Threshold Quantum Cryptography
This addresses the challenge of making quantum cryptography more flexible and implementable for secure communication systems, though it appears incremental as it builds on existing protocols like BB84 and three-stage.
The paper tackles the problem of quantum cryptography's reliance on single-photon transmission, which limits practical implementation and range, by proposing threshold quantum cryptography protocols that define security levels based on photon count thresholds, such as (p-k-n) systems where security varies from complete to partial to insecure as photon numbers increase.
Most current research on quantum cryptography requires transmission and reception of single photons that creates severe implementation challenges and limits range. This paper argues for the development of threshold quantum cryptography protocols in which the system is secure so long as the number of photons being exchanged between Alice and Bob is below a specified threshold. We speak of a (p-k-n) threshold system where if the number of photons exchanged is less than p, the system is completely secure, when it is between p and k, the system is partially secure, and when it exceeds k, the system is insecure. The BB84 protocol is (1-1-1) whereas the three-stage protocol appears to be (p-4p-n), where p is the least number of photons necessary to determine the polarization state of identically prepared photons. New quantum cryptography systems should be sought that provide greater flexibility in the choice of p and k.