libotr (OTR Messaging Library and Toolkit)

This is the portable OTR Messaging Library, as well as the toolkit to
help you forge messages.
OTR allows you to have private conversations over IM by providing:
 - Encryption: No one else can read your instant messages.
 - Authentication: You are assured the correspondent is who you think it is.
 - Deniability: The messages you send do not have digital signatures
 - Perfect forward secrecy: If you lose control of your private keys,
   no previous conversation is compromised.