RSA
step 1 : n = p*q = 5*17 = 85
step 2: $\Phi (n)$ = (p-1)(q-1) = 4*16= 64
step3 : e*d mod $\Phi (n)$ = 1 [ use extended Euclidian Algorithm to find value of e ]
e*13 mod 64 = 1 => e=5
Encryption
- Obtains the recipient B's public key (n, e).
- Represents the plaintext message as a positive integer m, 1 < m < n
- Computes the ciphertext c = me mod n.
- Sends the ciphertext c to RECEIVER
Deryption
- Uses his private key (n, d) to compute m = cd mod n.
- Extracts the plaintext from the message representative m.
[ given Encoding : A-1 , B-2 , C- 3....Z-26 ]
I -> 9 => 95 mod 85 = 59 => (59-52 = 7) =>G
I -> 9 => 95 mod 85 = 59 => (59-52 = 7) =>G
T->20 =>205 mod 85 = 5 => E
Sum Of Integers In cipher Text = 7+7+5 = 19
Good Read : https://gateoverflow.in/70939/ugcnet-aug2016-iii-30