A little beyond the powers of the average hacker Creating unbreakable ciphers using the basic principles of mechanics
The quantum
New York Times
Seventy years ago, Albert Einstein and other scientists tried to prove that quantum mechanics, the strange laws that describe the world of the smallest things, is wrong. Among other things, Einstein proved that, according to quantum mechanics, the measurement of one particle can instantly change the properties of another particle, regardless of how far they are from each other. He believed that this operation, which is done remotely and is called "entanglement", is too absurd to exist in nature and conducted complicated experiments to show the strange consequences such a phenomenon could have.
But studies documented in three articles recently published in the journal "Letters Physical Review" show how wrong Einstein was. The experiments not only indicate that the interlacing phenomenon does occur, something that has been known for some time, but also that it can be used to create unbreakable ciphers to secure information. "At first it seemed like pure philosophy," said Prof. Nicolas Giessen, a physicist at the University of Geneva, one of the authors of one of the studies. "We are now investigating whether those strange aspects of quantum mechanics may help secure the Internet network, for example."
The strange occurrence called "intertwining" can be compared to a situation in which two coins, which are on both sides of the earth, are repeatedly tossed at the same time, and each time fall on the same side - either on a "tree", or on a "peli". Coins of course do not behave like this; Quantum particles yes.
The interweaving phenomenon makes it possible to completely prevent eavesdropping and interpretation of information transmitted in the code, because every measurement of one of the transmitted particles - and an attempt to eavesdrop is actually a measurement - leaves its mark on the particle associated with it. That is, if someone tries to eavesdrop they will be detected immediately, no matter how technically sophisticated they are.
This guarantee for the safe transfer of information makes it possible to develop unbreakable ciphers while using the basic principles of quantum mechanics. This method is known as quantum encryption. It is completely different from all the existing encryption methods, whose developers go to great lengths to make them mathematically very complicated and therefore very difficult to crack. But even the most complicated encryption methods can, at least theoretically, be cracked. "The advantage of quantum encryption is that none of this should bother you anymore," said Dr. Paul Kvyat, co-author of one of the articles. "If you do it right, you're only limited by the laws of quantum physics." And Thomas Jenwein of the University of Vienna, the lead author of another paper, says that turning the theoretical ideas into available technology is no longer unthinkable: "We have created a complete quantum encryption system, almost ready to use."
All three teams relied on photons to create the ciphers, but their methods differed. Janewayne and his colleagues built a system that creates quantum ciphers and used them to encrypt a binary chain of 0's and 1's representing a digital color image. Then they sent the encrypted image over a regular computer network - the technique usually used - and displayed it on the other side. Dr. Kvyat's team managed to catch an eavesdropper who tried (for the purpose of the experiment) to initiate quantum communication, and showed that it is indeed impossible to do this without being detected. Professor Zeisen and his partners have built a system that may fit into existing communication systems.
As Einstein discovered, the most difficult thing about quantum theory is to make yourself believe that it actually exists in reality. According to quantum mechanics, particles have no absolute properties until they are observed or measured. By the time they are measured, particles can have a potential existence in two or more places at the same time. From the moment the measurement is made, the particle has an actual existence in only one of these points; The other option is eliminated.
This principle applies, among other things, to the polarization of a photon, the quantum carrier of light: the photon can vibrate both horizontally and vertically, or at two different diagonal angles, until it is measured. As soon as the photon encounters filters that only allow a photon with a certain polarization to pass (sunglasses are based on a similar principle), the photon's polarization becomes known and absolute. When two photons are entangled and one is measured and has horizontal polarization, the other photon will also have horizontal polarization. Correspondingly, if its polarization is vertical, the polarization of the second photon will also be vertical.
The essence of quantum encryption is to create such pairs of photons and send them to two people, traditionally called Alice and Bob, who wish to create and share a secret cipher. Bob and Alice, who are in two different places, receive a large amount of photons - every photon that Bob receives has a partner at Alice. Bob and Alice have a device that checks the polarization of each photon: is it horizontal or vertical. The measurement works so that only if the photon is, say, horizontal, will Bob and Alice get an answer. If the photons are polarized in a different direction, it is guaranteed that neither Alice nor Bob will have an answer.
After Bob and Alice have collected enough photons for their cipher, they call on an unsecured phone and reveal to each other what their question was—in this case, whether the polarization of the photon is horizontal or vertical—for each photon that passed through the device. Then they use only the results they got for the photons for which they both asked the same question. They don't reveal, of course, whether they received an answer or not. They don't have to do that. Thanks to the interweaving phenomenon, they know that they both received the same answer for the same question.
The results are then translated into a code: each answer is represented by the number 1; each non-answer to 0. The order, known only to Bob and Alice, becomes a code.
And what if an eavesdropper, commonly known as Eve, tries to measure the polarization of the photons? Bob and Alice can find this out by comparing some of their measurements. If they are not the same, it means that the interlacing phenomenon has been interrupted, that is, someone tried to eavesdrop.
New York Times {appeared in Haaretz newspaper, 16/5/2000{
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