Contents Introduction3 Cryptography3 Monoalphabetic substitution3 During World War I3 World War II4 Another use of cryptography4 Conclusion5 References6 Introduction. Cryptography is the science of encoding a message into a form that is unreadable and making sure only the proper people are capable of decoding the message back into its original form. This is usually done by using an encryption algorithm and a decryption algorithm (these two are often the same) and very often a secret key. Some of the early cryptographic systems did not use a key but instead kept the algorithm itself secret. The message sender uses the encryption algorithm and the key to encode the message, and then sends it to the receiver. The receiver then uses the decryption algorithm and the key to turn back the encrypted message into its original form and read it. If the message is intercepted others, they will only have unreadable data and will have gained nothing, unless they can figure out the decryption algorithm and obtain the key. This is why the key is never to be sent with the message, and has to be kept secret at all cost. If the key is compromised, the sender and the encrypted data is no longer safe. The sender and the receiver then usually agree on a new key to prevent any further damage. In ancient Greece, around 550 Bc, messages were sent encoded to generals and could only be decoded using special staff keys. The key actually consisted of a physical object, which was applied on the message to get the decrypted version of it. In 50 Bc., one of the most simple cryptographic algorithms ever used was the one called the Caesar cipher, that was used by Julius Caesar to send messages to his generals. It consisted simply of switching each letter with the letter that was 3 letters further down the alphabet. Monoalphabetic substitution. Monoalphabetic substitution is another simple step away from the ROT13 algorithm. In this algorithm, each letter correspond to another letter but in no particular order. For example a = d, d = x, f = e, etc for all 26 letters. This made it much harder to break but also made fairly big keys that couldn’t be memorized, since they consisted of 26 pairs of letters. During World War I. During World War I, American troops used Native Americans to send messages over the radio, which could only be understood by other native Indians, and almost nobody in Germany could understand it. Also in World War I, the Playfair algorithm was developed by the Allies, the key, like in the Vigenere cipher, is based on a little table and a short keyword, which were both changed periodically. The rules used with the table were much more complex and made it fairly safe. 2 World War II. In World War II, however, the Germans gave up on abstract algorithms and came up with a physical encrypting/decrypting machine called the Enigma. It had different wheels of different sizes which were to be tuned differently depending on the date, the different turnings were listed in a little booklet that came with the machine. It wasn’t broken before the Allies finally managed to capture enough pieces of the machine and collect enough data from operating errors by the Germans. Privacy of this type would not be worth going through the trouble of setting up unless you have an important secret to keep. However if it came standard with most operating systems then it would be convenient enough to use on a regular basis. For businesses, the only safe way to communicate through a medium where each single bit they send can be listened to is to encrypt all of their communications with a cipher strong enough to resist breaking attempts from the other businesses. Another use of cryptography. Another use of cryptography applied to business is the one used by a European television channel. It distributes a keycode to their TVs, but only the customers paying every month for the new keycode that corresponds to their decoder box will be able to decode the broadcasted programs. Without the use of encryption, broadcasting a premium channel would be stupid. Without cryptography it is very hard to implement a successful and convenient scheme for online money. And online money is something most online businesses and shoppers would love to have. Cryptography has its origins in wars and is therefore considered very much like a weapon because of the advantage it can give to one side or the other. Legally, any information about any kind of strong encryption is considered a weapon. What this means is that it is illegal to export it to another country in any way. Many government agencies takes this matter very seriously. 3 Conclusion. Cryptography will prove to be important in the present and future by ensuring that credit card numbers stay secure over the Internet. Other things it does is prevent fraud, military actions are not compromised through bad radio security, and information exchanged among the White House, Pentagon, and other governmental agencies are not compromised by hostile nations. 4 References. https://www.bestreferat.ru/referat-349561.html https://www.myunivercity.ru/Криптология/Криптография/2347_75283_страниц а1.html 5