2. The ciphertext MBR OJFGA SWNTE CNK QJDIL NURW MBR XHMR was obtained by encryp

Question

2. The ciphertext MBR OJFGA SWNTE CNK QJDIL NURW MBR XHMR was obtained by encrypting the plaintext THE QUICK BROWN FOX JUMPS OVER THE GATE using a Simple Substitution Cipher.
(a) How much of the key is determined if this plaintext/ciphertext pair are known?

b) How many different possible keys could have been used to encrypt the plaintext?

(c) Decrypt the ciphertext MBR TRHLRP WHE HTHV CWND PNEYNE ZNN, which is known to have been encrypted with the same key.
(d) What lesson can be learnt from conducting this exercise?

Explanation / Answer

A) answer 22 key is easily determined by above cipher and plain text as:

M-T,B-H,R-E,O-Q,J-U,F-I,G-C,A-K,S-B,W-R,N-O,T-W,E-N,C-F,K-X,Q-J,D-M,I-P,L-S,U-V,X-G,H-A

B) 26! key would be used to encrypt a plain text.

C) THE WEASEL BAN AWAY FROM LONDON ZOO.

D) if we know the frequency and both cypher text and plain text we can derive the whole key ieasily

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