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Item C: The Document
A famous simple example for a cipher is the Caesar Cipher. It was used by Julius Caesar to encrypt his messages so enemies weren’t able to read them.
It worked by shifting each letter x number of letters forwards. Assuming the key is 5, we shift each letter five times forwards, so A becomes F, B becomes G and so on. This cipher may have taken hours for someone to crack if they weren’t aware of how it worked, however now computers can defeat it in seconds, and even a person without a computer would be able to work it out quite easily.
A natural evolution to the Ceasar Cipher is the Vigenere Cipher. Imagine we had our key, for this example we’ll use the word ‘Stable’. By converting each letter into a number, so A equals 1, B equals , etc. We’ll get the numbers 19, 20, 1, 2, 12 and 5.
We then shift each letter of our message by those numbers in that order, repeating throughout the message we need to encrypt. If our message was “Hello World” it would become “Zxlmz Agkle”
This is still weak encryption however, and can be quickly cracked. By going back over the message and encrypting again, with a different key or perhaps even a different cipher, we can make our message even more secret.
One other application of the Ceaser Cipher is ROT13. As the English alphabet has 26 letters, shifting any letter by 13 twice will bring it back to what it was originally. This means that although it is weak for keeping a message secret, as the same algorithm is used to both encrypt and decrypt the message, it is quick and easy to use, having practical purposes in scrambling letters rather than security.
Your task will be to decrypt this simple message using what you know, see how difficult it is.
“Ysxa xhrv hcd syvvprhuca mlzu aqhmtkv.”