QKD Protocols

Quantum Cryptography

Explore quantum-secure communication and the future of cryptography

Quantum Key Distribution (QKD)

QKD uses quantum mechanics to detect eavesdropping and establish provably secure communication channels. Any attempt to intercept the quantum states will disturb them, alerting the communicating parties.

Key Principles:
  • No-cloning theorem: Quantum states cannot be perfectly copied
  • Measurement disturbance: Observation changes quantum states
  • Information-theoretic security: Security based on physics, not computational complexity

BB84 Protocol Demo

The BB84 protocol, developed by Bennett and Brassard in 1984, is the first quantum key distribution protocol.

Interactive BB84 Simulation
👩‍💻
Alice (Sender)
Ready
🕵️
Eve
👨‍💻
bOb (Receiver)
Ready
Protocol Steps:
1. Alice generates random bits and bases
2. Alice sends qubits using chosen bases
3. bOb measures using random bases
4. Alice and bOb compare bases publicly
5. Keep bits where bases match (sifted key)
6. Error detection and privacy amplification

Quantum Threat to Classical Cryptography

Quantum computers pose a significant threat to current cryptographic systems, particularly those based on integer factorization and discrete logarithms.

Cryptographic Algorithm Security Status
RSA

Status: vulnerable

Broken by Shor's algorithm

ECC

Status: vulnerable

Broken by Shor's algorithm

AES

Status: Weakened

Grover's algorithm halves key strength

Quantum Computer Threat Level:
Current: Low

Post-Quantum Cryptography

Post-quantum cryptography develops algorithms that remain secure against both classical and quantum computers.

NIST Post-Quantum Standards
2016

NIST begins post-quantum standardization process

2022

First standards published: CRYSTALS-Kyber, CRYSTALS-Dilithium

2024

Additional standards: ML-KEM, ML-DSA, slH-DSA

Future

Widespread adoption and implementation

Lattice-based

Example: CRYSTALS-Kyber

Key exchange

Hash-based

Example: SPHINCS+

Digital signatures

Code-based

Example: Classic McEliece

Key encapsulation

QKD Protocols

  • BB84: First QKD protocol
  • B92: Simplified version
  • e91: Entanglement-based
  • SARG04: Enhanced security
  • COW: Coherent one-way

Quantum Advantages

  • Unconditional Security: Based on physics
  • Eavesdropping Detection: Quantum disturbance
  • Perfect Forward Secrecy: Keys are not stored
  • No Computational Assumptions: Information-theoretic

Current Limitations

  • Distance limitations (~100-200 km)
  • Requires specialized hardware
  • vulnerable to implementation flaws
  • High cost and complexity

Applications

  • Government Communications
  • Financial Transactions
  • Healthcare Data
  • Critical Infrastructure
  • Quantum Internet