Cryptography

Question 1

What are the 4 fundamental goals of cryptography?

Answer 1

1. Confidentiality
2. Integrity
3. Authentication
4. Non repudiation

Question 2

What is a message called before and after it is encrypted?

Answer 2

Plaintext & cyphertext

Question 3

What is the Kerchoff principle?

Answer 3

States that a system should be secure even though everything is known.

Question 4

What is FIPS140-2?

Answer 4

Federal Information Processing Standard. It is the definition for hardware and software requirements for crypto.

Question 5

Logical AND

Answer 5

Both items need to be true.

Question 6

Logical OR

Answer 6

v

At least one is true

Question 7

Logical NOT

Answer 7

~

Inverse

Question 8

Exclusive OR (XOR)

Answer 8

+

Only one needs to be true

Question 9

Modulo

Answer 9

%

Remainder

Question 10

One way function is…

Answer 10

The basis of public crypto systems.

Question 11

What is a nonce?

Answer 11

Random number that acts as a placeholder for a variable in a formula.

Question 12

What is the concept of zero knowledge proof?

Answer 12

Ability for a third party to prove knowledge of a password without divulging the password.

Question 13

Split knowledge can also be called…

Answer 13

Separation of duties.

Question 14

What is M of N control?

Answer 14

M = minimum number of people needed to divulge.
N = Total population of key holders

Question 15

What is a transposition cipher vs substitution cipher?

Answer 15

rearranging letters vs substituting them

Question 16

What is a polyalphabetic cipher?

Answer 16

The use of multiple alphabets to encrypt the data.

Question 17

What is frequency analysis vs period analysis?

Answer 17

Studying the frequency of characters to break an encryption mechanism.

Question 18

What must be performed to ensure the integrity of a one time pad?

Answer 18

1. The one time pad must be truly random.
2. Pad must be kept secret and used once.
3. Key must be as long as the message.

Question 19

What is a major obstacle of one time pads?

Answer 19

They are not scalable.

Question 20

What is a running key cipher?

Answer 20

Cipher is from a known string of characters ie a book.

Question 21

What is a block cipher vs a stream cipher?

Answer 21

Block operates on a groups of characters at the same time vs stream does one at a time.

Question 22

What is confusion and what is diffusion?

Answer 22

Confusion - Complication of relationship between plaintext and ciphertext
Diffusion - One change causes additional downstream changes.

Question 23

What is a symmetric key system and what are its weaknesses

Answer 23

Key is shared amongst others.
Weaknesses: key distribution, scalability, no non-repudiation, new keys needed frequently.

Keys needed (n*(n-1))/2

Question 24

What is an asymmetric key system and what are its strengths/ weaknesses?

Answer 24

Public/ private key system
Strengths: group changes are less impactful, provided non-repudiation

Weaknesses: slower
Keys needed: n*2

Question 25

What is DES?

Answer 25

Uses a 64bit block. (56 bit key and 8bit checksum)

Question 26

What are the 5 modes of DES?

Answer 26

Electronic Code Book (ECB) - Most basic 64 bit block based. Used for small stuff. Cipher Block Chaining (CBC) - Each block is encrypted with previous block data. Cipher Feedback (CFB) - Encrypts each block as memory fills. Output Feedback Mode (OFB) - Like CEB but data is not encrypted with previous block. Counter Mode (CTR) - like others but seed is from a basic counter.

Question 27

What is triple DES?

Answer 27

Expansion of DES where text is encrypted 3 times. Keys are either 168 or 112 bits.

Question 28

What are the characteristics of Blowfish?

Answer 28

Operates on 64bit blocks and keys can range from 32-448 bits.

Question 29

What are the characteristics of Skipjack?

Answer 29

Operates on 64bit blocks and operates on an 80 bit key and supports key escrow.

Question 30

What are the characteristics of AES/ Rijndael?

Answer 30

Operates on 128 bit blocks with following key strengths: 128bit - 10 rounds of encryption 192bit - 12 rounds of encryption 256bit - 14 rounds of encryption.

Question 31

What is Diffie-Helman?

Answer 31

Method of exchanging keys without both parties meeting.

Question 32

``` What mistake did the Soviets make during the 1940's using a one time cipher? A. Key values not random B. Key values not long enough C. Key values used multiple times D. Key values were disclosed ```

Answer 32

A. Key values not random

Question 33

What is the minimum number of keys in a symmetric system?

Answer 33

One

Question 34

``` What DES operating mode can be used for large messages: A. Cipher Block Chaining (CBC) B. Electronic Codebook (ECB) C. Cipher Feedback (CFB) D. Output Feedback (OFB) ```

Answer 34

D. Output Feedback (OFB)

Question 35

``` Many crypto systems rely on the difficulty of factoring the product of large prime numbers. What characteristic is this? A. Diffusion B. Confusion C. One way function D. Kerchoff ```

Answer 35

C. One way function

Question 36

``` What AES function uses pre & post whitening techniques? A. Rijendael B. Twofish C. Blowfish D. Skipjack ```

Answer 36

B. Two fish