Capabilities of the program
===========================
- gather language statistics
- encrypt and decrypt texts using substitution cipher
- automatically crack encrypted texts
Starting the program
====================
For starting the program start the executable file "setup.exe" in
the SubstCipherGUI folder. After the first execution of this executable
file you can start the GUI also from the start menu. If you already
have an earlier version of the program installed, you first have to
uninstall the old version.
Introduction
============
OK, let's get started.
1) Language statistics
The first thing we need are language statistics for a given language.
In the dialog shown at the beginning select "Gather language statistics".
Then click on "Add files" and choose some sample texts. You can choose
more than one file in the dialog. I have provided some
english and german texts in the "data/texts" folder which you can use.
After having added all files click on "Calculate language statistics".
Choose a file name for the language statistics file. After having done
this, the language statistics are shown to you.
2) Encrypting/Decrypting a file
Now we want to encrypt a specific file. For doing this, we need a key. In
the initial dialog click on "Manage Keys" and create a random key by clicking on
the corresponding button. Then save the key to the disk. We will use the key
right away.
Now, in the initial dialog again, click on "Encrypt text with key". First
choose the key file just created, then select a file with the text to
be encrypted (can be again a text file from the "data/texts" folder, or
a text file with your own text). Finally, choose where the encrypted text
should be stored.
Decrypting an encrypted text is just as easy. Only click on
"Decrypt text with key" instead of "Encrypt text with key".
3) Cracking encrypted text
Now to the highlight: Let's crack an encrypted text automatically!
In the initial dialog, choose "Crack encrypted text". The program
prompts you to select a language statistics file to be used for
cracking. Choose a language statistics file for the language that
you expect is the original language of the encrypted text. In
the following, we want to crack an English text, so choose the
English language statistics file created in step 1).
Having done this, load the encrypted text via clicking on the
"Load encrypted text" button. I've provided a sample encrypted text
which you can use in the "data/encrypted/english" folder.
Now click on the "Start cracking" button.
You can see that the decrypted text, the key, and the similarity
value change. After some time, the automatical cracker finishes when it cannot
improve the decrypted text any more. You will now have a readable
decrypted text. Some letters are still incorrect, but you can now edit
the key to remove the last errors.
Done!
