One way to break a substitution cipher is to use frequency analysis. Let’s focus on the English language for now but the process works the same way for other languages. The character “e” occurs 12.7% in the Eglish language and the letter “t” occurs 9.35% and the letter “a” is 8.2% of the time. So, you can count each character in the ciphered text, compute its frequency and start replacing it. After you complete the first say 4 characters, you may want to change your strategy. Can you explain why you want to stop after the first 4 characters? The two-character “of” is about 4.16% and “to” is about 2%. Now try three characters frequency.
After a period of time, you will be able to decipher most of the text. I am going to ask you to do your first significant homework using frequency analysis.
Here is your homework – A character sub was used. Can you decipher as much of this text as you can? Submit your results in the drop box below (Frequency Analysis). You may use Python to code the solution.
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