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'use strict';

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var hash = require('hash.js');

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var elliptic = require('../elliptic');

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var utils = elliptic.utils;

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var assert = utils.assert;

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function HmacDRBG(options) {

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  if (!(this instanceof HmacDRBG))

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    return new HmacDRBG(options);

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  this.hash = options.hash;

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  this.predResist = !!options.predResist;

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  this.outLen = this.hash.outSize;

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  this.minEntropy = options.minEntropy || this.hash.hmacStrength;

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  this.reseed = null;

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  this.reseedInterval = null;

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  this.K = null;

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  this.V = null;

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  var entropy = utils.toArray(options.entropy, options.entropyEnc);

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  var nonce = utils.toArray(options.nonce, options.nonceEnc);

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  var pers = utils.toArray(options.pers, options.persEnc);

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  assert(entropy.length >= (this.minEntropy / 8),

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         'Not enough entropy. Minimum is: ' + this.minEntropy + ' bits');

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  this._init(entropy, nonce, pers);

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}

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module.exports = HmacDRBG;

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HmacDRBG.prototype._init = function init(entropy, nonce, pers) {

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  var seed = entropy.concat(nonce).concat(pers);

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  this.K = new Array(this.outLen / 8);

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  this.V = new Array(this.outLen / 8);

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  for (var i = 0; i < this.V.length; i++) {

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    this.K[i] = 0x00;

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    this.V[i] = 0x01;

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  }

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  this._update(seed);

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  this.reseed = 1;

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  this.reseedInterval = 0x1000000000000;  // 2^48

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};

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HmacDRBG.prototype._hmac = function hmac() {

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  return new hash.hmac(this.hash, this.K);

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};

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HmacDRBG.prototype._update = function update(seed) {

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  var kmac = this._hmac()

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                 .update(this.V)

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                 .update([ 0x00 ]);

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  if (seed)

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    kmac = kmac.update(seed);

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  this.K = kmac.digest();

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  this.V = this._hmac().update(this.V).digest();

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  if (!seed)

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    return;

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  this.K = this._hmac()

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               .update(this.V)

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               .update([ 0x01 ])

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               .update(seed)

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               .digest();

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  this.V = this._hmac().update(this.V).digest();

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};

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HmacDRBG.prototype.reseed = function reseed(entropy, entropyEnc, add, addEnc) {

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  // Optional entropy enc

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  if (typeof entropyEnc !== 'string') {

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    addEnc = add;

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    add = entropyEnc;

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    entropyEnc = null;

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  }

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  entropy = utils.toBuffer(entropy, entropyEnc);

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  add = utils.toBuffer(add, addEnc);

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  assert(entropy.length >= (this.minEntropy / 8),

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         'Not enough entropy. Minimum is: ' + this.minEntropy + ' bits');

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  this._update(entropy.concat(add || []));

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  this.reseed = 1;

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};

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HmacDRBG.prototype.generate = function generate(len, enc, add, addEnc) {

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  if (this.reseed > this.reseedInterval)

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    throw new Error('Reseed is required');

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  // Optional encoding

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  if (typeof enc !== 'string') {

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    addEnc = add;

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    add = enc;

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    enc = null;

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  }

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  // Optional additional data

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  if (add) {

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    add = utils.toArray(add, addEnc);

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    this._update(add);

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  }

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  var temp = [];

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  while (temp.length < len) {

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    this.V = this._hmac().update(this.V).digest();

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    temp = temp.concat(this.V);

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  }

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  var res = temp.slice(0, len);

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  this._update(add);

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  this.reseed++;

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  return utils.encode(res, enc);

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};

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