photons quantum key distribution
The theoretical basis for quantum key distribution assumes the use of single-photon sources. However, such sources are difficult to construct, and most real-world quantum cryptography systems use faint laser sources as a medium for information transfer. These multi-photon sources open the possibility for eavesdropper attacks, particularly a photon splitting attack. An eavesdropper, Eve, can split the multi-photon source and retain one copy for herself. The other photons are then transmitted to Bob without any measurement or trace that Eve captured a copy of the data. Scientists believe they can retain security with a multi-photon source by using decoy states that test for the presence of an eavesdropper. However, in 2016, scientists developed a near perfect single photon source and estimate that one could be developed in the near future.
