or pick it from your device.

  3. Read the result.

    It shows who signed and what they declared, such as AI use. It also shows if the file changed.

Where the label sits in a SFNT file

The file is a row of tagged chunks, segments or tables. The label gets one of its own.

In a JPEG, PNG, WebP or WAV file, the label is one tagged chunk or segment among the chunks that hold the picture or sound.
A SFNT file keeps the label in its own table, one of the named sections a font file is built from.

SFNT is the table-based layout under both OpenType and TrueType fonts. Font tools work with it directly.

What keeps the label on a SFNT file

Four of the five answers a provenance check can give: Verified, Modified after signing, Issuer not recognized, and No provenance found. The fifth is Could not verify.
A check reports who signed and whether the content changed. It never says whether the content is true.
  • Copying and installing the font file keep the label.
  • Changing a glyph or table after signing shows as a change.
  • Converting the font to another format makes a new file without the label.

For engineers

Show the technical detail
Embedding
JUMBF manifest store in an SFNT table with the tag C2PA
Accepted MIME types
font/sfnt, application/font-sfnt
Signing versions
C2PA 2.2, 2.4
Verification
Any version. The checker reads any C2PA manifest it can parse, and the report names the version it checked against.
curl -X POST https://api.encypher.com/api/v1/sign/media \
  -H "Authorization: Bearer $ENCYPHER_API_KEY" \
  -H "Idempotency-Key: $(uuidgen)" \
  -F "file=@example.sfnt" \
  -F "title=My SFNT file" \
  -F "action=c2pa.created"

Support rows come from the live API capability matrix. Full reference: C2PA media types.

Keep reading

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