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Security, Crypto, and Random Topics
Secure AIM, no respect 
1st-Nov-2006 08:56 pm
My co-worked Steve mentioned that he was in a bookstore the other day and saw a book on security in instant messaging systems. He said he flipped through the index and table of contents to see if he could find references to S/AIM, the feature we added to AIM (AOL Instant Messenger) in 2001.  (I wrote about this before)

Nope.  There were chapters talking about how to shoehorn PGP into IM clients and other hacks.  But nothing on the feature that's build into the AIM 5.x series. I find this odd given that you can search the web for "AIM certificates" and get pages that talk about it.

I just downloaded the AIM 5.9 client and found that the security is still in there.  Here's the preferences window.  At the bottom is the "Security" tab where you can import a valid certificate. We never got to implement our transparent certificate enrollment scheme, so this part of the UI is still a little clunky.  Still, if you have a certificate it's trivial to import it and to start to use it.


This next picture shows what a normal AIM conversation looks like in secure mode.Secure IM window As you can see (when you click on the image), the conversation is both encrypted and signed. It's very important that the messages you receive be signed.  It's not enough to just encrypt the messages.  Without signing, you can't really have encryption between the intended parties. (Think about it for a minute if that sounds wrong to you. It's important.) 

If you click on the lock icon, you can see a summary of the other person's certificate (who issued it, when it was issued, when it will expire, etc.)

In the main AIM buddy list window, you can see who among your friends also has a certificate by noting the presence of a lock icon to the left of his/her screen name. The system in its current form requires that both parties have certificates for the security to kick in.  When both parties have certificates, the client automatically sets up a secure channel when they start an IM session.  Users don't have to initiate anything or go into a secure mode.  It just happens.  Even when both parties use smart cards, there's no noticeable delay in the communications.

This system is based on the CMS (Cryptographic Message Syntax), which is used in systems like S/MIME. That means that it provides end-to-end security.  No evesdropper between you and your friend will be able to understand the gibberish that's being sent back and forth, including AOL.  It's all opaque to them.

I miss having real end-to-end security in my IM client.  If anyone from the GAIM team wants to learn more about how to put this great feature into that product, please give me a holler. We'd love to help.
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