/kloc-since the 0/9th century, the widespread use of telegrams, especially wireless telegrams, has provided extremely favorable conditions for cryptographic communication and third-party interception. Communication secrecy and detection and decoding have formed a hidden front with fierce struggle.
19 17, Britain deciphered the telegram of German Foreign Minister Qi Merman, which prompted the United States to declare war on Germany. 1942, the United States learned the Japanese army's operational intention and deployment of troops in midway from deciphering the Japanese navy's secret report, so as to break the main force of the Japanese navy with inferior forces and reverse the war situation in the Pacific region. In many famous historical events such as defending the British Isles, the success of password cracking has played an extremely important role. These examples also illustrate the important position and significance of password secrecy from the opposite side.
At present, the governments of major countries in the world attach great importance to cryptography. Some of them have established huge institutions, allocated huge funds, concentrated tens of thousands of experts and scientific and technological personnel, and invested a lot of high-speed computers and other advanced equipment in their work. At the same time, private enterprises and academic circles pay more and more attention to cryptography, and many mathematicians, computer scientists and experts in other related disciplines have also devoted themselves to the research of cryptography, which has accelerated the development of cryptography.
Now cryptography has become an independent discipline. Cryptography in the traditional sense is to study how to transform information into a hidden way to prevent others from obtaining it.
Cryptography is an interdisciplinary subject, which comes from many fields: it can be regarded as information theory, but it uses tools in many mathematical fields, such as number theory and finite mathematics.
Original information, that is, information that needs password protection, is called plaintext. Encryption is the process of transforming the original information into an unreadable form, which is a password. Decryption is the reverse process of encryption, and the original information is obtained from the encrypted information. Password is an algorithm used for encryption and decryption.
The earliest steganography only needed pen and paper and encryption to rearrange the order of letters; Replace encryption and replace a group of letters with other letters or symbols. The information of classical encryption methods is easily cracked by statistics. The more information, the easier it is to crack. It is a good method to use analysis frequency. Classical cryptography has not disappeared, and it often appears in intelligence games. At the beginning of the 20th century, some mechanical devices were invented for encryption, including the rotary wheel machine, the most famous of which was Enigma, a cipher machine used in World War II. The passwords generated by these machines greatly increase the difficulty of password analysis. For example, all kinds of attacks on Ingmar were successful only after considerable efforts.