The interlock protocol, as described by Ron Rivest and Adi Shamir, was designed to frustrate eavesdropper attack against two parties that use an anonymous key exchange protocol to secure their conversation. A further paper proposed using it as an authentication protocol, which was subsequently broken.
Read more about Interlock Protocol: Brief History, How It Works, The Bellovin/Merritt Attack, Forced-Latency Interlock Protocol