info - CS361 Introduction to Computer Security Information...

Info icon This preview shows pages 1–8. Sign up to view the full content.

View Full Document Right Arrow Icon
CS361: Introduction to Computer Security Information Theory Dr. Bill Young Department of Computer Sciences University of Texas at Austin Last updated: October 5, 2010 at 12:51 CS361 Slideset 4: 1 Information Theory
Image of page 1

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
What is Information Just what is information? The following is the fundamental paradigm of information theory: Sender Receiver a45 Transmission Medium Information is any content to be conveyed from the sender to receiver. It is sent in the form of one or more messages . Our goal is to quantify this sitution. CS361 Slideset 4: 2 Information Theory
Image of page 2
Some Information Theory Information theory is the field of study that quantifies the content of messages and the capacity of channels on which information may flow. It asks questions such as the following: 1 How much information is encoded in a particular message? 2 How efficiently can a given alphabet/language be transmitted? 3 What is the maximum capacity of a given transmission medium? 4 How is that capacity or efficiency reduced by interference /noise? These questions all have very precise and deep answers, that are beyond the scope of this course. We’ll only scratch the surface. CS361 Slideset 4: 3 Information Theory
Image of page 3

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Why Do We Care? Information theory is very important in computer science. It affects all communication, hardware design, protocol design, cryptography, fault-tolerance, etc. For example, in our current context it is useful to know how much information can be transmitted over a specific covert channel. This is the “bandwidth” of the channel. If the bandwidth is sufficiently small, perhaps we want to ignore it, but if it’s large that suggests a potential problem. CS361 Slideset 4: 4 Information Theory
Image of page 4
Quantifying Information: Thought Experiment How much information is contained in each of the following messages? How do you judge? A 1-bit binary number. An n -bit binary number. A single decimal digit. A two digit decimal number. “The attack will come at dawn.” “One if by land; two if by sea.” The King James Bible or the Collected Works of Poe. CS361 Slideset 4: 5 Information Theory
Image of page 5

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Information as Uncertainty “The concept in this theory at first seems disappointing and bizarre—disappointing because it has nothing to do with meaning, and bizarre because it deals not with a single message, but with the statistical character of a whole ensemble of messages.” –Warren Weaver “The word ‘information’ relates not so much to what you do say, as to what you could say. The mathematical theory of communication deals with the carriers of information, symbols and signals, not with information itself. That is, information is the measure of your freedom of choice when you select a message.” –Warren Weaver CS361 Slideset 4: 6 Information Theory
Image of page 6
Quantifying Information If you have n bits, you have 2 n possible messages. Why?
Image of page 7

Info iconThis preview has intentionally blurred sections. Sign up to view the full version.

View Full Document Right Arrow Icon
Image of page 8
This is the end of the preview. Sign up to access the rest of the document.

{[ snackBarMessage ]}

What students are saying

  • Left Quote Icon

    As a current student on this bumpy collegiate pathway, I stumbled upon Course Hero, where I can find study resources for nearly all my courses, get online help from tutors 24/7, and even share my old projects, papers, and lecture notes with other students.

    Student Picture

    Kiran Temple University Fox School of Business ‘17, Course Hero Intern

  • Left Quote Icon

    I cannot even describe how much Course Hero helped me this summer. It’s truly become something I can always rely on and help me. In the end, I was not only able to survive summer classes, but I was able to thrive thanks to Course Hero.

    Student Picture

    Dana University of Pennsylvania ‘17, Course Hero Intern

  • Left Quote Icon

    The ability to access any university’s resources through Course Hero proved invaluable in my case. I was behind on Tulane coursework and actually used UCLA’s materials to help me move forward and get everything together on time.

    Student Picture

    Jill Tulane University ‘16, Course Hero Intern