Symmetric Encryption and Message Confidentiality

 1 What are the essential ingredients of a symmetric cipher?

2 What are the two basic functions used in encryption algorithms?

3 How many keys are required for two people to communicate via a symmetric cipher?

4 What is the difference between a block cipher and a stream cipher?

5 What are the two general approaches to attacking a cipher?

6 Why do some block cipher modes of operation only use encryption while others use both encryption and decryption?

7 What is triple encryption?

8 Why is the middle portion of 3DES decryption rather than encryption?

Answer the above questions using the attached reference file only.