Overview

A concrete family of text soft-binding algorithms compatible with the C2PA Soft Binding framework, each registered in the C2PA soft binding algorithm list. A soft binding derives a content-keyed value that survives reformatting, re-encoding, excerpting, and light editing, so a manifest is recoverable when the hard binding — a byte-exact hash — has been broken.

| Module | Algorithm (list id) | Kind | |---|---|---| | simhash | com.writerslogic.text-fingerprint.1 (41) | surface fingerprint | | stego | com.writerslogic.zwc-watermark.2 (42) | zero-width watermark | | structure | com.writerslogic.text-structure.1 (43) | structural fingerprint | | minhash | com.writerslogic.text-minhash.1 (44) | excerpt/quotation fingerprint |

This crate is the perceptual/watermark recovery layer. It is distinct from the Variation-Selector transport used elsewhere in WritersProof, which is a hard binding (a c2pa.hash.data over normalized text) and is not soft binding. Registration in the algorithm list is not C2PA conformance certification.

Quick Start

[dependencies]
c2pa-text-binding = "0.1"

Emit and sign a c2pa.soft-binding assertion

soft_binding builds the normative CBOR assertion (it round-trips through the c2pa-rs reader — see tests/c2pa_roundtrip.rs); manifest signs it as a COSE_Sign1 / EdDSA envelope.

use c2pa_text_binding::{simhash::Fingerprint, soft_binding, sign_cose, SOFT_BINDING_LABEL};

let text = "…the document being bound…";
let secret_key = [7u8; 32];                   // caller-supplied Ed25519 secret
let assertion = soft_binding::from_fingerprint(&Fingerprint::compute(text));
let cbor = assertion.to_cbor()?;              // store under SOFT_BINDING_LABEL
let signed = sign_cose(&cbor, &secret_key)?;  // detached-key COSE_Sign1
# Ok::<(), c2pa_text_binding::Error>(())

Recover and classify a candidate

The verify path recomputes the fingerprint from the current text, compares it to the stored value at the algorithm's registered threshold, and returns a confidence tier. BOUND requires a durable fingerprint match (41/44, measured zero false matches) plus the anti-transfer cross-check; a structural (43) match or a watermark hit alone caps at LIKELY. Tier thresholds are grounded in ROBUSTNESS.md.

use c2pa_text_binding::{simhash::Fingerprint, soft_binding::{self, SoftBinding}, verify, Confidence};

let text = "…the document being bound…";
let cbor = soft_binding::from_fingerprint(&Fingerprint::compute(text)).to_cbor()?;

let candidate = SoftBinding::from_cbor(&cbor)?;
let tier = verify(text, &candidate, /*watermark_verified=*/ false, /*crosscheck_ok=*/ true);
assert_eq!(tier, Confidence::Bound);
# Ok::<(), c2pa_text_binding::Error>(())

Register with the Soft Binding Resolution API

These algorithms are registered in the C2PA soft binding algorithm list, so a c2pa.soft-binding assertion referencing them can drive decentralized manifest recovery.

Related Crates

| Crate | Description | |---|---| | c2pa-structured-text | Structured text embedding via ASCII armour delimiters | | c2pa-text | Unstructured text embedding via Unicode Variation Selectors | | c2pa-rs | Official C2PA SDK |

License

Licensed under either of Apache License, Version 2.0 or MIT License at your option.

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