Cryptography is a technique for keeping information secure, for instance in private documents or e-mail messages. The word “kryptos” in Greek means hidden. The art of secret writing is as old as writing itself. For instance, only few knew the meaning of hieroglyphs used in ancient Egypt. Secret messages have been used also in ancient Greek and Rome more than 2.000 years ago. For instance, Julius Caesar used a method by which he replaced each character of a text with a character that was three positions away in the alphabet. We will now learn which word is hidden in the text "TDJFODF". We illustrate this method by sliding our alphabet by one position,
A B C D E F G H I J K L M N O P Q R S T U V W X Y Z
B C D E F G H I J K L M N O P Q R S T U V W X Y Z A
Using this method, the word SCIENCE is written in "secret" form as TDJFODF. During the Second World War, military used mechanical cipher machines for writing secret messages. Modern cryptography methods are implemented as computer programs and are used in everyday life for private e-mail messages or online banking.