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Privacy - PowerPoint PPT Presentation

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Privacy Week 9 - March 15, 17 Privacy policies Policies let consumers know about site’s privacy practices Consumers can decide whether practices are acceptable, when to opt-out Presence increases consumer trust Make companies subject to FTC privacy-related enforcement

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Week 9 - March 15, 17

privacy policies
Privacy policies
  • Policies let consumers know about site’s privacy practices
  • Consumers can decide whether practices are acceptable, when to opt-out
  • Presence increases consumer trust
  • Make companies subject to FTC privacy-related enforcement
  • Rapid adoption 1998-2001*

* G.R. Milne and M.J. Culnan 2002. Using the Content of Online Privacy Notices to Inform Public Policy: A Longitudinal Analysis of the 1998-2002 US Web Surveys. The Information Society 18, 5, 245-359.

privacy policy problems
Privacy policy problems
  • BUT policies are often
    • difficult to understand
    • hard to find
    • take a long time to read
    • change without notice
privacy policy components
Identification of site, scope, contact info

Types of information collected

Including information about cookies

How information is used

Conditions under which information might be shared

Information about opt-in/opt-out

Information about access

Information about data retention policies

Information about seal programs

Security assurances

Children’s privacy

Privacy policy components

There is lots of informationto conveys -- but policyshould be brief andeasy-to-read too!

What is opt-in? What is opt-out?

web privacy concerns
Web privacy concerns
  • Data is often collected silently
    • Web allows large quantities of data to be collected inexpensively and unobtrusively
  • Data from multiple sources may be merged
    • Non-identifiable information can become identifiable when merged
  • Data collected for business purposes may be used in civil and criminal proceedings
  • Users given no meaningful choice
    • Few sites offer alternatives
browser chatter
Browsers chatter about

IP address, domain name, organization,

Referring page

Platform: O/S, browser

What information is requested

URLs and search terms


To anyone who might be listening

End servers

System administrators

Internet Service Providers

Other third parties

Advertising networks

Anyone who might subpoena log files later

Browser Chatter
typical http request with cookie
Typical HTTP request with cookie

GET /retail/searchresults.asp?qu=beer HTTP/1.0


User-Agent: Mozilla/4.75 [en] (X11; U; NetBSD 1.5_ALPHA i386)


Accept: image/gif, image/jpeg, image/pjpeg, */*


Cookie:buycountry=us; dcLocName=Basket; dcCatID=6773; dcLocID=6773; dcAd=buybasket; loc=; parentLocName=Basket; parentLoc=6773; ShopperManager%2F=ShopperManager%2F=66FUQULL0QBT8MMTVSC5MMNKBJFWDVH7; Store=107; Category=0

referer log problems
Referer log problems
  • GET methods result in values in URL
  • These URLs are sent in the referer header to next host
  • Example:>index.html

  • Access log example
  • What are cookies?
  • What are people concerned about cookies?
  • What useful purposes do cookies serve?
cookies 101
Cookies 101
  • Cookies can be useful
    • Used like a staple to attach multiple parts of a form together
    • Used to identify you when you return to a web site so you don’t have to remember a password
    • Used to help web sites understand how people use them
  • Cookies can do unexpected things
    • Used to profile users and track their activities, especially across web sites
how cookies work the basics
How cookies work – the basics
  • A cookie stores a small string of characters
  • A web site asks your browser to “set” a cookie
  • Whenever you return to that site your browser sends the cookie back automatically

Please store cookie xyzzy

Here is cookie xyzzy





First visit to site

Later visits

how cookies work advanced
Cookies are only sent back to the “site” that set them – but this may be any host in domain

Sites setting cookies indicate path, domain, and expiration for cookies

Cookies can store user info or a database key that is used to look up user info – either way the cookie enables info to be linked to the current browsing session

How cookies work – advanced

Send me with requests for index.html on for this session only

Send me with any request to until 2008

DatabaseUsers …

Email …

Visits …




cookie terminology
Cookie terminology
  • Cookie Replay – sending a cookie back to a site
  • Session cookie – cookie replayed only during current browsing session
  • Persistent cookie – cookie replayed until expiration date
  • First-party cookie – cookie associated with the site the user requested
  • Third-party cookie – cookie associated with an image, ad, frame, or other content from a site with a different domain name that is embedded in the site the user requested
    • Browser interprets third-party cookie based on domain name, even if both domains are owned by the same company
web bugs
Web bugs
  • Invisible “images” (1-by-1 pixels, transparent) embedded in web pages and cause referer info and cookies to be transferred
  • Also called web beacons, clear gifs, tracker gifs,etc.
  • Work just like banner ads from ad networks, but you can’t see them unless you look at the code behind a web page
  • Also embedded in HTML formatted email messages, MS Word documents, etc.
  • For software to detect web bugs see:
how data can be linked
How data can be linked
  • Every time the same cookie is replayed to a site, the site may add information to the record associated with that cookie
    • Number of times you visit a link, time, date
    • What page you visit
    • What page you visited last
    • Information you type into a web form
  • If multiple cookies are replayed together, they are usually logged together, effectively linking their data
    • Narrow scoped cookie might get logged with broad scoped cookie
ad networks

search for medical information

buy CD

replay cookie

set cookie



Ad networks

Ad companycan get yourname and address fromCD order andlink them to your search

Search Service

CD Store

what ad networks may know
Personal data:

