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

Question

Decrypt the message "WTAAD" using the Caesar Cipher with key =15

• A. LIPPS
• B. HELLO
• C. PLLEH
• D. DAATW

Answer 1

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.

Answer 2

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

So Option (1) is correct.

Comments

Official Ans key is given Option 2 as correct answer
 

 

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The answer should be option 2
Caeser cipher always shift the alphabet down
So WTAAD is encoded as hello
Each alphabet is reduced by given key =15

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@kmittal1908

Yes. Right.
Thanks.

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I think your answer is right with little bit correction required in explanation

Actually HELLO is encoded to WTAAD and thus WTTAD is decoded to HELLO

Please correct me if I am worong

Answer 3

message is in encrypted from  so ans is hello

Answer 4

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.

Comments

yes u r right and in case of encrypt se my answer