Quantum cryptography refers to cryptographic systems that rely on quantum mechanical effects and properties to perform cryptographic tasks.
This is in contrast to classical cryptography used on modern computers.
Contents
QKD
The main field in quantum cryptography is QKD.
QKD stands for Quantum Key Distribution.
Quantum mechanics reasonably lends itself to developing secure quantum communication systems.
The security of a quantum communication channel can also be reduced to a few highly minimal requirements.
One such condition is for the two legitimate parties to have some way to authenticate with each other.
Another requirement is simply that the laws of quantum mechanics apply.
The main issue for QKD comes from the difficulty of transmitting quantum information over significant distances.
Current research allows for suitable key agreement rates over optical fibers as long as 550km.
Beyond this distance, quantum repeaters are needed to ensure the signal is not lost in the noise.
Additionally, routing quantum communications over a quantum Internet would be challenging.
Current test systems tend to be point-to-point.
Other Fields of Research
Quantum effects can be utilized in the field of mistrustful quantum computing.
Here, two parties can cooperate without trusting each other.
The quantum system can be designed so that both parties can prove that the other was cheating.
These methods, however, also rely on non-quantum effects such as special relativity.
Quantum communication requires several things to be truly secure.
Firstly, optical transmissions need to be capable of sending single photons.
Current systems tend to use lasers that send multiple photons.
Theoretically, an adversary could intercept one of many photons without leaving a trace.
There is promising research in the development of single photon sources, though.
This issue is impossible to resolve fully without infinitely tight tolerances, an infeasible requirement.
Conclusion
Quantum cryptography refers to cryptography that makes use of quantum mechanical effects.
The current primary field is Quantum Key Distribution which uses quantum communication methods to transmit classical encryption keys.
Quantum cryptography should not be confused with post-quantum cryptography.
