PHP short hash like URL-shortening websites

Question

I am looking for a PHP function that creates a short hash out of a string or a file, similar to those URL-shortening websites like tinyurl.com

The hash should not be longer than 8 characters.

Answer 1

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 that’s unique and who’s sequence is difficult to deduce. 
 * I could run it out to md5 and trim the first n chars but that’s 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. 
 * I’d 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;
    }

}

Answer 2

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.)

Answer 3

Shortest hash is 32 character length, how ever you can use first 8 characters of md5 hash

echo substr(md5('http://www.google.com'), 0, 8);

Update: here is another class found here written by Travell Perkins which takes record number and create short hash for it. 14 digits number produce 8 digit string. By the date you reach this number you become more popular than tinyurl ;)

class BaseIntEncoder {

    //const $codeset = "0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
    //readable character set excluded (0,O,1,l)
    const codeset = "23456789abcdefghijkmnopqrstuvwxyzABCDEFGHIJKLMNPQRSTUVWXYZ";

    static function encode($n){
        $base = strlen(self::codeset);
        $converted = '';

        while ($n > 0) {
            $converted = substr(self::codeset, bcmod($n,$base), 1) . $converted;
            $n = self::bcFloor(bcdiv($n, $base));
        }

        return $converted ;
    }

    static function decode($code){
        $base = strlen(self::codeset);
        $c = '0';
        for ($i = strlen($code); $i; $i--) {
            $c = bcadd($c,bcmul(strpos(self::codeset, substr($code, (-1 * ( $i - strlen($code) )),1))
                    ,bcpow($base,$i-1)));
        }

        return bcmul($c, 1, 0);
    }

    static private function bcFloor($x)
    {
        return bcmul($x, '1', 0);
    }

    static private function bcCeil($x)
    {
        $floor = bcFloor($x);
        return bcadd($floor, ceil(bcsub($x, $floor)));
    }

    static private function bcRound($x)
    {
        $floor = bcFloor($x);
        return bcadd($floor, round(bcsub($x, $floor)));
    }
}

here is example how to use it:

BaseIntEncoder::encode('1122344523');//result:3IcjVE
BaseIntEncoder::decode('3IcjVE');//result:1122344523

Answer 4

URL shortening services rather use a auto incremented integer value (like a supplementary database ID) and encode that with Base64 or other encodings to have more information per character (64 instead of just 10 like digits).