pseudohash/lib/pseudo-hash.js

Short, reversable, alphanumeric pseudohash with hard-to-guess sequence.

// Generated by CoffeeScript 2.0.0-beta2

/*
 *
 * Javascript port of Crypt::Pseudo
 * https://github.com/CliffS/crypt-pseudo
 *
 * Originally ported from http://blog.kevburnsjr.com/php-unique-hash
 * (Now defunct).
 *
 */

(function() {
  var BigInt, PseudoHash, bigint, goldenPrimes, invert, power;

  BigInt = require('BigInt');


  /*
  goldenPrimes =
    1:                  '1'
    41:                 '59'
    2377:               '1677'
    147299:             '187507'
    9132313:            '5952585'
    566201239:          '643566407'
    35104476161:        '22071637057'
    2176477521929:      '294289236153'
    134941606358731:    '88879354792675'
    8366379594239857:   '7275288500431249'
    518715534842869223: '280042546585394647'
   */

  goldenPrimes = ['1', '41', '2377', '147299', '9132313', '566201239', '35104476161', '2176477521929', '134941606358731', '8366379594239857', '518715534842869223'];

  bigint = function(v, base = 10) {
    return BigInt.str2bigInt(v.toString(), base);
  };

  power = function(big, i) {
    var j, p, ref;
    p = bigint(1);
    if (i > 0) {
      for (j = 1, ref = i; 1 <= ref ? j <= ref : j >= ref; 1 <= ref ? j++ : j--) {
        p = BigInt.mult(big, p);
      }
    }
    return p;
  };

  invert = function(s) {
    return s.replace(/\w/g, function(c) {
      if (c.match('[a-z]')) {
        return c.toUpperCase();
      } else {
        return c.toLowerCase();
      }
    });
  };

  PseudoHash = class PseudoHash {
    constructor(bits = 62) {
      var i, k;
      if (!(bits === 36 || bits === 62)) {
        throw 'Bits must be 62 or 36';
      }
      this.bits = bits;
      bits = bigint(this.bits);
      this.mmi = (function() {
        var j, len1, results;
        results = [];
        for (i = j = 0, len1 = goldenPrimes.length; j < len1; i = ++j) {
          k = goldenPrimes[i];
          results.push(BigInt.inverseMod(bigint(k), power(bits, i)));
        }
        return results;
      })();
    }

    hash(num, len = 5) {
      var ceil, dec, hash, prime;
      ceil = power(bigint(this.bits), len);
      prime = goldenPrimes[len];
      dec = BigInt.multMod(bigint(prime), bigint(num), ceil);
      hash = BigInt.bigInt2str(dec, this.bits);
      while (hash.length < len) {
        hash = `0${hash}`;
      }
      return invert(hash);
    }

    unhash(hash) {
      var ceil, dec, len, mmi, num;
      len = hash.length;
      hash = invert(hash);
      ceil = power(bigint(this.bits), len);
      mmi = this.mmi[len];
      dec = bigint(hash, this.bits);
      num = BigInt.multMod(mmi, dec, ceil);
      return Number.parseInt(BigInt.bigInt2str(num, 10));
    }

  };

  module.exports = PseudoHash;

}).call(this);