CREST CREST Cryptography & Data Protection 2

Question 1

Which key exchange protocol allows two parties to establish a shared secret over an insecure channel without transmitting the secret?

Accepted Answer

Diffie-Hellman

Answer

Diffie-Hellman key exchange enables two parties to derive a shared secret using public values without ever transmitting the secret itself.

Question 2

What type of attack exploits weak random number generation to predict or recover cryptographic keys?

Accepted Answer

Entropy attack

Answer

An entropy attack exploits predictable or low-entropy random number generators to recover or predict cryptographic key material.

Question 3

Which attack on block ciphers exploits predictable CBC-mode padding to decrypt ciphertext without knowing the key?

Accepted Answer

Padding oracle attack

Answer

A padding oracle attack leverages server responses about invalid padding in CBC mode to iteratively decrypt ciphertext byte by byte.

Question 4

In the context of PKI, what does a Certificate Revocation List (CRL) contain?

Accepted Answer

Serial numbers of revoked certificates

Answer

A CRL is a list published by a CA containing the serial numbers of certificates that have been revoked before their expiry date.

Question 5

What is the primary purpose of a Hardware Security Module (HSM) in a cryptographic system?

Accepted Answer

Generating and protecting cryptographic keys in tamper-resistant hardware

Answer

An HSM is a dedicated hardware device that generates, stores, and manages cryptographic keys in a tamper-resistant environment.

(CREST) Council for Registered Ethical Security Testers Practice Test