PHP code encryption and decryption method

<?php
$key = "This is supposed to be a secret key!!!"; It's probably cloudy.
$key = "This is a secret yin";
function keyed ($txt, $encrypt _key)
{
$encrypt _key = MD5 ($encrypt _key);
$ctr = 0;
$tmp = "";
for ($i =0; $i <strlen ($txt); $i)
{
if ($ctr ==strlen ($encrypt _key)) $ctr = 0;
$tmp. = substr ($txt, $i, 1) ^ substr ($encrypt _key, $ctr, 1);
$ctr;
}
return $tmp;
}

function Encrypt ($txt, $key)
{
Srand (Double) microtime () *1000000);
$encrypt _key = MD5 (rand (0,32000));
$ctr = 0;
$tmp = "";
for ($i =0; $i <strlen ($txt); $i)
{
if ($ctr ==strlen ($encrypt _key)) $ctr = 0;
$tmp. = substr ($encrypt _key, $ctr, 1).
(Substr ($txt, $i, 1) ^ substr ($encrypt _key, $ctr, 1));
$ctr;
}
Return keyed ($tmp, $key);
}

function Decrypt ($txt, $key)
{
$txt = keyed ($txt, $key);
$tmp = "";
for ($i =0; $i <strlen ($txt); $i)
{
$MD 5 = substr ($txt, $i, 1);
$i;
$tmp. = (substr ($txt, $i, 1) ^ $md 5);
}
return $tmp;
}

$string = "strings that need to be encrypted, such as passwords, etc.";

Start encryption encrypt $string, and store it in $enc _text
$enc _text = Encrypt ($string, $key);

Start decrypting decrypt the encrypted text $enc _text, and store it in $dec _text
$dec _text = Decrypt ($enc _text, $key);

Print "Original string: $string <br>n";
Print "Encrypted string: $enc _text <br>n";
Print "After decryption string: $dec _text <br>n";
?>