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Реферат: Cryptography Essay Research Paper Cryptography is the

Название: Cryptography Essay Research Paper Cryptography is the
Раздел: Топики по английскому языку
Тип: реферат Добавлен 17:48:31 07 ноября 2010 Похожие работы
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Cryptography Essay, Research Paper

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.

For example “Stephen” would become “Vwhskhq”. To decrypt the message, the receivers would simply subtract 3 letters from each letter. This algorithm was later improved and called ROT13, where the letters could be shifted to any number between 1 and 25, and the number of letters shifted was the secret key. This very simple algorithm has been used on Usenet successfully to prevent people from inadvertently reading materials they might find offensive.

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.

In France during 1585, members of the king’s court liked to send romantic or gossip messages to each other and encrypt them for safety, which becomes almost a necessity. Blaise de Vigenere came up with a poly-alpabetic substitution known as the Vigenere cipher. Basically, the algorithm would encrypt messages several letters at a time instead of letter by letter. For example ab = fh, th = sq. To simplify the huge keys it would require, the key was broken into a table and a key, the table was fairly big but the key was small enough to be memorized, and the table was useless without the key. This cipher wasn’t totally safe but no totally sure method to break it was developed before early in the 20th century.

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.

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.

For most messages, computers would be the ideal carrier. Being able to encrypt our messages so that no one else can read them is great, but is this something we really need? Most of us do not need to have our transmissions encrypted, for the very simple reason that nobody is interested in intercepting and reading the average person?s things.

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.

But there are people out there that need to keep important secrets and aren’t terrorists or criminals or the army. Most businesses will not be able to use the Internet as a means of communication as long as all their online communications are vulnerable to industrial spying.

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 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.

Finally, one of the most useful uses of cryptography that we might all find useful is ?Digicash?. 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.

There are more or less equivalent laws in most other countries in the world as well. Illegal immigrants in France tattooed cryptographic data on their forearms so that it would be illegal to send them back to their country.

Since the Internet is worldwide, posting any strong encryption information on the web is the same as exporting it, and is therefore illegal. Which means that right now encrypted Internet communications are more or less illegal as well. Also, the government is now trying to impose the Clipper chip as a standard on all computers, and banning all other forms of cryptography, in order to have a unique cryptographic system which it has the ability to break.

The problem is, is that it is already too late to prevent these cryptography systems from being exported. Most foreign countries already have knowledge of them, and there are many foreign business companies that use strong cryptography. So prohibiting exportation of these materials is purely and simply useless. Furthermore, prohibiting US companies from being able to export strong cryptography results in loss of marketing opportunities for them. It also means that they won’t be able to conduct safe, private conversations when dealing with foreign companies because they cannot use encrypted communications.

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.

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