LinkedDataSignature.js

/*!
 * Copyright (c) 2017-2024 Digital Bazaar, Inc. All rights reserved.
 */
'use strict';

const constants = require('../constants');
const jsonld = require('jsonld');
const rdfCanonize = require('rdf-canonize');
const util = require('../util');
const {sha256digest} = require('../sha256digest');
const LinkedDataProof = require('./LinkedDataProof');

module.exports = class LinkedDataSignature extends LinkedDataProof {
  /**
   * Parent class from which the various LinkDataSignature suites (such as
   * `Ed25519Signature2020`) inherit.
   * NOTE: Developers are never expected to use this class directly, but to
   * only work with individual suites.
   *
   * @param {object} options - Options hashmap.
   * @param {string} options.type - Suite name, provided by subclass.
   * @typedef LDKeyPair
   * @param {LDKeyPair} LDKeyClass - The crypto-ld key class that this suite
   *   will use to sign/verify signatures. Provided by subclass. Used
   *   during the `verifySignature` operation, to create an instance (containing
   *   a `verifier()` property) of a public key fetched via a `documentLoader`.
   *
   * @param {string} contextUrl - JSON-LD context URL that corresponds to this
   *   signature suite. Provided by subclass. Used for enforcing suite context
   *   during the `sign()` operation.
   *
   * For `sign()` operations, either a `key` OR a `signer` is required.
   * For `verify()` operations, you can pass in a verifier (from KMS), or
   * the public key will be fetched via documentLoader.
   *
   * @param {object} [options.key] - An optional key object (containing an
   *   `id` property, and either `signer` or `verifier`, depending on the
   *   intended operation. Useful for when the application is managing keys
   *   itself (when using a KMS, you never have access to the private key,
   *   and so should use the `signer` param instead).
   *
   * @param {{sign: Function, id: string}} [options.signer] - Signer object
   *   that has two properties: an async `sign()` method, and an `id`. This is
   *   useful when interfacing with a KMS (since you don't get access to the
   *   private key and its `signer`, the KMS client gives you only the signer
   *   object to use).
   *
   * @param {{verify: Function, id: string}} [options.verifier] - Verifier
   *   object that has two properties: an async `verify()` method, and an `id`.
   *   Useful when working with a KMS-provided verifier.
   *
   * Advanced optional parameters and overrides:
   *
   * @param {object} [options.proof] - A JSON-LD document with options to use
   *   for the `proof` node (e.g. any other custom fields can be provided here
   *   using a context different from security-v2). If not provided, this is
   *   constructed during signing.
   * @param {string|Date} [options.date] - Signing date to use (otherwise
   *   defaults to `now()`).
   * @param {boolean} [options.useNativeCanonize] - Whether to use a native
   *   canonize algorithm.
   * @param {object} [options.canonizeOptions] - Options to pass to
   *   canonize algorithm.
   */
  constructor({
    type, proof, LDKeyClass, date, key, signer, verifier, useNativeCanonize,
    canonizeOptions, contextUrl
  } = {}) {
    super({type});
    this.LDKeyClass = LDKeyClass;
    this.contextUrl = contextUrl;
    this.proof = proof;
    const vm = _processSignatureParams({key, signer, verifier});
    this.verificationMethod = vm.verificationMethod;
    this.key = vm.key;
    this.signer = vm.signer;
    this.verifier = vm.verifier;
    this.canonizeOptions = canonizeOptions;
    if(date) {
      this.date = new Date(date);
      if(isNaN(this.date)) {
        throw TypeError(`"date" "${date}" is not a valid date.`);
      }
    }
    this.useNativeCanonize = useNativeCanonize;
    this._hashCache = null;
  }

  /**
   * @param {object} options - The options to use.
   * @param {object} options.document - The document to be signed.
   * @param {ProofPurpose} options.purpose - The proof purpose instance.
   * @param {Array} options.proofSet - Any existing proof set.
   * @param {function} options.documentLoader - The document loader to use.
   * @param {function} options.expansionMap - NOT SUPPORTED; do not use.
   *
   * @returns {Promise<object>} Resolves with the created proof object.
   */
  async createProof({
    document, purpose, proofSet, documentLoader, expansionMap
  }) {
    if(expansionMap) {
      throw new Error('"expansionMap" not supported.');
    }

    // build proof (currently known as `signature options` in spec)
    let proof;
    if(this.proof) {
      // shallow copy
      proof = {...this.proof};
    } else {
      // create proof JSON-LD document
      proof = {};
    }

    // ensure proof type is set
    proof.type = this.type;

    // set default `now` date if not given in `proof` or `options`
    let date = this.date;
    if(proof.created === undefined && date === undefined) {
      date = new Date();
    }

    // ensure date is in string format
    if(date && typeof date !== 'string') {
      date = util.w3cDate(date);
    }

    // add API overrides
    if(date) {
      proof.created = date;
    }

    proof.verificationMethod = this.verificationMethod;

    // add any extensions to proof (mostly for legacy support)
    proof = await this.updateProof(
      {document, proof, proofSet, purpose, documentLoader});

