Working of Post-Quantum Cryptography

The foundational principles of quantum physics, specifically the uncertainty principle, lay the groundwork for quantum cryptography. As the anticipated capabilities of future quantum computers include widely used cryptographic methods like AES, RSA, and DES, quantum cryptography emerges as a prospective solution. In practical terms, it is employed to create a shared, secret, and random sequence of bits facilitating communication between two systems, such as Alice and Bob. This process, known as Quantum Key Distribution, establishes a secure key between Alice and Bob, enabling subsequent information exchange through established cryptographic methods.

By Heisenberg’s Uncertainty Principle

BB84 Protocol

A single-photon pulse undergoes polarization when passed through a polarizer. Alice employs a specific polarizer to polarize the single-photon pulse, encoding binary bits based on the outcome’s polarizer type (vertical, horizontal, circular, etc.). Upon receiving the photon beam, Bob attempts to guess the polarizer used by Alice, aligning the cases to assess the accuracy of his guesses. In the event of Eve’s eavesdropping attempts, her polarizer’s interference would cause discrepancies in the matching cases between Bob and Alice, signaling potential eavesdropping. Consequently, any eavesdropping by Eve would be detected by Alice and Bob in this system.

1. The B92 protocol utilizes only two polarization states, in contrast to the original BB84, which employs four states.
2. BB84 also features a similar protocol, SSP, utilizing six states for bit encoding.
3. Another protocol, SARG04, employs attenuated lasers and demonstrates superior performance compared to BB84 in systems involving more than one photon.

By Quantum Entanglement

E91 Protocol: A single source emits a pair of entangled photons, with each particle received by Alice and Bob. Like the BB84 scheme, Alice and Bob exchange encoded bits and compare cases for each transferred photon. However, in this scenario, the outcomes of the matching cases between Alice and Bob will be opposite due to the Entanglement principle. Consequently, they will possess complementary bits in their interpreted bit strings. To establish a key, one of them can invert the bits. The absence of eavesdroppers can be confirmed through a test since Bell’s Inequality should not hold for entangled particles. Given the impracticality of having a third photon in entanglement with sufficient energy levels for non-detection, this system is deemed fully secure.

1. The models of the SARG04 and SSP protocols can be extended to incorporate the theory of entangled particles.

Attacks that can possibly affect Quantum Cryptography

1. Photon Number Splitting (PNS) Attack

   As sending a single photon is not feasible, a pulse is transmitted. Eve has the opportunity to capture some photons from the pulse. After Alice and Bob match the bits, Eve can employ the same polarizer as Bob to derive the key without detection.

2. Faked-State Attack

   Eve employs a duplicate of Bob’s photon detector, intercepting the photons designated for Bob and subsequently relaying them to him. Despite Eve being aware of the encoded bit, Bob believes he received it directly from Alice.

Quantum Cryptography Explained

Quantum cryptography is a unique field that leverages the principles of quantum mechanics to secure communication. Unlike classical cryptography, which relies on the mathematical complexity of problems, quantum cryptography utilizes the inherent properties of quantum mechanics to achieve a level of security theoretically unbreakable by certain attacks. Two main protocols are employed in quantum cryptography: Quantum Key Distribution (QKD) and Quantum Secure Direct Communication (QSDC).

Here’s a simplified breakdown of QKD:

1. Superposition

   QKD utilizes the concept of superposition, where a quantum system can exist in multiple states simultaneously.

2. Photon Polarization

   In QKD, information is often encoded on the polarization states of individual photons (light particles).

3. Heisenberg’s Uncertainty Principle

   This principle states that certain pairs of properties, like a particle’s position and momentum, cannot be precisely measured simultaneously.

4. Quantum Entanglement

   Entanglement is a crucial element in QKD, where two particles become linked and share the same fate, regardless of distance.

5. QKD Process

   • Alice (sender) transmits a stream of entangled photons to Bob (receiver). The information is encoded in the polarization states of these photons.

   • Bob measures the qubits (quantum bits) using randomly chosen bases (e.g., vertical/horizontal or diagonal/anti-diagonal).

   • Alice and Bob openly communicate the bases used for each qubit without revealing the actual measurement results.

   • Only qubits measured in the same basis are used to generate a shared secret key.

   • Any attempt by an eavesdropper (Eve) to intercept the qubits disrupts their quantum state, revealing their presence.

Similarly, QSDC utilizes the principles of entanglement and superposition to establish secure communication between two parties.

Applications of PQC

Quantum Cryptography holds the potential to transform communication methodologies by offering a secure channel impervious to cyber threats. Various applications of Quantum Cryptography encompass:

1. Financial transactions

   Quantum Cryptography presents a secure communication avenue for financial transactions, rendering it impossible for cybercriminals to intercept and steal sensitive financial data.

2. Military and government communication

   Military and government entities can leverage Quantum Cryptography to exchange sensitive information, eliminating concerns about interception confidentially.

3. Healthcare

   Quantum Cryptography finds application in securing healthcare data, safeguarding patient records, and medical research.

4. Internet of Things (IoT)

   Quantum Cryptography proves instrumental in securing communication channels for IoT devices, addressing vulnerabilities arising from their limited computing power and susceptibility to cyber threats.

Conclusion

In conclusion, Quantum Cryptography stands as a promising frontier in secure communication, leveraging the foundational principles of quantum physics. With its ability to address potential threats posed by future quantum computers, Quantum Cryptography, particularly through Quantum Key Distribution protocols like BB84 and E91, establishes secure communication channels between entities like Alice and Bob. The practical applications of Quantum Cryptography extend across diverse sectors, including finance, military and government communications, healthcare, and the Internet of Things (IoT), showcasing its potential to revolutionize cybersecurity. However, it’s essential to remain vigilant against potential attacks such as Photon Number Splitting (PNS) and Faked-State attacks. The integration of entangled particles in protocols like E91 adds an additional layer of security. As technology advances, Quantum Cryptography promises to reshape the landscape of secure communication, providing a resilient defense against evolving cyber threats.