This project is a pedagogical demonstration of the BB84 quantum key distribution protocol implemented in Qiskit.
The random bitstream used here does not come from built-in pseudorandom generators.
Instead, it is sourced from my other project, Chaos2Crypto,
where I developed an FFT-based random number generator with bias correction and cryptographic extraction.
- Alice encodes qubits according to her random key bits and chosen bases.
- Eve may intercept, measure in random bases, and resend the qubits.
- This introduces errors in the sifted key.
- Bob measures qubits in his own random bases.
- Sifting is performed to keep only bits where Alice’s and Bob’s bases matched.
- The result is a shared sifted key.
This project is for educational purposes only - it is not a production-ready cryptographic implementation.
I used Qiskit’s AerSimulator as backend constraints, this demo is limited to 28 qubits at a time.
- With 28 qubits:
- On average, 12–16 bases match between Alice and Bob.
- That’s roughly 47–53% agreement, which is exactly what theory predicts (basis matches occur with probability ½).
- This confirms the implementation behaves as expected.
Feel free to clone, modify, and extend this project to suit your needs! (Specially, I wanted to try making a Batch wise measurement to cover more number of qubits but I couldn't figure out a nice way to implement this, hence maybe anyone interested can try that as well)