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# Computer Science 314: Operating Systems
### Mo Khan - 3431709
Assignment 4
This assignment should be submitted after you have finished Unit 5.
It is worth 15% of your final grade for this course.
## Part 1: Concepts (20 marks; 4 marks each)
Please answer the following questions in complete sentences. Your answer for each question should be about 150 words.
1. Why is it important to distinguish between mechanisms of protection and policies of protection?
Protection mechanisms are used to constrain the potential senders and/or
receivers of a message and to make sure that data is transmitted securely.
This includes things like cryptographic/digital signatures to ensure that a
piece of data or message hasn't been tampered with and/or to verify that data
was produced by trusted parties. This is used in many different protocols such
as security assertion markup language (SAML) transactions, transport layer
security (TLS), OAuth 2.0 and more.
Protection policies are used to enforce constraints on what things can be
done. Examples of this include absolute and relative session timeout policies
and acceptable TLS cipher suites. Policies can change over time as modern
cipher suites are released and vulnerabilites, and knowledge is improved.
Separating mechanisum from policy is more flexible because policies are likely
to change over time. Policy changes might require changes in the underlying
mechanism.
Protection mechanisms determine **how** to do something and protection policies
determine **what** will be done.
1. What is an access matrix, and how can it be implemented?
1. How does a virus differ from a worm?
1. What is the difference between symmetric encryption and asymmetric encryption?
1. What are the two main varieties of authentication algorithms?
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