J. Karl Rove writes "Nikita Borisov and Ian Goldberg (of many, many other projects) have released Off the Record Messaging for Gaim. Encrypt an IM, prove (at the time) that it came from you, and deny it later. The authentication works only when the message is sent; anybody can forge all the messages he wants afterwards (toolkit included). Captured or archived messages prove nothing. And forward secrecy means Big Brother can't read your messages even if he wiretaps you AND grabs your computer later on. All the gooey goodness of crypto, with none of the consequences! They have a protocol spec, source code, and Debian and Fedora binaries."