Correct Answer - Option 3 : 37
Step:
RSA Algorithm:
1) Calculate value of n = p × q, where p and q are prime no.’s
2) calculate Ø(n) = (p-1) × (q-1)
3) consider d as public key such that Ø(n) and d has no common factors.
4) consider e as private key such that (e × d) mod Ø(n) = 1
5) Cipher text c = message i.e. md mod n
6) message = cipher text i.e. ce mod n
Calculation
p =7, q= 11, e = 13
Use step 2 and 4 of RSA algorithm to calculate private key.
Ø(n) = (7– 1) × (11 – 1) = 6 × 10 = 60
Now,
(e × d) mod Ø(n) = 1
(13 × d) mod 60 = 1
d = 37
So, key of A = 37