Data Encryption Standard (DES)

Question 1

Block Cipher Size?

Answer 1

64-bit

Question 2

Key Size?

Answer 2

56-bit

Question 3

How does it work?

Answer 3

Long series of XOR operations

Question 4

How many rounds?

Answer 4

16

Question 5

Electronic Codebook Mode

Answer 5

Each time the algorithm processes a 64-bit block, it simply encrypts the block using the chosen secret key.

Question 6

ECB Mode weakness?

Answer 6

If the algorithm encounters the same block multiple times it will produce the same encrypted block.

If an enemy were eavesdropping on the communications, they could simply build a “code book” of all the possible encrypted values.

Question 7

Cipher Block Chaining Mode

Answer 7

Each block of unencrypted text is XORed with the block of ciphertext immediately preceding it before it is encrypted using the DES algorithm.

Question 8

CBC Mode weakness?

Answer 8

If one block is corrupted during transmission it becomes impossible to decrypt.

Question 9

Cipher Feedback Mode

Answer 9

Streaming cipher version of CBC.

CFB operates against data produced in real time. Uses memory buffers of the same same block size. As the buffer becomes full, it is encrypted and then sent to the recipients.

Question 10

CFB Mode weakness

Answer 10

If one block is corrupted during transmission it becomes impossible to decrypt.

Question 11

Output Feedback Mode

Answer 11

Operates in almost the same fashion as it does in CFB mode.

Instead of XORing an encrypted version of the previous block of ciphertext, DES XORs the plaintext with a seed value. Future seed values are derived by running the DES algorithm on the previous seed value.

Question 12

Advantage of OFB mode?

Answer 12

There is no chaining and transmission errors do not propagate.

Question 13

Counter Mode

Answer 13

Uses a stream cipher similar to that used in CFB and OFB modes.

Creates a seed value for each encryption/decryption operations from the results of the previous seed values, it uses a simple counter that increments for each operation.

Question 14

Advantage of Counter mode?

Answer 14

Errors to do not propagate

Question 15

Triple DES Modes?

Answer 15

DES-EEE3
DES-EEE2
DES-EDE2

Question 16

DES-EEE3

Answer 16

Encrypts the plaintext three times

Has an effective key length of 168 bits

Question 17

DES-EDE2

Answer 17

Uses three keys but replaces the second encryption operation with a decryption operation.

Question 18

DES-EEE2

Answer 18

Uses only two keys.

Question 19

Advanced Encryption Standard

Answer 19

Standard only allows the processing of 128-bit blocks.

Rinjdael exceeded the specification.

128, 192, and 256

Question 20

International Data Encryption Algorithm (IDEA) block size?

Answer 20

64-bit

Question 21

International Data Encryption Algorithm (IDEA) key size?

Answer 21

128-bit key broken in a series of operations into 52 16-bit subkeys.

Question 22

Blowfish block size?

Answer 22

64-bit

Question 23

Blowfish key sizes?

Answer 23

32 through 448

Question 24

Twofish block size?

Answer 24

128-bit

Question 25

Twofish key sizes?

Answer 25

128 through 256

Question 26

Diffie-Hellman Key Agreement Protocol

Answer 26

Allows two parties to securely agree on a symmetric key via a public channel, such as the Internet, with no prior key exchange.

Uses discrete logarithms to provide security.

Question 27

Elliptic Curve Cryptography (ECC)

Answer 27

ECC leverages a one-way function that uses discrete logarithms as applied to elliptic curves.

Question 28

Asymmetric vs. Symmetric

Answer 28

Asymmetric is much slower than symmetric encryption, and is also weaker per bit of key length.

Question 29

Hash Functions

Answer 29

Provides encryption using an algorithm and no key. They are called “one-way hash functions” because there is no way to reverse encryption.

Question 30

MD5

Answer 30

Created by Ronald Rivest

Creates a 128-bit hash value.

MD6 is the newest version.

Question 31

SHA-1

Answer 31

160-bit hash value

Question 32

SHA-2

Answer 32

SHA-224, SHA-256, SHA-384, and SHA-512

Question 33

HAVAL

Answer 33

Hash of Variable Length – is a hash algorithm that creates message digests of 128, 160, 192, 224, or 256 bits in length, using 3, 4, or 5 rounds.

Uses some of the design principles behind the MD family of hash algorithms, and is faster than MD5.