vc.ts

/*
  Copyright (C) 2018-present evan GmbH.

  This program is free software: you can redistribute it and/or modify it
  under the terms of the GNU Affero General Public License, version 3,
  as published by the Free Software Foundation.

  This program is distributed in the hope that it will be useful,
  but WITHOUT ANY WARRANTY; without even the implied warranty of
  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
  See the GNU Affero General Public License for more details.

  You should have received a copy of the GNU Affero General Public License
  along with this program. If not, see http://www.gnu.org/licenses/ or
  write to the Free Software Foundation, Inc., 51 Franklin Street,
  Fifth Floor, Boston, MA, 02110-1301 USA, or download the license from
  the following URL: https://evan.network/license/
*/

import * as didJWT from 'did-jwt';
import { cloneDeep } from 'lodash';

import {
  nullAddress,
  nullBytes32,
  getEnvironment,
} from '../common/utils';

import {
  AccountStore,
  ContractLoader,
  DfsInterface,
  Did,
  Executor,
  Logger,
  LoggerOptions,
  NameResolver,
  SignerIdentity,
  Verifications,
} from '../index';

import { CryptoProvider } from '../encryption/crypto-provider';

/**
 * custom configuration for VC resolver
 */
export interface VcConfig {
  credentialStatusEndpoint: string;
}

/**
 * A VC's credential status property
 */
export interface VcCredentialStatus {
  id: string;
  type: string;
}

/**
 * Information about a VC's subject
 */
export interface VcCredentialSubject {
  id: string;
  data?: any;
  description?: any;
  uri?: string;
  name?: string;
}

/**
 * (Optional) Payload for a VC credential subject
 */
export interface VcCredentialSubjectPayload {
  name: string;
  value: string;
}

/**
 * A valid VC document
 */
export interface VcDocument {
  '@context': string[];
  id: string;
  type: string[];
  issuer: VcIssuer;
  validFrom: string;
  validUntil?: string;
  credentialSubject: VcCredentialSubject;
  credentialStatus?: VcCredentialStatus;
  proof?: VcProof;
}

/**
 * Template for a VC that will be converted into a valid VC by the resolver
 */
export interface VcDocumentTemplate {
  '@context'?: string[];
  id?: string;
  type?: string[];
  issuer: VcIssuer;
  validFrom: string;
  validUntil?: string;
  credentialSubject: VcCredentialSubject;
  credentialStatus?: VcCredentialStatus;
}

/**
 * The details of encryption/decryption of VC documents
 */
export interface VcEncryptionInfo {
  key?: string;
}

/**
 * The parts an VC ID in evan is made of
 */
export interface VcIdSections {
  environment: string;
  internalId: string;
}

/**
 * Issuer of a VC
 */
export interface VcIssuer {
  id: string;
  name?: string;
}

/**
 * Options for VC resolver
 */
export interface VcOptions extends LoggerOptions {
  accountStore: AccountStore;
  contractLoader: ContractLoader;
  dfs: DfsInterface;
  did: Did;
  executor: Executor;
  nameResolver: NameResolver;
  signerIdentity: SignerIdentity;
  verifications: Verifications;
  web3: any;
  cryptoProvider: CryptoProvider;
}

/**
 * The proof for a VC, containing the JWS and metadata
 */
export interface VcProof {
  type: string;
  created: string;
  proofPurpose: string;
  verificationMethod: string;
  jws: string;
}

/**
 * Holds a list of supported proof types for VC (JWS) proofs
 */
export const enum VcProofType {
  EcdsaPublicKeySecp256k1 = 'EcdsaPublicKeySecp256k1',
}

const JWTProofMapping = {};
JWTProofMapping[(VcProofType.EcdsaPublicKeySecp256k1)] = 'ES256K-R';

const vcRegEx = /^vc:evan:(?:(testcore|core):)?(0x(?:[0-9a-fA-F]{40}|[0-9a-fA-F]{64}))$/;

const w3cMandatoryContext = 'https://www.w3.org/2018/credentials/v1';

/**
 * Module for storing VCs in and retrieving VCs from the VC registry
 *
 * @class Vc
 */
export class Vc extends Logger {
  public credentialStatusEndpoint: string;

  private cache: any = {};

  private config: VcConfig;

  private options: VcOptions;

