Generate random 10 byte base58 identifiers

base58uid.js

var min = 7427658739644928; // min int value that is 10 bytes long in base58
var max = 9007199254740992; // max safe integer (exclusive), also 10 bytes

var alphabet = '123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ'; // base58
var base = alphabet.length;

function encode(num) {
  var mod, str = '';
  while (num >= base) {
    mod = num % base;
    str = alphabet[mod] + str;
    num = (num - mod) / base;
  }
  return alphabet[num] + str;
};

// returns random int between min (inclusive) and max (exclusive)
function randomInt(min, max) {
  return Math.floor(Math.random() * (max - min)) + min;
}

// generate 10 byte random base58 id with ~50 bits of entropy
function generateShortUid() {
  return encode(randomInt(min, max));
}

module.exports = {
  generateShortUid: generateShortUid
}

Angular Module:

angular.module('base58', [])
  .factory('base58uid', function () {
    var min = 7427658739644928; // min int value that is 10 bytes long in base58
    var max = 9007199254740992; // max safe integer (exclusive), also 10 bytes

    var alphabet = '123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ'; // base58
    var base = alphabet.length;

    function encode(num) {
      var mod, str = '';
      while (num >= base) {
        mod = num % base;
        str = alphabet[mod] + str;
        num = (num - mod) / base;
      }
      return alphabet[num] + str;
    }

    // returns random int between min (inclusive) and max (exclusive)
    function randomInt(min, max) {
      return Math.floor(Math.random() * (max - min)) + min;
    }

    // generate 10 byte random base58 id with ~50 bits of entropy
    function generateShortUid() {
      return encode(randomInt(min, max));
    }

    return {
      encode: encode,
      generateShortUid: generateShortUid
    };
  });

Base58uid

This code generates a random id using the javascript integer range that is guaranteed to encode to a 10 byte base 58 string (~50 Bits of entropy). This can for example be used for client generated database identifiers.

Example usage in node.js:

var base58uid = require('base58uid');
base58uid.generateShortUid(); // '2aSQkrU5hp'
base58uid.generateShortUid(); // '23QryQGzWU'

I've converted this code to Kotlin, in case anyone ever needs it:

object Base58 {

    private const val min = 7427658739644928 // min int value that is 10 bytes long in base58
    private const val max = 9007199254740992 // max safe integer (exclusive), also 10 bytes

    private const val alphabet = "123456789abcdefghijkmnopqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ" // base58
    private const val base = alphabet.length

    private fun encode(input: Long) : String{
        var num = input
        var str = ""
        while (num >= base) {
            val mod = (num % base).toInt()
            str = alphabet[mod] + str
            num = (num - mod) / base
        }
        return alphabet[num.toInt()] + str
    }

    // returns random int between min (inclusive) and max (exclusive)
    private fun randomInt(min: Long, max: Long): Long {
        return (floor(Math.random() * (max - min)) + min).roundToLong()
    }

    // generate 10 byte random base58 id with ~50 bits of entropy
    fun generateShortUid(): String {
        return encode(randomInt(min, max))
    }
}