Chapter 2

Question 1

Universal technique for providing confidentiality for transmitted/stored data

Answer 1

Symmetric Encryption

Question 2

Need strong encryption algorithm

Sender and receiver must have obtained copies of the secret key

Answer 2

2 requirements for Symmetric Encryption

Question 3

Cryptanalytic attacks

Brute-Force attack

Answer 3

Attacking Symmetric Encryption

Question 4

Rely on nature of algorithm

Knowledge of general characteristics of plain text

Answer 4

Cryptanalytic attacks

Question 5

Try all possible keys on ciphertext until plaintext is obtained

Answer 5

Brute-force attack

Question 6

Most widely used encryption scheme

Uses 64 bit plaintext block and 56 bit key to produce 64 bit ciphertext block

Answer 6

Data Encryption Standard (DES )

Question 7

Repeats DES algorithm 3 times using 2 or 3 unique keys
Pros: 168 bit key length overcomes vulnerability to brute-force
Cons: algorithm is sluggish in software
64 bit block size

Answer 7

Triple DES (3DES)

Question 8

Replaced 3DES
Symmetric block cipher
Improved efficiency

Answer 8

Advanced Encryption Standard (AES)

Question 9

Typical symmetric encryption is applied to a unit of data larger than a single 64 bit or 128 bit block

Answer 9

Practical Security Issues

Question 10

Simplest approach to multiple-block encryption

Answer 10

Electronic codebook (ECB) mode

Question 11

Processes the input one block of elements at a time
can reuse keys
More common

Answer 11

Block Cipher

Question 12

Processes the input elements continuously
Produces output one element at a time
Encrypts plaintext one byte at a time

Answer 12

Stream Cipher

Question 13

Protects against active attacks
Verifies received message is authentic
Can use conventional encryption

Answer 13

Message Authentication

Question 14

Can be applied to block of data of any size
Produces a fixed-length output
One-way or pre-image resistant

Answer 14

Hash function requirements

Question 15

Cryptoanalysis - exploit logical weaknesses in the algorithm

Brute-force attack - strength of hash function depends solely on the length of the hash code

Answer 15

2 approaches to attacking a secure hash function

Question 16

SHA most widely used algorithm

Answer 16

Security of Hash functions

Question 17

Passwords

Intrusion detection

Answer 17

Additional Secure hash functions

Question 18

Based on mathematical functions

Asymmetric - uses 2 separate keys

Answer 18

Public-key Encryption Structure

Question 19

Computationally easy:
- to create key pairs
- for sender knowing public key to encrypt messages
- for receiver knowing private key to decrypt ciphertext
…

Answer 19

Requirements for public-key cryptosystems

Question 20

RSA
Diffie-Hellman key exchange algorithm
Digital Signature Standard (DSS)
Elliptic curve Cryptography(ECC)

Answer 20

Assymmetric Encryption Algorithms

Question 21

Used for authenticating both source and data integrity

Answer 21

Digital Signatures

Question 22

Protects a message without needing to first arrange for sender and receiver to have same secret key

Answer 22

Digital Envelopes

Question 23

Keys for public-key algorithms

- stream key for symmetric stream cipher

Answer 23

Random Numbers

Question 24

Randomness - uniform distribution; independence

Unpredicatability - each number is statistically independent of other numbers

Answer 24

Random Number Requirements

Question 25

Cryptographic applications typically make use of algorithmic techniques for random number generation

Answer 25

Random vs Pseudorandom ( sequences produced that satisfy statistical randomness tests