Quantum Cryptography

(Towards ultra secure encryption)

Quantum Cryptography harnesses the Heisenberg Uncertainty Principle to define Quantum Key distribution (QKD), for guaranteeing secure communication between 2 parties. It allows the 2 parties to generate a shared random key for encryption & decryption.
It is important to notice here that the state of photon is used to produce the random bit string. As the photon can be measured only once, an eavesdropper can’t measure that and is unable to get the key. Huge no. of keys are produced per second, so the chance of getting required key information is insignificant or very limited.

By harnessing this uncertainty, we create a data-encryption scheme that's essentially unbreakable, called quantum cryptography. Quantum cryptography, uses quantum mechanics to guarantee secure communication. Any two parties can produce a shared random key known only to them to encrypt and decrypt messages between them.

Heisenberg Uncertainty Principle

This principle states that locating a particle in a small region of space makes the momentum of the particle uncertain; and conversely, that measuring momentum of a particle precisely makes the position uncertain.

Qubit Concept

As classical computer uses binary values of 0 and 1, a qubit can exist in 0 or 1 or a superposed value of 0 or 1 also. “Superposed value” means it can be in both the state of either 0 or 1 until the time its value can be measured or when the “qubit” comes to the actual value.

Example:- Schrödinger’s Cat Example
This example supposes that there is a box with a nozzle having a random probability of releasing poisonous gas. A cat is put inside the box. If the gas is released, then cat dies representing state 0. If gas is not released then cat is alive representing state 1. But when the cat is inside the box and we don’t know whether the gas is released or not, according to qubit concept, the cat is both dead AND alive in the box UNTIL we look inside the box to be sure or when qubit narrows down to the actual value.

Why Quantum Encryption is said to be unbreakable or ultra – secure?

Two particles of qubits in a quantum computer system can be entangled. States of the two particles rely on each other irrespective of the distance between them. Such entanglement is a key factor in the computations that is achieved with a quantum system. This property makes a quantum computer to guarantee integrity and an easy system to corrupt through malicious attack.


Attacks that can be made

Laser diodes used to transmit keys , sometimes transmit more than one photon at a time. A hacker could monitor the second photon, leaving the first photon without alerting anyone that the key transmission has been compromised.

Remedy

Scientists have added decoy photons to the key data so that when eavesdropper tries to monitor extra photons, he will also monitor decoy photons. Decoy photons are weaker on average and hence very rarely contain two or more photons. If an eavesdropper attempts a pulse-splitting attack, he will transmit a lower fraction of these decoy pulses than signal pulses. Monitoring separately the transmission of the decoy and signal pulses, compromise can be detected. Hence transmission becomes very much secure.

Recent Developments

• A encrypted quantum key transmitted over a distance of 184.6 km by researchers in the US, based at the Los Alamos National Laboratory (LANL) in New Mexico and the National Institute of Standards and Technology (NIST) in Boulder, Colorado.
• They used Transition-Edge Sensor (TES) technique which detected 65% of received photons, than the conventional photo diodes which detected 20% of photons.
  

Challenges

• Very nascent technology
• Very less commercial interest presently, although interest is increasing day by day by corporate & government agencies.
• Only be beneficial where protection of critical information is required.