The word "overview of military science, shooting, ballistics, internal ballistics, external ballistics, intermediate ballistics, terminal ballistics, missile ballistics, military geography, military topography, military engineering, military meteorology, military medicine, military operational research, warfare, cryptography, and cryptography of chemical warfare" logos from the Greek word ". And its use can be traced back to about four thousand years ago. In the year 2, the Egyptians carved a memorial on a tombstone. After that, people used to write on paper to send secret messages. In World War II, cryptography played an important role. Many people believe that the Allies won the war entirely because of the digital computer invented in World War II to crack the German and Japanese passwords. In 1949, Shannon put forward the first paper to discuss the communication theory of cryptographic systems. Modern cryptography can be said to have originated in Sri Lanka. Until 1975, Diffie and Hellman put forward the concept of public key cryptosystem, and the research direction of modern cryptography officially broke away from the pattern of secret key cryptosystem and flourished, which has been nearly 2 years. Up to now, there are two kinds of cryptographic systems. The first type is Symmetric Key cryptosystem, and the second type is asymmetric key cryptosystem. First of all, cryptography is studied by hippies on the World Wide Web, and it involves key transmission. The' 6s? 6? 8 ask the security guard to transfer the key; At the beginning of 7' s, it was discovered that this method was not easy to distinguish, and it was time-consuming and time-consuming. In 1965, the Department of Electrical Engineering of Stanford University in the United States-Merkel, Duffy and Herman-studied cryptography, but unfortunately they did not find it. In addition, Cerna, a secret organization of the British Communications Electronic Security Group (CESG), found the password-reduction type, but it cannot be made public because it belongs to a secret organization. It was not until 1977 that Reeves, a graduate student at the Massachusetts Institute of Technology, discovered a formula similar to Celmen's. They set up RSA Security Company (RSA is the prefix of their name), which is now worth $2.5 billion, and has played a great role in transmitting credit cards. RSA has installed 5 million sets of products. The small lock under IE and Netscape is RSA's product. The first discovery of mathematics hanging pin was not America, but? Was the first to be made public. Mathematical padlocks are easy to lock and difficult to restore, so they are widely used, that is, information coding is confidential. General example of mathematical padlock: one-way type for mathematical padlock: n = pxq <; -example n (composite number) = multiplication of two prime numbers 11x17=187=N reduction one-way formula: C=Me(mod N) *e is the number of m, Because I can't type * M*13*(mod 187)=C *13 is the number of m * c = 165x = 88 (password kiss) 88 * 13 * (mod 187) = 165 * 13 is the number of 88 * modn = m c * 1/e * mod (p = 88c = 165p = 11q = 17Answer: mod 187 = 88 Generally, two types of cryptography are used: symmetric key and public key (also called asymmetric key) cryptography. Give a simple example of symmetric key cryptography. Suppose you receive a notice from a friend. You and your friend agree to encrypt and decrypt your message. You will use the following algorithm: each letter will move up by three letters, for example, A=C, B=D, while Y and Z turn around and return to A and B. This equation ("three letters move up each letter") is the key used by the sender to encrypt the message; The receiver uses the same key to decrypt the message. No one can read the message without the key. Because the same key is regarded as practical to encrypt and decrypt the message, this method is a symmetric key algorithm. This kind of cryptography is known as secret key cryptography, because this key must be kept in secret between the sender and the receiver. To protect the integrity of data. Asymmetric cryptography Asymmetric or public key cryptography is different from symmetric cryptography in that its encryption key is only suitable for a single user. The key is divided into two parts: a private key, which only the user has. An public key can be publicly issued and distributed. Get it as long as it is required. Each key generates a function that is used to change the text. The private key generates a function that changes the text privately, while the public key generates a function that changes the text publicly. These functions are inversely related. For example, if a function is used to encrypt messages, The other function is used to decrypt the message. It doesn't matter what the order of the text functions is. The advantage of the public key system is that two users can communicate safely without exchanging secret keys. For example, suppose a sender needs to send a message to a recipient, and the confidentiality of the message is necessary, and the sender encrypts it with the recipient's public key. Only the private key of the recipient can decrypt this information. Public key cryptography is very suitable for providing authentication, integrity and undeniable services, all of which are digital signatures as we know them. Cryptography related to the two basic principles of website cryptography can be divided into two types: displacement and substitution. Shifting method is to change the order of the characters in the message according to certain rules. This method can show its advantages when the number of characters is large. For example, "Hello World" can have 