Caesar cipher

The Caesar cipher is named for Julius Caesar.

In cryptography, a Caesar cipher is an ancient form of substitution cipher. It is named in the honor of Roman emperor, Julius Caesar

Method

To encrypt a message with a Caesar cipher, each letter in the message is changed using a simple rule: shift by three. Each letter is replaced by the letter three letters later in the alphabet. A becomes D, B becomes E, and so on. For the last letters, we can think of the alphabet as a circle and "wrap around". W becomes Z, X becomes A, Y becomes B, and Z becomes C. To change a message back, each letter is replaced by the one three before it.

Weakness

However it is very easy to break a Caesar cipher, even if you change the "key number" to a different number. Using a more modern form of encryption would be better.

The Caesar cipher rule

Changing by three is the rule that the well known Julius Caesar used, but the same idea works for any number. ROT13 can be seen as a modern version of the Caesar cipher, with the same weaknesses.

The Caesar cipher is a substitution cipher: each letter is replaced by another. No substitution cipher is safe for sensitive information.

Caesar Cipher Media

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  The action of a Caesar cipher is to replace each plaintext letter with a different one a fixed number of places down the alphabet. The cipher illustrated here uses a left shift of three, so that (for example) each occurrence of E in the plaintext becomes B in the ciphertext.

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  Caesar cipher left shift of 3

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  The Caesar cipher is named for Julius Caesar, who used an alphabet where decrypting would shift three letters to the left.

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  A reproduction of the CSA's cipher disk at the NSA museumCivil War - CSA Cipher Disk

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  The distribution of letters in a typical sample of English language text has a distinctive and predictable shape. A Caesar shift "rotates" this distribution, and it is possible to determine the shift by examining the resultant frequency graph.