php的id加密

<?php
/**
* article url:http://kvz.io/blog/2009/06/10/create-short-ids-with-php-like-youtube-or-tinyurl/
*
* Translates a number to a short alhanumeric version
*
* Translated any number up to 9007199254740992
* to a shorter version in letters e.g.:
* 9007199254740989 --> PpQXn7COf
*
* specifiying the second argument true, it will
* translate back e.g.:
* PpQXn7COf --> 9007199254740989
*
* this function is based on any2dec && dec2any by
* fragmer[at]mail[dot]ru
* see: http://nl3.php.net/manual/en/function.base-convert.php#52450
*
* If you want the alphaID to be at least 3 letter long, use the
* $pad_up = 3 argument
*
* In most cases this is better than totally random ID generators
* because this can easily avoid duplicate ID's.
* For example if you correlate the alpha ID to an auto incrementing ID
* in your database, you're done.
*
* The reverse is done because it makes it slightly more cryptic,
* but it also makes it easier to spread lots of IDs in different
* directories on your filesystem. Example:
* $part1 = substr($alpha_id,0,1);
* $part2 = substr($alpha_id,1,1);
* $part3 = substr($alpha_id,2,strlen($alpha_id));
* $destindir = "/".$part1."/".$part2."/".$part3;
* // by reversing, directories are more evenly spread out. The
* // first 26 directories already occupy 26 main levels
*
* more info on limitation:
* - http://blade.nagaokaut.ac.jp/cgi-bin/scat.rb/ruby/ruby-talk/165372
*
* if you really need this for bigger numbers you probably have to look
* at things like: http://theserverpages.com/php/manual/en/ref.bc.php
* or: http://theserverpages.com/php/manual/en/ref.gmp.php
* but I haven't really dugg into this. If you have more info on those
* matters feel free to leave a comment.
*
* The following code block can be utilized by PEAR's Testing_DocTest
* <code>
* // Input //
* $number_in = 2188847690240;
* $alpha_in = "SpQXn7Cb";
*
* // Execute //
* $alpha_out = alphaID($number_in, false, 8);
* $number_out = alphaID($alpha_in, true, 8);
*
* if ($number_in != $number_out) {
* echo "Conversion failure, ".$alpha_in." returns ".$number_out." instead of the ";
* echo "desired: ".$number_in."\n";
* }
* if ($alpha_in != $alpha_out) {
* echo "Conversion failure, ".$number_in." returns ".$alpha_out." instead of the ";
* echo "desired: ".$alpha_in."\n";
* }
*
* // Show //
* echo $number_out." => ".$alpha_out."\n";
* echo $alpha_in." => ".$number_out."\n";
* echo alphaID(238328, false)." => ".alphaID(alphaID(238328, false), true)."\n";
*
* // expects:
* // 2188847690240 => SpQXn7Cb
* // SpQXn7Cb => 2188847690240
* // aaab => 238328
*
* </code>
*
* @author Kevin van Zonneveld <kevin@vanzonneveld.net>
* @author Simon Franz
* @author Deadfish
* @author SK83RJOSH
* @copyright 2008 Kevin van Zonneveld (http://kevin.vanzonneveld.net)
* @license http://www.opensource.org/licenses/bsd-license.php New BSD Licence
* @version SVN: Release: $Id: alphaID.inc.php 344 2009-06-10 17:43:59Z kevin $
* @link http://kevin.vanzonneveld.net/
*
* @param mixed $in String or long input to translate
* @param boolean $to_num Reverses translation when true
* @param mixed $pad_up Number or boolean padds the result up to a specified length
* @param string $pass_key Supplying a password makes it harder to calculate the original ID
*
* @return mixed string or long
*/
function alphaID($in, $to_num = false, $pad_up = false, $pass_key = null)
{
$out = '';
$index = 'abcdefghijklmnopqrstuvwxyz0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ';
$base = strlen($index);

if ($pass_key !== null) {
// Although this function's purpose is to just make the
// ID short - and not so much secure,
// with this patch by Simon Franz (http://blog.snaky.org/)
// you can optionally supply a password to make it harder
// to calculate the corresponding numeric ID

for ($n = 0; $n < strlen($index); $n++) {
$i[] = substr($index, $n, 1);
}

$pass_hash = hash('sha256',$pass_key);
$pass_hash = (strlen($pass_hash) < strlen($index) ? hash('sha512', $pass_key) : $pass_hash);

for ($n = 0; $n < strlen($index); $n++) {
$p[] = substr($pass_hash, $n, 1);
}

array_multisort($p, SORT_DESC, $i);
$index = implode($i);
}

if ($to_num) {
// Digital number <<-- alphabet letter code
$len = strlen($in) - 1;

for ($t = $len; $t >= 0; $t--) {
$bcp = bcpow($base, $len - $t);
$out = $out + strpos($index, substr($in, $t, 1)) * $bcp;
}

if (is_numeric($pad_up)) {
$pad_up--;

if ($pad_up > 0) {
$out -= pow($base, $pad_up);
}
}
} else {
// Digital number -->> alphabet letter code
if (is_numeric($pad_up)) {
$pad_up--;

if ($pad_up > 0) {
$in += pow($base, $pad_up);
}
}

for ($t = ($in != 0 ? floor(log($in, $base)) : 0); $t >= 0; $t--) {
$bcp = bcpow($base, $t);
$a = floor($in / $bcp) % $base;
$out = $out . substr($index, $a, 1);
$in = $in - ($a * $bcp);
}
}

return $out;
}