Study Notes Cryptography I – Cryptography History

The first week of the course basically provides a brief introduction to Cryptography history and I have learned a few ancient cipher.

(1) Substitution Cipher

(2) Caesar Cipher (shift by 3)

(3) Vigenere Cipher (I implemented the encryption in Python and still need to implement the decrypt and cryptanalysis on natural languages to hack the password)

It is also interesting to learn the common ways to decrypt by using frequency of english letters, pairs of letters.

For single letter, the most frequent letters are “E”, “T”, “A”..etc and the most frequent diagrams are “TH”, “ER”, “ON”, “AN” – > “theRonan”.

And when the professor talks about the “mechanical age” of cryptography, it is really amazing to learn the existence of those rotor machines, including the famous Enigma Machine.

In the end, I finished the video which covers OTP (one time pad). It is good to learn Shannon’s research about the full secrecy around cryptography – Shannon Secrecy

I took a screenshot of the professor’s lecture:

information_theoretic_security

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