Lecture 7 - Information Theory

Question 1

What happened in the case of Graham Dwyer?

Answer 1

• Irish architect, married with family - guilty of murder of Elaine O’Hara in 2015
• Murdered her in August 2012
• Case involved sado-masochist relationship - many comms uncovered on Elaine’s phone/computer which directly linked Dwyer to a relationship and murdering her
• Information theory was key to identifying Graham in court as the man who was responsible for her killing and sender/receiver of messages

Question 2

Expain this formula:

ΔS = - log2 Pr(X=x)

Answer 2

○ ΔS - change in uncertainty/entropy

○ - log2 - Information measured in bits (0 or 1 [=2!]), negative in front shows that as the probability of an event increases, the amount of information associated with observing that event decreases

Pr(X=x) - Probability of random variable X taking on a specific value x. Likelihood of observing a particular outcome from all possible outcomes. A birthday would be 1/365 (X=365, x=1)

Question 3

How many bits of data are required to unqiuely identify a person?

Answer 3

33 bits. The global population is over 8bn, equivalent to 2^33, coming from log2(2^33)=32.9… rounded to 33

Question 4

What is entropy in regards to information theory?

Answer 4

Entropy is a measure of how close a fact comes towards uniquely identifying someone, i.e. reducing the overall uncertainty

Question 5

What is information theory?

Answer 5

Information theory is about reaching 33 bits of data that can uncover an identity

Question 6

What sort of data can be leveraged from a user’s web browser to identify them?

Answer 6

IP address

Cookies

User agent strings - these are strings sent to a website to provide the best viewing experience, but can provide details such as operating system, screen size, system type (mobile/desktop), browser version, language packs etc.

Question 7

How can you stay safe online to prevent being identified?

Answer 7

Use TOR to hide your IP

Use a VPN

Use PAYG phones

Consider User Agent Switchers to make a desktop report it is a mobile device

Question 8

Name some secure operating systems and their features

Answer 8

TAILS - The Amnesic Incognito Live System. Free open-source Linux OS than runs on removeable media. It leaves no traces on the hardware and routes over TOR. It only stores data on encrypted persistent drives

Whonix - free open-source comprised of a gateway (using TOR for anonimity) and a desktop for the end user to connect to the gateway