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An Introduction to Cryptography

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November 9, 2023


Cryptography refers to the practice and study of hiding/coding information in order to ensure that only the intended person can access it, preventing third parties from reading private messages. The development of cryptography has roughly gone through three stages: classical cryptography, modern cryptography, and contemporary cryptography.


History of Cryptography


In the era of classical cryptography, information hiding mainly relied on the confidentiality of algorithms. During the Greek era, tribal leaders wrote information on the scalp of slaves and concealed it through their hair, achieving secure transmission of information between tribes. During the ancient Roman period, Gaius Julius Caesar invented the Caesar cipher, which achieved information hiding through letter shifting and was applied on the battlefield. During the Shang and Zhou dynasties, Jiang Ziya invented the "Yin Fu", which represented different battlefield information through the length of the fishing rod. During the Ming Dynasty, Qi Jiguang invented the “Fan Qie” code, which used a traditional method of indicating the pronunciation of a Chinese character by using two other Chinese characters to encode information.


Modern cryptography refers to the cryptographic technology that emerged during the period from World War I and World War II to 1976, mainly represented by Enigma designed by Arthur Scherbius of Germany in 1919. It combines mechanical and electronic systems, making Germany's secure communication technology at the forefront of that time.


With the advent of computers, this simple, easy-to-break design pattern can no longer meet the requirements for secure communication. In 1883, Kerckhoffs proposed that the security of a cryptographic system should not depend on immutable algorithms that are not easy to change, but on keys that can be changed at any time. In 1949, Shannon[1] published the classic paper A Mathematical Theory of Communication", which truly made cryptography a science. In 1976, Diffie and Hellman[2] first proposed the concept of public key cryptography in "New Directions in Cryptography", which provided new guidance for the subsequent development of cryptography and entered the modern cryptography stage.



Figure 1: A Brief History of Cryptography Development


What is Cryptography?


Cryptography originates from the Greek Krypt ó s (hidden, secret) and Gráphen (writing). It mainly studies how to carry out confidential communication in an insecure environment. To this end, cryptographers have designed a series of cryptographic algorithms, including symmetric cryptographic algorithms such as AES and SM4, and asymmetric cryptographic algorithms such as RSA and SM2.


Nowadays, the application of cryptographic technology has penetrated into every aspect of our lives. Therefore, understanding basic cryptography knowledge can not only broaden one's horizons, but also better protect personal information.


Stay tuned for more blog articles about the amazing world of cryptography!


[1] Shannon C E. Communication Theory of Secrecy Systems [J]. Bell System Technical Journal, 1949, 28(4): 656-715

[2] Diffie W, Hellman M. New Directions in Cryptography [J]. IEEE Transactions on Information Theory, 1976, 22(6): 644-654

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