    // allow purpose to update the proof; the `proof` is in the
    // SECURITY_CONTEXT_URL `@context` -- therefore the `purpose` must
    // ensure any added fields are also represented in that same `@context`
    proof = await purpose.update(
      proof, {document, suite: this, documentLoader});

    // create data to sign
    const verifyData = await this.createVerifyData(
      {document, proof, proofSet, documentLoader});

    // sign data
    proof = await this.sign({verifyData, document, proof, documentLoader});

    return proof;
  }

  /**
   * @param {object} options - The options to use.
   * @param {object} options.proof - The proof to be updated.
   * @param {Array} options.proofSet - Any existing proof set.
   * @param {function} options.expansionMap - NOT SUPPORTED; do not use.
   *
   * @returns {Promise<object>} Resolves with the created proof object.
   */
  async updateProof({proof, expansionMap}) {
    if(expansionMap) {
      throw new Error('"expansionMap" not supported.');
    }
    // extending classes may do more
    return proof;
  }

  /**
   * @param {object} options - The options to use.
   * @param {object} options.proof - The proof to be verified.
   * @param {object} options.document - The document the proof applies to.
   * @param {ProofPurpose} options.purpose - The proof purpose instance.
   * @param {Array} options.proofSet - Any existing proof set.
   * @param {function} options.documentLoader - The document loader to use.
   * @param {function} options.expansionMap - NOT SUPPORTED; do not use.
   *
   * @returns {Promise<{object}>} Resolves with the verification result.
   */
  async verifyProof({proof, document, proofSet, documentLoader, expansionMap}) {
    if(expansionMap) {
      throw new Error('"expansionMap" not supported.');
    }

    try {
      // create data to verify
      const verifyData = await this.createVerifyData(
        {document, proof, proofSet, documentLoader, expansionMap});

      // fetch verification method
      const verificationMethod = await this.getVerificationMethod(
        {proof, document, documentLoader, expansionMap});

      // verify signature on data
      const verified = await this.verifySignature({
        verifyData, verificationMethod, document, proof,
        documentLoader, expansionMap});
      if(!verified) {
        throw new Error('Invalid signature.');
      }

      return {verified: true, verificationMethod};
    } catch(error) {
      return {verified: false, error};
    }
  }

  async canonize(input, {documentLoader, expansionMap, skipExpansion}) {
    if(expansionMap) {
      throw new Error('"expansionMap" not supported.');
    }
    return _canonize(input, {
      algorithm: 'RDFC-1.0',
      // do not resolve any relative URLs or terms, throw errors instead
      base: null,
      format: 'application/n-quads',
      documentLoader,
      // throw errors if any values would be dropped due to missing
      // definitions or relative URLs
      safe: true,
      skipExpansion,
      useNative: this.useNativeCanonize,
      ...this.canonizeOptions
    });
  }

  async canonizeProof(proof, {document, documentLoader, expansionMap}) {
    if(expansionMap) {
      throw new Error('"expansionMap" not supported.');
    }
    // `jws`,`signatureValue`,`proofValue` must not be included in the proof
    // options
    proof = {
      '@context': document['@context'] || constants.SECURITY_CONTEXT_URL,
      ...proof
    };
    delete proof.jws;
    delete proof.signatureValue;
    delete proof.proofValue;
    return this.canonize(proof, {
      documentLoader,
      expansionMap,
      skipExpansion: false,
      ...this.canonizeOptions
    });
  }

  /**
   * @param {object} options - The options to use.
   * @param {object} options.document - The document to be signed/verified.
   * @param {object} options.proof - The proof to be verified.
   * @param {Array} options.proofSet - Any existing proof set.
   * @param {function} options.documentLoader - The document loader to use.
   * @param {function} options.expansionMap - NOT SUPPORTED; do not use.
   *
   * @returns {Promise<{Uint8Array}>}.
   */
  async createVerifyData({document, proof, documentLoader, expansionMap}) {
    if(expansionMap) {
      throw new Error('"expansionMap" not supported.');
    }
    // get cached document hash
    let cachedDocHash;
    const {_hashCache} = this;
    if(_hashCache && _hashCache.document === document) {
      cachedDocHash = _hashCache.hash;
    } else {
      this._hashCache = {
        document,
        // canonize and hash document
        hash: cachedDocHash =
          this.canonize(document, {documentLoader, expansionMap})
            .then(c14nDocument => sha256digest({string: c14nDocument}))
      };
    }

    // await both c14n proof hash and c14n document hash
    const [proofHash, docHash] = await Promise.all([
      // canonize and hash proof
      this.canonizeProof(
        proof, {document, documentLoader, expansionMap})
        .then(c14nProofOptions => sha256digest({string: c14nProofOptions})),
      cachedDocHash
    ]);

    // concatenate hash of c14n proof options and hash of c14n document
    return util.concat(proofHash, docHash);
  }

