Question 13

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Question 13

Post by TECHNOTHLON on Wed Jul 20, 2016 11:48 pm

As they proceed towards the castle, Tintin informs his fellow rebels that his spy has infiltrated in the castle and would be sending different encoded information that might be of help to them.

Question 13 :
The spy sent Tintin four messages which consists of only the letters from A to D, that are encoded in the following way:
A, B, C, D are equivalent to 00, 01, 10, 11 respectively.
An operation ‡ is defined over the numbers 0 and 1 as
‡ 0
eg. 1‡1=0.
1 1
further A‡B=00‡01=(0‡0)(0‡1)=01=B
All messages that Tintin receives are encoded as (Message)‡(Key) where Key is a fixed word that is used for encoding all the Messages. But, sadly, Tintin does not know the key. BDBDBD, AAAA, BDBBBB, DAACCC .
You forgot the messages corresponding to these encodings but you do remember that all of these four messages had ADC as its substring. Few seconds later, Tintin receives another message that was encoded as BBDBD. Can you tell what the actual message could possibly be?
Not clear? Want an example – let us have two messages AB and CD, and let the key be BC, then
A B C D
‡B C ‡B C
B D D B are the corresponding cypher texts.
[Hint: if (word1)‡(word2)=(word3) then (word1)=(word2)‡(word3)]
(a)ABACD (b)ABADC (c)ABABC (d)ABBDC

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