Q5,Paper 2,d 13. Using the RSA public key crypto system, if p = 13, q = 31 and d = 7, then the value of e is

(A) 101

(B) 103

(C) 105

(D) 107

Answer B.

Explanation.

N=pxq.=31x13=403.

Phi=(p-1)*(q-1).=360

Choose e such that (d*e)%phi=1

(7*103)%360=1. So  e=103.