Significant research has been focused on instant messaging protocols with advanced security features. Off-the-Record
Messaging (OTR) allows private conversations over instant messaging by providing encryption, authentication, deniability,
and perfect forward secrecy. Borisov et al. [8] introduces an Off-the-Record Messaging protocol for secure instant messaging. The protocol uses the Diffie-Hellman key exchange protocol to establish short-term keys that are impossible to rederive from the long-term key material. These keys are then discarded after a period of use, making any past messages permanently unrecoverable. The messages in this protocol are not digitally signed. It is thus impossible to prove who sent a message. Because of the frequent key exchanges necessary for secure communication, it is vulnerable to replay attacks that allow an attacker to impersonate the sender to any other party in the system. Now that PFC has proven its usability, researchers can explore ways to incorporate stronger security properties while still maintaining usability.