Lin Hsin Hsin Quantum Security Center
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BB84 Vulnerabilities & Exploits by Lin Hsin Hsin





    The BB84 protocol is theoretically secure but vulnerable to implementation flaws and specific attack vectors that exploit hardware imperfections or classical post-processing weaknesses.


    By injecting errors and monitoring parity information, an eavesdropper can fully recover the secret key with minimal interception, bypassing quantum detection mechanisms.


    To mitigate these risks, enhanced protocols employ decoy states to detect PNS attacks, active quantum entropy sources to prevent detector blinding, and entanglement-assisted authentication to secure the classical channel against leakage and impersonation





    Attack Vector Mechanism Impact
    Photon Number Splitting (PNS) Exploits multi-photon pulses from imperfect sources to split and store photons. Allows eavesdropping without introducing detectable errors.
    Detector Blinding Uses bright light to control single-photon detectors, forcing detectors into linear mode, bypassing quantum randomness Enables complete key recovery while remaining undetected.
    Manipulate-and-Observe Exploits parity leakage during classical error correction (reconciliation phase: (eg Cascade protocol)) Allows full key recovery by analyzing reconciliation data.
    Trojan Horse Injects light pulses into sender/receiver hardware to analyze internal states Reveals internal settings or keys without intercepting qubits
    Man-in-the-Middle Intercepts and replays messages, impersonating parties without authentication. Compromises the entire key exchange process