Ch. 3

Question 1

What are the two requirements for secure use?

Answer 1

• 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 2

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

Answer 2

Block Cipher

Question 3

Processes the input elements continuously
Produces output one element 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 stream is one that is unpredictable without knowledge of the input key

Answer 3

Stream Cipher

Question 4

What is the purpose of Message Authentication.

Answer 4

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