Question

Suppose you have intercepted a ciphertext message and when you determine the frequencies of letters in this mes- sage, you find the frequencies are similar to the frequency- of letters in English text. Which type of cipher do you suspect was used?

Name: Problem 17, Chapter 4: Discrete Mathematics and its Applications
Uploaded: 2020-02-23T03:23:21-08:00
Duration: 1 min 25 s
Channel: Bryan Lynn
Description: Suppose you have intercepted a ciphertext message and when you determine the frequencies of letters in this mes- sage, you find the frequencies are similar to the frequency- of letters in English text. Which type of cipher do you suspect was used?

   Suppose you have intercepted a ciphertext message and when you determine the frequencies of letters in this mes- sage, you find the frequencies are similar to the frequency- of letters in English text. Which type of cipher do you suspect was used?

Discrete Mathematics and its Applications

Kenneth Rosen 8th Edition

Chapter 4, Problem 17

Instant Answer

Solved by Expert Bryan Lynn

02/23/2020

Step 1

We find that the frequencies are similar to the frequency of letters in English text. This implies that the same letter in the plaintext is always transformed into the same letter in the ciphertext, and there are 26 possible letters. Show more…

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Suppose you have intercepted a ciphertext message and when you determine the frequencies of letters in this mes- sage, you find the frequencies are similar to the frequency- of letters in English text. Which type of cipher do you suspect was used?

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Key Concepts

Frequency Analysis

Frequency analysis is a cryptanalytic technique that examines the frequency of letters or groups of letters in a ciphertext. Because languages like English have well-known letter frequency distributions, a ciphertext that exhibits similar patterns often indicates that the encryption method did not fundamentally alter those frequencies, making it easier to deduce the mapping or permutation used.

Monoalphabetic Substitution Cipher

A monoalphabetic substitution cipher is an encryption method in which each plaintext letter is replaced by a fixed corresponding ciphertext letter. This type of cipher preserves the overall letter frequency distributions of the original text, which allows an analyst to match high-frequency letters in the ciphertext with common letters in the language, thereby revealing the cipher’s structure.

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