BB84 Quantum Key Distribution (QKD) Simulator

A modular C++23 simulator modelling the BB84 quantum key distribution protocol to generate shared cryptographic keys under realistic conditions and adversary strategies.

---

Key Features

• Optical Hardware Models:
  • End-to-End Key Generation: Simulates the complete 'QKD lifecycle' from quantum state generation and noisy fibre transmission to basis reconciliation and classical sifting, yielding concrete raw and sifted keys.
  • Source Models: Supports both ideal single photon sources and weak coherent pulses (WCP) governed by Poisson statistics.
  • Channel Physics: Models exponential fibre attenuation, single photon detector efficiency, optical misalignment error rates, and detector dark counts.
• Adversary Strategies:
  • Implements dynamic intercept-resend eavesdropping strategies with optimal interception parameter calculation.

---

Project Directory Structure

bb84_sim/
├── Makefile
├── .gitignore
├── README.md
├── include/
│   ├── bb84.hpp          # Core quantum nodes, hardware configs, and state models
│   └── simulator.hpp     # End-to-end pipeline orchestration and metrics
├── src/
│   ├── bb84.cpp          # Implementation of quantum generation, transmission, and measurement
│   ├── simulator.cpp     # Simulation loop, sifting, and QBER evaluation
│   └── main.cpp          # CLI application and performance summary dashboard
└── tests/
    ├── doctest.h         # Single-header testing framework
    └── tests.cpp         # Automated physics baseline and determinism tests

Getting Started

Prerequisites

• A modern C++23 compliant compiler (e.g., g++ version 13+ or equivalent).
• make utility.

Building and Running

• Compile everything and run the test suite:

make

• Run the main simulation CLI binary:

make run

• Clean up build artefacts:

make clean

Roadmap

This project is actively under development. Near-term milestones focus on introducing a Photon-Number-Splitting (PNS) attack module, decoy-state methods, classical post-processing pipelines (error correction and privacy amplification), and finite-key security analysis. Long-term objectives include extending the framework to support alternative QKD protocols and multi-hop quantum network simulations.

License

This project is open-source and is intended for academic use or learning purposes.