Quantum Key Distribution (QKD)
The Physics of Provable Security
Beyond Prime Numbers
Most modern encryption (like RSA) is based on the assumption that certain math problems are hard to solve. A sufficiently powerful Quantum Computer could potentially solve these problems in minutes. QKD solves this 'Quantum Threat' by using Quantum Mechanics.
The BB84 Protocol
The most famous QKD protocol is BB84. It uses four different polarizations of photons:
- Horizontal/Vertical (Rectilinear Basis)
- +45°/-45° (Diagonal Basis)
Alice sends photons using a random basis for each. Bob measures them using a random basis. They then communicate over a public channel to compare which *bases* they used (not the actual values).
BB84 Protocol Simulator
Quantum Key Distribution & Eavesdropping Detection
| Basis (A) | Bit (A) | EVE | Basis (B) | Bit (B) | Sift? | Result |
|---|---|---|---|---|---|---|
| No photons transmitted. Press "TX PHOTON" to start. | ||||||
Protocol Tip: In BB84, if Alice and Bob agree on the basis, they MUST agree on the bit. If Eve measures in the wrong basis (50% chance), she randomizes the photon. This leads to a 25% error rate in matched bits, which is physically impossible without interference.
Quantum vs. Classical MITM
In a classical Man-in-the-Middle (MITM) attack, Eve can intercept a message, copy it, and send it along perfectly. In QKD, the act of 'copying' is prevented by the Heisenberg Uncertainty Principle.
Conclusion
While still in its early deployment stages (mainly for government and financial backbones), QKD represents the ultimate destination for network security. It is the only known method of key exchange that provides Information-Theoretic Security—security that cannot be broken by any amount of computing power.