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  Компьютеры > Компьютерные технологии > Безопасность > Криптография
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Introduction to Cryptosystems

Cryptology is the hiding of information so that it is unintelligable to those we do not wish to read it and intelligable to those we do. In this section we present the fundamental or basic ideas needed to understand the science.

We start with the question, what information are we trying to hide? The answer can range from any number of things; however most importantly it is information that we want to keep private. For instance, bank account numbers and social security numbers are pieces of information that we don't want everyone to be able to obtain. For military purposes, anybody can see the need to keep plans of attack secret from the enemy, and cryptology offers a way to do this while still using standard lines of communication.

The most elementary idea in cryptology is the idea of a cryptosystem. This is a system in which information can be made unintelligible to all but the intended reader. The first component of a cryptosystem is the original set of information, called the plaintext. This may be the orders to attack, or the account number that we want to keep hidden from prying eyes. The next element of a cryptosystem is the algorithm, commonly known as the cipher. This is the process that makes the information unreadable to the common person. There are many ciphers and many kinds of ciphers; however for the most part all of them have the same purpose. The next part of a cryptosystem is the information that has been altered, which we call the ciphertext. This is the information that is not recognizable, and therefore can be sent out over public channels without fear of anybody understanding it. A good representation of a cryptosystem is as follows:

plaintext -> F -> ciphertext -> G -> plaintext

where F and G are functions or the ciphers.

The cipher can be very complex or very simple. Many common ciphers involve substituting one element of the information for another. For instance we have the message:

"THERE IS A WAR IN KASHMIR"

If we replace every 'A' with 'Z', we get

"THERE IS Z WZR IN KZSHMIR"

Thus, the text now doesn't make much sense (however it is easy to figure out what the message says). So usually substitutions are made for the entire alphabet.

There are also ciphers that use numbers to mask the information. This is done by first translating the alphabet into a number system, such as A = 1, B = 2, C = 3,...,Z = 26. For example, the message "A DOG" written numerically is

"1 4157"

It is very confusing and most would not even think to translate it into a series of letters. This truly is the idea behind cryptology.

Currently, because of computers, most modern cryptosystems all involve mathematical ciphers. This means that usually ciphertext looks like nothing more than a set of 1's and 0's, which is very hard to decode. This is why there is such security in digital data, such as electronic bank accounts.

Within cryptology, there are two sources of study, cryptography, and cryptanalysis. Cryptography is the study of encryption, or the transformation of information into unintelligible code. Cryptographers are the people who invent the ciphers. These people are the codemakers. Cryptanalysis is the study of decryption, or the breaking of those codes. It is usually done without the key. Cryptanalysists are codebreakers.

Cryptology now plays very important roles in today's society. Traditionally, cryptolgy has been purely a military matter; however currently it is part of our everyday lives.

            

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