TITLE:
Crypto Analysis Classical Ciphers Challenge.
Introduction:
Today we normally use strong ciphers such as AES for encryption.
Before the availability of such ciphers,so called classical ciphers were used, where encryption is
based on the substitution or transposition of characters.
These ciphers generally have three problems:
1_ Firstly character translation is linear; the same input will result in the same output,
keeping the frequency of character occurrences constant.
2_ Secondly the entropy using natural languages is small; even though each
character needs 8 bits (when ASCII encoded), the information value is much lower.
3_ And thirdly there is a simple relation between plaintext,
ciphertext and key: Knowing both plain and ciphertext, often allows to calculate the key.
Requirements:
We provide three ciphertexts C1, C2 and C3.
Goal (Crypto Analysis of given ciphers)
Three ciphertexts are given, each encrypted with either Caesar, Vigenere or the base64 encoded AES ciphers. The alphabet used for the classical ciphers is equivalent to the one used for base64 encoding. The following task needs to be accomplished:
1_ Assign each ciphertext to the correct cipher and explain how you found out.
2_ Find the encryption key for the Caesar ciphertext and decrypt it.
3_ Find the encryption key length and key for the Vigenère ciphertext and decrypt it.
4_ Explain how the classical ciphers compare to each other concerning their strength against ciphertext only attacks.
Security Questions:
We expect the following information in your solution to fully complete the challenge and receive maximum points
* Ciphertext/algorithm assignment.
* Plaintext and encryption key of the Caesar ciphertext.
* Plaintext and encryption key of the Vigenere ciphertext.
* Explanation which classical algorithm is stronger and why.
Solution:
C1 -> Vigenere cipher
Key Length:
7
Key:
classic
Identification Method:
IC (Index of Coincidence)
RESULT:
He came from the U.K. where being good at math is seen as being uncool. This is not the case even in France. The French love their math. It's quite cool to be a mathematician. Mathematicians in France are seen as great intellectuals. And being good at arithmetic in India is almost seen as a badge of national pride.
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C2 -> Base64
Identification Method:
padding = in the end give away the Identity.
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C3 -> Caesar Cipher
ROT:
49
Identification Method:
IC (Index of Coincidence)
Result (GERMAN LANGUAGE):
Gallien ist insgesamt in drei Teile unterteilt, von denen einen die Belgier bewohnen, den anderen die Aquitanier, und den Dritten die, welche in ihrer Sprache Kelten, in unserer Gallier genannt werden.
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BEST CIPHER:
Vigenere cipher is best in these classical ciphers, because it requires a key/password in order to decrypt it into proper message.