@cognitiveproof/softbinding-api-plugin-vsmark

Text-watermarking Extractor for @cognitiveproof/softbinding-api-server — the C2PA Soft Binding Resolution API server.

Hides a soft binding value inside plain-text or HTML content using invisible Unicode variation selectors. The carrier text displays unchanged (variation selectors are invisible to renderers and ignored by most text processing), but a watermarked copy can be traced back to the original binding even after metadata is stripped.

Install

npm install @cognitiveproof/softbinding-api-server @cognitiveproof/softbinding-api-plugin-vsmark

Usage

Register vsmarkExtractor so the server can recover binding values from watermarked text assets via POST /v1/matches/byContent and POST /v1/matches/byReference:

import { createServer } from '@cognitiveproof/softbinding-api-server';
import { vsmarkExtractor, VSMARK_ALGORITHM } from '@cognitiveproof/softbinding-api-plugin-vsmark';

const app = createServer({
  extractors: { [VSMARK_ALGORITHM]: vsmarkExtractor },
});

When publishing an asset, embed the manifest's binding value into its text using encode():

import { encode } from '@cognitiveproof/softbinding-api-plugin-vsmark';

const watermarkedArticle = encode(bindingValue, articleText);

decode() is also exported directly, for recovering a hidden value outside of createServer():

import { decode } from '@cognitiveproof/softbinding-api-plugin-vsmark';

const bindingValue = decode(watermarkedArticle); // string | undefined

API

| Export | Description | | ------------------------------------ | --------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------- | | vsmarkExtractor | An Extractor ((buffer, mimeType) => Promise<string \| null>). Decodes buffer as UTF-8 and returns the hidden binding value, or null if the asset isn't text or contains no watermark. | | VSMARK_ALGORITHM | The algorithm name 'com.cognitiveproof.vsmark.v1', for use as a key in createServer({ extractors }) and reflected in GET /v1/services/supportedAlgorithms. | | encode(secretMessage, carrierText) | Returns carrierText with secretMessage hidden inside it via invisible variation selectors. | | decode(text) | Returns the hidden message previously embedded with encode(), or undefined if none is found. |

How it works

Each byte of the message is encoded as one of 256 Unicode variation selectors (U+FE00–U+FE0F and U+E0100–U+E01EF) inserted after a character of the carrier text. The hidden payload is wrapped in a small framed format — a "VSR1" magic number, version byte, length-prefixed UTF-8 payload, and a CRC32 checksum — so decode() can reliably locate and validate the hidden data even if it's embedded partway through a larger text.

License

MIT