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  • Lara-Johanna Pirk

Cryptography

Cryptography is the art of writing codes so others cannot read the real message. It is often used to store and transmit data in a particular form so only those who the data is intended for can read and process it. Cryptography is used for many varied reasons. For example, it is used by military forces and other organisations that want to communicate privately but also by banks when they want to transmit valuable information. People who work in this field are called cryptographers.

There are many different cryptography techniques such as merging text with images, transforming text into sound, scrambling the plaintext into cyphertext (this is called encryption) and many more.

The most commonly used techniques are codes and cyphers. Though they might sound remarkably similar, they are quite different. Codes are used to substitute words or phrases. For example, you could use the word “hello” to substitute the phrase “I need help.” These different phrases are then often put into a code book for both the sending and receiving sides. Cyphers on the other hand always involve some sort of algorithm. To encrypt the plaintext with a cypher, you must follow the steps of the algorithm. To decrypt it, you must then do the exact opposite of those steps. Encryption and decryption have been used for many years with many different types of cyphers. Julius Caesar used a cypher when sending messages to his generals. This is why one of the most widely known cyphers is called the Caesar cypher. The following cyphers are easy but were once also commonly used. Because they are so simple, they are easily cracked by today's computers and are hardly used anymore.

  1. Caesar cypher

As mentioned above, this cypher was used by Julius Caesar. It is one of the simplest and easiest encryption methods. It is a substitution cipher, which involves replacing each letter of the alphabet with a different letter. The letters are usually a fixed number of positions apart in the alphabet. In Caesar's case, it was three letters further down the alphabet. This would mean A is substituted with D, B is substituted with E and so on.

Because each letter directly translates to another letter, frequency analysis can be used to decipher the message. For example, E is the most commonly used letter in English. If you go through the secret message, the most commonly used letter would most likely be E. Endings like ING and ES also help when deciphering this cypher.

Here is an example using the Caesar cypher:

Cyphertext: Wklv lv d vhfuhw phvvdjh. Plaintext: This is a secret message.

  1. Vigenère Cypher



The Vigenère Cypher is a little more complicated. For this cypher, you must choose a key. For this example, let's choose the key apple. We will encrypt the message ‘secret.’ To begin encrypting we must first assign each letter a number from 0 – 25 from the alphabet. This means A would equal 0, B would equal 1 and so on.

We then do this to the entire secret message. In the end, we would get 18 4 2 17 4 19. And then we must do the same thing with the key apple: 0 15 15 11 4. You then write the key below the secret message repeatedly. This would then look like this:

After this, you add the numbers that are on top of each other to get 18 19 17 28 8 19. For the numbers over 25, you do minus 26 (or mod 25). After applying this your row of numbers would be: 18 19 17 2 8 19. You then have to translate this back into letters. When all steps are applied correctly your encoded message will be: strcit

There are many more ways of encrypting messages. Most cyphers used today are way more complicated and more secure. They are used all across the world for various reasons. Many people also like creating their own cyphers to communicate with friends. More ways to encode and decrypt messages are invented every day with every single one more secure than the last.

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