The History of Practical Cryptography from Early Century BC to Modern Day

p The History of Practical Cryptography from Early Century BC to Modern Day

Cryptography has been in use for centuries to hide messages intended for a specific person or group of persons which are otherwise prohibited or undesirable to be known to others . Its primary use is for security and privacy purposes - that is to ensure secrecy in communications . Some of its early practical uses included military and political communication and even in private personal endearments

Cryptography refers to the study of concealing information with the use of mathemathical transformations (Bishop

2 . It involves the process of converting the ordinary information , called the plaintext , into a message , called the cyphertext , which would seem unintelligent and unreadable to anyone whose message is not intended to . This process is called encryption . A person who studies or practices cryptography is called a cryptographer

Decryption is the reverse process of encryption . Cryptographers use secret keys , called cyphers , to encrypt and decrypt messages . Cyphers could be expreesed mathematically as a pair of invertible funtions : fk known as the encyphering function which maps froma set S to a set T based on a quantity k called the encyphering key and gk , known as the deciphering function which is the inverse of fk . On the other hand cryptoanalysis refers to the practice of revealing information hidden by cryptography using analytical and mathematical techniques , without the consent of the cryptographer - that is without the complete knowledge of the cypher . One who practices cryptoanalysis is called a cryptoanalyst or simply codebreaker (Bishop 2 Singh 10

The earliest known use of cryptography occurred some 4000 years ago in Egypt where heiroglyphic inscriptions on the tomb of Khnumhotep II were written with a number of unusual symbols to confuse or obscure the meaning of the inscriptions (Cypher Research Laboratories [CYCOM] . In 500-600 BC , Hebrew scribes used a reversed alphabet - that is replacing the first letter of the alphabet with the last , the second with the second to the last , and vice versa - known as the atbash cypher to hide the names of people and places (CYCOM Cohen

At around 500 BC , The Spartans used a cryptographic device known as scytale which used a long strip of wound around a cylindrical staff to write down the message . After the message have been written the is then unwrapped from the staff , thereby rearranging the characters , and would have to be rewrapped in a staff of similar diameter from the one that was used to write in to read the message . The method used in this is called a transposition cypher (CYCOM Cohen Calabrese 182-183

Another method developed by the Greeks is the Polybius Square which lays down the alphabet in a five-by-five square . The rows and columns were numbered 1 to 5 so that each letter has a corresponding (row , column pair (CYCOM Cohen

At 50 BC , Julius Caesar uses a method of shifting the characters of the alphabet to obtain a cyphertext . This method is called a shift cypher now...