Digital signatures and certificates in Computer Networks - Practice Problems & Coding Challenges

Challenge - 5 Problems

🧠 Conceptual

intermediate

How does a digital signature ensure message integrity?

Which of the following best explains how a digital signature helps verify that a message has not been altered?

A It encrypts the entire message with the sender's private key so the receiver can decrypt it with the sender's public key.

B It adds a timestamp to the message to prove when it was sent.

C It uses the receiver's public key to encrypt the message, ensuring only the receiver can read it.

D It creates a unique hash of the message that is encrypted with the sender's private key, allowing the receiver to verify the hash matches the message.

💡 Hint

Think about how the receiver can check if the message content changed after signing.

A digital signature is created by hashing the message and encrypting that hash with the sender's private key. The receiver decrypts the signature with the sender's public key and compares the hash to the message's hash. If they match, the message is intact.

📋 Factual

intermediate

What role does a Certificate Authority (CA) play?

What is the primary function of a Certificate Authority in digital certificates?

A It generates private keys for users to sign messages.

B It verifies identities and issues digital certificates to bind public keys to those identities.

C It encrypts all internet traffic to ensure privacy.

D It stores all users' passwords securely.

💡 Hint

Consider who confirms that a public key belongs to a specific person or organization.

A Certificate Authority verifies the identity of entities and issues digital certificates that link a public key to that verified identity, helping others trust the key.

🔍 Analysis

advanced

Why might a digital certificate be considered invalid?

Which of the following situations would cause a digital certificate to be considered invalid or untrustworthy?

A The certificate's expiration date has passed.

B The certificate was issued by a trusted Certificate Authority.

C The certificate contains the correct public key for the sender.

D The certificate is stored on the sender's device.

💡 Hint

Think about the importance of certificate validity periods.

A digital certificate has a validity period. If the expiration date has passed, the certificate is no longer trusted because it may not reflect current ownership or security standards.

❓ Comparison

advanced

Difference between digital signature and encryption

Which statement correctly distinguishes a digital signature from encryption?

A Both encryption and digital signatures are used only to hide message content from others.

B Encryption verifies the sender's identity, while a digital signature hides the message content.

C Encryption hides the message content, while a digital signature verifies the sender's identity and message integrity.

D Digital signatures and encryption are the same processes using different keys.

💡 Hint

Consider the purpose of each process: hiding content vs proving authenticity.

Encryption protects message confidentiality by hiding content, while digital signatures prove who sent the message and that it was not changed.

❓ Reasoning

expert

What happens if a private key is compromised?

If an attacker gains access to a user's private key used for digital signatures, what is the most serious consequence?

A The attacker can create fake digital signatures that appear to come from the user.

B The attacker can revoke the user's digital certificate immediately.

C The attacker can decrypt all messages sent to the user.

D The attacker can only read messages but cannot impersonate the user.

💡 Hint

Think about what a private key is used for in signing messages.

The private key is used to create digital signatures. If compromised, an attacker can forge signatures, pretending to be the user and sending fake messages that appear authentic.