[5 marks] One failing of an encryption system occurs if we never let the encrypt

Question

[5 marks] One failing of an encryption system occurs if we never let the encrypted value of a letter be the same as the original, especially if a letter always encodes to the same value. Let’s see how we can exploit these weaknesses. Let’s assume that we know that the NOTHING is in an intercepted message. If we received the following transmission, what are the encrypted values (give the mapping s to their encrypted values ) of the letters N , O, T , H , I, G ?

QSRI13JSVRSXLMRK To test your detective skills, what is the original message (give the exact message) ?

Hint: It’s a simple cipher ... look for a unique patter n in NOTHING and because you are told that a character never encodes to itself and that a character always encodes to the same value, you can exploit this to find out where NOTHING will appear in the message

Explanation / Answer

The given message "NOTHING" is the last part of the given message "QSRI13JSVRSXLMRK"

From the intercepted transmission, the last 7 letters have a repetition of R (RSXLMRK) in the given pattern nothing. Here the repetition of a letter at an interval of 5 i.e., 4 letters in between them

Please observe here "SRI13JSV" and "RI13JSVR"and "SVRSXLMR" cannot be correct as there is a repetition of S and R, and there is only N that repeats in the given NOTHING. This is because the question clearly states that a given letter can be encoded to only a single same letter every time.

So, "RSXLMRK" decodes to "NOTHING"

hence,

N encrypts to R
O encrypts to S
T encrypts to X
H encrypts to L
I encrypts to M
G encrypts to K

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