# GATE Questions & Answers of Network Security: Authentication, Basics of Public Key and Private Key Cryptography

## What is the Weightage of Network Security: Authentication, Basics of Public Key and Private Key Cryptography in GATE Exam?

Total 8 Questions have been asked from Network Security: Authentication, Basics of Public Key and Private Key Cryptography topic of Computer Networks subject in previous GATE papers. Average marks 1.38.

In an RSA cryptosystem, the value of the public modulus parameter $n$ is 3007. If it is also known that $\mathrm\varphi\left(n\right)=2880$, where $\mathrm\varphi()$ denotes Euler’s Totient Function, then the prime factor of $n$ which is greater than 50 is ____________________.

A sender S sends a message m to receiver R, which is digitally signed by S with its private key. In this scenario, one or more of the following security violations can take place.

(I)  S can launch a birthday attack to replace m with a fraudulent message.

(II)  A third party attacker can launch a birthday attack to replace m with a fraudulent message.

(III)  R can launch a birthday attack to replace m with a fraudulent message.

Which of the following are possible security violations?

In a RSA cryptosystem, a participant A uses two prime numbers p=13 and q=17 to genrate her public and private keys. If the public key of A is 35, then the privae key of A is __________.

Anarkali digitally signs a message and sends it to Salim. Verification of the signature by Salim requires

Suppose that everyone in a group of N people wants to communicate secretly with the N-1 others using symmetric key cryptographic system. The communication between any two persons should not be decodable by the others in the group. The number of keys required in the system as a whole to satisfy the confidentiality requirement is

Which of the following are used to generate a message digest by the network security protocols?
(P) RSA (Q) SHA-1 (R) DES (S) MD5

Using public key cryptography, X adds a digital signature σ to message M, encrypts <M, σ>, and sends it to Y, where it is decrypted. Which one of the following sequences of keys is used for the operations?

In the RSA public key cryptosystem, the private and public keys are (e,n) and (d,n) respectively, where n=p*q and p and q are large primes. Besides, n is public and p and q are private. Let M be an integer such that 0<M<n and Φ(n) = (p-1)(q-1). Now consider the following equations.

I.   M' = Me mod n
M = (M')d mod n
II.  ed $\equiv$ 1 mod n
III. ed $\equiv$ 1 mod Φ(n)
IV. M' = Me mod Φ(n)
M = (M')d mod Φ(n)

Which of the above equations correctly represent RSA cryptosystem?