Question 1

The strength of a hash function against brute-force attacks depends solely on the length of the hash code produced by the algorithm.

Accepted Answer

True

Question 2

Because of the mathematical properties of the message authentication code function it is less vulnerable to being broken than encryption.

Accepted Answer

The message authentication code function is a cryptographic hash function that produces a fixed-size output from a variable-size input. This makes it less vulnerable to being broken than encryption, which produces a variable-size output from a fixed-size input.

Question 3

The private key is known only to its owner.

Accepted Answer

The private key in a cryptographic system is kept secret by the owner and is not shared with anyone else, ensuring the security of the encrypted data or communication.

Question 4

The __________ approach has two advantages: it provides a digital signature as well as message authentication and it does not require the distribution of keys to communicating parties.

Accepted Answer

The answer of The __________ approach has two advantages: it...

Question 5

Protection against active attacks (falsification of data and transactions) is known as ___________ .

Accepted Answer

The answer of Protection against active attacks (falsification of data...

Question 6

The two important aspects of encryption are to verify that the contents of the message have not been altered and that the source is authentic.

Accepted Answer

Encryption primarily ensures confidentiality by converting information into a code to prevent unauthorized access. Integrity and authentication, which verify that contents have not been altered and confirm the source's authenticity, are addressed by other mechanisms like digital signatures and message authentication codes.

Question 7

In the ECB mode of encryption if an attacker reorders the blocks of ciphertext then each block will still decrypt successfully, however, the reordering may alter the meaning of the overall data sequence.

Accepted Answer

In ECB (Electronic Codebook) mode, each block of plaintext is encrypted independently, so reordering the ciphertext blocks will not prevent each block from being decrypted successfully. However, the reordering will change the sequence of the plaintext blocks, potentially altering the meaning of the overall data.

Question 8

Public key algorithms are based on mathematical functions rather than on simple operations on bit patterns.

Accepted Answer

Public key algorithms, also known as asymmetric cryptography, rely on complex mathematical functions, such as factorization of large numbers or discrete logarithms, which are computationally difficult to reverse without the private key, rather than on straightforward operations on bit patterns which are typical of symmetric key algorithms.

Question 9

The key exchange protocol is vulnerable to a man-in-the-middle attack because it does not authenticate the participants.

Accepted Answer

The key exchange protocol, without mechanisms for authenticating the participants, is vulnerable to man-in-the-middle attacks because an attacker can intercept and modify the keys or messages between the participants without their knowledge.

Question 10

The __________ property guarantees that it is impossible to find an alternative message with the same hash value as a given message, thus preventing forgery when an encrypted hash code is used.

Accepted Answer

The answer of The __________ property guarantees that it is...

Question 11

Public key algorithms are useful in the exchange of conventional encryption keys.

Accepted Answer

Public key algorithms, also known as asymmetric cryptography, are indeed useful in the exchange of conventional (symmetric) encryption keys because they allow two parties to securely share a secret key over an insecure channel.

Question 12

The security of the Diffie-Hellman key exchange lies in the fact that, while it is relatively easy to calculate exponentials modulo a prime, it is very easy to calculate discrete logarithms.

Accepted Answer

The security of the Diffie-Hellman key exchange actually relies on the difficulty of calculating discrete logarithms modulo a prime, not the ease of it. Calculating exponentials modulo a prime is indeed relatively easy, which is necessary for the protocol to work efficiently, but the hard problem that secures it is the discrete logarithm problem.

Question 13

The main advantage of HMAC over other proposed hash based schemes is that HMAC can be proven secure, provided that the embedded hash function has some reasonable cryptographic strengths.

Accepted Answer

HMAC (Hash-based Message Authentication Code) is designed to work with any iterative cryptographic hash function, such as MD5 or SHA-1, in a way that is provably secure as long as the underlying hash function has certain cryptographic strengths. The security of HMAC does not rely on the hash function properties (like collision resistance) but rather on its ability to behave as a pseudorandom function. This means that if the hash function is secure in the sense of being a good pseudorandom function, then the HMAC construction can also be proven secure.

Question 14

Private key encryption is used to produce digital signatures which provide an enhanced form of message authentication.

Accepted Answer

Digital signatures are created using a private key for signing and a public key for verification, not encryption. They ensure message integrity and authenticity, but the signing process itself is not encryption.

Question 15

Like the MAC, a __________ accepts a variable size message M as input and produces a fixed size message digest H(M) as output.Unlike the MAC, it does not take a secret key as input.

Accepted Answer

The answer of Like the MAC, a __________ accepts a...

Question 16

Message encryption alone provides a secure form of authentication.

Accepted Answer

Message encryption ensures confidentiality by making the content unreadable to unauthorized users, but it does not inherently verify the identity of the sender or receiver, which is necessary for authentication.

Question 17

The __________ property is the "one-way" property and is important if the authentication technique involves the use of a secret value.

Accepted Answer

The answer of The __________ property is the "one-way" property...

Question 18

As with symmetric encryption, there are two approaches to attacking a secure hash function: brute-force attack and ___________ .

Accepted Answer

The answer of As with symmetric encryption, there are two...

Question 19

Cryptographic hash functions generally execute slower in software than conventional encryption algorithms such as DES.

Accepted Answer

Cryptographic hash functions are generally designed to be faster than conventional encryption algorithms like DES because they do not require key management and are optimized for speed in processing data.

Question 20

In addition to providing authentication, a message digest also provides data integrity and performs the same function as a frame check sequence.

Accepted Answer

A message digest, created through a hash function, ensures data integrity by producing a unique hash value for the original data. If the data changes, the hash value also changes, indicating a potential integrity issue. This function is similar to a Frame Check Sequence (FCS), which is used to detect errors in transmitted frames. Both mechanisms help in verifying that the data received is exactly as it was sent, without alteration.

Quiz 3: Public-Key Cryptography and Message Authentication