CAP Cryptography & Encryption 2 — Questions and Answers
Question 1: Which cryptographic concept ensures that a sender cannot later deny having sent a message?
- Confidentiality
- Integrity
- Non-repudiation (Correct answer)
- Availability
Correct answer: Non-repudiation
Non-repudiation, typically achieved via digital signatures, prevents a sender from falsely denying they originated a message.
Question 2: In the context of PKI, what is the role of a Certificate Revocation List (CRL)?
- It lists all valid certificates issued by a CA
- It identifies certificates that have been invalidated before their expiration date (Correct answer)
- It stores the public keys of all registered users
- It encrypts certificate data in transit
Correct answer: It identifies certificates that have been invalidated before their expiration date
A CRL is a list published by a Certificate Authority that identifies certificates that have been revoked prior to their scheduled expiration.
Question 3: Which key exchange protocol allows two parties to securely establish a shared secret over an insecure channel without prior shared secrets?
- RSA key exchange
- Diffie-Hellman (Correct answer)
- AES key wrapping
- HMAC-based key derivation
Correct answer: Diffie-Hellman
Diffie-Hellman key exchange enables two parties to derive a shared secret over a public channel without previously sharing any secret material.
Question 4: What distinguishes a stream cipher from a block cipher?
- Stream ciphers use asymmetric keys; block ciphers use symmetric keys
- Stream ciphers encrypt one bit or byte at a time; block ciphers encrypt fixed-size chunks (Correct answer)
- Stream ciphers require a PKI infrastructure; block ciphers do not
- Stream ciphers are always slower than block ciphers
Correct answer: Stream ciphers encrypt one bit or byte at a time; block ciphers encrypt fixed-size chunks
Stream ciphers process plaintext one bit or byte at a time using a keystream, whereas block ciphers encrypt data in fixed-size blocks.
Question 5: Which FIPS standard specifies the Advanced Encryption Standard (AES)?
- FIPS 140-2
- FIPS 186-4
- FIPS 197 (Correct answer)
- FIPS 199
Correct answer: FIPS 197
FIPS 197 formally specifies AES, which supports key lengths of 128, 192, and 256 bits.
Question 6: In public key cryptography, what is used to verify a digital signature?
- The signer's private key
- The signer's public key (Correct answer)
- A symmetric session key
- A shared HMAC secret
Correct answer: The signer's public key
A digital signature is created with the signer's private key and verified by anyone using the corresponding public key.
Question 7: Which block cipher mode of operation produces ciphertext that is the same length as the plaintext and does NOT require padding?
- CBC (Cipher Block Chaining)
- ECB (Electronic Codebook)
- CTR (Counter) (Correct answer)
- CFB (Cipher Feedback)
Correct answer: CTR (Counter)
CTR mode turns a block cipher into a stream cipher by encrypting a counter value, producing output the same length as the input without padding.
CAP Cryptography & Encryption 2
Which cryptographic concept ensures that a sender cannot later deny having sent a message?