Deck 20: Symmetric Encryption and Message Confidentiality

Question 1

It is possible to convert any block cipher into a stream cipher by usingthe cipher feedback (CFB) mode.

Answer 1

True

Question 2

"Each block of 64 plaintext bits is encoded independently using thesame key" is a description of the CBC mode of operation.

Answer 2

False

Question 3

In using encryption, we need to decide what to encrypt and where theencryption gear should be located.

Answer 3

True

Question 4

The National Bureau of Standards is now the National Institute ofStandards and Technology.

Question 5

One desirable property of a stream cipher is that the ciphertext be ofthe same length as the plaintext.

Question 6

Stream ciphers are far more common than block ciphers.

Question 7

If both sender and receiver use the same key the system is referred to asasymmetric.

Question 8

A brute-force approach involves trying every possible key until anintelligible translation of the ciphertext into plaintext is obtained.

Question 9

If the analyst is able to get the source system to insert into the system a message chosen by the analyst, then a ________ attack is possible.

A) known-plaintext
B) chosen-plaintext
C) chosen ciphertext
D) chosen text

Question 10

The most widely used encryption scheme is based on the _________ adopted in 1977 by the National Bureau of Standards.

A) AES
B) 3DES
C) CES
D) DES

Question 11

_________ is the original message or data that is fed into the algorithm as input.

A) Plaintext
B) Encryption algorithm
C) Decryption algorithm
D) Ciphertext

Question 12

The exact substitutions and transformations performed by the algorithm depend on the ________.

A) ciphertext
B) decryption algorithm
C) secret key
D) encryption algorithm

Question 13

The ciphertext-only attack is the easiest to defend against.

Question 14

AES uses a Feistel structure.

Question 15

"The plaintext is 64 bits in length and the key is 56 bits in length;longer plaintext amounts are processed in 64-bit blocks" is a description of the DES algorithm.

Question 16

One disadvantage of the link encryption approach is that the messagemust be decrypted each time it enters a frame switch.

Question 17

The _________ is the encryption algorithm run in reverse.

A) decryption algorithm
B) ciphertext
C) plaintext
D) secret key

Question 18

Key distribution can be achieved for two parties A and B by a thirdparty selecting the key and physically delivering it to A and
B.

Question 19

Symmetric encryption is also referred to as secret-key or single-keyencryption.

Question 20

Plaintext is the scrambled message produced as output.

Question 21

For general-purpose stream-oriented transmission you would typically use _______ mode.

A) CTR
B) CFB
C) ECB
D) CBC

Question 22

Cryptographic systems are generically classified by _________.

A) the type of operations used for transforming plaintext to ciphertext
B) the number of keys used
C) the way in which the plaintext is processed
D) all of the above

Question 23

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

Question 24

Unlike ECB and CBC modes, ________ mode requires only the implementation of the encryption algorithm and not the decryption algorithm.

Question 25

The _______ module performs end-to-end encryption and obtains session keys on behalf of users.

A) PKM
B) RCM
C) SSM
D) CCM

Question 26

For general-purpose block-oriented transmission you would typically use _______ mode.

A) CBC
B) CTR
C) CFB
D) OFB

Question 27

A ________ cipher processes the input one block of elements at a time, producing an output block for each input block.

Question 28

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.

Question 29

For stream-oriented transmission over noisy channel you would typically use _______ mode.

A) ECB
B) CTR
C) OFB
D) CBC

Question 30

There are _____ modes of operation defined by NIST that are intended to cover virtually all the possible applications of encryption for which a block cipher could be used.

A) three
B) five
C) seven
D) nine

Question 31

A symmetric encryption scheme has five ingredients: plaintext, encryption algorithm, ciphertext, decryption algorithm and _________.

Question 32

Public-key encryption was developed in the late ________.

A) 1950s
B) 1970s
C) 1960s
D) 1980s

Question 33

__________ is a term that refers to the means of delivering a key to two parties that wish to exchange data without allowing others to see the key.

A) Session key
B) Subkey
C) Key distribution technique
D) Ciphertext key

Question 34

The most powerful, and most common, approach to countering the threats to network security is ________.

Question 35

______ was designed in 1987 by Ron Rivest and is a variable key-size stream cipher with byte-oriented operations.

Question 36

"The input to the encryption algorithm is the XOR of the next 64 bits of plaintext and the preceding 64 bits of ciphertext" is a description of the ________ mode of operation.

Question 37

The _________ was issued as a federal information-processing standard and is intended to replace DES and 3DES with an algorithm that is more secure and efficient.

Question 38

A ________ is a key used between entities for the purpose of distributing session keys.

A) permanent key
B) session key
C) distribution key
D) all of the above

Question 39

______ mode is typically used for a general-purpose block-oriented transmission and is useful for high-speed requirements.

A) ECB
B) OFB
C) CFB
D) CTR

Question 40

A ________ cipher processes the input elements continuously, producing output one element at a time as it goes along.

Question 41

The three most important symmetric block ciphers are: 3DES, AES, and _____.

Question 42

All encryption algorithms are based on two general principles: substitution and _________.

Question 43

For symmetric encryption to work the two parties to an exchange must share the same _____, which must be protected from access by others.

Question 44

With _________ encryption the encryption process is carried out at the two end systems.

Question 45

With ______ encryption each vulnerable communications link is equipped on both ends with an encryption device.