$(20$pts$)$ Answer the following questions briefly:

$($a$)$ List three goals of security.

Prevention, Detection and Recovery

$($b$)$ Explain the difference between fabrication and modification attacks.

Fabrication creates new data and sends as if it is coming from a source.

Modification changes the data going from a source to a destination.

$($c$)$ What is the period of a keystream?

The generated keystream may repeat after sometime. This is referred to

as period.$($d$)$ Explain cryptanalysis briefly.

The science of recovering the plaintext or deducing the key without access

to the key.

$($e$)$ Why is ECB mode faster than CBC mode?

Because it can be implemented in a parallel manner. CBC cannot.