BB84 Key Sifting Statistics: Measured QBER vs the 25%…

What is BB84?

BB84 is a pioneering quantum cryptography protocol developed by Charles Bennett and Gilles Brassard. It allows two parties to generate a shared secret key securely over an insecure channel, leveraging the principles of quantum mechanics. The protocol involves encoding information in single photons using polarization states.

In BB84, one party (Alice) randomly chooses between two bases for each photon she sends to another party (Bob). Bob measures the photons using a random basis. By comparing their choices over an authenticated classical channel, Alice and Bob can identify which measurements were made in compatible bases.

Key Sifting Process

The key sifting process is crucial for BB84 as it filters out the bits that do not match between Alice and Bob. After comparing their measurement bases, they discard all pairs where their choices did not align. The remaining bits form the sifted key.

This process ensures that any eavesdropper (Eve) must measure in one of the two possible bases, leading to errors in the bits she intercepts.

live demo · related simulation● LIVE

Quantum Bit Error Rate (QBER)

The Quantum Bit Error Rate (QBER) is a critical metric that quantifies the error rate between Alice and Bob's sifted key. It is calculated by comparing their bits after sifting, and it provides an estimate of Eve’s presence.

In the absence of eavesdropping, QBER should be low. However, if Eve intercepts and resends photons using the intercept-resend strategy, she can introduce errors that increase the QBER.

Intercept-Resend Strategy

Eve’s intercept-resend strategy involves measuring each photon in one of the two bases Alice uses and then resending a new photon to Bob. This introduces errors into the sifted key, which can be detected by analyzing the QBER.

The protocol is designed such that if Eve intercepts more than 25% of the photons, the QBER will increase significantly, allowing Alice and Bob to detect her presence.

Frequently asked questions

How does BB84 ensure security against eavesdropping?

BB84 ensures security by comparing the bases used for measurements. If Eve intercepts and measures a photon, she must choose between two bases, leading to errors in her measurement that can be detected when Alice and Bob compare their bits.

What is QBER and why does it matter?

QBER stands for Quantum Bit Error Rate. It indicates the rate of bit errors after sifting between Alice and Bob, which helps them detect eavesdropping attempts by Eve.

Can BB84 be used in real-world applications?

Yes, BB84 has been implemented in various real-world scenarios for secure communication, such as financial transactions, military communications, and government networks.

Is the 25% intercept-resend limit absolute?

The 25% limit is a theoretical threshold. In practice, even lower levels of eavesdropping can be detected by carefully analyzing QBER trends over time.

Try it live

Everything above runs in your browser — open BB84 Key Sifting Statistics: Measured QBER vs the 25% Intercept-Resend Limit and change the parameters while it is running. Nothing is installed, nothing is uploaded, the whole model lives in one tab.

▶ Open BB84 Key Sifting Statistics: Measured QBER vs the 25% Intercept-Resend Limit simulation