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Character/ symbol frequency distribution analaysis on vintage ciphers

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Demonstrates character/ symbol frequency distribution analysis



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The objective is to demonstrate character/ symbol frequency distribution analysis (reference to the English language) on 2 vintage ciphers, namely Caesar cipher (a mono-alphabetic substitution cipher) and the Vigenere cipher (a poly-alphabetic substitution cipher).

Under the symbol frequency distribution analysis, the statistical characteristic of the language is still observable from the cipher text from the Caesar cipher, this give leads to breaking the code by remapping it to the possible substituted symbols. However, under the Vigenere cipher, such statistical characteristic has been modified in the cipher text to deter the same remapping recovery of the plain text message.

main executing reference usages:
1. usage_charFrequencyHistogram.m : no ciphering, just observation of plaintext distribution

2. usage_caesarCipher.m : Caesar cipher, standalone - text imput
3. usage_caesarCipherWithGraphPlot.m : Caesar cipher, with file input and graph plot of ciphered and deciphered (plaintext) distribution

usage_vigenereCipher.m : Vigenere cipher, standalone - text imput
usage_vigenereCipherWithGraphPlot.m : Vigenere cipher, with file input and graph plot of ciphered and deciphered (plaintext) distribution

* Caveat:
1. The vintage ciphers is not relevant for application of today's security solutions, however, they are still valuable to serve as basic examples for cryptanalysis.
2. For reference only.

If the illustrative demo has more elegant presentation, please do not hesitate to suggest and send feedback to the author.

Thank you.

Michael Chan JT

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ahmed (view profile)

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