  /**
   * @param verifyData {Uint8Array}.
   * @param document {object} document from which to derive a new document
   *   and proof.
   * @param proof {object}
   * @param proofSet {Array}
   * @param documentLoader {function}
   *
   * @returns {Promise<{object}>} The new document with `proof`.
   */
  async derive() {
    throw new Error('Must be implemented by a derived class.');
  }

  /**
   * @param document {object} to be signed.
   * @param proof {object}
   * @param documentLoader {function}
   */
  async getVerificationMethod({proof, documentLoader}) {
    let {verificationMethod} = proof;

    if(typeof verificationMethod === 'object') {
      verificationMethod = verificationMethod.id;
    }

    if(!verificationMethod) {
      throw new Error('No "verificationMethod" found in proof.');
    }

    // Note: `expansionMap` is intentionally not passed; we can safely drop
    // properties here and must allow for it
    const framed = await jsonld.frame(verificationMethod, {
      '@context': constants.SECURITY_CONTEXT_URL,
      '@embed': '@always',
      id: verificationMethod
    }, {documentLoader, compactToRelative: false, safe: true});
    if(!framed) {
      throw new Error(`Verification method ${verificationMethod} not found.`);
    }

    // ensure verification method has not been revoked
    if(framed.revoked !== undefined) {
      throw new Error('The verification method has been revoked.');
    }

    return framed;
  }

  /**
   * @param verifyData {Uint8Array}.
   * @param document {object} to be signed.
   * @param proof {object}
   * @param documentLoader {function}
   * @param expansionMap {function}
   *
   * @returns {Promise<{object}>} the proof containing the signature value.
   */
  async sign() {
    throw new Error('Must be implemented by a derived class.');
  }

  /**
   * @param verifyData {Uint8Array}.
   * @param verificationMethod {object}.
   * @param document {object} to be signed.
   * @param proof {object}
   * @param documentLoader {function}
   * @param expansionMap {function}
   *
   * @returns {Promise<boolean>}
   */
  async verifySignature() {
    throw new Error('Must be implemented by a derived class.');
  }

  /**
   * Ensures the document to be signed contains the required signature suite
   * specific `@context`, by either adding it (if `addSuiteContext` is true),
   * or throwing an error if it's missing.
   *
   * @param {object} options - Options hashmap.
   * @param {object} options.document - JSON-LD document to be signed.
   * @param {boolean} options.addSuiteContext - Add suite context?
   */
  ensureSuiteContext({document, addSuiteContext}) {
    const {contextUrl} = this;

    if(_includesContext({document, contextUrl})) {
      // document already includes the required context
      return;
    }

    if(!addSuiteContext) {
      throw new TypeError(
        `The document to be signed must contain this suite's @context, ` +
        `"${contextUrl}".`);
    }

    // enforce the suite's context by adding it to the document
    const existingContext = document['@context'] || [];

    document['@context'] = Array.isArray(existingContext) ?
      [...existingContext, contextUrl] : [existingContext, contextUrl];
  }
};

/**
 * Tests whether a provided JSON-LD document includes a context URL in its
 * `@context` property.
 *
 * @param {object} options - Options hashmap.
 * @param {object} options.document - A JSON-LD document.
 * @param {string} options.contextUrl - A context URL.
 *
 * @returns {boolean} Returns true if document includes context.
 */
function _includesContext({document, contextUrl}) {
  const context = document['@context'];
  return context === contextUrl ||
    (Array.isArray(context) && context.includes(contextUrl));
}

/**
 * See constructor docstring for param details.
 *
 * @returns {{verificationMethod: string, key: LDKeyPair,
 *   signer: {sign: Function, id: string},
 *   verifier: {verify: Function, id: string}}} - Validated and initialized
 *   key-related parameters.
 */
function _processSignatureParams({key, signer, verifier}) {
  // We are explicitly not requiring a key or signer/verifier param to be
  // present, to support the verify() use case where the verificationMethod
  // is being fetched by the documentLoader

  const vm = {};
  if(key) {
    vm.key = key;
    vm.verificationMethod = key.id;
    if(typeof key.signer === 'function') {
      vm.signer = key.signer();
    }
    if(typeof key.verifier === 'function') {
      vm.verifier = key.verifier();
    }
    if(!(vm.signer || vm.verifier)) {
      throw new TypeError(
        'The "key" parameter must contain a "signer" or "verifier" method.');
    }
  } else {
    vm.verificationMethod = (signer && signer.id) ||
      (verifier && verifier.id);
    vm.signer = signer;
    vm.verifier = verifier;
  }

  if(vm.signer) {
    if(typeof vm.signer.sign !== 'function') {
      throw new TypeError('A signer API has not been specified.');
    }
  }
  if(vm.verifier) {
    if(typeof vm.verifier.verify !== 'function') {
      throw new TypeError('A verifier API has not been specified.');
    }
  }

  return vm;
}

async function _canonize(input, options) {
  // convert to RDF dataset and do canonicalization
  const opts = {
    rdfDirection: 'i18n-datatype', ...options, produceGeneralizedRdf: false,
  };
  delete opts.format;
  const dataset = await jsonld.toRDF(input, opts);
  return rdfCanonize.canonize(dataset, options);
}