117834914358 arrangements with only 1 letters. Another method, substitution method, can also be divided into two types, one is word substitution and the other is letter substitution. The principle of the two methods is the same, that is, the original article is changed by using the correspondence of the relative order of words. For example, we can move the English letters back three places. Namely: ABC D E F G H I J K L M N O P Q R S T U V X Y Z D E F G H I J K L M N O P Q R S T U V W X Y Z A general example: Hello World How Are You Khor Zuog Krz. Duh brx's sentence becomes illegible, and if there is an agreement between the sender and the receiver, you can also delete the blank space between the words. Anyway, when you translate it back, you can guess the timing of sentence break by the meaning of the sentence. The word substitution is to replace each word with another corresponding word, so as to rewrite the original text and turn it into an encrypted file whose meaning cannot be recognized. Of course, there is not only one shift method, but there are 25 different methods regardless of the case of English letters. Each encryption method can be regarded as an encryption method, which we call the combination of algorithm and a KEY. The key is used to specify the calculation details of the encryption program. Take the shift method as an example. The algorithm only replaces the letters in the plaintext letter set with the letters in the cipher letter set, and the key is the cipher letter set defined by the sender and receiver. In the whole process of cryptography development, it is very important to identify and find new algorithms and protect keys from being discovered by decryptors, because even if the algorithms are the same or too simple, it is still difficult for us to crack encrypted files without encryption keys. If English letters are exchanged letter by letter instead of translation, regardless of case, there are 432914611266565584 different keys that must be tested to get the original plaintext. Application of Cryptography 1. Digital Signature: This is an electronic signature generated by cryptography according to the content of EDI message and the sender's Private Key. No one can generate the signature unless he has the private key, so it is much safer than handwritten signature. The receiver verifies the digital signature with the sender's public key. 2. Digital Envelope: This is a cryptographic method in which some confidential information is encrypted by the public key of the recipient, and then decrypted by the recipient's private key to read the confidential information. No one can decrypt the encrypted message except the person who owns the private key, just like those materials are packed in a strong envelope, and no one can open the envelope except the recipient. 3. Secure receipt: The reply information calculated by the receiver according to the content of the message is digitally signed by the receiver's private key and sent back to the sender, which not only ensures that the content of the message received by the receiver is correct, but also enables the receiver to deny that it has received the original message. 4. Security authentication: After generating their own public key, everyone applies for registration with a public security authentication center, and the authentication center is responsible for issuing Certificate to ensure the correspondence and correctness of personal identity and public key. Quantum cryptography (Jennewein et al., Quantum cryptography with angled photonics, physical review letters, May 15, 2, Vol 84, ISS 2, pp.4729-4732) proved for the first time that it is feasible to construct passwords by using quantum ghost characteristics. This study provides a way to prevent computer hackers from committing crimes in the future. In this latest-and safest-data encryption and decryption architecture (that is, quantum cryptography), researchers use a pair of angled photons, and even if the particles are separated by a long distance, they still have close interaction. entanglement-based quantum cryptography has unique transmission characteristics that cannot be eavesdropped. If an eavesdropper wants to steal data, it can be easily detected. In short, the entanglement process can establish a complete and random sequence of s and 1s to provide data transmission for both users. If a hacker extracts data from it, this message sequence will be changed, and the user will find the eavesdropper and authorize to give up the eavesdropped data. This digital random sequence, Or "golden key", and then calculate with the data (such as exclusive or gated XOR), that is, the encryption program, so that this data string forms a completely random sequence. This method is known as one-time pad cipher. Similarly, the receiver also relies on the golden key to decrypt the program. In the study, Los Alamos researchers simulated an eavesdropper to steal the transmitted data. It was successfully detected and authorized the user to give up the stolen data. In Australia, the research team established a kilometer-long optical fiber to connect two completely independent transmissions and receiving stations to verify the entangled cryptography theory. They established the golden key and successfully transmitted Venus images. At the same time, more than several kilometers of optical fiber were built in the University of Geneva team. In these experiments, although their transmission rate is slow, entanglement-based cryptography theory is likely to surpass non-entangled quantum cryptography theory in the future, not only in terms of transmission rate, but also in terms of preventing data from being stolen.