It's probably going to be easier to encrypt the file after sending it (but really not very useful). Is the same host downloading the file? Unless the same host that is downloading the file, you'll need to send some sort of encryption key. This site will likely have all that you need to get started: http://www.devhood.com/Tutorials/tutorial\_details.aspx?tutorial\_id=489 A secure and useful method would be to open a secure communication using a public/private key pair and then the server could send an encryption code for the client to encrypt the file. The client would then send the encrypted file to the server and there the server could decrypt the file since it knows the encryption code. That way is going to be a lot more difficult, but more practical. Hope that helps.