This set of Computer Networks Multiple Choice Questions & Answers (MCQs) focuses on “Digital Signatures”.

1. What can it be called, if an attacker determines the private key of the user, after breaking the signature scheme?

a) Universal forgery

b) Total break

c) Selective forgery

d) Existential forgery

View Answer

Explanation: Total break is finding private key and Universal forgery is finding signing algorithm. Selective forgery is doing forgery of signature for particular message. Atleast one message can have forgery signature.

2. Which of the following is not a requirement of digital signatures?

a) Easy to produce

b) Easy to recognize

c) Easy to verify

d) Computationally feasible

View Answer

Explanation: If a digital signature is computationally feasible, then it is very easy for a hacker to attack the signing scheme. He may forge the signature for the new message or change the signature for the present message.

3. Who will be the involving parties in the direct digital signature scheme?

a) source and destination

b) Source and third party

c) Destination and third party

d) Source and destination and third party

View Answer

Explanation: In general, there will be a third party, who authenticate the digital signatures. But there is no rule that everyone should believe the third party. So, the direct digital signature scheme involves sender and receiver. And receiver knows from where the message is coming using public key of the sender.

4. Which of the following sentence is incorrect in case for digital signatures?

a) Signature key is of signing and public key for verification

b) Public key for verification and signature is for authentication

c) Signature key is for verification and public key for signing

d) Both signing and verification is done by public key

View Answer

Explanation: In digital signature, private key is the signature key, that is used to create digital signature. And this private key belongs to the signer. Public key belongs to the receiver who receives the message. These two keys are used in digital signature algorithm.

5. What is the advantage of digital signing a hash instead of signing the entire data in RSA?

a) Time saving

b) Security

c) Time saving and computationally less expensive

d) Secured and less time requires

View Answer

Explanation: RSA uses expressions with exponential, that is modular exponentiation. So, it is difficult to let the large data be signed using modular exponentiation. Hash value of the message is small compared to the whole message. So, it saves time and computation power to use hash to be signed.

6. Which of the following cannot be achieved by the digital signature in symmetric key encryption?

a) Message authentication

b) Data integrity

c) Non-repudiation

d) Security of the message

View Answer

Explanation: Channel security is not in hands of digital signature, even the secret key is being transmitted between sender and receiver. Security of the message will be depending on the channel that is being used.

7. Which of the following digital signature technique is based on elliptic curve cryptography?

a) ECDSA

b) DSA

c) RSA PSS

d) RSA

View Answer

Explanation: ECDSA stands for elliptic curve digital signature algorithm. ECDSA has huge acceptance, because it uses small key bit length, elliptic curve cryptography and secured.

8. Which of the following is not a digital signature algorithm?

a) ECDSA

b) DSA

c) RSA – PSS

d) SHA

View Answer

Explanation: SHA(secured hash function) is the hash algorithm which uses MD4 hash function. ECDSA, DSA and RSA – PSS are the three algorithms in digital signatures. ECDSA stands for elliptic curve digital signature algorithm, RSA – PSS is probabilistic signature scheme. DSA is digital signature algorithm.

9. In which year, NIST proposed Elgamal algorithm in its new DSS(digital signature standard)?

a) 1993

b) 1992

c) 1991

d) 1990

View Answer

Explanation: After RSA public key algorithm, ElGamal was introduced for digital signatures. But it is claimed by the government, that this algorithm is too slow, insecure, new and secret to meet the cyptographic standards.

10. A signature function must be performed before the confidentiality function on a plain text in symmetric key digital signatures.

a) True

b) False

View Answer

Explanation: Confidentiality function involves receivers public key for encryption, and private key for decryption. The sender cannot deceive the receiver when the digital signature function is inside. Because decryption of the message cannot be done by the sender without receiver’s private key. And the sender cannot change the digital signature.

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