CHAPTER 12 / MESSAGE AUTHENTICATION CODES

Message authentication is a mechanism or service used to verify the integrity of a message. (T/F)

T

The order in which the frame check sequence and encryption functions are performed is not critical for authentication (T/F)

F

The MAC does not provide a digital signature because both sender and receiver share the same key (T/F)

T

A recipient in possession of the secret key cannot generate an authentication code to verify the integrity of the message (T/F)

F

One means of forming a MAC is to combine a cryptographic hash function in some fashion with a secret key (T/F)

T

A brute-force attack on a MAC is easier than a brute-force attack on a hash function. (T/F)

F

Message authentication may also verify sequencing and timeliness. (T/F)

T

The security of any MAC function based on an embedded hash function depends in some way on the cryptographic strength of the underlying hash function (T/F)

T

Message encryption by itself cannot provide a measure of authentication. (T/F)

F

If the calculated frame check sequence is equal to the incoming frame check sequence the message is considered authentic (T/F)

T

The straightforward use of public-key encryption provides confidentiality and authentication (T/F)

F

A CTR-based authenticated encryption approach is the most efficient mode of operation for high-speed packet networks (T/F)

T

An important characteristic of the MAC algorithm is that it needs to be reversible (T/F)

F

As with encryption algorithms and hash functions cryptanalytic attacks on MAC algorithms seek to exploit some property of the algorithm to perform some attack other than an exhaustive search. (T/F)

T

To attack MD5, the attacker can choose any set of messages and work on these offline on a dedicated computing facility to find a collision. (T/F)

T

_________ encryption provides authentication among those who share the secret key.

symmetric

Insertion of messages into the network from a fraudulent source is a __________ attack.

source repudiation

Confidentiality can be provided by performing message encryption __________ the MAC algorithm.

before or after

A __________ is an algorithm that requires the use of a secret key.

MAC

"Release of message contents to any person or process not possessing the

appropriate cryptographic key" is a __________ attack.

disclosure

With _________ authentication an opponent would have difficulty generating

ciphertext that when decrypted would have valid error control bits.

internal error control

The MAC function is a __________ function.

many-to-one

The appeal of __________ is that its designers have been able to prove an exact relationship between the strength of the embedded hash function and the strength of this form of authentication.

HMAC

The _________ attack is when the attacker is looking for two messages M and M1 that produce the same hash: H(M)=H(M1)

birthday

__________assures that data received are exactly as sent and that the purposed identity of the sender is valid.

message authentication

Discovery of the pattern of traffic between parties is a __________attack.

traffic analysis

A __________takes a variable length message and a secret key as input and produces an authentication code.

message authentication code (MAC)

One approach to constructing a MAC is to use a symmetric block cipher in

such a way that it produces a __________ output for a variable length input.

fixed length

Any modification to a sequence of messages between parties, including

insertion, deletion, and reordering is a __________ attack.

sequence modification

The types of functions that may be used to produce an authenticator are

grouped into three classes: hash function, message authentication code, and ___________

message encryption

An alternative authentication technique involves the use of a secret key to

generate a small fixed size block of data known as a __________or MAC that is appended to the message

cryptographic checksum

When an entire message is encrypted for confidentiality using either

symmetric or asymmetric encryption the security of the scheme generally

depends on the __________ of the key.

bit length

Attacks on MACs can be grouped into two categories: brute-force attacks and __________.

cryptoanalysis

The __________algorithm can be defined as using the cipher block chaining mode of operation of DES with an initialization vector of zero.

Data Authentication Algorithm (DAA)

__________is a term used to describe encryption systems that simultaneously protect confidentiality and authenticity of communications.

Authenticated encryption (AE)

HMAC is a widely used standardized _________function and is implemented in many protocols and applications.

MAC