Some random thoughts...
Pidgin provides a lot of security features and support a lot of sec protocols and it provides strong encryption. It is Free and Open Source.
- Automatically creates a public/private key pair for you upon loading the plugin.
- Automatically transmits your public key to other users.
- Supports 512 - 4096 bit keys.
- Saves keys of known users, and warns you if their public key has changed.
- Embeds all encryption and keys inside HTML, so if the other user doesn't have the plugin, they will get a little message telling them about the plugin, and won't get a screen full of garbage.
- Stores keys in human readable files in your .gaim/.pidgin directory, in case you ever need to copy/edit them by hand. Which you really shouldn't have to do.
- Automatically recognizes if you are chatting with someone who has the plugin- see the Preferences dialog.
- Available for the Windows version of Pidgin.
- Modular and extensible. If you want to define a different type of encryption, you can use this plugin as a wrapper to take care of transporting the encrypted binary over the IM pipe.
And also it provides Off-the-Record Messaging. Off-the-Record (OTR) Messaging allows you to have private conversations over instant messaging by providing:
No one else can read your instant messages.
You are assured the correspondent is who you think it is.
The messages you send do not have digital signatures that are checkable by a third party. Anyone can forge messages after a conversation to make them look like they came from you. However, during a conversation, your correspondent is assured the messages he sees are authentic and unmodified.
Perfect forward secrecy
If you lose control of your private keys, no previous conversation is compromised.
OTR can be used by Pidgin and Adium
Also Extensible Messaging and Presence Protocol (XMPP) (previously named as Jabber), is used by A LOT of clients, and provides strong security. You can see some of the security of XMPP here and here. You can also choice from a very long list of clients that support Jabber. Off-the-Record Messaging is also provided by many Jabber clients. And if you are paranoid enough you can run your own Jabber server ( see here, here and here)
If you user VoIP IM clients, you may also want to have a look at Zfone. It is created by Phil Zimmermann, the creator of the PGP encryption software. Zfone has been tested with the following VoIP clients: X-Lite, Gizmo5, XMeeting, Google Talk VoIP client, and SJphone.
AESPad is browser-based, so you dont have anything to install.
And finally Torchat has some unique features:
- TorChat just runs from an USB drive on any Windows PC.
- Nobody will be able to find out where you are.
- If they are already observing you and sniff your internet connection they will not be able to find out
- what you send or receive (everything is end-to-end encrypted)
- to whom you are sending or receiving from
- where your contacts are located