What is the Caesar Cipher?

Most civilizations have used ciphers, codes, and other methods of encryption in some form or other throughout history to prevent unauthorized persons from understanding messages. They have significantly increased in sophistication throughout history, and are commonly used today.

One of the oldest and simplest forms of encrypting a message is the Caesar Cipher, also known as a shift cypher. The cipher was named in honor of Julius Caesar who used it to encrypt military and other official messages according to Suetonius. Since most of the enemies of Rome were illiterate at this time the cipher remained secure for a while. By the 9th Century AD, after the fall of Rome, records exist of methods to crack it using frequency analysis from Al-Kindi.

It is a type of substitution cipher in which each letter in the original message (which is called the plaintext in cryptography) is replaced by a letter corresponding to a certain number of letters shifted up or down the alphabet.

For each letter of the alphabet, you would take its position in the alphabet, say 3 for the letter ‘C’, and shift it by the key number. If we had a +3 key, that ‘C’ would be moved down to ‘F’ – and that same process would be applied to each letter in plain text.

In this way, a message that initially was quite readable, ends up in a form that cannot be understood at a simple glance.

For example, here’s the Caesar Cipher encryption of a full message, using a left shift of 3.



As unreadable as the resulting ciphertext may appear, the Caesar Cipher is one of the weakest forms of encryption one can employ for the following reasons:

  • The key space is very small. Using a brute force attack method, one could easily try all (25) possible combinations to decrypt the message without initially knowing the key.
  • The structure of the original plaintext remains intact. This makes the encryption method vulnerable to frequency analysis – by looking at h ow often certain characters or sequences of characters appear, one can discover patterns and potentially discover the key without having to perform a full brute force search.

However, the Caesar Cipher gives you a good entry point into trying out encrypted messages. So try it out! 

Kdyh d jrrg gdb!

Check out my related post: What is a VPN?

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