mcrypt and PHP to encrypt values to be passed to differend server

Hello!

I'm trying to use mcrypt to encrypt some values (login and password) I have
to pass from one website to another.
I thook this code from the php.net website as an example:

<?php
/* Open the cipher */
$td = mcrypt_module_open ('rijndael-256', '', 'ofb', '');

/* Create the IV and determine the keysize length */
$iv = mcrypt_create_iv (mcrypt_enc_get_iv_size($td), MCRYPT_DEV_RANDOM);
$ks = mcrypt_enc_get_key_size ($td);

/* Create key */
$key = substr (md5 ('very secret key'), 0, $ks);

/* Intialize encryption */
mcrypt_generic_init ($td, $key, $iv);

/* Encrypt data */
$encrypted = mcrypt_generic ($td, 'This is very important data');

/* Terminate encryption handler */
mcrypt_generic_deinit ($td);

/* Initialize encryption module for decryption */
mcrypt_generic_init ($td, $key, $iv);

/* Decrypt encrypted string */
$decrypted = mdecrypt_generic ($td, $encrypted);

/* Terminate decryption handle and close module */
mcrypt_generic_deinit ($td);
mcrypt_module_close ($td);

/* Show string */
echo trim ($decrypted)."\n";
?>

I put this in the page starting from:

<?php
$adminlogin = $row1["adminlogin"];
$adminpw = $row1["adminpw"];
// both are queried from a database

$td = mcrypt_module_open ('rijndael-256', '', 'ofb', '');
$iv = mcrypt_create_iv (mcrypt_enc_get_iv_size($td), MCRYPT_DEV_RANDOM);
$ks = mcrypt_enc_get_key_size ($td);
$key = substr (md5 ('a key fsfqz'), 0, $ks);
mcrypt_generic_init ($td, $key, $iv);

/* Encrypt data */
$encryptedlogin = mcrypt_generic ($td, $adminlogin);
$encryptedpassw = mcrypt_generic ($td, $adminpw);

mcrypt_generic_deinit ($td);
mcrypt_module_close ($td);
?>
<a href="destinationpage.php?login=<?php echo("$encryptedlogin");
?>&password=<?php echo("$encryptedpassw"); ?>" target="_blank">link</a>


In the destination page (destinationpage.php, on a different server) I have
this:

$td = mcrypt_module_open ('rijndael-256', '', 'ofb', '');
$iv = mcrypt_create_iv (mcrypt_enc_get_iv_size($td),
MCRYPT_DEV_RANDOM);
$ks = mcrypt_enc_get_key_size ($td);
$key = substr (md5 ('a key fsfqz'), 0, $ks);
mcrypt_generic_init ($td, $key, $iv);

/* Decrypt encrypted string */
$login = mdecrypt_generic ($td, $login);
$login = trim ($login);
$password = mdecrypt_generic ($td, $password);
$password = trim ($password);

mcrypt_generic_deinit ($td);
mcrypt_module_close ($td);

and then an echo("$login - $password<br>"); to check if the values are
correct.

But they are not!!
What am I doing wrong?? Is it because both are on a different server?
I would very much appreciate your help. Or if someone has an other good way
of encrypting values, please let me know!

Thanks!!!

Mark.