Solution
Step 1
Convert the letters into the numbers that matches alphabet
(A=0,B=1,C=2,D=3,E=4,….Y=24,Z=25)
Step 2
Calculate
Y=(X+K) mod 26
Step 3
Now convert the Y into letter matches
a)
Pompeii, key = D
|
P
|
O
|
M
|
P
|
E
|
I
|
I
|
|
                    Â
15
|
14
|
12
|
15
|
4
|
8
|
8
|
Now Key=D
D=3
|
P
|
O
|
M
|
P
|
E
|
I
|
I
|
|
                    Â
15
|
14
|
12
|
15
|
4
|
8
|
8
|
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
|
18
|
17
|
15
|
18
|
7
|
11
|
11
|
Step4
|
|
P
|
O
|
M
|
P
|
E
|
I
|
I
|
|
|
                    Â
15
|
14
|
12
|
15
|
4
|
8
|
8
|
|
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
|
(mod 26)
|
18
|
17
|
15
|
18
|
7
|
11
|
11
|
|
|
18
|
17
|
15
|
18
|
7
|
11
|
11
|
Step 5
Now convert back to letters
|
|
P
|
O
|
M
|
P
|
E
|
I
|
I
|
|
|
                    Â
15
|
14
|
12
|
15
|
4
|
8
|
8
|
|
|
3
|
3
|
3
|
3
|
3
|
3
|
3
|
|
(mod 26)
|
18
|
17
|
15
|
18
|
7
|
11
|
11
|
|
|
18
|
17
|
15
|
18
|
7
|
11
|
11
|
|
|
S
|
R
|
P
|
S
|
H
|
K
|
K
|
Therefore Answer is
SRPSHKK
---
b)
Vespasian, key = P
|
|
V
|
E
|
S
|
P
|
A
|
S
|
I
|
A
|
N
|
|
|
21
|
4
|
18
|
15
|
0
|
18
|
8
|
0
|
13
|
|
key P
|
15
|
15
|
15
|
15
|
15
|
15
|
15
|
15
|
15
|
|
|
36
|
19
|
33
|
30
|
15
|
33
|
23
|
15
|
28
|
|
(mod 26)
|
10
|
19
|
7
|
4
|
15
|
7
|
23
|
15
|
2
|
|
|
K
|
U
|
H
|
E
|
P
|
H
|
X
|
P
|
C
|
Therefore Answer is
KUHEPHXPC
---
c)
Caligula, key = H
|
|
C
|
A
|
L
|
I
|
G
|
U
|
L
|
A
|
|
|
2
|
0
|
11
|
8
|
6
|
20
|
11
|
0
|
|
key H
|
7
|
7
|
7
|
7
|
7
|
7
|
7
|
7
|
|
|
9
|
7
|
18
|
15
|
13
|
27
|
18
|
7
|
|
(mod 26)
|
9
|
7
|
18
|
15
|
13
|
1
|
18
|
7
|
|
|
J
|
H
|
S
|
P
|
N
|
B
|
S
|
H
|
Therefore Answer is
JHSPNBSH
---
d)
Nero, key = T
|
|
N
|
E
|
R
|
O
|
|
|
13
|
4
|
17
|
14
|
|
key T
|
19
|
19
|
19
|
19
|
|
|
32
|
23
|
36
|
33
|
|
(mod 26)
|
6
|
23
|
10
|
7
|
|
|
G
|
X
|
K
|
H
|
Therefore Answer is
GXKH
