Cryptography is one of the oldest fields of technical study we can find records of, going back at least 4 000 years. Ciphering has always been considered vital for diplomatic and military secrecy. Cryptography probably began in or around 2000 B.C. in Egypt, where hieroglyphics were used to decorate the tombs of deceased rulers and kings. These hieroglyphics told the story of the life of the king and proclaimed the great acts of his life. They were purposefully cryptic, but not apparently intended to hide the text. Rather, they seem to have been intended to make the text seem more regal and important. As time went by, these writings became more and more complicated, and eventually the people lost interest in deciphering them. The practice soon died out. The ancient Chinese used the ideographic nature of their language to hide the meaning of words. Messages were often transformed into ideographs for privacy, but no substantial use in early Chinese military conquests is apparent. Genghis Khan, for example, seems never to have used cryptography. In India, secret writing was apparently more advanced, and the government used secret codes to communicate with a network of spies spread throughout the country. Early Indian ciphers consisted mostly of simple alphabetic substitutions often based on phonetics.
Some of these were spoken or used as sign language. The cryptographic history of Mesopotamia was similar to that of Egypt, in that cuneiforms were used to encipher text. This technique was also used in Babylon and Assyria. In the Bible, a Hebrew ciphering method is used at times. In this method, the last letter of the alphabet is replaced by the first, and vice versa. This is called 'atbash'. The Greek writer Polybius invented the 5 x 5 Polybius Square, widely used in various cryptographic systems. Julius Caesar used a system of advancing each letter four places, commonly called a Caesar shift.
During the Middle Ages, cryptography started to progress. All of the Western European governments used cryptography in one form or another, and codes started to become more popular. The earliest ciphers involved only vowel substitution (leaving consonants unchanged).
By 1860 large codes were in common use for diplomatic communications, and cipher systems had become a rarity for this application. Cipher systems prevailed, however, for military communications except for high-command communications because of the difficulty of protecting codebooks from capture or compromise in the field.
The invention of telegraph and radio pushed forward the development of cryptographic protection of telecommunications: the speed and the volumes of data traffic became considerable and more vulnerable to interception and decryption. The radio espionage was closely following the development of new telecommunications technologies, but paradoxically, the telegraphic and radio exchange of information was mainly in clear or done in plain ciphers. It was not until the 20th century mathematical theory and computer science have both been applied to cryptanalysis. As the science of cryptology becomes increasingly sophisticated, most nations have found it necessary to develop special governmental bureaus to handle diplomatic and military security (the National Security Agency in the United States). The widespread use of computers and data transmission in commerce and finance is making cryptography very important in these fields as well. Recent successes in applying certain aspects of computer science to cryptography seem to be leading to more versatile and more secure systems in which encryption is implemented with sophisticated digital electronics. Industry, however, have argued over who will have ultimate control over data encryption and, as a result, over government access to encrypted private transmissions.