Cryptanalysis
Cryptanalysis is studying secret messages to break the code.
Letter Frequencies
Letter frequencies tell you how often a letter appears in a text. If you look at a long text, you see a pattern: a few letters appear very often, and other letters appear only rarely. This pattern is different for each language. That is why you can use letter frequencies in cryptanalysis. You look at which letters appear often in a secret message. Then you compare those letters with the normal frequencies of a language. Step by step, you can discover which letter is which. In this way, letter frequency analysis helps you break codes.
Read more about Letter Frequencies on Wikipedia.
How did the use of letter frequencies begin?
Letter frequency analysis was invented more than a thousand years ago by a clever scholar from Baghdad named Al-Kindi.
He noticed that in every language, some letters appear much more often than others. For example: in Dutch, English, and German, the letter ‘e’ is used most often. After that come ‘n’ and ‘a’ in Dutch, ‘t’ and ‘a’ in English, and ‘n’ and ‘i’ in German.
Al-Kindi realized that you can use this pattern to break secret messages. You count how often each letter appears in the code and compare that with the normal frequencies of the language. Step by step, you can then figure out which letter is which.
His idea later spread to Europe and was used for centuries to read secret messages. It was only in the twentieth century, when more complex coding algorithms were invented, that this method became less powerful.
The Letter Frequencies (Crypto Analysis) function
In GC Wizard you can find this function in the folder Encryption and Codes → Letter Frequencies (Crypto Analysis).
How does the function work?
This function counts how often each letter appears in your text. It then lets you compare these results with the standard letter frequencies of different languages.
Input
At the top there is a text field. Type the text you want to analyze here.
Settings
Below the input field there are two drop-down menus. With these you choose a language and how the results are shown.
Compare with
In this menu you choose a language. The app knows the letter frequencies of sixteen languages, such as English, German, French and Dutch. After your choice, the table shows which letters appear often in that language. This way you can compare your text with a normal text in that language.
Sort by
Here you choose the order of the results. There are three options:
- Alphabetical: the letters are shown from A to Z. This is useful if you want to find a specific letter quickly.
- Count (aligned): the letters are shown in order of how often they appear in your text. Next to each letter you see the comparison value of the chosen language.
- Count (independent order): the letters are shown from most frequent to least frequent. The comparison language is shown in a separate column. The app looks at which letters appear most often in your text.
Output
Under Output you see the table with the results. The table shows the letters, how many times they appear and the percentage. Next to the comparison language you also see the standard percentage for that language.
Behind each letter there is a copy button 
. With this button you can copy the results directly.
When you choose the option Count (independent order), a button appears: Export to the Substitution tool. With this button you send the automatically matched letters directly to the Substitution tool. There you can continue working with your guesses to break the code.
