Deck 3: Block Ciphers and the Data Encryption Standard

Question 1

All other things being equal,smaller block sizes mean greater security.

Answer 1

False

Question 2

An advantage of key-dependent S-boxes is that because they are not fixed,it is impossible to analyze the S-boxes ahead of time to look for weaknesses.

Answer 2

True

Question 3

Greater complexity in the subkey generation algorithm should lead to greater difficulty of cryptanalysis.

Answer 3

True

Question 4

DES exhibits the classic __________ block cipher structure,which consists of a number of identical rounds of processing.

A)Feistel
B)SAC
C)Shannon
D)Rendell

Question 5

A prime concern with DES has been its vulnerability to brute-force attack because of its relatively short key length.

Question 6

__________ is when each plaintext element or group of elements is uniquely replaced by a corresponding ciphertext element or group of elements.

A)Substitution B)Diffusion
C)Streaming
D)Permutation

Question 7

A problem with the ideal block cipher using a small block size is that it is vulnerable to a statistical analysis of the plaintext.

Question 8

The Feistel cipher structure,based on Shannon's proposal of 1945, dates back over a quarter of a century and is the structure used by many significant symmetric block ciphers currently in use.

Question 9

The vast majority of network based symmetric cryptographic applications make use of stream ciphers.

Question 10

Fast software encryption/decryption and ease of analysis are two considerations in the design of a Feistel cipher.

Question 11

A __________ cipher is one that encrypts a digital data stream one bit or one byte at a time.

A)product
B)block
C)key
D)stream

Question 12

One criteria for an S-box is: "If two inputs to an S-box differ in exactly one bit,the outputs must also differ in exactly one bit."

Question 13

The heart of a Feistel block cipher is the function F,which relies on the use of S-boxes.

Question 14

The strict avalanche criterion and the bit independence criterion appear to weaken the effectiveness of the confusion function.

Question 15

The vast majority of network-based symmetric cryptographic applications make use of ________ ciphers.

A)linear
B)block
C)permutation
D)stream

Question 16

A __________ cipher is one in which a block of plaintext is treated as a whole and used to produce a ciphertext block of equal length.

A)bit
B)product
C)stream
D)block

Question 17

The key schedule algorithm is more popular and has received more attention than S-box design.

Question 18

If the bit-stream generator is a key-controlled algorithm the two users only need to share the generating key and then each can produce the keystream.

Question 19

A sequence of plaintext elements is replaced by a __________ of that sequence which means that no elements are added,deleted or replaced in the sequence,but rather the order in which the elements appear in the sequence is changed.

A)permutation
B)diffusion
C)stream
D)substitution

Question 20

Confusion seeks to make the statistical relationship between the plaintext and ciphertext as complex as possible in order to thwart attempts to deduce the key.

Question 21

Feistel's is a practical application of a proposal by Claude Shannon to develop a product cipher that alternates confusion and ________ functions.

Question 22

Key sizes of __________ or less are now considered to be inadequate.

A)128 bits
B)32 bits
C)16 bits
D)64 bits

Question 23

The __________ criterion states that output bits j and k should change independently when any single input bit i is inverted for all i,j and k.

Question 24

The ________ cipher structure,which dates back over a quarter century and which,in turn,is based on Shannon's proposal of 1945,is the structure used by many significant symmetric block ciphers currently in use.

Question 25

Feistel proposed that we can approximate the ideal block cipher by utilizing the concept of a __________ cipher,which is the execution of two or more simple ciphers in sequence in such a way that the final result or product is cryptographically stronger than any of the component ciphers.

A)linear
B)permutation
C)differential
D)product

Question 26

In ___________ the statistical structure of the plaintext is dissipated into long-range statistics of the ciphertext.This is achieved by having each plaintext digit affect the value of many ciphertext digits.

Question 27

Two alternatives to DES are AES and _________ DES.