Chapter 2

The most important symmetric algorithms, all of which are block ciphers, are the DES, triple DES, and the _______.

AES

______ is the scrambled message produced as output.

Ciphertext

Public-key encryption was first publicly proposed by __________ in 1976.

Diffie and Hellman

T/F: Cryptanalytic attacks try every possible key on a piece of ciphertext until an intelligible translation into plaintext is obtained.

F

T/F: Like the MAC, a hash function also takes a secret key as input.

F

T/F: Public-key algorithms are based on simple operations on bit patterns.

F

T/F: The advantage of a stream cipher is that you can reuse keys.

F

T/F: The purpose of the DSS algorithm is to enable two users to securely reach agreement about a shared secret that can be used as a secret key for subsequent symmetric encryption of messages.

F

T/F: Triple DES takes a plaintext block of 64 bits and a key of 56 bits to produce a ciphertext block of 64 bits.

F

__________ is a block cipher in which the plaintext and ciphertext are integers between 0 and n-1 for some n.

RSA

T/F: A message authentication code is a small block of data generated by a secret key and appended to a message.

T

T/F: An important element in many computer security services and applications is the use of cryptographic algorithms.

T

T/F: Modes of operation are the alternative techniques that have been developed to increase the security of symmetric block encryption for large sequences of data.

T

T/F: Public-key cryptography is asymmetric.

T

T/F: Some form of protocol is needed for public-key distribution.

T

T/F: Symmetric encryption is used primarily to provide confidentiality.

T

T/F: The secret key is input to the encryption algorithm.

T

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

T

T/F: Two of the most important applications of public-key encryption are digital signatures and key management.

T

A __________ processes the plaintext input in fixed-size blocks and produces a block of ciphertext of equal size for each plaintext block.

block cipher

There are two general approaches to attacking a symmetric encryption scheme: cryptanalytic attacks and __________ attacks.

brute-force

A __________ is to try every possible key on a piece of ciphertext until an intelligible translation into plaintext is obtained.

brute-force attack

A ________ attack exploits the characteristics of the algorithm to attempt to deduce a specific plaintext or to deduce the key being used.

cryptanalytic

Transmitted data stored locally are referred to as __________ .

data at rest

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

decryption

The ____ is the encryption algorithm run in reverse.

decryption algorithm

A __________ is created by using a secure hash function to generate a hash value for a message and then encrypting the hash code with a private key.

digital signature

On average, _____ of all possible keys must be tried in order to achieve success with a brute-force attack.

half

The purpose of a __________ is to produce a "fingerprint" of a file, message, or other block of data.

hash function

Combined one byte at a time with the plaintext stream using the XOR operation, a __________ is the output of the pseudorandom bit generator.

keystream

__________ is a procedure that allows communicating parties to verify that received or stored messages are authentic.

message authentication

The original message or data that is fed into the algorithm is:

plaintext

Digital signatures and key management are the two most important applications of __________ encryption.

public-key

A __________ processes the input elements continuously, producing output one element at a time.

stream cipher

A _________ protects against an attack in which one party generates a message for another party to sign.

strong hash function

Also referred to as single-key encryption, the universal technique for providing confidentiality for transmitted or stored data is _________ .

symmetric encryption

If the only form of attack that could be made on an encryption algorithm is brute force, then the way to counter such attacks would be to _________.

use longer keys