  /**
   * Creates a new `Vc` instance
   *
   * @param      {VcOptions}  options  options for `Vc`
   * @param      {Did}        did      Instance of `Did` used for resolving DIDs
   */
  public constructor(options: VcOptions, config: VcConfig) {
    super(options as LoggerOptions);
    this.options = options;
    this.credentialStatusEndpoint = config.credentialStatusEndpoint;
  }

  /**
   * Associates the active identity with a new ID in the registry to store a VC at.
   *
   * @returns     {Promise<string>}  The reserved ID.
   */
  public async createId(): Promise<string> {
    const id = await this.options.executor.executeContractTransaction(
      await this.getRegistryContract(),
      'createId', {
        from: this.options.signerIdentity.activeIdentity,
        event: { target: 'VcRegistry', eventName: 'VcIdRegistered' },
        getEventResult: (event, args) => args.vcId,
      },
    );

    return this.convertInternalVcIdToUri(id);
  }

  /**
   * Creates a new VC document from a template.
   *
   * @param      {VcDocumentTemplate}  vcData  Template for the VC document containing the relevant
   *                                           data.
   * @returns     {Promise<VcDocument} The final VC document as it is stored in the registry.
   */
  public async createVc(vcData: VcDocumentTemplate): Promise<VcDocument> {
    if (!vcData.id) {
      throw new Error('VC misses id');
    }

    const types = vcData.type ? vcData.type : ['VerifiableCredential'];

    const context = vcData['@context'] ? vcData['@context'] : [w3cMandatoryContext];
    if (!context.includes(w3cMandatoryContext)) {
      context.push(w3cMandatoryContext);
    }

    const vcDocument: VcDocument = {
      '@context': context,
      type: types,
      ...(vcData as VcDocument),
    };

    vcDocument.proof = await this.createProofForVc(vcDocument);

    await this.validateVcDocument(vcDocument);

    return vcDocument;
  }

  /**
   * Returns a key.
   *
   * @returns     {Promise<any}  it returns a key for encrypting data which can
   *                             be passed to `storeVc`.
   */
  public async generateKey(): Promise<any> {
    const cryptor = this.options.cryptoProvider.getCryptorByCryptoAlgo('aes');

    return cryptor.generateKey();
  }

  /**
   * get the Revoke status of a given VC document
   *
   * @param      {string}  vcId      The registry ID the VC document is associated with.
   * @return     {revokationStatus}  A boolean value. False = not revoked, True = revoked
   */
  public async getRevokeVcStatus(vcId: string): Promise<void> {
    const environment = await this.getEnvironment();
    const vcIdHash = vcId.replace(`vc:evan:${environment}:`, '');
    // `vcId` usually comes from a VC document, so non-existing VCs can be considered an edge case,
    // running both requests in parallel to improve performance
    const [revoked] = await Promise.all([
      this.options.executor.executeContractCall(
        await this.getRegistryContract(),
        'vcRevoke',
        vcIdHash,
      ),
      (async () => {
        const owned = await this.options.executor.executeContractCall(
          await this.getRegistryContract(),
          'vcOwner',
          vcIdHash,
        );
        if (owned === nullAddress) {
          throw new Error(`Given "${vcId}" is not a valid evan VC`);
        }
      })(),
    ]);
    return revoked;
  }

  /**
   * Returns a VC document for a given ID.
   *
   * @param      {string}            vcId              The registry ID the VC document
   *                                                   is associated with.
   * @param      {VcEncryptionInfo}  encryptionInfo    The encryption information for decryption.
   * @returns    {Promise<VcDocument}                  A VC document stored in the registry.
   * @throws           If an invalid VC ID is given or no document is registered under this ID or
   *                   wrong decryption key is provided.
   */
  public async getVc(vcId: string, encryptionInfo?: VcEncryptionInfo): Promise<VcDocument> {
    // Check whether the full URI (vc:evan:[vcId]) or just the internal ID was given
    let identityAddress = vcId;
    if (!identityAddress.startsWith('0x')) {
      const groups = vcRegEx.exec(vcId);
      if (!groups) {
        throw new Error(`Given VC ID ("${vcId}") is no valid evan VC ID`);
      }
      const [, vcEnvironment = 'core', address] = groups;
      identityAddress = address;
      const environment = await this.getEnvironment();
      if ((environment === 'testcore' && vcEnvironment !== 'testcore')
          || (environment === 'core' && vcEnvironment !== 'core')) {
        throw new Error(`Given VC ID environment "${vcEnvironment}" does not match current "${environment}"`);
      }
    }

