Security Questions

(SEC)



(Fall 2012 - Tygar & D.Song):


Instructions: Choose three of the following four questions to answer 
1. What does .secure. mean in the phrase .secure system.? Give a definition,
or list the key security properties that a secure system should satisfy. 

2. A major challenge for PKI is certificate revocation. Give at least five
distinct reasons why certificate revocation is difficult. 

3. Describe a system for time-stamping documents that does not rely on a
trusted-third party timestamp service. Such a system does not need to provide
exact time stamps, but it must at least preserve the order of documents that
are time-stamped; e.g., if document A is time-stamped before document B,
then timestamp(A) < timestamp(B). 

4. Company X wants to design a new cloud service for sharing documents
(along the lines of Google Docs.) To satisfy this, Company X needs to make
sure that its system is usable. Describe how Company X could design an
experiment to test the usability of the security parts of its system. 



Questions
========

Q1: Direct Manipulation and Computational Wear

* List the core principles of direct manipulation user interfaces.
* Consider two types of mobile UIs: touch-controlled and voice-controlled.
  Which type of interface is more "direct" and why?
* Draw the user-system dialog. Where do articulatory and semantic
  distances appear? What is the difference between them? Give a concrete
  example how interfaces may reduce one type of distance.
* What are computational forms of "wear" and how do they conceptually
  fit into the direct manipulation paradigm?

Q2: Contextual Inquiry from Beyer and Holzblatt

Describe the relationship that should hold in contextual inquiry between
researcher and subject.

List the four principles of contextual inquiry (Context, Partnership,
Interpretation, Focus).For each principle, give concrete examples of *how*
it should be applied, and *why* it contributes to understanding of user
practices.

Q3: Evaluation Methods
* Tohidi et al. claim that "Testing many is better than testing one".
  What concrete evaluation methodology do they argue for - and what advantages
  do they claim?
* Kohavi also advocates for testing alternatives - contrast his approach
  with Tohidi et al.'s. What are the strengths and limitations of each
  approach? At which stage of design is each appropriate?
* You are building a website and want to increase the time your users
  spend on the site. Think of a design intervention and how you would test it.
  What would your independent and dependent variables be? What kind of
  statistical tests would you apply and what would they tell you about the
  results?

Q4: End-User Software Engineering from the reading by Andrew Ko et al.

How did Ko et al. define "end-user software engineering?"

List the 5 stages of EUSE practice (Requirements, Design and Specification,
Reuse, Testing, Debugging).Using these 5 stages, contrast the practices of
EU programmers and
professional programmers.

In the process, list some common EU programming examples (spreadsheets,
web design, scripts,...)



(Spring 2013 . Paxson and Tygar):


A.  Consider a blogging site that allows users to post content they author
and also make comments on each other's posts.

	1.  Discuss how a worm could propagate within such a site.  What
	would you expect the progression of the infection to look like, in terms
	of infections present at a given time?

	2.  Suppose the goal is to make the blogging site immune to the
	problem of worms.  Explain the steps you could take, and the
	benefits and costs of each.

	3.  Suppose the costs of prevention are viewed as too high, or
	its efficacy to uncertain.  Sketch a detector for identifying
	that such a worm is spreading.

	4.  For your detection mechanism, qualitatively assess its
	properties in terms of false negatives and false positives.

	5.  Suppose you have concrete values for false positive and
	false negative rate.  How does the Base Rate Fallacy come into
	consideration when interpreting these?

	6.  Suppose you have two mechanisms for detecting such a worm.
	 The first analyzes the timing of the activity of individual users.
	 The second assesses the prevalence of particular strings of content
	as seen globally across the site.  Discuss the issues that arise
	when assessing which of these detectors works better.


B.  Google has a cluster of thousands of machines.  They want to log
security-relevant events that occur on those machines: e.g., each command
that an operator types into a root shell, each time a user resets their
Gmail password, and so on.

	1.  Describe a possible design to accommodate this -- it doesn't
	need to be fancy -- and describe what security properties it does
	and doesn't have.

	2.  Now let's say we want to store all those audit log entries in
	the cloud, on some server, but we don't want to trust that server
	in the cloud.  What can we do?  Suggest a scheme, and describe
	what security properties it does and doesn't provide.




(Fall 2012 - Tygar and D. Song):


Instructions: Choose three of the following four questions to answer 

1. What does .secure. mean in the phrase .secure system.? Give a definition,
or list the key security properties that a secure system should satisfy. 

2. A major challenge for PKI is certificate revocation. Give at least five
distinct reasons why certificate revocation is difficult. 

3. Describe a system for time-stamping documents that does not rely on a
trusted-third party timestamp service. Such a system does not need to
provide exact time stamps, but it must at least preserve the order of
documents that are time-stamped; e.g., if document A is time-stamped
before document B, then timestamp(A) < timestamp(B). 

