PHP の暗号化と復号化の内部アルゴリズムはどのように実装されていますか?

<?php 
function passport_encrypt($txt, $key) { 
srand((double)
microtime
() * 1000000); 
$encrypt_key = md5(rand(0, 32000)); 
$ctr = 0; 
$tmp = &#39;&#39;; 
for($i = 0;$i < strlen($txt); $i++) { 
$ctr = $ctr == strlen($encrypt_key) ? 0 : $ctr; 
$tmp .= $encrypt_key[$ctr].($txt[$i] ^ $encrypt_key[$ctr++]); 
} 
return base64_encode(passport_key($tmp, $key)); 
} 
function passport_decrypt($txt, $key) { 
$txt = passport_key(base64_decode($txt), $key); 
$tmp = &#39;&#39;; 
for($i = 0;$i < strlen($txt); $i++) { 
$md5 = $txt[$i]; 
$tmp .= $txt[++$i] ^ $md5; 
} 
return $tmp; 
} 
function passport_key($txt, $encrypt_key) { 
$encrypt_key = md5($encrypt_key); 
$ctr = 0; 
$tmp = &#39;&#39;; 
for($i = 0; $i < strlen($txt); $i++) { 
$ctr = $ctr == strlen($encrypt_key) ? 0 : $ctr; 
$tmp .= $txt[$i] ^ $encrypt_key[$ctr++]; 
} 
return $tmp; 
} 
?>

//string.php 
<?php 
include
 “fun.php”; 
$txt = “This is a test”; 
$key = “testkey”; 
$encrypt = passport_encrypt($txt,$key); 
$decrypt = passport_decrypt($encrypt,$key); 
echo $txt.”<br><hr>”; 
echo $encrypt.”<br><hr>”; 
echo $decrypt.”<br><hr>”; 
?> 
//array.php 
<?php 
include “fun.php”; 
$array = array( 
"a" => "1", 
"b" => "2", 
"c" => "3", 
"d" => "4" 
); 
//serialize产生一个可存储的值,返回一个
字符串
,unserialize还原 
$txt = serialize($array); 
$key = “testkey”; 
$encrypt = passport_encrypt($txt,$key); 
$decrypt = passport_decrypt($encrypt,$key); 
$decryptArray = unserialize($decrypt); 
echo $txt.”<br><hr>”; 
echo $encrypt.”<br><hr>”; 
echo $decrypt.”<br><hr>”; 
echo $decryptArray.”<br><hr>”; 
?>

//login.php 
<?php 
session_start(); 
include “fun.php”; 
$_SESSION[“userid”]; 
$_SESSION[“username”]; 
$_SESSION[“userpwd”]; 
header("Location: http://$domain/process.php?s=".urlencode(passport_encrypt(serialize($_SESSION),"sessionkey"))); 
?>

//process.php 
<?php 
session_start(); 
include “fun.php”; 
$_SESSION=unserialize(passport_decrypt($_GET["s"],"sessionkey")); 
header("Location: http://$domain/index.php"); 
?>