/** @fileOverview Javascript SRP implementation.
 *
 * This file contains a partial implementation of the SRP (Secure Remote
 * Password) password-authenticated key exchange protocol. Given a user
 * identity, salt, and SRP group, it generates the SRP verifier that may
 * be sent to a remote server to establish and SRP account.
 *
 * For more information, see http://srp.stanford.edu/.
 *
 * @author Quinn Slack
 */

/**
 * Compute the SRP verifier from the username, password, salt, and group.
 * @class SRP
 */
sjcl.keyexchange.srp = {
  /**
   * Calculates SRP v, the verifier. 
   *   v = g^x mod N [RFC 5054]
   * @param {String} I The username.
   * @param {String} P The password.
   * @param {Object} s A bitArray of the salt.
   * @param {Object} group The SRP group. Use sjcl.keyexchange.srp.knownGroup
                           to obtain this object.
   * @return {Object} A bitArray of SRP v.
   */
  makeVerifier: function(I, P, s, group) {
    var x;
    x = this.makeX(I, P, s);
    x = sjcl.bn.fromBits(x);
    return group.g.powermod(x, group.N);
  },

  /**
   * Calculates SRP x.
   *   x = SHA1(<salt> | SHA(<username> | ":" | <raw password>)) [RFC 2945]
   * @param {String} I The username.
   * @param {String} P The password.
   * @param {Object} s A bitArray of the salt.
   * @return {Object} A bitArray of SRP x.
   */
  makeX: function(I, P, s) {
    var inner = sjcl.hash.sha1.hash(I + ':' + P);
    return sjcl.hash.sha1.hash(sjcl.bitArray.concat(s, inner));
  },

  /**
   * Returns the known SRP group with the given size (in bits).
   * @param {String} i The size of the known SRP group.
   * @return {Object} An object with "N" and "g" properties.
   */
  knownGroup:function(i) {
    if (typeof i !== "string") { i = i.toString(); }
    if (!this._didInitKnownGroups) { this._initKnownGroups(); }
    return this._knownGroups[i];
  },

  /**
   * Initializes bignum objects for known group parameters.
   * @private
   */
  _didInitKnownGroups: false,
  _initKnownGroups:function() {
    var i, size, group;
    for (i=0; i < this._knownGroupSizes.length; i++) {
      size = this._knownGroupSizes[i].toString();
      group = this._knownGroups[size];
      group.N = new sjcl.bn(group.N);
      group.g = new sjcl.bn(group.g);
    }
    this._didInitKnownGroups = true;
  },

  _knownGroupSizes: [1024, 1536, 2048],
  _knownGroups: {
    1024: {
      N: "EEAF0AB9ADB38DD69C33F80AFA8FC5E86072618775FF3C0B9EA2314C" +
         "9C256576D674DF7496EA81D3383B4813D692C6E0E0D5D8E250B98BE4" +
         "8E495C1D6089DAD15DC7D7B46154D6B6CE8EF4AD69B15D4982559B29" +
         "7BCF1885C529F566660E57EC68EDBC3C05726CC02FD4CBF4976EAA9A" +
         "FD5138FE8376435B9FC61D2FC0EB06E3",
      g:2
    },

    1536: {
      N: "9DEF3CAFB939277AB1F12A8617A47BBBDBA51DF499AC4C80BEEEA961" +
         "4B19CC4D5F4F5F556E27CBDE51C6A94BE4607A291558903BA0D0F843" +
         "80B655BB9A22E8DCDF028A7CEC67F0D08134B1C8B97989149B609E0B" +
         "E3BAB63D47548381DBC5B1FC764E3F4B53DD9DA1158BFD3E2B9C8CF5" +
         "6EDF019539349627DB2FD53D24B7C48665772E437D6C7F8CE442734A" +
         "F7CCB7AE837C264AE3A9BEB87F8A2FE9B8B5292E5A021FFF5E91479E" +
         "8CE7A28C2442C6F315180F93499A234DCF76E3FED135F9BB",
      g: 2
    },

    2048: {
      N: "AC6BDB41324A9A9BF166DE5E1389582FAF72B6651987EE07FC319294" +
         "3DB56050A37329CBB4A099ED8193E0757767A13DD52312AB4B03310D" +
         "CD7F48A9DA04FD50E8083969EDB767B0CF6095179A163AB3661A05FB" +
         "D5FAAAE82918A9962F0B93B855F97993EC975EEAA80D740ADBF4FF74" +
         "7359D041D5C33EA71D281E446B14773BCA97B43A23FB801676BD207A" +
         "436C6481F1D2B9078717461A5B9D32E688F87748544523B524B0D57D" +
         "5EA77A2775D2ECFA032CFBDBF52FB3786160279004E57AE6AF874E73" +
         "03CE53299CCC041C7BC308D82A5698F3A8D0C38271AE35F8E9DBFBB6" +
         "94B5C803D89F7AE435DE236D525F54759B65E372FCD68EF20FA7111F" +
         "9E4AFF73",
      g: 2
    }
  }

};