post-e-voting/source-code/scytl-cryptolib/cryptolib-js-zkproof/lib/handlers/plaintext-exponent-equality-proof-handler.js

/*
 * Copyright 2018 Scytl Secure Electronic Voting SA
 *
 * All rights reserved
 *
 * See our extended copyright notice in *file 'Copyright.txt' which is part of this source code package
 */
/* jshint node:true */
'use strict';

var ZeroKnowledgeProofProver = require('../prover');
var ZeroKnowledgeProofVerifier = require('../verifier');
var ZeroKnowledgeProof = require('../proof');
var ZeroKnowledgeProofPreComputation = require('../pre-computation');
var PhiFunction = require('../phi-function');
var ProgressMeter = require('../progress-meter');
var validator = require('../input-validator');

module.exports = PlaintextExponentEqualityProofHandler;

/**
 * @class PlaintextExponentEqualityProofHandler
 * @classdesc Encapsulates a handler for the plaintext exponent equality
 *            zero-knowledge proof of knowledge generation, pre-computation and
 *            verification processes. To instantiate this object, use the method
 *            {@link
 *            ZeroKnowledgeProofService.newPlaintextExponentEqualityProofHandler}.
 * @param {ZpSubgroup}
 *            group The Zp subgroup to which all exponents and Zp group elements
 *            required for the proof generation are associated or belong,
 *            respectively.
 * @param {MessageDigestService}
 *            messageDigestService The message digest service.
 * @param {MathematicalService}
 *            mathematicalService The mathematical service.
 */
function PlaintextExponentEqualityProofHandler(
    group, messageDigestService, mathematicalService) {
  var NUM_PHI_INPUTS = 2;
  var DEFAULT_AUXILIARY_DATA = 'PlaintextExponentEqualityProof';

  var prover_ =
      new ZeroKnowledgeProofProver(messageDigestService, mathematicalService);
  var verifier_ =
      new ZeroKnowledgeProofVerifier(messageDigestService, mathematicalService);
  var progressCallback_;
  var progressPercentMinCheckInterval_;
  var measureProgress_ = false;

  var baseElements_;

  /**
   * Initializes the handler with the provided base elements.
   *
   * @function init
   * @memberof PlaintextExponentEqualityProofHandler
   * @param {ZpGroupElement[]}
   *            baseElements The base elements.
   * @returns {PlaintextExponentEqualityProofHandler} A reference to this
   *          object, to facilitate method chaining.
   * @throws {Error}
   *             If the input data validation fails.
   */
  this.init = function(baseElements) {
    validator.checkZpGroupElements(
        baseElements,
        'Base elements for plaintext exponent eqaulity proof handler initialization',
        group);

    baseElements_ = baseElements;

    return this;
  };

  /**
   * Generates a plaintext exponent equality zero-knowledge proof of
   * knowledge. Before using this method, the handler must have been
   * initialized with base elements, via the method
   * {@link PlaintextExponentEqualityProofHandler.init}.
   *
   * @function generate
   * @memberof PlaintextExponentEqualityProofHandler
   * @param {Exponent}
   *            firstSecret The "ephemeral key" used to generate the gamma
   *            element of the ciphertext, the knowledge of which must be
   *            proven.
   * @param {Exponent}
   *            secondSecret The "message key" used to generate the phi
   *            elements of the ciphertext, the knowledge of which must be
   *            proven.
   * @param {ElGamalEncryptedElements}
   *            ciphertext The ciphertext.
   * @param {Object}
   *            [options] An object containing optional arguments.
   * @param {Uint8Array|string}
   *            [options.data='PlaintextExponentEqualityProof'] Auxiliary
   *            data.
   * @param {ZeroKnowledgeProofPreComputation}
   *            [options.preComputation=Generated internally] A
   *            pre-computation of the plaintext exponent equality
   *            zero-knowledge proof of knowledge.
   * @returns {ZeroKnowledgeProof} The plaintext exponent equality
   *          zero-knowledge proof of knowledge.
   * @throws {Error}
   *             If the input data validation fails.
   */
  this.generate = function(firstSecret, secondSecret, ciphertext, options) {
    if (typeof baseElements_ === 'undefined') {
      throw new Error(
          'Cannot generate plaintext exponent equality proof; Associated handler has not been initialized with any base elements');
    }

