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UGC NET CSE | July 2018 | Part 2 | Question: 48

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In Caesar Cipher algorithm:

If we have to Decrypt the message, Decrease(count backwards) the value given key(15 in this question) times.

If we have to Encrypt the message, Increase(count forward) the value given key times.

Here, we have to Decrypt WTAAD:

W=23, T=20, A=1, A=1, D=4 and key = 15.

So, as already mentioned above we have decrypt by 15.

W = 23-15 = 8 = H

T = 20-15 = 5 = E

A = 1-15 = -14 = -14+26 = 12 = L  // You can also simply get it by counting 15 times backwards from A, like z,y,x,w.......

A = 1-15 = -14 = -14+26 = 12 = L

D = 4-15 = -11 = -11+26 = 15 = O

Hence, Option (B) is correct.

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WTAAD -> Simply Replace each Letter with 15th Alphabet->LIPPS

So Option (1) is correct.
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The message "WTAAD"  is already encrypted.

we need to decrypt it by simply shifting the keys by 15 places in reverse order.

hence W shifted 15 places in reverse order corresponds to H. similary

T->E

A->L

D->O

hence ans is HELLO, option 2.
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