Using a modulo 26 substitution cipher where the letters A to Z of the alphabet are given a value of 0
to 25, respectively, encrypt the message OVERLORD BEGINS. Use the key K =NEW and D =3 where D
is the number of repeating letters representing the key. The encrypted message is:

A.
BFAEPKEH XRKFAW

B.
BFAEPKEH XRKEAW

C.
BFAERKEH XRKEAW

D.
BFAEQKEH XRKFAW

E.
BZAEPKEH XRKFAW

F.
BZAEPKEH XRKEAW

G.
BZAERKEH XRKEAW

H.
BZAEQKEH XRKFAW

Explanation:
The solution is as follows: OVERLORD becomes 14 21 4 17 11 14 17 3 BEGINS becomes 1 4 6 8 13 18
The key NEW becomes 13 4 22 Adding the key repetitively to OVERLORD BEGINS modulo 26 yields 1
5 0 4 15 10 4 7 23 17 10 4 0 22, which translates to BZAEPKEH XRKEAW More in detail: