On Mon, 17 Aug 2009 04:19:35 +0200
Xianwen Chen <xianwen.chen@gmail.com> wrote:

> I'm looking for a network message encryption method. Please kindly
> tell me if you know any Instant Messenger which supports encryption.
> Thank you very much!

I'm using gajim with TLS-enabled (transport-level encryption) connection
to the servers and built-in GPG plugin to encrypt messages, containing
some auth info, which I occasionally have to pass.
I believe pidgin also had support for such feature via one of the
standard plugins.

TLS is widely-deployed on XMPP (jabber) servers, but encryption ends at
the server in question, so it can intercept / mangle the messages, so it
might be good idea to prefer large and reliable servers to
possibly-compromised or malicious small ones.
Furthermore, in case of XMPP, your (source) server is free to pass the
message in unencrypted form to destination server, so message can be
caught by any IP-sniffers on the route.
Then there's also remote client connection, which can be unencrypted
(no TLS/SSL) and likewise intercepted on TCP/IP level.

GPG encryption requires clients on both sides to support it, but has
benefit that all cryptographic operations are happening on client
machines, so server (or any intermediate host) is unable to spoof
conversation, provided the encryption (GPG) keys aren't compromised.

-- 
Mike Kazantsev // fraggod.net