Now let's assume that there is a listener E, who is trying to eavesdrop on the message, who has the same polarizer as B, and who needs to choose to filter the photons in a straight or diagonal line. Pen @ fun @ pavilion wWw. ｂｉｑUｇE。 ｉｎｆｏ

However, he faced the same problem as B, which was that there was a half chance that he would choose the wrong polarizer. B's advantage is that he can confirm with A the type of polarizer used, whether it is straight or diagonal; and whether the vibration pattern is up and down, or left and right.

There is no way for E, and there is a half chance that she will choose the wrong detector and misinterpret the photon information to form the final bond, rendering it useless.

So how will A and B know if Eve is listening on them?

There is another level of security inherent in quantum cryptography, which is intrusion detection. The fact that E is actually on the photonic line will be very easy to spot for the following reasons:

Let's assume that A transmits photons numbered 349 to B in an upper-right/lower-left fashion, but in this case, E uses a linear polarizer to accurately measure photons of the up-and-down or left-right type. If B uses a linear polarizer, then it doesn't matter, because he will discard the photon from the last key.

But if B uses a diagonal polarizer, the problem arises, he may make the correct measurement, or the wrong measurement according to Heisenberg's uncertainty theory. E changes the state of the photon with the wrong polarizer, and B can make an error even with the correct polarizer.

Once E's bad behavior is discovered, A and B must take the above steps to obtain a unique key sequence consisting of 0s and 1s, which will not contradict each other unless it has already been stolen. At this point, they take further action to check the validity of the key-value. It would be foolish and unnecessary to compare the last key value of a binary number on an insecure channel.

Let's assume that the final key value contains 4000 binary digits, and what A and B need to do is to randomly select a subset of these numbers, 200 bits, and compare them according to the two states (number 2, 34, 65, 911, etc.) and the number state (0 or 1), and if they all match, it can be assumed that E is not listening.

If she is listening, then the chance of not being detected is 1 in a trillion, that is, it is impossible not to be detected.

A and B will no longer use this key when they find someone listening, and they will restart the key-value exchange on the secure channel where E is not reachable, although the above comparison can be done on the unsecured channel.

If A and B deduce that their key value is safe because they tested with 200 bits, those 200 bits will be discarded from the last key value, and 4000 bits will become 3800 bits.

And the remaining 3800 bits are the information they really want to exchange, and all B has to do is translate the 3800 bits of 1 or 0 into the corresponding letters.

"In fact, this system model has been proven in IBM laboratories in Britannia, but it is only suitable for relatively short distances. Over long distances, fiber optic cables with extremely pure optical characteristics successfully transmit photons up to 60 kilometers. It's just that BERs (error rates), which are closely linked to Heisenberg's uncertainty principle and microimpurities in the fiber, make the system not work stably. Although there have been studies that have been successful in transporting through air, the transmission distance is still very short in ideal weather conditions. ”

Speaking of this, Kyosuke Takasaka raised his head rather proudly: "But who are we?" We're amalgam! In front of whisperers, such a thing can also be counted? V.V. When that Lotta was still laying out the white house, we were in low earth orbit... ”

Syllable!

Seamus pressed Kyosuke Takasaka's hairy head, pressed his entire body against his futon, buried his head in the gap between his legs, and said in a threatening tone, "Don't tear me off!" Tell me how to do it! ”

Knowing that the other party was already angry, Takasaka's dead sister blushed, maybe because she was overwhelmed by the quilt, maybe because her current posture was too shameful, in short, he quickly fumbled and took out a box from his pants pocket and held it in front of Seamu.

"Woo (that's it)!"

It was a sealed black metal box, with a streamlined concave and convex stripes on a high-tech surface, reminiscent of an integrated circuit, and gilded text on the top.

Mr. Seamus, who saw the real thing, let go of his hand and took the box over. And after noticing Seamo's movements, Kyosuke Takasaka immediately pushed forward with both hands so that his body could hold up.

At this time, Mr. Seamus had already opened the box through fingerprint verification at the bottom, and there was a piece of contact lens lying quietly in the transparent unknown liquid.

At this moment, a slight flush of unnatural blush appeared on Kyosuke Takasaka's face, and while Mr. Seamo's attention was not on him, he quickly changed a few breaths, adjusted his mood, and then introduced Seamu.

"This is a new product that we developed on the basis of the Bassard experiment, and the specific operation and configuration are similar to your previous contact lenses, relying on bioelectricity to maintain their operation, and 16 preset modes can emit and catch infrared rays.

Although the so-called glasses that can see infrared rays often appear in science fiction movies, it is a joke for the ignorant audience. Actually, as you know, usually infrared cameras will convert infrared light into visible light after receiving it, which is green.

In addition, the image is not clear, so it is difficult to be seen by ordinary optical instruments when emitting beams with infrared. Not to mention the naked eye.

And the purpose of this pair of eyes is not to let you see infrared light, but to take infrared light and translate it into binary bits, of course, the premise of correct translation is that you choose the right mode and angle. I don't need to say more about how to translate binary into text after that, right? ”

Mr. Seamus nodded, closed the lid casually, and looked at Kyosuke Takasaka with a serious expression of scrutiny, which made the latter a little uneasy.

"How... What's wrong? ”

Kyosuke Takasaka asked with some restraint, he was very worried about whether Seamus had found something.

"I already know the principle, but..." Mr. Seamu, who sighed lightly, lifted the text on the top cover of the box and said to Kyosuke Takasaka: "Why is this thing called the Evil King's True Eye!" ”

[What~ This is it! ] Yes! It scared the hell out of me! 】

Relieved, Kyosuke Takasaka activated his skill, which was 45 degrees diagonally upward, to avoid Mr. Seamo's gaze.

"What, you see, it can emit light, and it can also allow you to see the realm line that ordinary people can't see, so the first thing that the developers at that time thought of was the 'Evil King's True Eye'~ And the most important thing is that it is very handsome! Hey~"

Syllable!

"Hit someone! Hit someone! Deaf! Hit someone! ”

There was a voice in the infirmary of Kyosuke Takasaka, who had failed to sell moe, being ravaged tragically, because in Mr. Seamo's words, the "evil king" or something:

"Not halal at all!" (To be continued.) )