Permissive Action Links, Nuclear Weapons, and the History of Public Key Cryptography

From a security perspective, command and control of nuclear weapons presents a challenge. The security mechanisms are supposed to be so good that they're impossible to bypass. But how do they work? Beyond that, there are reports linking these mechanisms to the early history of public key cryptography. We'll explore the documented history of both fields and speculate on just how permissive action links—the "combination locks" on nuclear weapons—actually work.