Does anyone know the development of cryptography in ancient times, please?

Cryptography is the study of the preparation of codes and codebreaking technical science. The study of the objective law of the change of the code, applied to the preparation of the code in order to keep the secret of communication, known as coding; applied to the deciphering of the code in order to obtain the communication intelligence, known as deciphering, the general name of cryptography.

Code is an important means of communication between the two sides according to the agreed laws of special transformation of information. According to these laws, change the plaintext for the ciphertext, known as encryption transformation; change the ciphertext for the plaintext, known as decryption transformation. Passwords in the early days of text or digital only for encryption and decryption transformation, with the development of communications technology, voice, image, data, etc. can be implemented to encrypt and decrypt the transformation.

Cryptography is in the struggle between encoding and deciphering practice gradually developed, and with the application of advanced science and technology, has become a comprehensive and cutting-edge technical science. It has a wide and close connection with linguistics, mathematics, electronics, acoustics, information theory, computer science and so on. Its real-life research results, especially governments now use the preparation of codes and deciphering means are highly confidential.

The law of explicit and secret transformation is called the system of cipher. The parameters that indicate this transformation are called keys. They are an important part of cryptography. The basic types of cipher system can be divided into four types: Misconfiguration - changing the position of plaintext letters or digits, etc. to become ciphertext in accordance with the prescribed patterns and lines; Substitution - replacing plaintext letters or digits, etc. to ciphertext with one or more substitution tables; Cipher text -- with pre-programmed letters or numbers of the cipher group, instead of a certain phrase words, etc. to change the plaintext for the ciphertext; plus chaotic -- with a limited number of elements composed of a string of sequences as a chaotic number, according to the prescribed algorithm, with the combination of the plaintext sequence into the ciphertext. The above four cryptographic systems, can be used alone, can also be used in combination, in order to develop a variety of very high complexity of the practical password.

Since the 1970s, some scholars have proposed a public key system, that is, the use of one-way function of the mathematical principles, in order to achieve the separation of encryption and decryption keys. The encryption key is public and the decryption key is secret. This new cryptographic system has attracted extensive attention and discussion in the cryptographic community.

Using the laws of text and cipher, under certain conditions, take various technical means, through the analysis of the intercepted ciphertext, in order to obtain the plaintext, restore the cipher preparation, that is, deciphering the cipher. Deciphering passwords of different strengths requires different, or even very different, conditions.

The means of secret communication in ancient China already had some prototypes close to ciphers. Song Zeng Gongliang, Ding Du and other compilers of "martial arts" "word test," recorded that in the early Northern Song Dynasty, in combat, there was a pentameter poem of 40 Chinese characters, respectively, representing 40 kinds of situations or requirements, this approach has already had the characteristics of the system of the secret book.

In 1871, the Shanghai Dabei Waterline Telegraph Company chose 6,899 Chinese characters to be substituted for four-code numbers, which became China's first commercialized plain-code book, and at the same time, it also devised a method of rearranging the plain-code book into a secret book and adding chaos. On this basis, it was gradually developed into a variety of more complex ciphers.

In Europe, in 405 B.C., the Spartan general Lysander used the original misplaced code; in the first century B.C., the Roman Emperor Julius Caesar used the orderly single table instead of the code; and then it gradually developed into the secret book, multi-table instead of the code system, such as adding chaos.

In the early twentieth century, the first practical mechanical and electric ciphers were produced, and at the same time, commercial cipher machine companies and markets appeared.

After the sixties, electronic ciphers have been developed faster and widely used, which has made the development of the cipher enter a new stage.

Cipher decipherment was created and developed gradually with the use of ciphers.In 1412, the encyclopedia compiled by the Persian Qalqashandi contained methods for deciphering simple substitutes for ciphers. By the end of the 16th century, some European countries had full-time decipherers to decipher intercepted secret messages. In 1863, Prussian Kassisky wrote "Cipher and Deciphering Techniques", and in 1883, French Kirkhoff wrote "Military Cryptography" and other works, all of which made some discussions and explorations on the theory and method of cryptography, and in 1949, American Shannon published "Communication Theory of the Secret System", which analyzed some basic problems of cryptography by applying the principle of information theory. In 1949, the American Shannon published the article "The Communication Theory of Secret Systems", which analyzed some basic problems in cryptography by applying information theory principles.

Since the 19th century, due to the widespread use of telegraphy, especially wireless telegraphy, the interception of coded communications and third parties have provided extremely favorable conditions. The secrecy of communications and the detection and decipherment of the formation of a very fierce struggle on the hidden front.

In 1917, Britain deciphered the telegram of German Foreign Minister Zimmermann, which led to the declaration of war against Germany by the U.S. In 1942, the U.S. learned from the deciphering of the Japanese navy's secret message the Japanese army's intention and deployment of troops in the Midway area, so that it could break the Japanese navy's main force with inferior troops and reverse the war situation in the Pacific. In the defense of the British Isles and many other famous historical events, the success of the code-breaking have played an extremely important role, these examples also from the reverse side of the cryptographic confidentiality of the important status and significance.

Today's governments of the world's major countries attach great importance to cryptographic work, some set up huge organizations, allocate huge sums of money, tens of thousands of experts and scientific and technological personnel, and invest in a large number of high-speed electronic computers and other advanced equipment for the work. At the same time, the private sector and the academic community also pay more attention to cryptography, many mathematicians, computer scientists and experts in other related disciplines are also involved in cryptography research ranks, and accelerated the development of cryptography.

Nowadays, cryptography has become a separate discipline. Traditionally, cryptography is the study of how to convert information into a hidden way and prevent others from getting it.

Cryptography is an interdisciplinary subject that derives from many fields: it can be seen as information theory, but uses a large number of tools from the field of mathematics, well known such as number theory and finite mathematics.

The original message, the one that needs to be protected by a cipher, is called plaintext. Encryption is the process of converting the original message into an unreadable form, also known as a cipher. Decryption is the reverse process of encryption, where the original message is obtained from the encrypted message. cipher is the algorithm used in encryption and decryption.

The earliest ciphers required only pen and paper and are now known as classical cryptography. Its two main categories are substitution cryptography, in which the order of letters is rearranged, and substitution cryptography, in which one set of letters is replaced with other letters or symbols. Information in classical cryptography is susceptible to statistical attack; the more information there is, the easier it is to crack, and using analytical frequencies is a good way to do this. Classical cryptography is still alive and well, often appearing in mind games. In the early twentieth century, a number of mechanical devices were invented for cryptographic use, including the rotary machine, most notably the Enigma, a cipher machine used in World War II. The ciphers produced by these machines made cryptanalysis considerably more difficult. For example, a variety of attacks against the Enigma were successful only after considerable effort.