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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))

Codes :

(1) I and II         (2) I and III         (3) II and III         (4) I and IV

In RSA algorithm

1) Cipher text is obtained as $Cipher Text = (Plain Text)^{public\ key} \ mod n$

2) Plain Text is obtained as $Plain Text = (Cipher Text)^{private\ key} \ mod n$

3) e should be chosen in such a way that it satisfy $e*d = 1(mod)\phi (n)$

Hence option (2) is correct