Quantum Cryptography

What is Quantum Cryptography?

• Quantum mechanics: This is the foundation for quantum cryptography. Quantum mechanics describes small particles like electrons and photons. Superposition, entanglement, and the uncertainty principle enable safe cryptographic systems. These concepts make eavesdropping detectable by disturbing quantum information when measured or intercepted.
• Cryptography: Cryptography protects data by making it unreadable without the right key. Complex mathematical tasks like factoring huge numbers or calculating discrete logarithms protect data in classical cryptography. It uses symmetric-key and asymmetric-key cryptography.
• Quantum cryptography: Quantum cryptography secures data by applying the principles of quantum physics. Unlike conventional approaches, its security depends on physics, not computing capability. It securely transmits data so any interception attempt is obvious. This makes it theoretically indestructible.
• Quantum key distribution (QKD): QKD is quantum cryptography's most practical and widespread use. Two parties can produce a secret key over a quantum channel. The most used protocol, BB84, encodes bits with polarized photons.  Users are alerted to vulnerability if an intruder measures the transmission and changes photon states.
• Quantum resistance (Post-Quantum Cryptography): Quantum computers can destroy many cryptographic systems utilizing Shor's or Grover's algorithms. Quantum resistance involves creating cryptography methods that can withstand quantum computer assaults. Future-proofing digital security requires lattice-based, hash-based, and multivariate polynomial cryptosystems.

1. What is post-quantum cryptography?

• Post-quantum cryptography (PQC) techniques can withstand a quantum computer attack. Quantum cryptography involves quantum physics, whereas PQC uses conventional mathematical methods that are immune to quantum attacks.
• PQC aims to improve cryptographic technologies like internet browsers, financial apps, and digital signatures to be functional and safe when quantum computers become widespread.

2. Quantum-resistant algorithms

• Cryptographic methods known as "quantum-resistant algorithms" do not rely on issues like factoring or discrete logarithms that are readily resolved by quantum computers. Its top categories include:
• Lattice-based encryption (such as CRYSTALS-Kyber and CRYSTALS-Dilithium): Quick and flexible solutions to challenging vector space-based mathematics issues.
• Hash-based signatures (SPHINCS+): Digital signatures benefit from cryptographic hash algorithms.
•  Code-based cryptography (Classic McEliece): Error-correcting codes; secure but big key sizes.
• Multivariate polynomial cryptography: Based on solving systems of nonlinear equations.
• Isogeny-based cryptography: Compact and new, yet untested in real life.

3. Differences Between QC and PQC

• Quantum Cryptography (QC) is built on the principles of quantum physics, while Post-Quantum Cryptography (PQC) is grounded in classical mathematics. QC primarily uses Quantum Key Distribution (QKD) as its main tool, whereas PQC relies on algorithms designed to resist attacks from quantum computers. QC requires specialized quantum hardware for its infrastructure, whereas PQC works seamlessly on traditional classical computers. The security of QC is ensured by the fundamental laws of physics, while PQC derives its security from the computational difficulty of specific mathematical problems. When it comes to deployment, QC tends to be complex and expensive, whereas PQC is easier to implement within existing systems.
• In short, QC is physics-based and hardware-intensive, while PQC is software-based and easier to adopt.

4. Important reasons to switch to quantum-resistant systems

• Quantum threat: Once strong enough, quantum computers might break conventional encryption schemes, endangering decades of data and future communication.
• Active defense: Moving to PQC protects sensitive data from “harvest now, decrypt later” attacks, where encrypted data is taken today to be decrypted later utilizing quantum capabilities.
• Standardization: Organizations like NIST (National Institute of Standards and Technology) are standardizing PQC algorithms.  Early adoption keeps governments, companies, and individuals ahead of the threat.
• Global readiness: PQC secures essential infrastructure (banking, healthcare, defense) and consumer-level apps in the quantum age.

• High cost and complex infrastructure: One of the most difficult aspects of QC is the requirement for specialized quantum gear, such as single-photon generators, detectors, and ultra-sensitive optical components.  This infrastructure is expensive and complicated to set up and maintain, making widespread adoption challenging.
• Limited transmission distance: Photon loss and noise in optical fibers weaken quantum communications over long distances.  This restricts Quantum Key Distribution (QKD) range, especially without quantum repeaters, which are currently being developed.
• Scalability: Implementing QC over large networks, notably cities or nations, needs substantial coordination and physical infrastructure.  QKD installations are usually point-to-point, making scaling difficult compared to software-based cryptographic methods.
• Quantum states are fragile: Temperature, vibration, and light affect qubits greatly.  This makes quantum communication systems delicate and prone to transmission mistakes and signal loss.
• Lack of standardization: Quantum cryptography protocols have no uniform standard, despite advances.  This might cause compatibility concerns and industry reticence for reliable, generally acknowledged solutions.
• No full replacement: QC, particularly QKD, only handles key distribution, not encryption.  It's a hybrid approach since it requires encrypting and decoding data with traditional cryptography techniques.
• Physical security is still needed: QC can identify eavesdropping but not hardware assaults or insider threats.  Physical infrastructure security is still needed for system security.