AutoGenerating Authorization for Downloadable products ?

[zonzo_1]

I've been serching for a shopping cart mod that would auto generate a code that could be included in the clients invoice when he succesfuly purchases something. Later this code could be used to make sure that the client actualy did buy something (like a gift cartificate). The code would need to be new for every order.

Has any one had any luck finding a mod like this, or does any one have any idea how i might acomplish something like this ?