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   by Synopsis - member of excluded-team                       |_____|
   translated by feylamia     
        

Caesar (Rot13)

May 2003 - translated July 2005

The most simpliest known method to encode a text, will be the caesar chiffre.
Which is also known under the name ROT-13.
I will later explain the meaning of the word ROT-13.

To encode a text with ROT-13, we need an alphabet.
In this tutorial we will use the common western alphabet, to visualize
the method.

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

Each letter will now be assigned a digit from 1 - 26
 
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
1 2 3 4 5 6 7 8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Here we can clearly see, that 'A' is the first letter, 'F' is the second, and so on.
Now it comes to the meaning of ROT13. ROT stands for rotation, and 13 is the count about that we will rotate.
If for example we want to encode the letter 'S' with ROT13, we would count 13 letters from 'S' on. 
When we get to the last
letter, we start from the beginning, hence- rotation. Thus, for the letter 'S', we receive the code 'F'. 
As 13 is exactly the half of 26, it doesn't matter, whether we count forward or backword. 
To encode words or whole sentences, just approach them
letter by letter. Here some examples:

 word        encrypted word
"text"        "grkg"
"secret"      "frperg"
"picture"     "cvpgher"

Decrypting a ROT13 encoded text, is, because of the rotation by 13 letters (exactly half the alphabets length)
the same technique which is used for encrypting. To decode the examples simply rotate them about 13 letters again:

 
encrypted word    word
"grkg"           "text"
"frperg"         "secret"
"cvpgher"        "picture"

 
Of course this method can also be used with different rotation values, 
like 7 or 24. Caesar used a shift of 3 letters to the left, 
but though it is named after him, he only used, not invented it. But, as you can see this encryption is very insecure.

I hope, I was able to give a little entry into cryptography, and I also hope, that you keep up with this topic.

Questions, suggestions or critics go to Synopsis@excluded.org

General questions about cryptography can be asked in the excluded board (www.excluded.org), 
where I and some others will try to answer them.

This tutorial may be freely copied and distributed, as long as content, author and for the english version, 
the translater remain unchanged.