ZWC Text Watermark
C2PA Soft Binding Algorithm — com.writerslogic.zwc-watermark.1
A zero-width character watermark for text documents, providing invisible content-bound attestation as part of the WritersProof proof-of-process protocol. Embeds a cryptographic tag directly into document text using Unicode zero-width characters — invisible to readers, verifiable by anyone.
How It Works
From document content to an invisible, verifiable watermark in four steps.
HMAC-SHA256 computed from the signing key, MMR root, and document content hash. The content hash is SHA-256 over NFC-normalized document text.
Tag truncated to 64 bits, encoded as 32 zero-width Unicode characters at 2 bits each: U+200B = 00, U+200C = 01, U+200D = 10, U+FEFF = 11.
Characters placed at deterministic word-boundary positions via HMAC-seeded Fisher-Yates shuffle. Positions are reproducible given the same key material.
Blind extraction requires no access to the original unwatermarked document. The tag is verified against the evidence chain.
Technical Specification
Properties
Robust
Survives copy-paste, re-encoding, and format conversion. Zero-width characters persist across text editors, word processors, and web platforms.
Content-Bound
Any modification to the document text invalidates the watermark. Content changes require re-attestation — this is by design, not a limitation.
Blind Extraction
Verification requires no access to the original unwatermarked document. Extract, verify against the evidence chain, done.
C2PA Integration
Soft Binding per C2PA v2.3 Section 12.3
This algorithm is registered as a soft binding in the C2PA specification. Soft bindings provide a content-to-manifest association that survives transformations where hard bindings (like c2pa.hash.data) would break. For text documents, hard bindings fail on copy-paste, re-encoding, and format conversion — exactly the operations ZWC watermarks are designed to survive.
ZWC watermarks can be used alongside hard bindings. When the hard binding is intact, it provides byte-exact verification. When the hard binding breaks (e.g., after copy-paste), the soft binding still associates the content with its provenance manifest.
Assertion Details
com.writerslogic.pop-attestation.v1com.writerslogic.zwc-watermark.1