## The Un-Amplifiable Signal

Quantum Key Distribution (QKD) promises mathematically unhackable internet. It uses the laws of quantum mechanics to encode encryption keys onto single photons of light. If a hacker tries to look at the photon in transit, the wave function collapses, instantly alerting the sender and receiver that the line is tapped.

### FAQ

**Q: If QKD is perfectly unhackable, why don't banks use it instead of public-key encryption?**
A: The No-Cloning Theorem. Fiber optic cables are made of glass. Even the purest glass in the world absorbs light. Over 100 kilometers, 99% of photons fired into a cable will hit a microscopic impurity and vanish. In normal ethernet, we fix this by putting laser "Amplifiers" every 50km to copy and boost the signal. But the fundamental law of Quantum Mechanics (the No-Cloning Theorem) states that it is physically impossible to make a perfect copy of an unknown quantum state. Therefore, you cannot amplify a QKD signal. If you try to send a single photon from New York to Chicago, the odds of it surviving the glass are lower than winning the lottery. You will generate only 1 byte of encryption key every 5,000 years.