Gaps between equations and experiments in quantum cryptography
John M. Myers, F. Hadi Madjid · Journal of Optics B Quantum and Semiclassical Optics · 2002
Traditional methods of cryptographic key distribution rest on judgments about an attacker.With the advent of quantum key distribution (QKD) came proofs of security for the mathematical models that define the protocols BB84 and B92; however, applying such proofs to actual transmitting and receiving devices has been questioned.Proofs of QKD security are propositions about models written in the mathematical language of quantum mechanics, and the issue is the linking of such models to actual devices in an experiment on security.To explore this issue, we adapt Wittgenstein's method of language games to view quantum language in its application to experimental activity involving transmitting and receiving devices.We sketch concepts with which to think about models in relation to experiments, without assuming the experiments accord with any model; included is a concept of one quantummechanical model enveloping another.For any model that agrees with given experimental results and implies the security of a key, there is an enveloping model that agrees with the same results while denying that security.As a result there is a gap between equations and the behavior recorded from devices in an experiment, a gap bridged only by resort to something beyond the reach of logic and measured data, well named by the word guesswork.While this recognition of guesswork encourages eavesdropping, a related recognition of guesswork in the design of feedback loops can help a transmitter and receiver to reduce their vulnerability to eavesdropping.