MDI-QKD: Detector-Blind Quantum Key Distribution

Measurement-Device-Independent Quantum Key Distribution closes the biggest real-world hole in quantum cryptography: attacks on the single-photon detectors themselves. Instead of Alice and Bob measuring each other's photons directly, both send randomly-encoded polarized photons to an untrusted relay that performs a Bell-state measurement and only announces whether a valid coincidence occurred — never which bits were sent. This simulator streams photon pairs from Alice and Bob to a central relay in real time, applies the Hong-Ou-Mandel bunching/anti-bunching rule that governs which pulses can herald a click, sifts a secret key from the survivors, and estimates the quantum bit error rate live. Flip on the "malicious relay" toggle to hack the detectors yourself and watch the QBER climb past the 11% security threshold that forces the protocol to abort the key — the exact mechanism that makes MDI-QKD immune to the detector-blinding attacks that have broken real commercial QKD systems.