my $user_string = "VendorTxCode=1298062774&Amount=43.01&Currency=GBP&Description=Goods&SuccessURL=http://www.happy.com/success.html&FailureURL=http://www.unhappy.com/failure.html&BillingSurname=Bloggs&BillingFirstnames=Fred&BillingAddress1=30 Peyton Place&BillingCity=Somewhere&BillingPostCode=AB1 2CD&BillingCountry=UK&DeliverySurname=Bloggs&DeliveryFirstnames=Bill&DeliveryAddress1=30 Peyton Place&DeliveryCity=Somewhere&DeliveryPostCode=AB1 2CD&DeliveryCountry=UK";

my $key = "TuDQUBZVA4kPfeM7";

my $size = length($user_string);
my $encode = $key x $size;

my $portion = substr($encode, 0, $size); 

my $result = $user_string ^ $portion;


my $base_encoded = encode_base64($result,'');
my $base_key = encode_base64($key,'');