Encryption, an ancient art. During the ancient Roman war, the general sent a war report to the emperor, and he had to send a secret code that the enemy could not understand - the Caesar code of "three wrong backs" was born. The Yin Charm and Yin Book commonly used in the military in the pre-Qin period of the mainland are also a set of encryption methods.
When the wheel of history enters the age of the Internet, the complexity of cryptography is beyond Caesar's imagination, but it may be a technological revolution that will subvert the existing public cryptographic system - quantum computing, which goes beyond classical computing methods, and makes confidential communication a surprising footnote to the old adage that "the only thing that is certain is uncertainty".
Quantum communication, say goodbye to "eavesdropping"
In 1994, the Bank of England password needed to be set to 155 bits to ensure that it could not be deciphered.
Why are large numbers so hard to decompose? It's like we have a huge Lego castle in front of us, made of thousands of bricks of different colors. The combination of building blocks is so complex that no one can remember the location and color of each block at a glance. The process of decryption is like dismantling a huge castle, and it is a daunting task.
"In 1994, deciphering a 155-bit cipher required 20 years of continuous computing by the most advanced computers of the time. With a quantum computer, it takes only 0.3 seconds to decipher a code of this length. Long Guilu, vice president of scientific research at the Beijing Institute of Quantum Information Science and professor at Tsinghua University, said.
In the face of such a rapid code cracking by quantum computers, confidential communication naturally needs to be continuously upgraded if it wants to be "high".
"Classic confidential communication is like 'talking black' so that no one else can understand it. And quantum secure communication is like saying 'whispers' so that no one else can hear them at all. Long Guilu explained that there are two main types of quantum secure communication, one is to use the quantum state to generate the key, and the classical communication to transmit the encrypted information of the quantum key distribution, the advantage is the high transmission rate, the other is the quantum direct communication with the quantum state to directly transmit information, in case of eavesdropping, the quantum state can self-destruct to ensure information security.
Researchers work in the general control center of the quantum communication "Beijing-Shanghai trunk line" Photo by Liu Junxi
Taking advantage of the properties of quantum states, we can check and communicate while information is being transmitted. If there is a third party eavesdropping in quantum communication, both parties will be aware of it: because eavesdropping will cause the state of the quantum state to change, the receiver will take measures to protect the information in time if it finds an abnormality. That is, eavesdropping quantum communicators can neither hide eavesdropping nor steal any information.
Quantum telephony is not a myth
Landline, BP, Big Brother, Smartphone...... Over the past 30 years, you and I have witnessed the rapid development of means of communication. But people may not believe that quantum telephony with quantum key distribution technology has entered our lives.
"All you need is an Android phone in your hand and a quantum SIM card to make quantum calls. Zhang Tao, technical director of the call and quantum product line of China Telecom Quantum Information Technology Group Co., Ltd., said lightly.
Taking a mobile phone as an example, first of all, the mobile phone that can make a quantum phone transforms the dialing component of an ordinary mobile phone, and protects the identity authentication information of the caller through the quantum session key, so as to realize the identity authentication based on quantum encryption. The second is the built-in "quantum security middleware", which is used to mobilize the charging key of the quantum SIM card as an "outpost" for session key authentication and decryption.
Every time a mobile phone equipped with a quantum SIM card initiates a "quantum secret phone", a quantum key in the chip will be randomly selected to establish a connection with the background and verify the identity information. After the authentication is passed, a new key is generated as the session key in real time. The authentication key is distinguished from the session key and is discarded after use.
"Even if the key of this call can be cracked with a huge amount of calculations, the next time the key is new, the previous crack will be useless. End-to-end encryption ensures that the voice message of a call cannot be obtained by someone else, Zhang said. Of course, quantum secret calls require both the caller and the callee to replace the quantum SIM card.
Quantum-safe U shield product photo by Liu Junxi
Not only quantum phones, but also quantum text messages that are like "burning after reading" have also appeared. Zhang Tao showed the reporter the quantum text message he had just received from his colleague, a few emojis and a few greeting phrases on the right side, flashing a 60-second countdown. When "01:00" becomes "00:00", memes and greeting phrases instantly disappear.
How far from "quantum freedom of communication".
In order for quantum communication to be applied on a large scale, it must pass the threshold of signal loss over long distances. Since 1984, when the American physicist Bennett began to explore the application of quantum communication, the industry consensus is to first use optical fiber to build a network in the city, and then use the relay to realize the connection between cities, and realize longer-distance quantum communication through satellite relay.
What is the key? Long Guilu said in one sentence: "We need to form a quantum network. However, there is no "practical version" of the quantum relay devices needed to build a quantum network.
Long Guilu, vice president of scientific research of Beijing Institute of Quantum Information Science, introduced the research results
It is gratifying to note that it has become a reality to build a trusted relay quantum network with the help of classical relays. Translated, this process is equivalent to the signal being transmitted over a certain distance through quantum direct communication (currently 50-100 kilometers is no problem), to a place called "relay", where the ciphertext is first converted into a classical signal, and then converted into a new quantum signal, starting the next "relay" of quantum direct communication until the recipient receives it.
In addition, classic cipher encryption can be used to further strengthen the security of the signal at the relay.
"If you use the analogy of mailing letters, classic encryption is to write letters in cipher. Long Guilu explained that quantum direct communication is like a mail car with a closed carriage, and the classic relay is the letter transfer station. Documents written in cipher are transmitted in a closed mail car, which is then forwarded to the next mail car at a transit station. "At the time of handover, people only see the code, not the 'true face' of the document. Only the last recipient can read the code and decrypt the file. ”
Today, the second-generation quantum direct communication prototype has a communication rate of kilobits per second, which can achieve stable image and text transmission. Long Guilu and other scientists have initially built a quantum direct communication network for secure relay in the laboratory, which has developed from "one-to-one" communication to multi-person "group chat". The next effort is to focus on wide-area end-to-end secure relay quantum networks, which are expected to support a variety of applications.
Researchers from the Beijing Institute of Quantum Information Science are working in the laboratory
Quantum technology is advancing day by day, and the Long Guilu team has set their sights on space. Soon, direct quantum communication will not only be limited to terrestrial fiber optic networks, but direct quantum dialogue between space and earth will also become possible. Perhaps by then, "quantum communication freedom" will no longer be far away.
Source: Half Moon Talk