Email address

Full name

Mailing address (street, city, state, and Zip code)

Phone number

Transactional data:

Details of plane trips

Search phrases used at search engines

Health conditions

What ad networks may know…

“It was not necessary for me to click on the banner ads for information to be sent to DoubleClick servers.”

– Richard M. Smith

online and offline merging
Online and offline merging
  • In November 1999, DoubleClick purchased Abacus Direct, a company possessing detailed consumer profiles on more than 90% of US households.
  • In mid-February 2000 DoubleClick announced plans to merge “anonymous” online data with personal information obtained from offline databases
  • By the first week in March 2000 the plans were put on hold
    • Stock dropped from $125 (12/99) to $80 (03/00)
offline data goes online
Offline data goes online…

The Cranor family’s 25 most

frequentgrocerypurchases (sorted by nutritional value)!

  • Data on online activities is increasingly of interest in civil and criminal cases
  • The only way to avoid subpoenas is to not have data
  • In the US, your files on your computer in your home have much greater legal protection that your files stored on a server on the network
original idea behind p3p

P3P: Introduction

Original Idea behind P3P
  • A framework for automated privacy discussions
    • Web sites disclose their privacy practices in standard machine-readable formats
    • Web browsers automatically retrieve P3P privacy policies and compare them to users’ privacy preferences
    • Sites and browsers can then negotiate about privacy terms
p3p history

P3P: Introduction

P3P history
  • Idea discussed at November 1995 FTC meeting
  • Ad Hoc “Internet Privacy Working Group” convened to discuss the idea in Fall 1996
  • W3C began working on P3P in Summer 1997
    • Several working groups chartered with dozens of participants from industry, non-profits, academia, government
    • Numerous public working drafts issued, and feedback resulted in many changes
    • Early ideas about negotiation and agreement ultimately removed
    • Automatic data transfer added and then removed
    • Patent issue stalled progress, but ultimately became non-issue
  • P3P issued as official W3C Recommendation on April 16, 2002
p3p1 0 a first step

P3P: Introduction

P3P1.0 – A first step
  • Offers an easy way for web sites to communicate about their privacy policies in a standard machine-readable format
    • Can be deployed using existing web servers
  • This will enable the development of tools that:
    • Provide snapshots of sites’ policies
    • Compare policies with user preferences
    • Alert and advise the user
the basics

P3P: Introduction

The basics
  • P3P provides a standard XML format that web sites use to encode their privacy policies
  • Sites also provide XML “policy reference files” to indicate which policy applies to which part of the site
  • Sites can optionally provide a “compact policy” by configuring their servers to issue a special P3P header when cookies are set
  • No special server software required
  • User software to read P3P policies called a “P3P user agent”
what s in a p3p policy

P3P: Enabling your web site – overview and options

What’s in a P3P policy?
  • Name and contact information for site
  • The kind of access provided
  • Mechanisms for resolving privacy disputes
  • The kinds of data collected
  • How collected data is used, and whether individuals can opt-in or opt-out of any of these uses
  • Whether/when data may be shared and whether there is opt-in or opt-out
  • Data retention policy
p3p xml encoding

P3P version

Location ofhuman-readableprivacy policy

P3P policy name

Site’s nameandcontactinfo

Access disclosure


How data maybe used


Data recipients

Data retention policy

Types of data collected

P3P/XML encoding

<POLICIES xmlns="">

<POLICY discuri=""










<DATA ref="">Web Privacy With P3P</DATA>





<CONSEQUENCE>We keep standard web server logs.</CONSEQUENCE>





<DATA ref="#dynamic.clickstream"/>

<DATA ref="#dynamic.http"/>





p3p1 0 spec defines

P3P: Introduction

P3P1.0 Spec Defines
  • A standard vocabulary for describing set of uses, recipients, data categories, and other privacy disclosures
  • A standard schema for data a Web site may wish to collect (base data schema)
  • An XML format for expressing a privacy policy in a machine readable way
  • A means of associating privacy policies with Web pages or sites
  • A protocol for transporting P3P policies over HTTP
a simple http transaction