    const vcDfsHash = await this.options.executor.executeContractCall(
      await this.getRegistryContract(),
      'vcStore',
      identityAddress,
    );

    if (vcDfsHash === nullBytes32) {
      throw Error(`VC for address ${vcId} does not exist`);
    }

    let document = JSON.parse(await this.options.dfs.get(vcDfsHash) as any);
    if (!encryptionInfo) {
      await this.validateProof(document as VcDocument);
      return document;
    }

    const cryptor = this.options.cryptoProvider.getCryptorByCryptoAlgo('aes');
    document = Buffer.from(document.data);
    try {
      const decryptedDocument = await cryptor.decrypt(document, { key: encryptionInfo.key });
      await this.validateProof(decryptedDocument);
      return decryptedDocument;
    } catch {
      throw new Error('Incorrect key: decryption failed');
    }
  }

  /**
   * Revokes a given VC document
   *
   * @param      {string}  vcId    The registry ID the VC document is associated with.
   * @return     {Promise<void>}   resolved when done
   */
  public async revokeVc(vcId: string): Promise<void> {
    const environment = await this.getEnvironment();
    const vcIdHash = vcId.replace(`vc:evan:${environment}:`, '');
    await this.validateVcIdOwnership(vcIdHash);
    await this.options.executor.executeContractTransaction(
      await this.getRegistryContract(),
      'revokeVC',
      { from: this.options.signerIdentity.activeIdentity },
      vcIdHash,
    );
  }

  /**
   * Stores the given VC document in the registry under the provided ID.
   * The ID has to be a valid and registered VC ID.
   * Creates a proof if none is given or validates it if one is given.
   *
   * @param      {VcDocumentTemplate}  vcData            Template for the VC document containing
   *                                                     the relevant data.
   * @param      {VcEncryptionInfo}    encryptionInfo    The encryption information for encryption.
   * @returns    {Promise<VcDocument}                    The final VC document as it
   *                                                     is stored in the registry.
   */
  public async storeVc(vcData: VcDocumentTemplate, encryptionInfo?: VcEncryptionInfo):
  Promise<VcDocument> {
    const dataTemplate: VcDocumentTemplate = cloneDeep(vcData);
    let internalId;

    if (!dataTemplate.id) {
      dataTemplate.id = await this.createId();
      internalId = (await this.validateVcIdAndGetSections(dataTemplate.id)).internalId;
    } else {
      // We prefix the ID specified in the document with
      // the evan identifier (vc:evan:[core|testcore]:)
      // However, we only need the actual ID to address the registry
      const sections = await this.validateVcIdAndGetSections(dataTemplate.id);
      internalId = sections.internalId;
      // Is the given VC ID valid and the active identity the owner of the VC ID?
      await this.validateVcIdOwnership(internalId);
    }

    dataTemplate.credentialStatus = {
      id: `${this.credentialStatusEndpoint}${dataTemplate.id}`,
      type: 'evan:evanCredential',
    };

    const documentToStore = await this.createVc(dataTemplate);
    let vcDfsAddress;
    if (!encryptionInfo) {
      vcDfsAddress = await this.options.dfs.add('vc',
        Buffer.from(JSON.stringify(documentToStore), 'utf-8'));
    } else {
      const cryptor = this.options.cryptoProvider.getCryptorByCryptoAlgo('aes');
      const encryptedDocumentToStore = await cryptor.encrypt(documentToStore,
        { key: encryptionInfo.key });
      vcDfsAddress = await this.options.dfs.add('vc',
        Buffer.from(JSON.stringify(encryptedDocumentToStore), 'utf-8'));
    }
    await this.options.executor.executeContractTransaction(
      await this.getRegistryContract(),
      'setVc',
      { from: this.options.signerIdentity.activeIdentity },
      internalId,
      vcDfsAddress,
    );
    return documentToStore;
  }

