hello, I need your help in my information security course: homework question: if

Question

hello, I need your help in my information security course: homework question: if you have the following 5 plain text/cipher text pairs which are generated by play fair under the same (unknown key). find the play fair key from these texts:

Plaintext 0 is We are that far from a turnkey totalitarian state

Ciphertext 0 is ZGCHDQWGPLCHHFTAMOCFBXDZQSOMFDOMFENMTQMORQ

Plaintext 1 is Never underestimate the time and expense your opponent will take to break your code

Ciphertext 1 is CBZIFCMBRZBQPDCNQDOLDQDUGCMBBZQIBNDZPAHQSVOSCBMSVGKYYMNHDQSGZRNHWTCFAQEI

Plaintext 2 is Cryptography is best left to those of a paranoid mindset

Ciphertext 2 is EZVTQSEHUOLWBPDITQRDLPQSOLSTGQHUOUHCASGEUDMBQBQY

Plaintext 3 is Cypherpunks write code Cypherpunks publish their code

Ciphertext 3 is MZOFRZUIBXOXFEQDAQEIMZOFRZUIBXTONIFDOKOLIGZETGRQ

Plaintext 4 is We are legion We do not forgive We do not forget Expect us

Ciphertext 4 is ZGCHDRIBGPAXIESASQHPHEFPGZIESASQHPHEDQBZQIMQNP

please help me to figure out the key!

Explanation / Answer

Let's start by explaining how Playfair works normally to encrypt a message.

First, you create a 5x5 table by writing the keyword letter-by-letter across the top of the table, from left to right, skipping duplicate letters; you then fill in the remaining characters in alphabetical order after the keyword (combining i&j or j&k into a single box).

Here's an example with the keyword of BRIANBROWN.

You then take the first two characters of the plaintext, and imagine this pair of characters is at the corner of a rectangle. The ciphertext characters are at the opposite corners of the rectangle from the plaintext characters. Let's use HELLOWORLD as the message.

Imagine a rectangle formed by HE as the corners. I've capitalized the opposite corners, LC. One common set of rules are:

Start with the first two letters of HELLOWORLD, HE.

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