I have this question and i have answered two of them using this http://www.richk
ID: 3862914 • Letter: I
Question
I have this question and i have answered two of them using this http://www.richkni.co.uk/php/crypta/caesar.php website. can you answer rest of it. its a python coding class.
The following ciphertext is encrypted using Caesar’s shift cipher with an unknown key. Answer the questions below.
NPSTBBMJSYMFYMTYQNSJGQNSLYMFYHFSTSQDRJFSTSJYMNSL
. (a) What key was used to encrypt this message? Answer:
. (b) Write the decryption of this message below.
I KNOW WHEN THAT HOTLINE BLING THAT CAN ONLY MEAN ONETHING
. (c) What is the name for the method of cryptanalysis/attack you performed to break this cipher? Answer: It is called a _____attack.
. (d) What is the keyspace of the Caesar shift cipher?
SHIFT 21
. (e) Describe how the attack from answer (c) works. Why is this not a viable method of attack against most ciphertexts?
Explanation / Answer
The following ciphertext is encrypted using Caesar’s shift cipher with an unknown key. Answer the questions below.
NPSTBBMJSYMFYMTYQNSJGQNSLYMFYHFSTSQDRJFSTSJYMNSL
. (a) What key was used to encrypt this message?
Answer: The shift key is: 21.
. (b) Write the decryption of this message below.
Answer: IKNOWWHENTHATHOTLINEBLINGTHATCANONLYMEANONETHING
So, in clear sentence is: I KNOW WHEN THAT HOTLINE BLING THAT CAN ONLY MEAN ONE THING
. (c) What is the name for the method of cryptanalysis/attack you performed to break this cipher?
Answer: It is called a __brute force__ attack.
. (d) What is the keyspace of the Caesar shift cipher?
The key space is: {1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26}.
. (e) Describe how the attack from answer (c) works. Why is this not a viable method of attack against most ciphertexts?
As the key space is very small, we can generate all possible decryptions for the given encrypted text.
And the one text which makes human readable meaningful words will be considered as the solution.
But this is not the case most most cipher texts. This is because, for other techniques, the
key space will be very large, and decryption using bruteforce will become almost impossible.