Hi, I've been poking around Oscar (ICQ/AIM) protocol parsing and had a look at Trillian's SecureIM handshake protocol.
For those who don't know, Trillian is a very popular multi- protocol instant messanging application for Windows. One of its notable features, for which is got some rave/positive reviews, is an ability to encrypt ICQ/AIM IMs exchanged by two Trillian instances. AOL made repeated attempts to block SecureIM, but eventually stopped them [1]. The protocol is closed, but it was reversed engineered by some guys over at GAIM project. It appeared to be a Blowfish encryption of bulk IMs using a key derived from an anonymous DH exchange [2]. This was also indirectly confirmed by another project [3]. Leaving aside the lack of authentication and replay protection, here's what is even more striking - SecureIM handshake between two version 3.1 (latest) clients takes about .. 48 bytes. That's altogether, 32 bytes in one direction, and 16 in another. And that's between the clients that have never talked to each other before, so there's no "session resuming" business happenning. If that's DH exchange, then it's 128 bit one. Fertile ground for some interesting speculation, don't you think ? Alex [1] http://en.wikipedia.org/wiki/Trillian_%28instant_messenger%29#Entry_into_mai nstream_and_the_.22IM_Wars.22 [2] http://sourceforge.net/tracker/download.php?group_id=235&atid=300235&file_id =56799&aid=777300 [3] http://code.google.com/p/joscar/wiki/TrillianSecureIm --------------------------------------------------------------------- The Cryptography Mailing List Unsubscribe by sending "unsubscribe cryptography" to [EMAIL PROTECTED]