Question

One failing of an encryption system occurs if a letter (or number) always encodes to the same value. Let’s see how we can exploit these weaknesses. Let’s assume that we know that the word SECRET is in an intercepted message. What are the encrypted values (i.e., give the mappings) of the letters S, E, R, C, T (i.e., S -> ?, E -> C, R -> ?, C -> ?, and T -> ?) for the following encrypted message: MHIL75K7MTF7LL397V

To test your detective skills, what is the exact original message?

Answer 1

We can see that there are two letters in SECRET, E which occurs at a spacing of two values, Therefore there will be repetition in encoded values as well in encrypted message. In encrypted message the digit 7 gets repeated after two values therefore E maps to 7. On placing SECRET we can find the mappings as S-> L, E-> 7, C-> 5, R->K,T-> M. The whole mapping is in turn:

(A,B,C, D,E,F,G,H,I,J......Z ) -> (3,4,5,6,7,8,9,A,B,C.......S). So on decrypting the above mesaage we get the original message as "TOP SECRET MESSAGE"