What will be the plain text corresponding to cipher text "KEPWSN" if running key cipher is used with keyword as "DATASTRUCTURE"?

Solution (By Examveda Team)

Running Key Cipher: In a running key cipher, the plaintext is encrypted by combining it with a keyword. The keyword is repeated as needed to match the length of the plaintext.

Given:
Ciphertext: "KEPWSN"
Keyword: "DATASTRUCTURE"

Steps to Decrypt Using Running Key Cipher:
Step 1: Convert the keyword "DATASTRUCTURE" and the ciphertext "KEPWSN" to their numeric values.
Keyword: D=4, A=0, T=19, A=0, S=18, T=19, R=18
Ciphertext: K=10, E=4, P=15, W=22, S=18, N=13

Step 2: Align the numeric values of the keyword with the ciphertext:
Ciphertext: K=10, E=4, P=15, W=22, S=18, N=13
Keyword: D=4, A=0, T=19, A=0, S=18, T=19

Step 3: Subtract the keyword values from the ciphertext values and take modulo 26 to get the plaintext values:
For K - D:
(10 - 4) mod 26 = 6 = G
For E - A:
(4 - 0) mod 26 = 4 = E
For P - T:
(15 - 19) mod 26 = 22 = W
For W - A:
(22 - 0) mod 26 = 22 = W
For S - S:
(18 - 18) mod 26 = 0 = A
For N - T:
(13 - 19) mod 26 = 20 = U

Conclusion: The decrypted plaintext from the ciphertext "KEPWSN" using the Running Key cipher with the keyword "DATASTRUCTURE" is "GEWWAU". Therefore, the correct answer is Option A: GEWWAU.