01
True or false
1 point
In symmetric encryption, the sender and receiver use the same secret key to encrypt and decrypt data.
Free Practice Quiz Question List
2 Symmetric Encryption and Authenticated Encryption Online Quiz Questions
Use this free practice quiz with 20 questions to review 2 Symmetric Encryption and Authenticated Encryption, test your knowledge, and prepare for your next test or exam.
20 questions
02
True or false
1 point
When AEAD authenticates associated data, that data is encrypted and hidden from observers.
- A
True
- B
False
03
Choose one
1 point
A file contains repeated identical plaintext blocks. Which statement best explains why ECB can reveal patterns when encrypting it?
- A
ECB, because it combines each block with the preceding ciphertext block.
- B
ECB, because identical plaintext blocks produce identical ciphertext blocks under the same key.
- C
CTR, because it requires padding for messages of varying length.
- D
CBC, because it authenticates each ciphertext block.
04
Fill in the blank
1 point
In CBC mode, before encryption, each plaintext block is combined with the .
05
Written response
1 point
What widely used block cipher transforms fixed-size blocks under a key, with a mode of operation specifying how to apply it to messages of varying length?
06
Choose one
1 point
A system needs a confidentiality mode that can process blocks in parallel and does not require padding. Which description fits CTR?
- A
It combines each plaintext block with the preceding ciphertext block and typically requires padding.
- B
It encrypts successive counter values to produce a keystream, needs no padding, and supports parallel processing.
- C
It encrypts each plaintext block independently, concealing repeated-block patterns.
- D
It authenticates data without using a separate authentication mechanism.
07
Choose all
1 point
Which statements about AEAD are correct? Select all that apply.
- A
It protects plaintext confidentiality.
- B
It identifies which holder of a shared key created the message.
- C
It detects attempts to alter ciphertext.
- D
It encrypts associated data so observers cannot read it.
08
Fill in the blank
1 point
During AEAD decryption, the application must before accepting or acting on the plaintext.
09
Written response
1 point
A common GCM nonce length is how many bits? Enter the number only.
10
Choose one
1 point
A team uses AEAD with a key shared by several services. What can the authentication result establish about who created a valid message?
- A
The message must have been produced by a specific, identifiable key holder.
- B
The message has public-key nonrepudiation.
- C
Someone holding the shared key produced the data, but the specific key holder cannot be identified from this alone.
- D
The message is confidential, but AEAD cannot detect alteration.
11
Choose all
1 point
A service is being designed to encrypt messages with an AEAD algorithm. Which practices follow the material's safety guidance? Select all that apply.
- A
Use a well-reviewed cryptographic library's AEAD interface.
- B
Track nonce use across all devices or processes sharing a key when the algorithm requires unique nonces.
- C
Accept decrypted plaintext first and check its tag only if an error later appears.
- D
Authenticate relevant visible metadata as AAD and reject a message if its tag does not verify.
12
Open ended
1 point
A legacy system must continue using CBC. What protection does CBC provide, what important protection does it lack, and what should the system add to address that gap?
13
Choose one
1 point
An engineer is configuring GCM and asks whether the nonce must be secret. Which statement gives the most accurate guidance?
- A
The nonce must be secret, but it may be repeated with the same key.
- B
The nonce usually need not be secret, but for common AEAD constructions such as GCM it must not be reused with the same key.
- C
The nonce must be identical for every message encrypted with a given key.
- D
A nonce is only needed when the plaintext is longer than one block.
14
Written response
1 point
In AEAD, what does the abbreviation AAD stand for?
15
Choose one
1 point
A system encrypts data with a secret key, and its receiver decrypts the data using that same key. Which kind of encryption is the system using?
- A
Use symmetric encryption with a shared secret key.
- B
Use a public-key signature as the encryption and decryption method.
- C
Use an initialization vector as the secret key.
- D
Use authenticated data as the decryption key.
16
Choose one
1 point
A file encrypted with ECB contains repeated plaintext blocks. What pattern-related risk remains?
- A
It requires padding, which hides all repetition in the plaintext.
- B
Identical plaintext blocks produce identical ciphertext blocks under the same key.
- C
It authenticates ciphertext, so repeated blocks cannot be observed.
- D
It encrypts each block using a unique counter value.
17
True or false
1 point
True or false: A nonce or initialization value must always be kept secret for encryption to be secure.
- A
True
- B
False
18
Written response
1 point
In AEAD, what is the term for visible information—such as a message header—that is authenticated but not encrypted?
19
Choose one
1 point
A legacy system must keep using CBC. What should it add to protect against undetected ciphertext alteration?
- A
CBC authenticates ciphertext automatically, so no further protection is needed.
- B
CBC cannot provide confidentiality unless its IV is secret.
- C
Add a separate, correctly designed authentication mechanism.
- D
Replace the IV with a nonce that is reused for every message.
20
Choose one
1 point
An application uses CTR mode with one key for multiple messages. Which rule must it follow for counter inputs?
- A
Never repeat counter inputs under the same key.
- B
Use padding to ensure each message has a whole number of blocks.
- C
Keep every counter input secret from the receiver.
- D
Authenticate the counter by encrypting it independently with ECB.