What is quantum cryptography? How does it work?

What is quantum cryptography? How does it work? 

  Quantum Cryptography 

  Quantum cryptography is a branch of quantum information science that focuses on securing communication channels using the principles of quantum mechanics. Unlike classical cryptography which relies on mathematical algorithms that can potentially be broken by quantum computers quantum cryptography takes advantage of the fundamental principles of quantum physics to achieve provable security. One of the key features of quantum cryptography is its ability to detect eavesdropping attempts providing a high level of security assurance.

    basic concepts

1. Quantum Superposition

     This property is known as superposition. Quantum cryptographic systems use this concept to represent multiple bits of information simultaneously.

2. Quantum Entanglement

      Entanglement is a quantum phenomenon where particles become correlated in such a way that the state of one particle instantly affects the state of the other regardless of the distance between them. Quantum cryptography uses entangled particles for secure key distribution.

    3. Quantum Uncertainty Principle

      The uncertainty principle a fundamental concept in quantum mechanics states that some pairs of properties (such as position and momentum) cannot be measured simultaneously accurately. Quantum cryptography uses this principle to detect any attempt to measure information transmitted without detection.

    Quantum Key Distribution (QKD) Algorithm

 The primary algorithm used in quantum cryptography is quantum key distribution (QKD). The most famous QKD protocol is the BBM92 (BB84) protocol developed by Charles Bennett and Gilles Brassard in 1984

    1. Main Generation

      Alice (sender) generates a sequence of quantum bits (qubits) in one of two possible bases (usually represented by two orthogonal states such as the vertical and horizontal polarization of the photon).

      Then it sends these qubits to Bob (the receiver) over the quantum communication channel.

   2. Quantum Measurement

     Bob randomly chooses a base (measurement direction) for each incoming orbit.

      When Bob receives a qubit he measures it on the chosen basis. The measurement result is either 0 or 1.

3. Public Communication

      Alice and Bob communicate publicly (over a classical communication channel) to disclose the basis used for each qubit without revealing the actual measurement results.

   4. Checking error

      A subset of transmitted qubits is randomly selected for error checking. Alice and Bob compare the bases used for these qubits. If they used the same basis chances are that Bob measured the qubit correctly. If different grounds were used this indicates possible eavesdropping.

  5. Main Distillation

     Alice and Bob discard the qubit used for error checking and retain the bits from the measured qubit on the same basis. These bits form a secret key that is known only to Alice and Bob.

    6. Security Certification

     The security of QKD depends on the principles of quantum mechanics. Any attempt by an eavesdropper (Eve) to intercept the qubits will perturb their quantum state producing errors that can be detected by Alice and Bob.

How Quantum Cryptography Works

1. Quantum Key Distribution

     QKD is used to securely distribute cryptographic keys between two parties commonly called Alice and Bob. The shared key generated through QKD is used to encrypt and decrypt messages in traditional cryptographic systems.

  2. Photon Transmission

      QKD typically uses photons (individual particles of light) to transmit qubits. These photons are often polarized in different directions to represent binary values (0 and 1).

   3. Entanglement for key distribution

     In some QKD protocols entangled particles are used to create shared keys. When the entangled particles are measured their positions become correlated allowing Alice and Bob to safely share a key. Any attempt by an eavesdropper to intercept these entangled particles will disrupt their entanglement thereby exposing the eavesdropper.

 4. Conversation Tracking

     The uncertainty principle prevents an eavesdropper from completely measuring the quantum states of transmitted particles without being detected. If an eavesdropper attempts to intercept and measure quantum states the act of measurement perturbs the particles causing errors that can be detected by Alice and Bob during the error-detection phase.

    5. Secure Key Generation

      After error checking and discarding insecure bits Alice and Bob are left with a shared secret key that is safe from eavesdropping attempts. This key can be used for secure communications using traditional cryptographic algorithms.

6. Real World Implementation

     Practical implementations of quantum cryptography involve specialized hardware such as quantum key distribution systems. These systems use components such as single-photon sources detectors and quantum gates to manipulate and measure quantum states.

  Iconclusion 

    quantum cryptography takes advantage of the principles of quantum mechanics to enable secure communications and key distribution. The BBM92 (BB84) QKD protocol among others forms the basis of secure key generation. Despite current challenges in practical implementation ongoing research and advancements in quantum technologies hold promise for the future of quantum cryptography and its role in securing communications against quantum threats.