Kish Cypher
The Kish cypher is categorized as a technique for secure communication, similar in application to Quantum encryption and Public Key cryptography. The simplified explanation is that it works by measuring the resistance of the communication medium (i.e. a circuit, or some wire) between 2 parties. One party can “send” messages by changing the resistance of the medium (i.e. placing a resistor on the wire). The other party can “read” messages by deriving the difference between the amount that the resistance has changed and the amount of resistance they are contributing to the wire as well.
Ideally, an eavesdropper would not be able to read the messages since he can’t derive this difference (he doesn’t know both resistances), hence Kish’s usefulness for secure communication.
The cool part about Kish (besides its name) is that it’s such a simple system to build from a component standpoint. In fact, most of the infrastructure for this type of system already exists– the medium itself can be any single wire connecting two parties.
But how secure is it?
From the homepage:
- Status of the idealistic circuit scheme: Unconditionally secure; it has not been cracked.
- Status of the practical (non-ideal) system with inaccuracies and stray elements (hacking):
A small information leak of raw bits, similarly to quantum communicators. The amount of leaking information can be controlled (Alice and Bob determine the amount of information Eve can have). The scheme cannot be cracked but it can be jammed (similarly to quantum key exchange, when Eve randomly measures and supplies back a small fraction of photons; an operation which cannot be detected by Alice and Bob because it yields too small quantum error rate). However, for a major difference from quantum communicators, note that Alice and Bob are fully aware of all the information Eve knows. Thus they are in the position to discard or manipulate the information Eve has.
Apparently, it can hold its own from a security perspective (it’s certainly been scrutinized enough). And despite not winning any popularity contests, Kish’s unique physical nature means that there may be some very specific situations where it would be the only solution for secure communications.
