Question 1

The _________ algorithm takes the ciphertext and the same secret key and produces the original plaintext.

Accepted Answer

decryption

Question 2

The security of symmetric encryption depends on the secrecy of the algorithm, not the secrecy of the key.

Accepted Answer

The security of symmetric encryption primarily depends on the secrecy of the key, not the algorithm. The algorithms are often public, and security relies on keeping the key secret.

Question 3

The primary advantage of a stream cipher is that stream ciphers are almost always faster and use far less code than do block ciphers.

Accepted Answer

Stream ciphers encrypt plaintext one byte or bit at a time, making them generally faster and more efficient in terms of code and memory usage compared to block ciphers, which operate on larger, fixed-size blocks of plaintext.

Question 4

Smaller block sizes mean greater security but reduced encryption/decryption speed.

Accepted Answer

Smaller block sizes do not inherently mean greater security; in fact, they can make an encryption algorithm more susceptible to certain attacks. The security of a block cipher depends on various factors, including its design, key size, and mode of operation, not just the block size.

Question 5

Triple DES was first standardized for use in financial applications in ANSI standard X9.17 in 1985.

Accepted Answer

Triple DES (3DES) was indeed standardized for use in financial applications in the ANSI X9.17 standard in 1985, providing a more secure alternative to the original Data Encryption Standard (DES) by using multiple encryption keys.

Question 6

An encryption scheme is __________ if the cost of breaking the cipher exceeds the value of the encrypted information and/or the time required to break the cipher exceeds the useful lifetime of the information.

Accepted Answer

The answer of An encryption scheme is __________ if the...

Question 7

With the use of symmetric encryption, the principal security problem is maintaining the secrecy of the _________ .

Accepted Answer

The answer of With the use of symmetric encryption, the...

Question 8

The Feistel structure is a particular example of the more general structure used by all symmetric block ciphers.

Accepted Answer

The Feistel structure is a specific design model used in many symmetric block ciphers, but not all symmetric block ciphers use the Feistel structure. It is a particular example of a symmetric design, but there are other designs like the Substitution-Permutation Network (SPN) used in symmetric block ciphers as well.

Question 9

Public-key encryption is also referred to as conventional encryption, secret-key, or single-key encryption.

Accepted Answer

Public-key encryption is known as asymmetric encryption because it uses two keys (a public key and a private key) for encryption and decryption, unlike conventional or secret-key encryption, which uses a single key and is also known as symmetric encryption.

Question 10

The ciphertext-only attack is the easiest to defend against because the opponent has the least amount of information to work with.

Accepted Answer

In a ciphertext-only attack, the attacker only has access to the ciphertext, making it the scenario where they have the least amount of information about the encryption scheme, keys, or plaintext, thus making it generally easier to defend against compared to other types of attacks where more information might be available to the attacker.

Question 11

Three broad categories of cryptographic algorithms are commonly used to create PRNGs: Asymmetric ciphers, Hash functions and message authentication codes, and ___________ .

Accepted Answer

The answer of Three broad categories of cryptographic algorithms are...

Question 12

Random numbers play an important role in the use of encryption for various network security applications.

Accepted Answer

Random numbers are used to generate keys and initialization vectors for encryption algorithms, and also for generating random challenges and nonces for authentication and key exchange protocols. Therefore, random numbers are crucial for ensuring the security of network communications.

Question 13

Ciphertext is the scrambled message produced as output.

Accepted Answer

Ciphertext is the result of encryption applied to plaintext, where the original message is scrambled into an unreadable format for security purposes.

Question 14

The most commonly used symmetric encryption algorithms are stream ciphers.

Accepted Answer

The most commonly used symmetric encryption algorithms include both stream ciphers and block ciphers, with block ciphers like AES being more widely used in many standard encryption protocols and applications.

Question 15

The essence of a symmetric block cipher is that a single round offers inadequate security but that multiple rounds offer increasing security.

Accepted Answer

A symmetric block cipher typically uses multiple rounds of encryption to enhance security. Each round applies a series of transformations to the plaintext, and while a single round might be vulnerable to attacks, multiple rounds significantly increase the complexity and security of the cipher against various cryptographic attacks.

Question 16

The principal drawback of 3DES is that the algorithm is relatively sluggish in software.

Accepted Answer

3DES (Triple Data Encryption Standard) is slower in software implementations compared to other algorithms because it applies the DES encryption process three times to each data block, significantly increasing the time required for encryption and decryption.

Question 17

The advantage of a block cipher is that you can reuse keys.

Accepted Answer

Block ciphers allow for the reuse of keys because they encrypt data in fixed-size blocks, making it efficient to use the same key for multiple blocks of data.

Question 18

AES uses a Feistel structure.

Accepted Answer

AES (Advanced Encryption Standard) does not use a Feistel structure. Instead, it is based on a substitution-permutation network (SPN) architecture.

Question 19

The process of attempting to discover the plaintext or key is known as _________ .

Accepted Answer

The answer of The process of attempting to discover the...

Question 20

A _________ cipher processes the plaintext input in fixed sized blocks and produces a block of ciphertext of equal size for each plaintext block.

Accepted Answer

The answer of A _________ cipher processes the plaintext input...

Quiz 2: Symmetric Encryption and Message Confidentiality