  /**
   * Converts an interal VC ID (0x...) to a URI (vc:evan:...)
   *
   * @param internalVcId Internal 32bytes ID
   * @returns The VC's URI
   */
  private async convertInternalVcIdToUri(internalVcId: string): Promise<string> {
    const environment = await this.getEnvironment();

    return `vc:evan:${environment}:${internalVcId}`;
  }

  /**
   * Create a JWT over a VC document
   *
   * @param      {VcDocument}   vc         The VC document
   * @param      {VcProofType}  proofType  The type of algorithm used for generating the JWT
   */
  private async createJwtForVc(vc: VcDocument, proofType: VcProofType): Promise<string> {
    const signer = didJWT.SimpleSigner(
      await this.options.accountStore.getPrivateKey(this.options.signerIdentity.underlyingAccount),
    );

    const jwt = await didJWT.createJWT(
      {
        vc,
        exp: vc.validUntil,
      }, {
        alg: JWTProofMapping[proofType],
        issuer: vc.issuer.id,
        signer,
      },
    );

    return jwt;
  }

  /**
   * Creates a new `VcProof` object for a given VC document, including generating a JWT token over
   * the whole document.
   *
   * @param      {VcDocument}   vc         The VC document to create the proof for.
   * @param      {VcProofType}  proofType  Specify if you want a proof type different from the
   *                                       default one.
   * @returns    {VcProof}                 A proof object containing a JWT.
   * @throws           If the VC issuer identity and the signer identity differ from each other
   */
  private async createProofForVc(vc: VcDocument,
    proofType: VcProofType = VcProofType.EcdsaPublicKeySecp256k1): Promise<VcProof> {
    let issuerIdentity;
    try {
      issuerIdentity = await this.options.did.convertDidToIdentity(vc.issuer.id);
    } catch (e) {
      throw Error(`Invalid issuer DID: ${vc.issuer.id}`);
    }

    if (this.options.signerIdentity.activeIdentity !== issuerIdentity) {
      throw Error('You are not authorized to issue this VC');
    }

    const jwt = await this.createJwtForVc(vc, proofType);

    const verMethod = await this.getPublicKeyUriFromDid(vc.issuer.id);

    const proof: VcProof = {
      type: `${proofType}`,
      created: new Date(Date.now()).toISOString(),
      proofPurpose: 'assertionMethod',
      verificationMethod: verMethod,
      jws: jwt,
    };

    return proof;
  }

  /**
   * Get current environment ('testcore:' || 'core'). Result is cached.
   *
   * @returns     {Promise<string>}  current environment
   */
  private async getEnvironment(): Promise<string> {
    if (!this.cache.environment) {
      this.cache.environment = await getEnvironment(this.options.web3);
    }
    return this.cache.environment;
  }

  /**
   * Retrieves the ID of the public key of an VC's issuer's DID document that matches the active
   * identity's public key.
   *
   * @param      {string}  issuerDid  DID of the VC issuer.
   * @throws           If there is no authentication material given in the DID or no key matching
   *                   the active identity is found.
   */
  private async getPublicKeyUriFromDid(issuerDid: string): Promise<string> {
    const doc = await this.options.did.getDidDocument(issuerDid);

    if (!(doc.authentication || doc.publicKey || doc.publicKey.length === 0)) {
      throw Error(`Document for ${issuerDid}`
        + 'does not provide authentication material. Cannot sign VC.');
    }

    let keyId;
    const signaturePublicKey = (await this.options.signerIdentity.getPublicKey(
      this.options.signerIdentity.underlyingAccount,
    )).toLocaleLowerCase();
    const account = this.options.signerIdentity.underlyingAccount.toLocaleLowerCase();
    for (const entry of doc.publicKey) {
      if (('ethereumAddress' in entry && entry.ethereumAddress.toLocaleLowerCase() === account)
      || ('publicKeyHex' in entry && entry.publicKeyHex.toLocaleLowerCase() === signaturePublicKey)) {
        keyId = entry.id;
        break;
      }
    }

    if (!keyId) {
      throw Error('The signature key of the active account is not associated to its DID document. Cannot sign VC.');
    }

