Encrypt & Decript PHP

<?php

function encrypt( $q ) {

$cryptKey  = 'qJB0rGtIn5UB1xG03efyCp';

$qEncoded      = base64_encode( mcrypt_encrypt( MCRYPT_RIJNDAEL_256, md5( $cryptKey ), $q, MCRYPT_MODE_CBC, md5( md5( $cryptKey ) ) ) );

return( $qEncoded );

}

function decrypt( $q ) {

$cryptKey  = 'qJB0rGtIn5UB1xG03efyCp';

$qDecoded      = rtrim( mcrypt_decrypt( MCRYPT_RIJNDAEL_256, md5( $cryptKey ), base64_decode( $q ), MCRYPT_MODE_CBC, md5( md5( $cryptKey ) ) ), "\0");

return( $qDecoded );

}

?>

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<?php

 $id = "USR13";

$Encrypted = encrypt($id);

$Decrypted = decrypt($Encrypted);

?>

<a href="index.php?id=<?php echo $Encrypted?>">Enkrip</a>

<a href="index.php?id=<?php echo $Decrypted?>">Dekript</a>

?>