Quantum Field Kit

BB84 Protocol Simulation

Simulate the BB84 quantum key distribution protocol with realistic physical effects.

Number of bits to simulate

int (min: 1)

Distance between Alice and Bob (km)

float (min: 0.0)

Hardware type (fiber, satellite, trapped_ion)

select

Additional noise probability

float (min: 0.0)

Eavesdropper present

bool

Eavesdropper strategy (intercept_resend, beam_splitting, trojan)

select

Run detailed quantum simulation

bool

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Simulation Results

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Quantum Simulation

Configure parameters and run the simulation to see results.

Quantum Explanation

BB84 Quantum Key Distribution

BB84 is the first quantum cryptography protocol, developed by Charles Bennett and Gilles Brassard in 1984. It allows two parties to establish a shared secret key using quantum communication.

Key Quantum Concept: The security of BB84 relies on the no-cloning theorem and the fact that measuring a quantum state disturbs it in a detectable way.

BB84 Protocol: Quantum Key Distribution

The BB84 protocol, developed by Charles Bennett and Gilles Brassard in 1984, was the first quantum cryptography protocol designed to create a secure secret key between two parties (conventionally called Alice and Bob).

Classical vs. Quantum: In classical cryptography, key exchange is vulnerable to eavesdroppers who can potentially copy communications without detection. Quantum key distribution makes this impossible due to the fundamental properties of quantum mechanics.

How BB84 Works: Step-by-Step

Quantum Bit Preparation: Alice prepares qubits in one of four polarization states, representing bits 0 or 1 in one of two bases (rectilinear or diagonal).
Quantum Transmission: Alice sends these qubits to Bob through a quantum channel.
Random Basis Measurement: Bob measures each qubit using a randomly chosen basis (rectilinear or diagonal).
Basis Reconciliation: Alice and Bob publicly share which bases they used, but not the measurement results.
Key Sifting: They keep only the bits where they happened to use the same basis, discarding the rest.
Error Estimation: They publicly compare a subset of their bits to detect any eavesdropping.
Privacy Amplification: If the error rate is acceptably low, they perform additional processing to obtain a final secure key.

The Two Bases Used in BB84

Rectilinear basis (horizontal/vertical polarization) and diagonal basis (45°/135° polarization) used to encode bits.

Key Quantum Principles in BB84

No-Cloning Theorem: It's impossible to create a perfect copy of an unknown quantum state. This prevents eavesdroppers from copying qubits.
Heisenberg Uncertainty Principle: Measuring a quantum system disturbs it. If an eavesdropper measures a qubit, they'll introduce detectable errors.
Quantum Superposition: Qubits can exist in a superposition of states, allowing encoding in different bases.
Quantum Measurement: Measuring a qubit in the wrong basis gives random results, securing information against incorrect measurements.

Real-World Applications

BB84 and other quantum key distribution protocols have moved beyond theoretical interest to practical implementations:

Commercial QKD Systems: Companies like ID Quantique and Toshiba now offer commercial QKD systems.
Quantum Networks: Experimental quantum networks in various countries use QKD for secure communications.
Financial Sector: Some banks use QKD to secure transactions between offices.
Government Communications: Various government agencies are exploring QKD for highly sensitive communications.

Limitations and Challenges

Distance Limitations: Current technology limits QKD to distances of around 100-200 km without quantum repeaters.
Hardware Vulnerabilities: Physical implementations may have vulnerabilities that theoretical protocols don't account for.
Authentication Requirement: QKD requires an initial authenticated channel to prevent man-in-the-middle attacks.
Cost and Complexity: QKD systems remain expensive and complex compared to classical cryptography.

Beginner's Analogy: Understanding BB84

Imagine Alice sends Bob a series of locks (qubits) that can be opened with either a square key or a star key (representing the two bases). Alice randomly chooses which type of lock to send and which position to set it in (locked or unlocked, representing 0 or 1).

Bob doesn't know which type of lock Alice sent, so he randomly tries either his square key or star key on each lock. Sometimes he guesses right and gets the correct information; other times he guesses wrong and gets random results.

Later, Alice and Bob publicly discuss which type of lock was used for each transmission (but not whether they were locked or unlocked). They keep only the results where Bob used the right type of key, discarding the rest.

If Eve tries to inspect the locks during transmission, she'll disturb them in a detectable way, alerting Alice and Bob to her presence.

Further Learning Resources

BB84 on Wikipedia

BB84 Video Explanation

Academic Paper on QKD

BB84 Quantum Key Distribution

BB84 is the first quantum cryptography protocol, developed by Charles Bennett and Gilles Brassard in 1984. It allows two parties to establish a shared secret key using quantum communication.

Key Quantum Concept: The security of BB84 relies on the no-cloning theorem and the fact that measuring a quantum state disturbs it in a detectable way.