    return keyId;
  }

  /**
   * Get web3 contract instance for VC registry contract via ENS. Result is cached.
   *
   * @returns     {Promise<any>}  VC registry contract
   */
  private async getRegistryContract(): Promise<any> {
    if (!this.cache.vcRegistryContract) {
      const vcRegistryDomain = this.options.nameResolver.getDomainName(
        this.options.nameResolver.config.domains.vcRegistry,
      );
      const vcRegistryAddress = await this.options.nameResolver.getAddress(vcRegistryDomain);

      this.cache.vcRegistryContract = this.options.contractLoader.loadContract(
        'VcRegistry', vcRegistryAddress,
      );
    }

    return this.cache.vcRegistryContract;
  }

  /**
   * Validates the JWS of a VC Document proof
   *
   * @param      {VcDocument}    document  The VC Document
   * @returns    {Promise<void>}           Resolves when done
   */
  private async validateProof(document: VcDocument): Promise<void> {
    // Mock the did-resolver package that did-jwt usually requires
    const didResolver = this.options.did;
    const resolver = {
      async resolve() {
        const doc = await didResolver.getDidDocument(document.issuer.id);
        return doc as any;
      },
    };

    // fails if invalid signature
    const verifiedSignature = await didJWT.verifyJWT(document.proof.jws, { resolver });

    // fails if signed payload and the VC differ
    const payload = {
      ...verifiedSignature.payload.vc,
    };
    delete payload.proof;
    const prooflessDocument = {
      ...document,
    };
    delete prooflessDocument.proof;

    const proofPayloadHash = await this.options.nameResolver.soliditySha3(JSON.stringify(payload));
    const documentHash = await this.options.nameResolver.soliditySha3(
      JSON.stringify(prooflessDocument),
    );
    if (proofPayloadHash !== documentHash) {
      throw Error('Invalid proof. Signed payload does not match given document.');
    }
  }

  /**
   * Checks various criteria a VC document has to meet
   *
   * @param      {VcDocument}    document  The VC document to check.
   * @returns    {Promise<void>}           If the checks are succesfull.
   * @throws           If any of the criteria is not met.
   */
  private async validateVcDocument(document: VcDocument): Promise<void> {
    // Subject
    if (!document.credentialSubject.id || document.credentialSubject.id === '') {
      throw new Error('No Subject ID provided');
    }
    await this.options.did.validateDid(document.credentialSubject.id);

    // Issuer
    if (!document.issuer.id || document.issuer.id === '') {
      throw new Error('No Issuer ID provided');
    }
    await this.options.did.validateDid(document.issuer.id);

    // Proof
    if (!document.proof || !document.proof.jws || document.proof.jws === '') {
      throw new Error('VC misses proof');
    } else if (!document.proof.type) {
      throw new Error('VC proof misses type');
    }
    await this.validateProof(document);
  }

  /**
   * Validates whether a given ID is a valid evan VC ID and returns
   * its sections (environment and internal ID)
   *
   * @param   {string}        vcId   VC ID
   * @returns {VcIdSections}         Sections of the ID
   */
  private async validateVcIdAndGetSections(vcId: string): Promise<VcIdSections> {
    const groups = vcRegEx.exec(vcId);
    if (!groups) {
      throw new Error(`Given VC ID ("${vcId}") is no valid evan VC ID`);
    }
    const [, vcEnvironment = 'core', internalId] = groups;
    const environment = await this.getEnvironment();
    if ((environment === 'testcore' && vcEnvironment !== 'testcore')
        || (environment === 'core' && vcEnvironment !== 'core')) {
      throw new Error(`VCs environment "${environment} does not match ${vcEnvironment}`);
    }

    return { environment: vcEnvironment, internalId };
  }

  /**
   * Checks if the given VC ID is associated to the active identity at the VC registry
   *
   * @param    {string} vcId   VC ID registered at the VC registry
   * @returns  {Promise<void>} Resolves when successful
   * @throws   {Error}         If the ID is not valid or the identity is not the ID owner
   */
  private async validateVcIdOwnership(vcId: string): Promise<void> {
    const ownerAddress = await this.options.executor.executeContractCall(
      await this.getRegistryContract(),
      'vcOwner',
      vcId,
    );

    if (this.options.signerIdentity.activeIdentity !== ownerAddress) {
      throw Error(`Active identity is not the owner of the given VC ID ${await this.convertInternalVcIdToUri(vcId)}`);
    }
  }
}