Deck 2: Symmetric Encryption and Message Confidentiality

Question 1

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

Answer 1

decryption

Question 2

The security of symmetric encryption depends on the secrecy of the algorithm, not the secrecy of the key.

Answer 2

False

Question 3

The primary advantage of a stream cipher is that stream ciphers are almost always faster and use far less code than do block ciphers.

Answer 3

True

Question 4

Smaller block sizes mean greater security but reduced encryption/decryption speed.

Question 5

Triple DES was first standardized for use in financial applications in ANSI standard X9.17 in 1985.

Question 6

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 7

With the use of symmetric encryption, the principal security problem is maintaining the secrecy of the _________ .

Question 8

The Feistel structure is a particular example of the more general structure used by all symmetric block ciphers.

Question 9

Public-key encryption is also referred to as conventional encryption, secret-key, or single-key encryption.

Question 10

The ciphertext-only attack is the easiest to defend against because the opponent has the least amount of information to work with.

Question 11

Three broad categories of cryptographic algorithms are commonly used to create PRNGs: Asymmetric ciphers, Hash functions and message authentication codes, and ___________ .

Question 12

Random numbers play an important role in the use of encryption for various network security applications.

Question 13

Ciphertext is the scrambled message produced as output.

Question 14

The most commonly used symmetric encryption algorithms are stream ciphers.

Question 15

The essence of a symmetric block cipher is that a single round offers inadequate security but that multiple rounds offer increasing security.

Question 16

The principal drawback of 3DES is that the algorithm is relatively sluggish in software.

Question 17

The advantage of a block cipher is that you can reuse keys.

Question 18

AES uses a Feistel structure.

Question 19

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

Question 20

A _________ cipher processes the plaintext input in fixed sized blocks and produces a block of ciphertext of equal size for each plaintext block.

Question 21

In the _________ mode the input to the encryption algorithm is the XOR of the current plaintext block and the preceeding ciphertext block; the same key is used for each block.

Question 22

The three most important symmetric block ciphers are: triple DES (3DES), the Advanced Encryption Standard (AES), and the ___________ .

Question 23

All encryption algorithms are based on two general principles: _________, in which each element in the plaintext is mapped into another element, and transposition, in which elements in the plaintext are rearranged.

Question 24

Many symmetric block encryption algorithms including DES have a structure first described by _________ of IBM in 1973.

Question 25

__________ is a stream cipher used in the Secure Sockets Layer/Transport Layer Security standards that have been defined for communication between Web browsers and servers and is also used in WEP and WPA protocols.

Question 26

The ________ source is drawn from the physical environment of the computer and could include things such as keystroke timing patterns, disk electrical activity, mouse movements, and instantaneous values of the system clock.

Question 27

Two requirements for secure use of symmetric encryption are: sender and receiver must have obtained copies of the secret key in a secure fashion and a strong __________ is needed.

Question 28

A PRNG takes as input a fixed value called the ________ and produces a sequence of output bits using a deterministic algorithm.

Question 29

Also referred to as conventional encryption, secret-key, or single-key encryption, _________ encryption was the only type of encryption in use prior to the development of public-key encryption in the late 1970's.