Chapter2

Question 1

• The universal technique for providing confidentiality for transmitted or stored data
• Also referred to as conventional encryption or single key encryption

Answer 1

Symmetric Encryption

Question 2

Two requirements for secure use:

Answer 2

• Need a strong encryption algorithm

- Sender and receiver must have obtained copies of the secret key in a secure fashion and must keep the key secure

Question 3

Two ways to attack Symmetric Encryption

Answer 3

• Cryptanalytic Attacks

- Brute Force Attack

Question 4

Cyptanalytic Attacks rely on:

Answer 4

• Nature of the algorithm
• Some knowledge of the general characteristics of the plaintext
• Some sample plaintext-cipertext pairs

Question 5

exploits the characteristics of the algorithm to attempt to deduce a specific plaintext or the key being used

Answer 5

Crytanalytic Attacks:

Question 6

Brute-force attack

Answer 6

Try all possible keys on some ciphertext until an intelligible translation into plaintext is obtained

Question 7

Data Encryption Standard (DES)

Answer 7

• The most widely used encryption scheme

- Most studied encryption algorithm in existence

Question 8

DES strength concerns:

Answer 8

• concerns about algorithm
• Uses 56-bit key
• EFF(Electronic Frontier foundation) announced in July 1998 that it had broked a DES encryption

Question 9

Triple DES (3DES)

Answer 9

• Repeats basic DES algorithm three times using either two or three unique keys
• First standardized for use in financial applications in ANSI standard X9.17 in 1985

Question 10

Attractions in 3DES

Answer 10

• 168-bit key length overcomes the vulnerability to brute-force attack of DES
• Underlying encryption algorithm is the same as in DES

Question 11

Drawback of 3DES

Answer 11

• Algorithm is sluggish in software

- Uses a 64-bit block size

Question 12

Advanced Encryption Standard (AES)

Answer 12

• have security strength equal to or better than 3DES
• improved efficiency
• symmetric block cipher
• 128 bit data and 128/192/256 bit keys
• Published as FIPS 197
• Rijndael

Question 13

Practical Security Issues:

Answer 13

• Typical symmetric encryption is applied to a unit of data larger than a single 64-bit or 128-bit block
• Electronic codebook (ECB) mode is the simplest approach to multiple-block encryption which is not secure
• Modes of operation instead of ECB

Question 14

Electronic CodeBook (ECB)

Answer 14

• Each block of plaintext is encrypted using the same key

- Cryptanalyst may be able to exploit regularities in the plaintext

Question 15

Modes of operation

Answer 15

• Alternative technique to increase security

- overcame weakness of ECB

Question 16

Block Cipher

Answer 16

• Processes the input once block of elements at a time
• Produces an output block for each input block
• Can reuse keys
• More common

Question 17

Stream cipher

Answer 17

• Processes the input elements continuously
• Produces output one elements at a time
• Primary advantage is that they are almost always faster and use far less code
• Encrypts plaintext one byte at a time
• Pseudorandom stram is one that is unpredictable without knowledge of the input key

Question 18

Hash Function Requirements

Answer 18

• can be applied to a block of data of any size
• produces a fixed-length output
• H(x) is relatively easy to compute for any given x
• One-way or pre image resistant
• Computationally infeasible to find find y ≠ x such that H(y) = H(x)
• Collision resistant or strong collision resistance

Question 19

Two ways to attack Hash Function

Answer 19

Cryptanalysis and Brute-force

Question 20

SHA

Answer 20

most widely used hash algorithm

Question 21

hash function applications

Answer 21

• passwords

- intrusion detection

Question 22

Public key encryption structure

Answer 22

• Based on mathematical function

Question 23

Asymmetric Encryption

Answer 23

• Uses two separate keys

- public key and private key

Question 24

Plaintext

Answer 24

• Readable message or data that is fed into the algorithm as input

Question 25

Encryption Algorithm

Answer 25

• Performs transformations on the plaintext

Question 26

Public and private key

Answer 26

• pair of keys

Question 27

Ciphertext

Answer 27

• scrambled message produced as output

Question 28

decryption key

Answer 28

• Produces the original plaintext

Question 29

Asymetric encyption algorithms

Answer 29

• RSA (Riverst, Shamir, Adleman)
• Diffie-Hellman key exchange
• Digital Signature Standard (DSS)
• Elliptic Curve Cryptography (ECC)