PHP short hash like URL-shortening websites
TinyURL doesn't hash anything, it uses Base 36 integers (or even base 62, using lower and uppercase letters) to indicate which record to visit.
Base 36 to Integer:
intval($str, 36);
Integer to Base 36:
base_convert($val, 10, 36);
So then, instead of redirecting to a route like /url/1234 it becomes /url/ax instead. This gives you a whole lot more use than a hash will, as there will be no collisions. With this you can easily check if a url exists and return the proper, existing, ID in base 36 without the user knowing that it was already in the database.
Don't hash, use other bases for this kind of thing. (It's faster and can be made collision-proof.)
I wrote a tiny lib to generate obfuscated hashes from integers.
http://web.archive.org/web/20130727034425/http://blog.kevburnsjr.com/php-unique-hash
$ids = range(1,10);
foreach($ids as $id) {
echo PseudoCrypt::unhash($id) . "\n";
}m8z2p 8hy5e uqx83 gzwas 38vdh phug6 bqtiv xzslk k8ro9 6hqqy
7/14/2015: Adding the actual code below, since it has become difficult to find:
<?php
/**
* PseudoCrypt by KevBurns (http://blog.kevburnsjr.com/php-unique-hash)
* Reference/source: http://stackoverflow.com/a/1464155/933782
*
* I want a short alphanumeric hash thatâs unique and whoâs sequence is difficult to deduce.
* I could run it out to md5 and trim the first n chars but thatâs not going to be very unique.
* Storing a truncated checksum in a unique field means that the frequency of collisions will increase
* geometrically as the number of unique keys for a base 62 encoded integer approaches 62^n.
* Iâd rather do it right than code myself a timebomb. So I came up with this.
*
* Sample Code:
*
* echo "<pre>";
* foreach(range(1, 10) as $n) {
* echo $n." - ";
* $hash = PseudoCrypt::hash($n, 6);
* echo $hash." - ";
* echo PseudoCrypt::unhash($hash)."<br/>";
* }
*
* Sample Results:
* 1 - cJinsP - 1
* 2 - EdRbko - 2
* 3 - qxAPdD - 3
* 4 - TGtDVc - 4
* 5 - 5ac1O1 - 5
* 6 - huKpGQ - 6
* 7 - KE3d8p - 7
* 8 - wXmR1E - 8
* 9 - YrVEtd - 9
* 10 - BBE2m2 - 10
*/
class PseudoCrypt {
/* Key: Next prime greater than 62 ^ n / 1.618033988749894848 */
/* Value: modular multiplicative inverse */
private static $golden_primes = array(
'1' => '1',
'41' => '59',
'2377' => '1677',
'147299' => '187507',
'9132313' => '5952585',
'566201239' => '643566407',
'35104476161' => '22071637057',
'2176477521929' => '294289236153',
'134941606358731' => '88879354792675',
'8366379594239857' => '7275288500431249',
'518715534842869223' => '280042546585394647'
);
/* Ascii : 0 9, A Z, a z */
/* $chars = array_merge(range(48,57), range(65,90), range(97,122)) */
private static $chars62 = array(
0=>48,1=>49,2=>50,3=>51,4=>52,5=>53,6=>54,7=>55,8=>56,9=>57,10=>65,
11=>66,12=>67,13=>68,14=>69,15=>70,16=>71,17=>72,18=>73,19=>74,20=>75,
21=>76,22=>77,23=>78,24=>79,25=>80,26=>81,27=>82,28=>83,29=>84,30=>85,
31=>86,32=>87,33=>88,34=>89,35=>90,36=>97,37=>98,38=>99,39=>100,40=>101,
41=>102,42=>103,43=>104,44=>105,45=>106,46=>107,47=>108,48=>109,49=>110,
50=>111,51=>112,52=>113,53=>114,54=>115,55=>116,56=>117,57=>118,58=>119,
59=>120,60=>121,61=>122
);
public static function base62($int) {
$key = "";
while(bccomp($int, 0) > 0) {
$mod = bcmod($int, 62);
$key .= chr(self::$chars62[$mod]);
$int = bcdiv($int, 62);
}
return strrev($key);
}
public static function hash($num, $len = 5) {
$ceil = bcpow(62, $len);
$primes = array_keys(self::$golden_primes);
$prime = $primes[$len];
$dec = bcmod(bcmul($num, $prime), $ceil);
$hash = self::base62($dec);
return str_pad($hash, $len, "0", STR_PAD_LEFT);
}
public static function unbase62($key) {
$int = 0;
foreach(str_split(strrev($key)) as $i => $char) {
$dec = array_search(ord($char), self::$chars62);
$int = bcadd(bcmul($dec, bcpow(62, $i)), $int);
}
return $int;
}
public static function unhash($hash) {
$len = strlen($hash);
$ceil = bcpow(62, $len);
$mmiprimes = array_values(self::$golden_primes);
$mmi = $mmiprimes[$len];
$num = self::unbase62($hash);
$dec = bcmod(bcmul($num, $mmi), $ceil);
return $dec;
}
}