Browser Encryption

[phreaqo]

I am creating a webserver in java from scratch. I am able to successfully transfer files when a webuser requests it.
On my webserver, I have an encrypted file that I want to share with my friends. Each of my friends have the key to that encrypted file in a separate text file on each of their own computers and standard webbrowswers (firefox, IE). Is there any way I can transfer that encrypted file to my friends with their browsers automatically decrypting it?

For example, I have an encrypted document stored on my java webserver. The webuser requests the file and the webserver transfers it. Either when the webuser receives the file or while the webuser receives the file, the browser uses the key and decrypts it without any outside program's help. So now that document is readable to the webuser.

[Oak]

The key would have to be submitted along with the request using either a form or query string.

You are asking if this functionality can occure independently once the request has already been received and processed by the server. I believe this would require additional software of some description.

Why not authenticate the user on the server and if they are valid then allow them to download a decrypted version?