4. Company X wants to design a new cloud service for sharing documents
(along the lines of Google Docs.) To satisfy this, Company X needs to
make sure that its system is usable. Describe how Company X could design
an experiment to test the usability of the security parts of its system 





(Spring 2012 - Wagner and Paxson):


A.  Consider a blogging site that allows users to post content they author
    and also make comments on each other's posts.

    1.  Discuss how a worm could propagate within such a site.  What would
	you expect the progression of the infection to look like, in terms
	of infections present at a given time?

    2.  Suppose the goal is to make the blogging site immune to the problem
	of worms.  Explain the steps you could take, and the benefits and
	costs of each.

    3.  Suppose the costs of prevention are viewed as too high, or its
	efficacy to uncertain.  Sketch a detector for identifying that
	such a worm is spreading.

    4.  For your detection mechanism, qualitatively assess its properties in
	terms of false negatives and false positives.

5.  Suppose you have concrete values for false positive and false negative
    rate.  How does the Base Rate Fallacy come into consideration when
    interpreting these?

    6.  Suppose you have two mechanisms for detecting such a worm.  The first
	analyzes the timing of the activity of individual users.  The second
	assesses the prevalence of particular strings of content as seen
	globally across the site.

	Discuss the issues that arise when assessing which of these detectors
	works better.


B.  Google has a cluster of thousands of machines.  They want to log
    security-relevant events that occur on those machines: e.g., each
    command that an operator types into a root shell, each time a user
    resets their Gmail password, and so on.

    1.  Describe a possible design to accommodate this -- it doesn't need
	to be fancy -- and describe what security properties it does and
	doesn't have.

    2.  Now let's say we want to store all those audit log entries in the
	cloud, on some server, but we don't want to trust that server in
	the cloud.  What can we do?  Suggest a scheme, and describe what
	security properties it does and doesn't provide.



(Fall 2011 - D. Song and Paxson):


1. Consider the problem of defending a web site from a DDoS attack.

   a) An attacker sends a stream of spoofed SYN packets to port 80 of the
      web server. Discuss two techniques that could be employed to find the
      hosts sending the flood.  How effectively would they work in
      today's Internet?

   b) For the same attack, discuss techniques a site can use by itself
      (i.e., not requiring cooperation by the broader network) to defend
      against the attack.  How well do these approaches work, and what are
      their drawbacks?

   c) Suppose that during the flood an ISP upstream of yours activates a
      monitoring box that inspects packets heading to your site and uses
      anomaly detection to identify and block likely spoofed packets.
      If they do this without your permission, have they violated the
      Wiretap Act?

   d) Now suppose that the attacker launches a DDoS attack using non-spoofed
      packets.  To what degree does that change the opportunities available to
      the attacker?  What about for the defenses you mentioned?

2.  Sketch the problem of buffer overflow attacks.  Discuss the range of
    defenses and their pros and cons.

3.  This question concerns TLS.

   a) Sketch an attack on TLS.

      [ultimately, the examination for this sub-question drove towards
      the problem of stolen certs / compromised CAs.]

   b) How might we detect that a given TLS session is using a stolen
      certificate or stems from a compromised CA?

   c) How effective is such detection, in terms of false positives and
      false negatives?

   d) Sketch, to the degree that you can, how DNSSEC works.  (NOTE: we
      recognize that DNSSEC was not on the syllabus, and sketch it for
      students as needed.)

   e) Suppose that instead of using CA's, clients retrieve public keys
      for use in TLS via DNSSEC queries.  Compare the properties of this
      approach with how TLS works today.

(Fall 2008 - Tygar & Wagner):
1. Bounce message spam typically occurs when a spammer sends many spam
emails with the From: line containing a forged email address -- say,
to make it appear that the spam emails were from me.  Many of those
spam emails will be undeliverable or will be destined to an invalid
email message, and thus a bounce message will be sent back to the
email address listed in the From: line -- i.e., back to me.  Consequently
when a spammer sends one million spam emails with my email address in
the From: line, my inbox may become clogged with thousands of bounce
messages for emails I never sent.  This is a nuisance.

(a) Design a mechanism to protect me against bounce message spam.
I don't want to see nuisance bounce messages, but I always want to
see bounce messages for emails that I do send.

(b) What are the privacy implications?

(c) How can we minimize the storage requirements?

(c) New requirement: I want to read and send email from several
different email clients, such as my laptop and my cellphone.  I want
to configure them once, but I want to minimize the amount of state
that they must save and avoid the need for my clients to exchange
data.  Augment your scheme to provide this property.

2. Name as many ways as you can think of that a user Alice on the
Berkeley email system could prevent me from reading my email for
the next 24 hours.


3. The FastTrack system is an automated system for toll payment.
The authorities send you a battery-powered transponder that you
put in the car; when you drive over the Bay bridge, their equipment
interrogate your transponder wirelessly and then bill you monthly.


(a) Describe the security goals that such a system ought to provide.

(b) How well does the current system meet these goals?

(c) Sketch how you would design the system, if you wanted to
    ensure that all of these goals were met.


June 2011