PHP code encryption and decryption method

<? Php
// $ Key = "This is supposed to be a secret key !!! "; It is estimated that the password is overcast.
$ Key = "this is a secret ";
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)
{
$ Md5 = substr ($ txt, $ I, 1 );
$ I;
$ Tmp. = (substr ($ txt, $ I, 1) ^ $ md5 );
}
Return $ tmp;
}

$ String = "strings to be encrypted, such as passwords .";

// 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 "decrypted string: $ dec_text <Br> n ";
?>