History of cryptology

History of cryptology

10B1 조형우

    Cryptography is derived from combination of two ancient Greek Words krypto meaning hidden and grafo meaning to write. Therefore the literal meaning of cryptology is “hidden writing” which is crucial tool for secure communication. Nevertheless, the first intention of the cryptography was not related to concealing the message, it was utilized to decorate tombs to make one’s life seem noble in Egypt, around 2,000 B.C. Cryptology have started from decoration but it developed and started to function as a tool to conceal messages. This history of cryptology is widely classified in three eras: from ancient civilizations to 1940s, around Second World War, after Second World War to modern society.

   

Cryptography was used for mainly three purposes in the ancient society which is private communications, delineation of religion and secure communication for military. The most important function in the ancient period was delineation of religion and decoration of tombs. For example, in the Book of Jeremiah, a few English words transformed into other English words: "hob"="sly", "hold"="slow", "holy"="slob", "horn"="slim", "zoo"="all", "irk"="rip", "low"="old", "glow"="told, and "grog"="tilt". Furthermore, it was sometimes used for secrete communications such as Caesar cipher which was used for politic purpose. This was a method shifting alphabet three positions so that e 'a' is transformed into 'd', 'f' into 'i', 'z' into 'c'. For example, if there is a word “Term paper” it will be enciphered to “Whuo SdShu”. So, the plaintext would be term paper, ciphertext would be whuo sdshu and the key would be shifting alphabet for three positions. Even though this technique might be seen easy to decipher, majority was not able to read such codes in the time of Julio Caesar which made cipher powerful. After Caesar cipher the development of cryptology was unnoticeable. Nevertheless the French diplomat Blaise de Vigenère have developed polyalphabetic cipher in 16^th century. This cipher has been called “the unbreakable cipher” and actually has been unable to be broken for the four centuries. It has been deciphered by numerous researchers between the end of the 19^th century and the beginning of 20^th century. Another important, more modern, substitution cipher in the history of cryptography was The Hill cipher, a polygraphic substitution cipher. It was the first cipher which enabled use more than two symbols for a word.  Instead of substituting one letter for another letter, a polygraphic cipher one can substitute a word by more than a two group of words. This has made frequency analysis (a technique based on the fact that inside a text certain letters and combinations of letters occur with varying frequencies). attack ineffective since a word could be substituted by various words.

   

As time passed, when it became Second World War, people began to recognize the importance of machine in cryptography since machine was capable of making cipher more complicated and also easier to create cryptography. Therefore, Germans have made enigma machine which have played significant role win Second World War, which was used to encrypt and decrypt the cipher. As the war continued, however, allies were able to decrypt the cipher so that they could receive information about Germany. Therefore, some people believe that deciphering enigma was one of the main reasons of ally’s victory. As a result cryptography has played a significant role in the World’s History.

 

After Second World War, modern cryptology starts with the work that Claude Shannon have done during Second World War. He established the robust basis of cryptography by introducing the term called confusion and diffusion. First, confusion is a skill making the relationship between the key and the ciphertext complicated. On the other hand, diffusion is a skill spreading the influence of the plaintext over numerous ciphertexts. After introduction of two skills there were not significant developments at the beginning of the 1970s. However, in the mid 1970s there have been two major developments in the history of cryptography.  The first was the development of Data Encryption Standard by IBM which was used to develop secure electronic communication. Even though DES itself was not powerful enough, the alternatives made by using similar method was powerful enough to guarantee people secure communication. The second major development was development of new process, distributing cryptographic keys. It has raised the level of cryptography significantly since it have introduced asymmetric key algorithm to the world. Asymmetric key algorithm enables decrypting and encrypting key different. Therefore, we can designate one key of the pair as one private key and one public key(visible) so that no secure channel is needed for key exchange. So long as the private key stays secret, the public key can be widely known for a very long time without compromising security. In modern society, this is the ultimate version of the cryptography used in real life such as digital signatures and online purchasing.