Saturday, 23 May 2020

The Substitution Cipher and How to break the Cipher

The Substitution Cipher and How to break the Cipher
Breaking The Substitution Cipher
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.

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