Education

Intro to Cryptosystems

Cryptanalysis

The Zimmermann Telegram

Edgar Allan Poe

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Introduction to Cryptosystems

Cryptology is the hiding of information so it is unintelligible to those we do not wish to read it, and intelligible to those we do. What information are we trying to hide? The answer can range to any number of things, however most importantly it is information we want to keep private. For instance, bank account numbers and social security numbers are pieces of information we do not 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 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 to make the information unreadable to the common person. There are many ciphers and many kinds of ciphers, however for the most part, all have the same purpose. The next part of a cryptosystem is the information having been altered which we call the ciphertext. This information 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 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 if we have the message THERE IS A WAR IN KASHMIR, and replace every A with Z, we get THERE IS Z WZR IN KZSHMIR. Thus, the text now does not make much sense, although it is easy to figure out what the message says. Usually substitutions are made for the entire alphabet.
There are also ciphers using 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 people 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 the ciphertext looks like nothing more than a set of ones and zeros, 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, cryptology has been purely a military matter, however currently it is part of our everyday lives.