if you have vb.net / c# dll then you can easily use it with Classic Asp or Vb6.
Create a new project (Class Library Project)
In your Class Add the Code
Right Click on Project Properties and Click on Compile & Check "Register for COM intercop"
Compile and Copy the DLL to server
on Server Run the following within your FrameWork version Directory:
Regasm [Your DLL Path] /codebase
Then in you Classic ASP Page:
<%
' Encrypt and Decrypt the Cc info
Set t = Server.CreateObject("NameSpaceName.ClassName")
enc = t.Encrypt("4111121111")
Response.Write(enc)
set t = nothing
%>
Thats all.