ACL Cryptography & Encryption 2

Question 1

Which encryption mode of operation turns a block cipher into a stream cipher by XORing plaintext with an encrypted counter value?

Accepted Answer

CTR

Answer

Counter (CTR) mode encrypts a sequentially incrementing counter and XORs the result with plaintext, effectively creating a keystream like a stream cipher.

Question 2

In an ACL environment, what is the primary purpose of a Key Encryption Key (KEK)?

Accepted Answer

Encrypting other cryptographic keys for secure storage or transmission

Answer

A KEK is used to encrypt other keys (such as data encryption keys), enabling secure key distribution without exposing the keys in plaintext.

Question 3

Which property ensures that an encrypted message cannot be linked to the plaintext even if an attacker sees multiple ciphertexts of the same message?

Accepted Answer

Semantic security (IND-CPA)

Answer

IND-CPA (indistinguishability under chosen-plaintext attack) ensures that encrypting the same plaintext twice yields ciphertexts that an attacker cannot distinguish.

Question 4

A network administrator wants to ensure that session keys are not compromised even if the server's long-term private key is later stolen. Which technique provides this?

Accepted Answer

Perfect forward secrecy (PFS)

Answer

Perfect forward secrecy uses ephemeral key exchanges (e.g., DHE or ECDHE) so that each session generates a unique key that is not derivable from the long-term private key.

Question 5

Which hashing algorithm is considered cryptographically broken and should NOT be used for integrity verification in modern ACLs or security policies?

Accepted Answer

MD5

Answer

MD5 is considered cryptographically broken due to demonstrated collision attacks, making it unsuitable for security-critical integrity verification.

(ACL) Access Control Lists Practice Test

(ACL) Access Control Lists Practice Test

ACL Cryptography & Encryption 2