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Quantum Cryptography

Secure keys through
the laws of physics

Quantum Key Distribution lets two parties establish a shared secret key over an insecure channel - and mathematically guarantees that any eavesdropper will leave a detectable trace.

01 Foundations & Principles
02 Comparison to PKC
03 QKD Protocols
04 BB84 Protocol
05 Live Demo
06 Future Outlook & Alternatives
01
Foundations and Principles
Quantum Mechanical Principles
  • Measurement Disturbance Principle
  • No-Cloning Theorem
  • Superposition
  • Entanglement
Core Goals
  • Produce a shared random secret key
  • Use that key for secure message encryption
Security Mechanism
  • Eavesdropping detection
  • Abort key if intrusion is detected
  • Information-theoretic security (laws of physics)
  • Authenticated classical channel
02
Comparison to Public Key Cryptography

PKC

  • Relies on mathematical computational difficulty
  • Vulnerable to quantum computers
  • Eavesdropping is undetectable

QKD Advantages

  • Information-theoretic security (physics-based)
  • Resistant to quantum computer attacks
  • Immediate eavesdropping detection
03
QKD Protocols
BB84 Protocol
Coherent · Decoy-State
E91 Protocol
BBM92 Protocol
Measurement Device Independent QKD
Device Independent QKD
Twin-Field QKD
Counterfactual QKD
Quantum Secret Sharing Protocol
Kak's Three-Stage Protocol
Continuous Variable QKD
Discrete Variable QKD
SARG04 Protocol
Coherent One Way Protocol
Distributed Phase Shifting Protocol
Round Robin (RR) Protocol
Semi-QKD
Quantum Conference Key Distribution Protocol
04
BB84 - Bennett & Brassard, 1984
①
First and foundational protocol
The original QKD scheme, still the most widely studied and deployed.
⚛
Principles used
Superposition · No-Cloning Theorem
◎
Qubits encoded onto photons
Each bit is carried by a single photon's polarization state.
±
Encoding using conjugate bases
Rectilinear basis (+): vertical = 0, horizontal = 1  ·  Diagonal basis (×): 45° = 0, 135° = 1
🔒
Security guarantee
Measurement disturbs quantum states → any eavesdropping is revealed through elevated error rates in the sifted key.
05
Live Demo
Interactive simulation
Try the BB84 simulation
Adjust photon count, toggle Eve, and watch the sifted key and error rate update in real time.
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06
Future Outlook and Alternatives
Primary Alternative - PQC
  • Classical implementation - no special hardware needed
  • Functional completeness - handles authentication and more
  • Lower cost and easier deployment at scale
Governmental Position & QKD Depreciation
  • Reliance on trusted nodes / relays
  • High cost and specialization
  • Security is implementation-dependent
  • Currently niche application status
Future Outlook
  • Overcoming distance limitations via quantum repeaters
  • Future research challenges for network security