UGC-NET | UGC NET CS 2017 Jan – III | Question 29
In RSA public key cryptosystem suppose n = p ∗ q where p and q are primes. (e, n) and (d, n) are public and private keys respectively. Let M be an integer such that o < M < n and φ(n) = (p – 1)(q – 1). Which of the following equations represent RSA public key cryptosystem ?
I. C ≡ Me(mod n) M ≡ (C)d(mod n) II.ed ≡ 1(mod n) III.ed ≡ 1(mod φ(n)) IV. C ≡ Me(mod φ(n)) M ≡ Cd(mod φ(n))
(A) I and II
(B) I and III
(C) II and III
(D) I and IV
Explanation: I is true because
Encrypted-Text = (Plain-Text)e mod n Plain-Text = (Encrypted-Text)d mod n
III is true because
d-1 = e mod ϕ(n) Or ed = 1 mod ϕ(n)
II and IV is wrong.
So, option (B) is correct.
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