By Kurt Seifried, [email protected], Copyright Kurt Seifried
One of the simplest examples of cryptography is the Caesar cipher. You have a pre-arranged code for switching letters in the alphabet, which you use to encipher your message. For example using the following code:
| A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X | Y | Z |
| Q | A | Z | W | S | X | E | D | C | R | F | V | T | G | B | Y | H | N | U | J | M | I | K | O | L | P |
So if your message were:
meet me at six
The text you are ciphering would be turned into a stream of letters without spaces:
MEETMEATSIX
And the corresponding ciphertext would be:
TSSJTSQJUCO
This is of course an extremely weak cipher, cryptographic analysis of a large amount of text would be absurdly simple for several reasons:
1) the cipher does not change, the substitution is very simple
2) the frequency of letters in the English language (and any language for that matter) can be compared to this, in English the most common letter is "e", if you had a large amount of text enciphered with this method you could simply analyze the frequencies, and easily get some of the more common letters like e, t, r, s and so on.
For a more detailed description of cryptography see the next section.