Cryptography & Encryption Flashcards
7 cards from real ACL practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.
Read the first 7 Cryptography & Encryption flashcards as text
Which encryption mode of operation turns a block cipher into a stream cipher by XORing plaintext with an encrypted counter value?
Answer: CTR
Counter (CTR) mode encrypts a sequentially incrementing counter and XORs the result with plaintext, effectively creating a keystream like a stream cipher.
In an ACL environment, what is the primary purpose of a Key Encryption Key (KEK)?
Answer: Encrypting other cryptographic keys for secure storage or transmission
A KEK is used to encrypt other keys (such as data encryption keys), enabling secure key distribution without exposing the keys in plaintext.
Which property ensures that an encrypted message cannot be linked to the plaintext even if an attacker sees multiple ciphertexts of the same message?
Answer: Semantic security (IND-CPA)
IND-CPA (indistinguishability under chosen-plaintext attack) ensures that encrypting the same plaintext twice yields ciphertexts that an attacker cannot distinguish.
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?
Answer: Perfect forward secrecy (PFS)
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.
Which hashing algorithm is considered cryptographically broken and should NOT be used for integrity verification in modern ACLs or security policies?
Answer: MD5
MD5 is considered cryptographically broken due to demonstrated collision attacks, making it unsuitable for security-critical integrity verification.
When RSA is used for encryption, what makes it computationally infeasible to decrypt without the private key?
Answer: The difficulty of factoring large prime products
RSA security relies on the integer factorization problem: it is easy to multiply two large primes but computationally hard to factor their product back into primes.
Which certificate field specifies the cryptographic algorithms that a Certificate Authority used to sign a digital certificate?
Answer: Signature Algorithm
The Signature Algorithm field in an X.509 certificate identifies the algorithm (e.g., SHA-256 with RSA) that the CA used to produce the certificate's digital signature.