BB84 Intercept-Resend Eavesdropping Detector

Quantum key distribution's security guarantee is physical, not computational: BB84 encodes each key bit on a single photon's polarization in one of two conjugate bases, and the no-cloning theorem means an eavesdropper cannot measure that photon without a real chance of disturbing it. This simulator streams individual polarized photons from Alice to Bob along a real BB84 channel — each rendered as a 3D bar tilted to its actual polarization angle — and lets you switch on an intercept-resend attacker, Eve, who measures a fraction of the photons in a guessed basis and resends her own collapsed state. Watch the sifted-key quantum bit error rate climb from a clean channel's baseline toward the theoretical 25% ceiling as Eve's interception probability rises, and see the live security verdict flip once the QBER crosses the real-world 11% abort threshold used in deployed quantum key distribution systems.