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Quantum Key Distribution with BB84: Breidbart-Based Eavesdropping and Channel Noise Effects

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Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2025, Tutors: Bruno Juliá Díaz, Artur Garcia Saez

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This work presents a security analysis of the BB84 quantum key distribution protocol, focusing on intercept-and-resend attacks and the effects of channel noise. We study two eavesdropping strategies—naive and Breidbart-based—and evaluate the probabilities of Eve (the spy) correctly measuring Alice’s (the sender) bit and Bob (the receiver) measuring an incorrect one.
We analyze the impact of bit-flip, phase-flip, and combined noise, derive theoretical expressions, and identify optimal attack parameters. A cost function is introduced to balance Eve’s information gain and detectability. Finally, simulations carried out confirm the theoretical predictions. The results offer insight into the robustness of BB84 under both ideal and noisy conditions and confirm its security against intercept-and-resend attacks.

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Quantum Key Distribution with BB84: Breidbart-Based Eavesdropping and Channel Noise Effects