Ch6

Question 1

a remote user is asked to encrypt a message using a key known only to the communicating parties

Answer 1

Challenge Response protocol

Question 2

symmetric protocols, block and key size

Answer 2

Name          Blocksize     Keysize
AES             128               128, 192, 256
Rijndael       Variable       128, 192, 256
Blowfish      Variable       1-448
DES             64                 56
IDEA            64                 128
RC2             64                 128
RC4             Streaming    128
RC5             32,64,128     0-2040
Skipjack      64                 80
3DES           64                 112 or 168
Twofish       128                1-256

Question 3

what encryption algorithm uses pre/post whitening

Answer 3

Twofish

Question 4

how many rounds of encryption for 128 bit key; 192bit; 256bit

Answer 4

10, 12, 14 rounds of encryption

Question 5

What algorithm was used by US government supported escrow of encryption keys in Clipper and Capstone encryption chips

Answer 5

Skipjack - National Institute of Standards and Technology (NIST) and the Department of the Treasury, hold a portion of the information required to reconstruct a Skipjack
key.

Question 6

begins its operation with a 128-bit key. This key is broken up in a series of operations into 52 16-bit subkeys and is used in PGP

Answer 6

IDEA

Question 7

DES-EDE3

Answer 7

triple DES but replaces the second encryption operation with a decryption operation

Question 8

Assymetric Protocols

Answer 8

• RSA
• Diffie-Hellman
• Digital Signature Algorithm
• ElGamal
• ECDSA
• XTR

Question 9

• extension of Diffie-Hellman key
• predecessor of DSA
• doubles the length of any message it encrypts

Answer 9

El Gamal

Question 10

• most commonly used asymmetric algorithm
• used both for encryption and for digital signatures
• uses prime numbers

Answer 10

RSA

Question 11

cryptographic systems of symbols that operate on words or phrases; sometimes secret but do not always provide confidentiality

Answer 11

codes

Question 12

always meant to hide the true meaning of a message

Answer 12

cipher

Question 13

change in the plain text results in multiple changes spread throughout the ciphertext

Answer 13

diffusion

Question 14

extremely powerful substitution cipher that are randomly generated, physically protected, used only once and key is as long as the message to be encrypted

Answer 14

one-time pads

Question 15

another name for one-time pad

Answer 15

vernam cipher

Question 16

a communication concept where a specific type of information is exchanged but no real data is transferred, such as with digital signatures and certificates

Answer 16

zero-knowledge proof

Question 17

what are the four operational modes of DES

Answer 17

ECB
CBC
CFB
OFB

Question 18

Electronic Codebook

Answer 18

least secure & used for only short messages

Question 19

Cipher Block Chaining

Answer 19

• each block of unencrypted text is XORed with the
  block of ciphertext immediately preceding it before it is encrypted using the DES algorithm
• uses an IV
• errors will propagate

Question 20

Cipher Feedback Mode

Answer 20

• same as CBC but is a streaming cipher version

Question 21

Output Feedback Mode

Answer 21

• same as CFB
• instead of XORing an encrypted version of the previous block of ciphertext, DES XORs the plain text with a seed value
• no chaining so no error propagation

Question 22

Counter Mode

Answer 22

• used in parallel computing

- uses stream cipher with counter that increments for each operation

Question 23

what is vulnerable to frequency analysis attacks

Answer 23

Caesar cipher and other simple substitution ciphers

Question 24

a cryptographic system should be secure

even if everything about the system, except the key, is public knowledge

Answer 24

Kerchoff principle

Question 25

MD5 produces a ____bit message digest for ANY input

Answer 25

128