Deniable authentication
In cryptography, deniable authentication is message authentication between a set of participants where the participants themselves can be confident in the authenticity of the messages, but it cannot be proved to a third party after the event. In practice, deniable authentication between two parties can be achieved through the use of message authentication codes (MACs) by making sure that if an attacker is able to decrypt the messages, they would also know the MAC key as part of the protocol, and would thus be able to forge authentic-looking messages.