hi everyone, I need your help in my information security course: homework questi

Question

hi everyone, 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!

Explanation / Answer

The Playfair cipher is also known as Playfair square or Wheatstone-Playfair cipher or Wheatstone cipher.

Playfair cipher is a manual symmetric encryption technique and was the first literal digram substitution cipher.

The Playfair cipher uses a 5 by 5 table containing a key word or phrase. Memorization of the keyword and 4 simple rules was all that was required to create the 5 by 5 table and use the cipher.

To generate the key table, one would first fill in the spaces in the table with the letters of the keyword (dropping any duplicate letters), then fill the remaining spaces with the rest of the letters of the alphabet in order (usually omitting "Q" to reduce the alphabet to fit; other versions put both "I" and "J" in the same space). The key can be written in the top rows of the table, from left to right, or in some other pattern, such as a spiral beginning in the upper-left-hand corner and ending in the center.

The keyword together with the conventions for filling in the 5 by 5 table constitute the cipher key.

To encrypt a message, one would break the message into diagrams (groups of 2 letters) such that, for example, "EveryOne" becomes "EV ER YO NE", and map them out on the key table. If needed, append an uncommon monogram to complete the final diagram. The two letters of the diagram are considered as the opposite corners of a rectangle in the key table. Note the relative position of the corners of this rectangle.

Then apply the following 4 rules, in order, to each pair of letters in the plaintext:

To decrypt, use the INVERSE (opposite) of the last 3 rules, and the 1st as-is (dropping any extra "X"s, or "Q"s that do not make sense in the final message when finished).

So applying the rule here

Plaintext 0 is      We ar et ha tf ar fr om at ur nk ey to ta li ta ri an st at e

Ciphertext 0 is   ZG CH DQ WG PL CH HF TA MO CF BX DZ QS OM FD OM FE NM TQ MO RQ

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