Deck 3: Public-Key Cryptography and Message Authentication

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.

Answer 1

True

Question 2

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

Answer 2

True

Question 3

The private key is known only to its owner.

Answer 3

True

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.

Question 5

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

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.

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.

Question 8

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

Question 9

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

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.

Question 11

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

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.

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.

Question 14

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

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.

Question 16

Message encryption alone provides a secure form of authentication.

Question 17

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

Question 18

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

Question 19

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

Question 20

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

Question 21

The key algorithmic ingredients of __________ are the AES encryption algorithm, the CTR mode of operation, and the CMAC authentication algorithm.

Question 22

__________ is a term used to describe encryption systems that simultaneously protect confidentiality and authenticity (integrity) of communications.

Question 23

A __________ is when the sender "signs" a message with its private key, which is achieved by a cryptographic algorithm applied to the message or to a small block of data that is a function of the message.

Question 24

The _________ was developed by NIST and published as a federal information processing standard in 1993.

Question 25

The __________ algorithm accepts the ciphertext and the matching key and produces the original plaintext.

Question 26

Bob uses his own private key to encrypt the message.When Alice receives the ciphertext she finds that she can decrypt it with Bob's public key, thus proving that the message must have been encrypted by Bob.No one else has Bob's private key and therefore no one else could have created a ciphertext that could be decrypted with Bob's public key.Therefore the entire encrypted message serves as a _________ .

Question 27

A _________ is when two sides cooperate to exchange a session key.

Question 28

The two most widely used public key algorithms are RSA and _________ .

Question 29

Using an algorithm that is designed to provide only the digital signature function, the _________ makes use of the SHA-1 and cannot be used for encryption or key exchange.