1. Which cryptographic method uses the same key for encryption and decryption?
a) Asymmetric
b) Symmetric ✅
c) Hash Function
d) Digital Signature
→ Explanation: Symmetric cryptography uses one key for both encryption and decryption.
2. Which of the following is a property of a secure hash function?
a) High entropy
b) Collision resistance ✅
c) Key-based reversibility
d) Low latency
→ Explanation: Collision resistance ensures no two inputs produce the same hash output.
3. What is the primary use of a digital signature?
a) Encrypt large files
b) Ensure confidentiality
c) Authenticate sender and ensure integrity ✅
d) Compress data
→ Explanation: Digital signatures confirm authenticity and integrity.
4. What does the “X.509” standard specify?
a) Encryption algorithm
b) Hashing algorithm
c) Public key certificate format ✅
d) Key generation method
→ Explanation: X.509 defines the format of digital certificates.
5. Which component in PKI is responsible for issuing certificates?
a) Registration Authority (RA)
b) Certificate Authority (CA) ✅
c) Repository
d) Hash Function
→ Explanation: CA issues and signs digital certificates.
6. Which hash algorithm is considered secure as of now?
a) MD5
b) SHA-1
c) SHA-256 ✅
d) DES
→ Explanation: SHA-256 is part of the SHA-2 family and is currently secure.
7. What is used in asymmetric cryptography to verify a digital signature?
a) Private key
b) Symmetric key
c) Public key ✅
d) Initialization vector
→ Explanation: Public key verifies a signature created using a private key.
8. What is the main challenge in symmetric key cryptography?
a) Encryption speed
b) Key length
c) Secure key distribution ✅
d) Algorithm complexity
→ Explanation: Safely sharing the secret key is the main challenge.
9. Which element is not part of an X.509 certificate?
a) Validity period
b) Issuer name
c) Hash algorithm ✅
d) Subject’s public key
→ Explanation: The hash algorithm is used but not directly stored in the certificate.
10. What role does a Key Distribution Center (KDC) play?
a) Signing digital certificates
b) Storing all public keys
c) Sharing symmetric session keys ✅
d) Managing X.509 certificates
→ Explanation: A KDC provides symmetric keys to authenticated users.
11. What is the purpose of a Certificate Revocation List (CRL)?
a) To renew expired certificates
b) To revoke public keys automatically
c) To list certificates that are no longer valid ✅
d) To archive old certificates
→ Explanation: CRL lists certificates that have been revoked before their expiry.
12. Which of the following algorithms is primarily used for digital signatures?
a) AES
b) DSA ✅
c) SHA-256
d) Diffie-Hellman
→ Explanation: DSA (Digital Signature Algorithm) is designed for digital signing.
13. Which property of a hash function ensures that a small change in input drastically
changes the output?
a) Collision resistance
b) Pre-image resistance
c) Avalanche effect ✅
d) Determinism
→ Explanation: Avalanche effect means even 1-bit change alters the hash completely.
14. What does non-repudiation ensure in cryptography?
a) Data is encrypted
b) Sender cannot deny sending the message ✅
c) Receiver knows the sender
d) Keys are not leaked
→ Explanation: Non-repudiation means the sender can’t deny authorship of a message.
15. What is a limitation of the RSA algorithm?
a) It cannot be used for encryption
b) It requires large key sizes for strong security ✅
c) It doesn’t support authentication
d) It’s a symmetric algorithm
→ Explanation: RSA needs large key sizes (2048+ bits) to stay secure.
16. What is a hybrid cryptosystem?
a) Uses same key for all users
b) Uses outdated algorithms
c) Combines symmetric and asymmetric cryptography ✅
d) Compresses encrypted data
→ Explanation: Hybrid systems use asymmetric cryptography to share symmetric session keys.
17. What is the purpose of the Registration Authority (RA) in PKI?
a) Revoking keys
b) Signing certificates
c) Validating user identities before certificate issuance ✅
d) Encrypting data
→ Explanation: RA validates identities and forwards the request to CA.
18. Which cryptographic concept is used to verify data integrity?
a) Encryption
b) Hashing ✅
c) Key exchange
d) Certificate
→ Explanation: Hashing ensures data has not been modified.
19. What does the term “pre-image resistance” mean in hashing?
a) Hash values are encrypted
b) Hash functions are reversible
c) It's hard to find an input for a given output ✅
d) No hash collisions can occur
→ Explanation: Pre-image resistance prevents deriving input from the hash.
20. In digital signature creation, what step happens before signing the message?
a) Encrypting with public key
b) Decrypting the message
c) Hashing the message ✅
d) Verifying the sender
→ Explanation: The message is first hashed, then the hash is signed using the sender’s private
key.
21. Which attack aims to find two different inputs that produce the same hash value?
a) Replay attack
b) Brute force attack
c) Birthday attack ✅
d) Timing attack
→ Explanation: The birthday attack exploits the probability of hash collisions.
22. What key concept is used in SSL/TLS to initiate a secure session?
a) Asymmetric encryption for entire session
b) Shared password-based session
c) Public key for handshake, symmetric key for session ✅
d) Only hashing for integrity
→ Explanation: TLS uses asymmetric encryption during handshake and symmetric encryption
afterward.
23. Which part of an X.509 certificate provides the issuer’s identity?
a) Subject field
b) Public Key Info
c) Issuer field ✅
d) Extensions
→ Explanation: The "Issuer" field states who issued the certificate.
24. Which is not typically part of a Public Key Infrastructure (PKI)?
a) Certificate Authority (CA)
b) Registration Authority (RA)
c) Key Logger ✅
d) Certificate Repository
→ Explanation: Key loggers are malicious tools, unrelated to PKI.
25. What ensures the authenticity of a public key in a certificate?
a) CA’s digital signature ✅
b) MAC code
c) Secure Hash Algorithm
d) User verification
→ Explanation: CA digitally signs certificates to vouch for the authenticity of the public key.
26. What makes asymmetric encryption more computationally intensive than symmetric
encryption?
a) Uses longer passwords
b) Involves only hashing
c) Involves large prime number operations ✅
d) Requires multiple certificates
→ Explanation: Public-key cryptography involves large-number modular arithmetic (e.g., RSA,
ECC).
27. In digital certificates, what does the 'validity period' define?
a) Time taken to issue the certificate
b) Date range the certificate is valid ✅
c) Certificate version
d) Certificate’s hash
→ Explanation: Validity period defines start and end dates of certificate usage.
28. What is one benefit of Elliptic Curve Cryptography (ECC) over RSA?
a) More secure with longer keys
b) Same security with smaller keys ✅
c) Easier to implement
d) Replaces hashing
→ Explanation: ECC offers same level of security as RSA with shorter key lengths, improving
efficiency.
29. What happens if a private key is compromised in a digital signature system?
a) Only hashing is affected
b) Future signatures remain secure
c) Anyone can forge the sender’s signature ✅
d) Certificate auto-renews
→ Explanation: If the private key is leaked, attackers can impersonate the key owner.
30. Which of the following is true about Message Authentication Code (MAC)?
a) It uses asymmetric encryption
b) It provides confidentiality
c) It ensures message integrity using a shared secret ✅
d) It replaces digital signatures
→ Explanation: MAC is a symmetric method ensuring data integrity and authenticity using a
shared key.
