PHP5 numeric string plus decryption code _php tips

<?php
/* ----------------------------------------------------------------------------
* Script Name:encrypt.php
* Creation Date:2008-4-7 10:36
* Last modified:2008-4-12 16:00
* Author:meyu
* Copyright (c) 2007
* Purpose: Simple encryption and decryption of digital strings
* ----------------------------------------------------------------------------*/

Class Encryption {
/**
* Final ciphertext code, can be set to any repeat 10-bit English characters a-za-z
*/
Private $replacement = ' urskydmeiv ';

/**
* Added ciphertext first, can be set to 1 digits except 0 integers, that is 1-9
*/
Private $prefix = "8";

/**
* Public key, a positive integer less than 8 bits in length
*/
Private $match = "111111";

/**
* After conversion of the comparison array
*/
Private $replaceenc;
Private $replacedec;

function __construct () {
For ($i =0 $i < $i + +) {
$this->replaceenc['/'. $i. '/'] = $this->replacement{$i};
$this->replacedec['/'. $this->replacement{$i}. ' /'] = $i;
}
}

Public function Encrypt ($STR) {
Return Preg_replace (
Array_keys ($this->replaceenc),
$this->replaceenc,
$this->mynotin (Preg_replace) ("/(.) (.) /"," ${2}${1} ", $str))
);
}

Public function Decrypt ($STR) {
Return Preg_replace ("/(.) (.) /"," ${2}${1} ",
$this->mynotout (preg_replace array_keys ($this->replacedec), $this->replacedec, $str))
);
}

Private Function Mynotin ($STR) {
$str _out = "";
$i = 0;
while (Isset ($str {7* $i})) {
$str _out. = ($this->prefix.substr ($str, $i *7, 7)) +0 ^ $this->match;
$i + +;
}
return $STR _out;
}

Private Function Mynotout ($STR) {
$str _out = "";
$i = 0;
while (Isset ($str {8* $i})) {
$str _out. = substr (substr ($str, $i *8, 8) +0) ^ $this->match, 1);
$i + +;
}
return $STR _out;
}
}
?>