Information Security has been one of the most important sciences since human invented the way to communicate. Let's go back to the Roman Empire. In about BC 50, people did not have telegram or phone to communicate with each other. So when Caesar wanted to convey his orders or communicate with his subordinates, the first thing he would consider would be whether the enemies would understand what he said. What would Caesar do?
As an emperor, he did not want others learn what he was thinking about. So here comes to the Caesar Cipher or called Caesar Code. This method of cipher which used by Caesar may considered as the first time that humans using cipher to protect what they communicated with friends. Caesar Cipher is not only the earliest cipher method that humans used, but also the most widely used. The core of this cipher method is shift. It is a type of substitute cipher which means the plain text are substituted by another letter in the alphabet. Generally, scientists think that Caesar used D to replace A, E for B, F for C and so on. Then used A to replace X, B for Y and C for Z at the end. On the other hand, some people think Caesar used the Greek alphabet to substitute the Latin alphabet (not replaced in the order of letters). However, no matter how Caesar replace his plain text, the way to transfer the ciphered text to plain text (how the letters are shifted or replaced) was only known by Caesar's friends or generals.Though Caesar Code was widely used at that time and it did have a strong result for Roman Empire, this cipher method is easy to break for us nowadays especially when there are spaces between every words. We can search for some easy words like "is" or "are" and find how much the letters are shifted. Then we can easily break the whole sentence. We can also use the frequency analysis to break Caesar Code. On the other hand, Caesar is not a strong method to cipher texts, but the idea of Caesar Code presented in many other methods of cipher.
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