Who knows the history of cryptography?

Cryptography (in Western European languages, it comes from the Greek words kryptós "hiding" and gráphein "writing") is a subject that studies how to secretly transmit information. In modern times, especially the mathematical research on information and its transmission is often regarded as a branch of mathematics and computer science, and it is also closely related to information theory.

Ron Rivest, a famous cryptographer, explained: "Cryptography is about how to communicate in the presence of enemies", which is equivalent to seeing the similarities and differences between cryptography and pure mathematics from the perspective of self-engineering. Cryptography is the core of information security and other related issues, such as authentication and access control. The main purpose of cryptography is to hide the meaning of information, not the existence of information.

Cryptography also promotes computer science, especially technologies used in computer and network security, such as access control and information confidentiality. Cryptography has been applied in daily life, including ATM chip cards, computer users' access passwords, e-commerce and so on.

Cryptography is an important secret means for communication parties to convert special information according to agreed rules. According to these laws, changing plaintext into ciphertext is called encryption transformation; Turning ciphertext into plaintext is called decryption transformation. In the early days, passwords only changed the encryption and decryption of characters or numbers. With the development of communication technology, voice, image and data can be encrypted and decrypted.

Cryptography is gradually developed in the practice of the struggle between encoding and decoding, and with the application of advanced science and technology, it has become a comprehensive frontier technology science. It is closely related to linguistics, mathematics, electronics, acoustics, information theory and computer science. Its actual research results, especially the encryption and decoding methods used by governments all over the world, are highly confidential.

The law of secret conversion is called cryptosystem. The parameter indicating this conversion is called the key. They are an important part of cryptography.

The basic types of cryptographic systems can be divided into four types: scrambling according to prescribed figures and lines, changing the position of plaintext letters or numbers to become ciphertext; Replacement-replacing plaintext letters or numbers with ciphertext by one or more replacement tables; Codebook-Converts plaintext into ciphertext by replacing certain phrases and words with pre-programmed alphanumeric cipher sets.

Scrambling-a series of finite elements are used as random numbers, which are combined with plaintext sequences according to the specified algorithm to form ciphertext. The above four cryptographic systems can be used separately or mixed to compile various practical passwords with high complexity.

Since 1970s, some scholars have proposed public key system, that is, using the mathematical principle of one-way function to realize the separation of encryption and decryption keys. The encryption key is public and the decryption key is confidential. This new cryptosystem has attracted extensive attention and discussion in the field of cryptography.

Based on the laws of characters and passwords, under certain conditions, by analyzing the intercepted ciphertext, plaintext can be obtained, and the password can be restored, that is, the password can be cracked. Deciphering passwords with different strengths requires different conditions, even very different.

In fact, in BC, secret letters were used in war. Herodotus, the father of western historiography, recorded some of the earliest secret stories in history. In the 5th century BC, in order to resist slavery and aggression, the Greek city-states had many conflicts and wars with Persia.

In 480 BC, Persia secretly assembled a powerful army and launched a surprise attack on Athens and Sparta.

Greek Demaratus saw the rally in Susa, Persia, conveniently covered the words on the board with a layer of wax, and sent it to Greece and Persia to inform them of the plot. Finally, the Persian navy was destroyed in Salamis Bay near Athens.

Because most people in ancient times could not read, the earliest form of secret writing was only pen and paper or equivalent. With the improvement of literacy rate, real cryptography is needed. The two most classic encryption technologies are:

Transposition password: rearrange the alphabetical order, such as' help me' becoming' ehplem'.

Substitution cipher: systematically replace a group of letters with other letters or symbols, for example,' fly at once' becomes' gmz bu podf' (each letter is replaced by the next letter).

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Xidian university cryptography, as the main subject of information security, ranks first in China.

1959, instructed by Qian Xuesen, xidian university took the lead in developing cryptography research in China. 1988 Xidian took the lead in offering a master's degree in cryptography, and 1993 was allowed to offer a doctoral degree in cryptography. It is one of the two earliest doctoral programs in cryptography in China, and it is also the only doctoral program outside the military. 1997, Changjiang scholars began to set up.

200 1 offers information security specialty on the basis of cryptography, which is the first batch of universities in China to offer this specialty.

Xidian university Information Security Specialty is established by relying on the national first-class key discipline "Information and Communication Engineering" (the second in China) and the national second-class key discipline "Cryptography" (the first in China). It is the innovation platform of 985 engineering advantage discipline and 2 1 1 engineering key construction discipline.

It has several national, provincial and ministerial research platforms, such as the State Key Laboratory of Integrated Service Network Theory and Key Technologies, the National Engineering Laboratory of Wireless Network Security Technology, the Research Center of Modern Switching and Network Coding (Chinese University of Hong Kong-xidian university), the Key Laboratory of Computer Network and Information Security, and the Key Laboratory of Electronic Information Countermeasure, Attack and Defense and Simulation Technology of the Ministry of Education.

Among the 34 directors of China Cryptography Society, Xidian holds 12, and both vice presidents graduated from Xidian. China's only member in the International Cryptography Society is also from Xidian. It is no exaggeration to say that Xidian has become the core base for cultivating talents in cryptography and information security in China.

The following is a brief introduction of some graduates of Xidian: Lai, member of the International Cryptography Society and designer of the IDEA block cipher algorithm; Chen Lidong, a researcher at the American Bureau of Standards; Ding Cunsheng, Professor, Hong Kong University of Science and Technology; Xing Chaoping, Professor NTU, Singapore; Feng Dengguo, Director of National Laboratory of Information Security of China Academy of Sciences and Vice Chairman of China Cryptography Society.

Zhang, executive director of China Cryptography Society, professor and president of Wuhan University; He, Vice Chairman of China Cryptography Society, Professor and President of Southwest Jiaotong University; He Liangsheng, chief cryptographer of the General Staff of China People's Liberation Army; Ye Qing Ji, Director of Key Management Center of China People's Liberation Army.

Xidian university has three China leaders in the field of information security: Xiao Guozhen, Wang Yumin and Wang Xinmei. Among them, Professor Xiao Guozhen is one of the main pioneers of modern cryptography research in China. His concept of statistical independence of combination function and the spectral characteristic theorem of correlation immunity of combination function are called Shaw-Marcy theorem internationally.

He has become one of the basic tools of cryptography research and opened up a new field of stream cryptography research. He is a member of the Executive Committee of the Cryptographic Society of Asia, a vice chairman of the Cryptographic Society of China and an advisor to the editorial board of IJIS.

In 200 1 year, WAPI, a mandatory standard for wireless network security, led by xidian university, shocked the whole world. China has completely independent intellectual property rights of this technology, breaking the monopoly of American IEEE in the world. The Wall Street Journal reported at that time that "China's encryption standard for wireless technology caused panic in the industry".

This technology is also one of the few major scientific and technological advances that China has made in the IT field with world influence.

Xidian university's information security major ranks first in the country for many years in a row, which is the best embodiment of the school's leading position in the field of national information security.

Baidu encyclopedia-cryptography