C 103: Monoalphabetic Substitution Cipher with CrypTool 2

What you need

Purpose

To crack a monoalphabetic substitution cipher with two attacks, both based on frequency analysis.

Getting CrypTool 2

On your Windows machine, download Cryptool 2.0 Stable from this URL:

https://www.cryptool.org/ct2download/Builds/CrypTool%202.0%20(Stable%20Build%206222.1).zip

Using the Wizard to Crack a Classical Monoalphabetic Substitution Cipher

Open CrypTool 2, as shown below.

On the left side, in the "Main Functions" section, click the Wand icon labelled "Use the wizard...".

In the "TASK SELECTION" screen, on the left side, click Cryptanalysis, as shown below.

Then click Next.

In the "AGE SELECTION" screen, accept the default selection of "Classic Encryption" and click Next.

In the "ALGORITHM SELECTION" screen, select "Monoalphabetic Substitution", as shown below, and click Next.

In the "MONOALPHABETIC SUBSTITUTION ANALYSIS" screen, some example ciphertext appears, as shown below.

Leave the "Language" set to English and click Next.

The next screen shows the analysis progress. It takes only a few seconds to find the key, as shown below:

Scroll down to see the "Deciphered Ciphertext", as shown below.

Understanding the Attacks Used

At the top right of the Cryptool window, click Help.

In the middle, there is a row of letters in aphabetic order. Click M. Click "Monoalphabetic Substitution Analyzer".

Read about the two attacks used, as shown below.


C 103.1: A Simple English Paragraph (10 pts)

Decrypt this:
B WBGG HUBGD T AQOTS WTGG -- TJD JKHKDY HUBGDR WTGGR HOSSOQ SLTJ IO, HOGBOVO IO -- TJD B'GG HUBGD SLOI VOQY BJOXMOJRBVOGY. B WBGG HUBGD T AQOTS, AQOTS WTGG KJ KUQ RKUSLOQJ HKQDOQ, TJD B WBGG ITFO IOXBEK MTY NKQ SLTS WTGG. ITQF IY WKQDR.
The flag is the first six words of that quote in capital letters, like this:

I DON'T WANT TO GROW UP


C 103.2: A Simple English Sentence (10 pts)

Decrypt this:
BFNKTAB TM BDD BLHQP MINNR. SHP, GBMPX, LBR-BMM MINNR.

Hint

The text is so short that Cryptool fails. Try finding other tools to use.
The flag is the first five words of that quote in capital letters, like this:

KEEP CALM AND CARRY ON


Posted 6-10-17 by Sam Bowne
Updated 9-14-17
Put in Crypto Hero 4-15-18