qvirus (version 0.0.5)

run_bb84_simulation: BB84 Quantum Key Distribution (QKD) Simulation

Description

Simulates the BB84 protocol for quantum key distribution (QKD), illustrating the difference in the Quantum Bit Error Rate (QBER) between an ideal channel (no interference) and a channel under eavesdropping (Eve). The simulation models the encoding, transmission, and measurement of quantum bits (qubits) following the original Bennett–Brassard (1984) protocol.

Usage

run_bb84_simulation(
  eavesdropping_active = FALSE,
  key_length = 1000,
  test_ratio = 0.2
)

Value

A list of class "BB84Simulation" containing:

QBER

The observed Quantum Bit Error Rate between Alice's and Bob's bits.

Sifted_Length

Number of bits retained after basis reconciliation.

Final_Key_Length

Number of bits remaining after error testing.

Eavesdropping

Logical flag indicating whether eavesdropping was active.

Arguments

eavesdropping_active

Logical. If TRUE, the simulation includes an eavesdropper (Eve) who performs a measure-and-resend attack, introducing errors. If FALSE, the simulation runs under ideal, interference-free conditions. Default is FALSE.

key_length

Integer. Length of the quantum key sequence to be simulated. The default is 1000, which provides good statistical stability.

test_ratio

Numeric. Proportion (between 0 and 1) of bits that Alice and Bob compare to detect eavesdropping during the verification phase. Default is 0.2.

Details

The BB84 protocol proceeds through the following stages:

1. Preparation: Alice generates random bits and bases and encodes photons accordingly.

2. Transmission: Photons are sent over a quantum channel.

3. Eavesdropping (optional): Eve intercepts each photon, measures it using a random basis, and resends a new photon, introducing potential errors.

4. Measurement: Bob measures the incoming photons using his own random bases.

5. Sifting: Alice and Bob retain only bits measured with matching bases.

6. Error estimation: A random subset of the sifted bits is compared to estimate QBER.

If the measured QBER exceeds a security threshold (commonly 15–25%), it indicates that eavesdropping has occurred and the key must be discarded. In the absence of interference, the QBER should be close to zero.

References

Bennett, C. H., & Brassard, G. (1984). Quantum cryptography: Public key distribution and coin tossing. Proceedings of IEEE International Conference on Computers, Systems and Signal Processing, 175–179.

Nielsen, M. A., & Chuang, I. L. (2010). Quantum Computation and Quantum Information. Cambridge University Press.

Rieffel, E. G., & Polak, W. H. (2011). Quantum Computing: A Gentle Introduction. MIT Press.

Examples

# Scenario 1: Perfect Channel (No Eavesdropping)
results_no_eve <- run_bb84_simulation(eavesdropping_active = FALSE)
cat("--- Scenario 1: No Eavesdropping ---\n")
cat(paste("Sifted Key Length:", results_no_eve$Sifted_Length, "\n"))
cat(paste("Final Key Length:", results_no_eve$Final_Key_Length, "\n"))
cat(paste("Quantum Bit Error Rate (QBER):", round(results_no_eve$QBER * 100, 2), "%\n"))
cat("Result: Secure key established successfully.\n")

# Scenario 2: Measure-and-Resend Attack
results_with_eve <- run_bb84_simulation(eavesdropping_active = TRUE)
cat("\n--- Scenario 2: With Eavesdropping ---\n")
cat(paste("Sifted Key Length:", results_with_eve$Sifted_Length, "\n"))
cat(paste("Final Key Length:", results_with_eve$Final_Key_Length, "\n"))
cat(paste("Quantum Bit Error Rate (QBER):", round(results_with_eve$QBER * 100, 2), "%\n"))

if (results_with_eve$QBER > 0.15) {
  cat("High QBER detected. Eavesdropping likely — key discarded.\n")
} else {
  cat("No eavesdropping detected (unlikely in theory).\n")
}