Within a few cycles, researchers displayed the system in the lab, and today quantum cryptography is displaying commercially viable recognition to companies such as ID Quantique in Geneva, Switzerland.
But the entire device is a little counterintuitive. The private information is not sent using quantum workers at all. Instead, physicists use quantum means to send a code called a one-time pad that is used to encrypt the initial message. The encrypted message is then sent over an average telecommunications carrier and decoded in the usual way. The method is called quantum key distribution.
Computer scientists know that an information encoded using a one-time pad package be broken. So the security comes from the knowledge to send the one-time pad with perfect privacy, which is what this suggestion guarantees.
And that raises an intriguing question. If it’s possible to send the one-time pad securely using quantum workers, why not just send the primary message that way?
Today, Wei Zhang at Tsinghua University in Beijing and a few friends say they have done just this. The new method is called quantum secure direct communication, and the Chinese team has used it completed 500 meters of fiber-optic cable for the first time.
The reason scientists have relied on one-time pads in the past is simple. At issue is whether a communication has been overheard. Physicists can check this because quantum bits cannot be measured without consuming the information they contain.
So when photons are transmitted, if they arrive in the same state they were sent in, a listener cannot have extracted the data they contain. But if they arrive in a different state, that is clear evidence that the data has leaked into the background and the message is not secure.
In practice, physicists can be sure that a data is secure as long as this leakage is below some sharp threshold.
The difficulty is that the leakage becomes possible only after it has occurred. So a listener would already have the data by the time scientists found out about the ruse.
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