A public key is a fundamental component of asymmetric cryptography, designed to enable secure communication and data protection. It is part of a key pair that includes a corresponding private key, where the public key can be freely shared with others.
In practice, the public key is used for encryption: any message encrypted with it can only be decrypted using the associated private key. This ensures that even if the public key is widely distributed, only the owner of the private key can access the encrypted information.
Public keys also play a key role in digital signatures, where they verify the authenticity and integrity of signed data. For example, a sender can sign a message with their private key, and the recipient can use the sender’s public key to confirm the signature’s validity.
This system enhances security by allowing open sharing without exposing sensitive information, making it essential for applications like secure email (e.g., PGP), HTTPS web traffic, and blockchain transactions.
Public keys are typically generated using algorithms such as RSA, ECC (Elliptic Curve Cryptography), or DSA, and they are often encoded in formats like PEM or DER for easy distribution and storage.
Table of contents
- Part 1: OnlineExamMaker AI quiz generator – The easiest way to make quizzes online
- Part 2: 20 public key quiz questions & answers
- Part 3: Automatically generate quiz questions using AI Question Generator
Part 1: OnlineExamMaker AI quiz generator – The easiest way to make quizzes online
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Part 2: 20 public key quiz questions & answers
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1. What is the primary purpose of public key cryptography?
A. To provide fast symmetric encryption
B. To enable secure communication without sharing a secret key beforehand
C. To replace all forms of symmetric encryption
D. To ensure data integrity only
Answer: B
Explanation: Public key cryptography uses a pair of keys (public and private) to allow secure communication, as the public key can be shared openly while the private key remains secret.
2. In RSA, what is the role of the public key?
A. To decrypt messages
B. To encrypt messages and verify signatures
C. To generate random numbers
D. To hash data
Answer: B
Explanation: The public key in RSA is used for encrypting data and verifying digital signatures, while the private key is used for decryption and signing.
3. Which algorithm is commonly used for key exchange in public key cryptography?
A. AES
B. DES
C. Diffie-Hellman
D. SHA-256
Answer: C
Explanation: Diffie-Hellman allows two parties to establish a shared secret key over an insecure channel without exchanging the key directly.
4. What happens if an attacker obtains the public key in a public key system?
A. They can decrypt all messages encrypted with it
B. They can impersonate the owner
C. Nothing significant, as it’s designed to be public
D. They can generate the private key
Answer: C
Explanation: The public key is intended for public distribution and does not compromise security, as only the private key can decrypt or sign messages.
5. In digital signatures, what is signed with the private key?
A. The entire message
B. A hash of the message
C. The public key
D. A symmetric key
Answer: B
Explanation: Digital signatures typically involve signing a hash of the message with the private key to ensure authenticity and integrity without encrypting the full message.
6. Which of the following is a characteristic of elliptic curve cryptography (ECC)?
A. It uses large prime numbers like RSA
B. It requires shorter key lengths for equivalent security
C. It is slower than RSA for the same key size
D. It only works for symmetric encryption
Answer: B
Explanation: ECC provides the same level of security as RSA with smaller key sizes, making it more efficient for devices with limited resources.
7. What is the main advantage of using public key cryptography over symmetric key cryptography?
A. Faster encryption speed
B. Easier key distribution
C. Better for large data encryption
D. Secure key exchange without prior sharing
Answer: D
Explanation: Public key cryptography eliminates the need to securely share a secret key in advance, making it ideal for initial communications.
8. In a public key infrastructure (PKI), what does a certificate authority (CA) do?
A. Encrypts all user data
B. Issues and verifies digital certificates
C. Generates random keys
D. Decrypts intercepted messages
Answer: B
Explanation: A CA is responsible for issuing digital certificates that bind public keys to entities, ensuring trust in the key’s ownership.
9. If Alice wants to send a secure message to Bob using public key cryptography, what should she do?
A. Encrypt the message with Bob’s private key
B. Encrypt the message with her own private key
C. Encrypt the message with Bob’s public key
D. Use a symmetric key for everything
Answer: C
Explanation: Alice encrypts the message with Bob’s public key so that only Bob, with his private key, can decrypt it.
10. What is man-in-the-middle attack in the context of public key cryptography?
A. An attacker replaces keys during exchange
B. An attacker encrypts data multiple times
C. An attacker uses symmetric keys only
D. An attacker verifies digital signatures
Answer: A
Explanation: In a man-in-the-middle attack, an attacker intercepts and alters the public keys exchanged between parties, compromising communication security.
11. Which component of RSA is used to create the public and private key pair?
A. Modular exponentiation
B. Prime factorization
C. Bitwise operations
D. Hash functions
Answer: B
Explanation: RSA relies on the difficulty of prime factorization; the public key is derived from the product of two large primes, while the private key factors them.
12. Why is public key cryptography considered asymmetric?
A. It uses two different keys for operations
B. It only works with symmetric algorithms
C. It requires identical keys for encryption and decryption
D. It is faster than symmetric methods
Answer: A
Explanation: Asymmetric cryptography uses a public key for one operation (e.g., encryption) and a private key for the inverse (e.g., decryption).
13. In PGP (Pretty Good Privacy), how are messages typically encrypted?
A. Using only symmetric keys
B. Using a hybrid approach with public key for key exchange
C. Encrypting with the recipient’s private key
D. Directly with a digital signature
Answer: B
Explanation: PGP uses public key cryptography to securely exchange a symmetric key, which then encrypts the actual message for efficiency.
14. What does a digital certificate contain?
A. Only the public key
B. The public key and identity information
C. The private key and encryption algorithms
D. Symmetric keys for all users
Answer: B
Explanation: A digital certificate includes the public key along with details like the owner’s identity, issued by a trusted CA.
15. Which of the following is NOT a public key algorithm?
A. RSA
B. ECC
C. AES
D. Diffie-Hellman
Answer: C
Explanation: AES is a symmetric encryption algorithm, whereas RSA, ECC, and Diffie-Hellman are asymmetric or key exchange algorithms.
16. How does public key cryptography ensure non-repudiation?
A. By encrypting messages with a symmetric key
B. By using digital signatures with the private key
C. By sharing keys publicly
D. By hashing data multiple times
Answer: B
Explanation: Digital signatures created with the private key prove that only the owner could have signed the message, ensuring non-repudiation.
17. What is the security of RSA based on?
A. The difficulty of discrete logarithm
B. The hardness of factoring large primes
C. Random number generation
D. Elliptic curve operations
Answer: B
Explanation: RSA’s security relies on the computational difficulty of factoring the product of two large prime numbers.
18. In a key exchange using Diffie-Hellman, what do participants exchange?
A. Their private keys
B. A shared secret directly
C. Public values derived from private keys
D. Encrypted messages only
Answer: C
Explanation: Participants exchange public values, which allow each to compute the same shared secret without transmitting it directly.
19. Why might public key cryptography be less efficient for large files?
A. It requires more computational power
B. It uses shorter keys
C. It is faster than symmetric methods
D. It doesn’t support file encryption
Answer: A
Explanation: Public key operations are computationally intensive, making them impractical for encrypting large amounts of data compared to symmetric algorithms.
20. What is the purpose of the private key in public key cryptography?
A. To encrypt public messages
B. To decrypt messages encrypted with the public key
C. To be shared with everyone
D. To generate new public keys
Answer: B
Explanation: The private key is kept secret and used to decrypt data encrypted with the corresponding public key or to create digital signatures.
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