Halo Decoding CD Key

decodeCDKey.php

<?php
/**
 * decodeCDKey (11/21/2012)
 *
 * Taking the registry entry from Halo, this function can decode the entry back into the original
 * CD Key.  One must procure this entry through an alternative program, such as regedit or a batch
 * script.  Navigate to registry folder "HKLM\SOFTWARE\Microsoft\Microsoft Games\Halo"
 * Open the key "DigitalProductID" and copy the 72nd byte to 96th byte.  Make sure there are zeroes
 * surrounding this section of bytes.   Reverse the bytes and send to decodeCDKey($in).
 * 
 * Try with sample input: decodeCDKey("012405bd55dd2af6e7abc5915de144")
 * Expected output should be: GQV8J-73GC2-RQ2K2-C82HJ-PX2Q6
 * 
 * @author     Sashank Tadepalli <dijjit@gmail.com>
 * @license    Creative Commons Attribution 3.0 Unported License.
 * @version    1.0
 * @link       http://dijjit.com/halo/decoding-halo-cd-key/
 */
function decodeCDKey($in){
    // Initial character arrays for base conversion and replacing
    $search = str_split('0123456789abcdefghijklmn');

    // Uppercase for Microsoft styling
    $replace = str_split('BCDFGHJKMPQRTVWXY2346789');

    // Check for gmp_init, to speed up base conversion
    if( function_exists('gmp_init') ){
        $result = gmp_strval(gmp_init($in, 16), 24);
    } else {
        $result = base_conv($in, $search, str_split('0123456789abcdef'));
    }

    // Manually replace each character in sequence
    for( $i = 0;$i < 25; $i++ ){
        $result{$i} = $replace[array_search($result{$i}, $search)];
    }

    // Add the infamous Microsoft hyphens
    return  substr($result, 0, 5) . "-" . substr($result, 5, 5) . "-" .
            substr($result, 10, 5) . "-" . substr($result, 15, 5) . "-" .
            substr($result, 20, 5);
}

/* Thanks Core Xii, http://stackoverflow.com/questions/352434/ */
function base_conv($val, &$baseTo, &$baseFrom){
    return base_arr_to_str(
                base_conv_arr(base_str_to_arr($val, $baseFrom), count($baseTo), count($baseFrom)),
           $baseTo);
}

function base_conv_arr($val, $baseToDigits, $baseFromDigits){
    $valCount = count($val);
    $result = array();
    do {
        $divide = 0;
        $newlen = 0;
        for( $i = 0; $i < $valCount; ++$i ){
            $divide = $divide * $baseFromDigits + $val[$i];
            if( $divide >= $baseToDigits ){
                $val[$newlen ++] = (int) ($divide / $baseToDigits);
                $divide = $divide % $baseToDigits;
            } else if( $newlen > 0 ){
                $val[$newlen ++] = 0;
            }
        }
        $valCount = $newlen;
        array_unshift($result, $divide);
    }
    while ($newlen != 0);
    return $result;
}

function base_arr_to_str($arr, &$base){
    $str = '';
    foreach( $arr as $digit ){
        $str .= $base[$digit];
    }
    return $str;
}

function base_str_to_arr($str, &$base){
    $arr = array();
    while( $str === '0' || !empty($str) ){
        foreach( $base as $index => $digit ){
            if( mb_substr($str, 0, $digitLen = mb_strlen($digit)) === $digit ){
                $arr[] = $index;
                $str = mb_substr($str, $digitLen);
                continue 2;
            }
        }
        throw new Exception();
    }
    return $arr;
}
echo decodeCDKey("012405bd55dd2af6e7abc5915de144");
?>