Deck 6: Block Cipher Operation

Question 1

It is possible to convert a block cipher into a stream cipher using cipher feedback,output feedback and counter modes.

Answer 1

True

Question 2

A number of Internet based applications have adopted two-key 3DES,including PGP and S/MIME.

Answer 2

False

Question 3

The XTS-AES mode is based on the concept of a tweakable block cipher.

Answer 3

True

Question 4

The XTS-AES standard describes a method of decryption for data stored in sector-based devices where the threat model includes possible access to stored data by the adversary.

Question 5

Cipher Feedback Mode conforms to the typical construction of a stream cipher.

Question 6

In the first instance of multiple encryption plaintext is converted to __________ using the encryption algorithm.

A)block cipher
B)ciphertext
C)S-AES mode
D)Triple DES

Question 7

Once the plaintext is converted to ciphertext using the encryption algorithm the plaintext is then used as input and the algorithm is applied again.

Question 8

Cipher Block Chaining is a simple way to satisfy the security deficiencies of ECB.

Question 9

A mode of operation is a technique for enhancing the effect of a cryptographic algorithm or adapting the algorithm for an application.

Question 10

The _________ and _________ block cipher modes of operation are used for authentication.

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

Question 11

Given the potential vulnerability of DES to a brute-force attack,an alternative has been found.

Question 12

There are no practical cryptanalytic attacks on 3DES.

Question 13

Another important mode,XTS-AES,has been standardized by the __________ Security in Storage Working Group.

A)IEEE
B)ISO
C)NIST
D)ITIL

Question 14

OFB mode requires an initialization vector that must be unique to each execution of the encryption operation.

Question 15

Cipher Feedback CFB)is used for the secure transmission of single values.

Question 16

A typical application of Output Feedback mode is stream oriented transmission over noisy channel,such as satellite communication.

Question 17

S-AES is the most widely used multiple encryption scheme.

Question 18

Triple DES makes use of __________ stages of the DES algorithm,using a total of two or three distinct keys.

A)nine
B)six
C)twelve
D)three

Question 19

The sender is the only one who needs to know an initialization vector.

Question 20

__________ modes of operation have been standardized by NIST for use with symmetric block ciphers such as DES and AES.

A)Three
B)Five
C)Nine
D)Seven

Question 21

The requirements for encrypting stored data,also referred to as ___________ ,differ somewhat from those for transmitted data.

Question 22

The__________ is a technique in which an encryption algorithm is used multiple times.

Question 23

Both __________ produce output that is independent of both the plaintext and the ciphertext.This makes them natural candidates for stream ciphers that encrypt plaintext by XOR one full block at a time.

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

Question 24

Because of the opportunities for parallel execution in __________ mode,processors that support parallel features,such as aggressive pipelining,multiple instruction dispatch per clock cycle,a large number of registers,and SIMD instructions can be effectively utilized.

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

Question 25

__________ mode is suitable for parallel operation.Because there is no chaining,multiple blocks can be encrypted or decrypted simultaneously.Unlike CTR mode,this mode includes a nonce as well as a counter.

A)OFB
B)S-AES
C)3DES
D)XTS-AES

Question 26

One of the most widely used multiple-encryption scheme is __________ .

Question 27

A __________ is a technique for enhancing the effect of a cryptographic algorithm or adapting the algorithm for an application,such as applying a block cipher to a sequence of data blocks or a data stream.

Question 28

The __________ block cipher mode of operation is a general purpose block oriented transmission useful for high speed requirements.

Question 29

"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 __________ mode.

Question 30

"Input is processed s bits at a time.Preceding ciphertext is used as input to the encryption algorithm to produce pseudorandom output,which is XORed with plaintext to produce next unit of ciphertext",is a description of the _________ mode of operation.

Question 31

The __________ mode operates on full blocks of plaintext and ciphertext,as opposed to an s-bit subset.

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

Question 32

Five modes of operation have been standardized by NIST for use with symmetric block ciphers such as DES and AES: electronic codebook mode,cipher block chaining mode,cipher feedback mode,__________,and counter mode.

Question 33

_________ mode is similar to Cipher Feedback,except that the input to the encryption algorithm is the preceding DES output.

A)Cipher Feedback
B)Counter
C)Output Feedback
D)Cipher Block Chaining

Question 34

The __________ algorithm will work against any block encryption cipher and does not depend on any particular property of DES.

A)cipher block chaining
B)meet-in-the-middle attack
C)counter mode attack
D)ciphertext stealing

Question 35

The __________ method is ideal for a short amount of data and is the appropriate mode to use if you want to transmit a DES or AES key securely.

A)cipher feedback mode
B)counter mode
C)output feedback mode
D)electronic codebook mode

Question 36

The output of the encryption function is fed back to the shift register in Output Feedback mode,whereas in ___________ the ciphertext unit is fed back to the shift register.

A)Cipher Block Chaining mode
B)Electronic Codebook mode
C)Cipher Feedback mode
D)Counter mode

Question 37

The simplest mode of operation is the ___________ mode,in which plaintext is handled one block at a time and each block of plaintext is encrypted using the same key.

Question 38

The most significant characteristic of __________ is that if the same b-bit block of plaintext appears more than once in the message,it always produces the same ciphertext.

Question 39

"Each block of plaintext is XORed with an encrypted counter.The counter is incremented for each subsequent block",is a description of ___________ mode.

A)Cipher Block Chaining
B)Counter
C)Cipher Feedback
D)Electronic Codebook

Question 40

The simplest form of multiple encryption has __________ encryption stages and __________ keys.

A)four,two
B)two,three
C)two,two
D)three,two

Question 41

The plaintext of a sector or data unit is organized in to blocks of 128 bits.For encryption and decryption,each block is treated independently.The only exception occurs when the last block has less than 128 bits.In that case the last two blocks are encrypted/decrypted using a ___________ technique instead of padding.

Question 42

Hardware efficiency,software efficiency,preprocessing,random access,provable security,and simplicity are all advantages of __________ mode.

Question 43

A __________ cipher can operate in real time and eliminates the need to pad a message to be an integral number of blocks.

Question 44

The _________ must be a data block that is unique to each execution of the encryption operation and may be a counter,a timestamp,or a message number.