    options = options || {};

    checkGenerationData(firstSecret, secondSecret, ciphertext, options);

    var data = options.data;
    if (typeof data === 'undefined') {
      data = DEFAULT_AUXILIARY_DATA;
    }

    var preComputation = options.preComputation;

    var privateValues = [firstSecret, secondSecret];
    var publicValues = generatePublicValues(ciphertext);
    if (typeof preComputation === 'undefined') {
      preComputation = this.preCompute();
    }

    return prover_.prove(
        group, privateValues, publicValues, data, preComputation);
  };

  /**
   * Pre-computes a plaintext exponent equality zero-knowledge proof of
   * knowledge. IMPORTANT: The same pre-computed values must not be used
   * twice. Before using this method, the handler must have been initialized
   * with base elements, via the method {@link
   * PlaintextExponentEqualityProofHandler.init}.
   *
   * @function preCompute
   * @memberof PlaintextExponentEqualityProofHandler
   * @returns {ZeroKnowledgeProofPreComputation} The plaintext exponent
   *          equality zero-knowledge proof of knowledge pre-computation.
   */
  this.preCompute = function() {
    if (typeof baseElements_ === 'undefined') {
      throw new Error(
          'Cannot pre-compute plaintext exponent equality proof; Associated handler has not been initialized with any base elements');
    }

    var phiFunction = newPhiFunction(group, baseElements_);

    if (!measureProgress_) {
      return prover_.preCompute(group, phiFunction);
    } else {
      var preComputation = prover_.preCompute(
          group, phiFunction, newProgressMeter(baseElements_));
      measureProgress_ = false;

      return preComputation;
    }
  };

  /**
   * Verifies a plaintext exponent equality zero-knowledge proof of knowledge.
   * Before using this method, the handler must have been initialized with
   * base elements, via the method {@link
   * PlaintextExponentEqualityProofHandler.init}.
   *
   * @function verify
   * @memberof PlaintextExponentEqualityProofHandler
   * @param {Proof}
   *            proof The plaintext exponent equality zero-knowledge proof of
   *            knowledge to verify.
   * @param {ElGamalEncryptedElements}
   *            ciphertext The ciphertext.
   * @param {Object}
   *            [options] An object containing optional arguments.
   * @param {Uint8Array|string}
   *            [options.data='PlaintextExponentEqualityProof'] Auxiliary
   *            data. It must be the same as that used to generate the proof.
   * @returns {boolean} <code>true</code> if the plaintext exponent equality
   *          zero-knowledge proof of knowledge was verified,
   *          <code>false</code> otherwise.
   * @throws {Error}
   *             If the input data validation fails.
   */
  this.verify = function(proof, ciphertext, options) {
    if (typeof baseElements_ === 'undefined') {
      throw new Error(
          'Cannot verify plaintext exponent equality proof; Associated handler has not been initialized with any base elements');
    }

    options = options || {};

    checkVerificationData(proof, ciphertext, options);

    var data = options.data;
    if (typeof data === 'undefined') {
      data = DEFAULT_AUXILIARY_DATA;
    }

    var phiFunction = newPhiFunction(group, baseElements_);
    var publicValues = generatePublicValues(ciphertext);

    if (!measureProgress_) {
      return verifier_.verify(group, proof, phiFunction, publicValues, data);
    } else {
      var verified = verifier_.verify(
          group, proof, phiFunction, publicValues, data,
          newProgressMeter(baseElements_));
      measureProgress_ = false;

      return verified;
    }
  };

  /**
   * Indicates that a progress meter is to be used for the next plaintext
   * exponent equality zero-knowledge proof of knowledge operation to be
   * performed.
   *
   * @function measureProgress
   * @memberof PlaintextExponentEqualityProofHandler
   * @param {function}
   *            callback The callback function for the progress meter.
   * @param {Object}
   *            [options] An object containing optional arguments.
   * @param {number}
   *            [minCheckInterval=10] The minimum interval used to check
   *            progress, as a percentage of the expected final progress
   *            value.
   * @returns {PlaintextExponentEqualityProofHandler} A reference to this
   *          object, to facilitate method chaining.
   * @throws {Error}
   *             If the input data validation fails.
   */
  this.measureProgress = function(callback, minCheckInterval) {
    validator.checkProgressMeterData(
        callback, minCheckInterval,
        'Plaintext exponent equality zero-knowledge proof');

    progressCallback_ = callback;
    progressPercentMinCheckInterval_ = minCheckInterval;

    measureProgress_ = true;

    return this;
  };

  function generatePublicValues(ciphertext) {
    return [ciphertext.gamma].concat(ciphertext.phis);
  }

  function newPhiFunction(group, baseElements) {
    var numOutputs = ((baseElements.length - 1) / 2) + 1;
    var computationRules = generateComputationRules(numOutputs);

    return new PhiFunction(
        NUM_PHI_INPUTS, numOutputs, computationRules, baseElements);
  }

  function generateComputationRules(numOutputs) {
    var rules = [];

    rules[0] = [];
    rules[0][0] = [];
    rules[0][0].push(1);
    rules[0][0].push(1);

    for (var i = 1; i < numOutputs; i++) {
      rules[i] = [];

      rules[i][0] = [];
      rules[i][1] = [];

      rules[i][0].push(i + 1);
      rules[i][0].push(1);
      rules[i][1].push(i + numOutputs);
      rules[i][1].push(2);
    }

    return rules;
  }

  function newProgressMeter(baseElements) {
    var progressMax = baseElements.length;

    return new ProgressMeter(
        progressMax, progressCallback_, progressPercentMinCheckInterval_);
  }

  function checkGenerationData(firstSecret, secondSecret, ciphertext, options) {
    validator.checkExponent(
        firstSecret,
        'First secret exponent for plaintext exponent equality proof generation',
        group.q);
    validator.checkExponent(
        secondSecret,
        'Second secret exponent for plaintext exponent equality proof generation',
        group.q);
    validator.checkElGamalEncryptedElements(
        ciphertext,
        'Ciphertext ElGamal encrypted elements for plaintext exponent equality proof generation',
        group);
    checkCiphertextLength(ciphertext, baseElements_);
    if (typeof options.data !== 'undefined' &&
        typeof options.data !== 'string') {
        validator.checkIsInstanceOf(
            options.data, Uint8Array, 'Uint8Array',
            'Non-string auxiliary data for plaintext exponent equality proof generation');
    }
    if (typeof options.preComputation !== 'undefined') {
      validator.checkIsInstanceOf(
          options.preComputation, ZeroKnowledgeProofPreComputation,
          'ZeroKnowledgeProofPreComputation',
          'Pre-computation for plaintext exponent equality proof generation');
    }
  }

  function checkVerificationData(proof, ciphertext, options) {
    validator.checkIsInstanceOf(
        proof, ZeroKnowledgeProof, 'ZeroKnowledgeProof',
        'Plaintext exponent equality zero-knowledge proof');
    validator.checkElGamalEncryptedElements(
        ciphertext,
        'Ciphertext ElGamal encrypted elements for plaintext exponent equality proof verification',
        group);
    checkCiphertextLength(ciphertext, baseElements_);
    if (typeof options.data !== 'undefined' &&
        typeof options.data !== 'string') {
        validator.checkIsInstanceOf(
            options.data, Uint8Array, 'Uint8Array',
            'Non-string auxiliary data for plaintext exponent equality proof verification');
    }
  }

  function checkCiphertextLength(ciphertext, baseElements) {
    var numPhisFound = ciphertext.phis.length;
    var numPhisExpected = (baseElements.length - 1) / 2;

    if (numPhisFound !== numPhisExpected) {
      throw new Error(
          'Expected number of ElGamal phi elements in ciphertext used for plaintext exponent equality proof opertion to be: ' +
          numPhisExpected + ' ; Found: ' + numPhisFound);
    }
  }
}