P3P: Introduction

GET /index.html HTTP/1.1


. . . Request web page

HTTP/1.1 200 OK

Content-Type: text/html

. . . Send web page

A simple HTTP transaction


with p3p 1 0 added

P3P: Introduction

GET /w3c/p3p.xml HTTP/1.1


Request Policy Reference File

Send Policy Reference File

Request P3P Policy

Send P3P Policy

GET /index.html HTTP/1.1


. . . Request web page

HTTP/1.1 200 OK

Content-Type: text/html

. . . Send web page

… with P3P 1.0 added



P3P: Introduction

  • P3P clients can check a privacy policy each time it changes
  • P3P clients can check privacy policies on all objects in a web page, including ads and invisible images|2|68523|1|146|ADFORCE

p3p in ie6

P3P: Introduction

P3P in IE6

Automatic processing of compact policies only;

third-party cookies without compact policies blocked by default

Privacy icon on status bar indicates that a cookie has been blocked – pop-up appears the first time the privacy icon appears


P3P: Introduction

Users can click on privacy icon forlist of cookies; privacy summariesare available atsites that are P3P-enabled


P3P: Introduction

Privacy summary report isgenerated automaticallyfrom full P3P policy

p3p in netscape 7

P3P: Introduction

P3P in Netscape 7

Preview version similar to IE6, focusing, on cookies; cookies without compact policies (both first-party and third-party) are “flagged” rather than blocked by default

Indicates flagged cookie


P3P: Introduction

Users can view English translation of (part of) compact policy in Cookie Manager


P3P: Introduction

A policy summary can be generated automatically from full P3P policy

at t privacy bird

P3P: Introduction

AT&T Privacy Bird
  • Free download of beta from
  • “Browser helper object” forIE 5.01/5.5/6.0
  • Reads P3P policies at all P3P-enabled sites automatically
  • Puts bird icon at top of browser window that changes to indicate whether site matches user’s privacy preferences
  • Clicking on bird icon gives more information
  • Current version is information only – no cookie blocking
why web sites adopt p3p

P3P: Introduction

Why web sites adopt P3P
  • Demonstrate corporate leadership on privacy issues
    • Show customers they respect their privacy
    • Demonstrate to regulators that industry is taking voluntary steps to address consumer privacy concerns
  • Distinguish brand as privacy friendly
  • Prevent IE6 from blocking their cookies
  • Anticipation that consumers will soon come to expect P3P on all web sites
  • Individuals who run sites value personal privacy
p3p early adopters

P3P: Introduction

P3P early adopters
  • News and information sites – CNET,, BusinessWeek
  • Search engines – Yahoo, Lycos
  • Ad networks – DoubleClick, Avenue A
  • Telecom companies – AT&T
  • Financial institutions – Fidelity
  • Computer hardware and software vendors – IBM, Dell, Microsoft, McAfee
  • Retail stores – Fortunoff, Ritz Camera
  • Government agencies – FTC, Dept. of Commerce, Ontario Information and Privacy Commissioner
  • Non-profits - CDT

P3P: The future

  • Somewhat early to evaluate P3P
  • Some companies that P3P-enable think about privacy in new ways and change their practices
    • Systematic assessment of privacy practices
    • Concrete disclosures – less wiggle room
    • Disclosures about areas previously not discussed in privacy policy
  • Hopefully we will see greater transparency, more informed consumers, and ultimately better privacy policies
discussion questions
Discussion questions
  • What elements are needed in order to facilitate a robust market for privacy of personal information?
  • How can P3P help realize such a market?
homework discussion
Homework discussion
  • Argue for or against placing privacy-related restrictions on public web cams.
  • P3P and privacy policies
    • What aspects of each privacy policy you liked and what aspects you did not like
    • Compare the experience of reading the privacy policies with using each P3P user agent
  • Pick one new-technology-related privacy concern that you believe to be particularly significant. Explain the privacy issue and why you think it is a significant concern. What might be done to mitigate the concern?
degrees of anonymity
Degrees of anonymity

Absolute privacy: adversary cannot observe communication

Beyond suspicion: no user is more suspicious than any other

Probable innocence: each user is more likely innocent than not

Possible innocence: nontrivial probability that user is innocent

Exposed (default on web): adversary learns responsible user

Provably exposed: adversary can prove your actions to others



the anonymizer





The Anonymizer
  • Acts as a proxy for users
  • Hides information from end servers
  • Sees all web traffic
  • Adds ads to pages (free service; subscription service also available)




cryptography basics
Cryptography Basics
  • Encryption algorithm
    • used to make content unreadable by all but the intended receivers

E(plaintext,key) = ciphertext

D(ciphertext,key) = plaintext

  • Symmetric (shared) key cryptography
    • A single key is used is used for E and D

D( E(p,k1), k1 ) = p

  • Management of keys determines who has access to content
    • E.g., password encrypted email
public key cryptography
Public Key Cryptography
  • Public Key cryptography
    • Each key pair consists of a public and private component: k+ (public key), k- (private key)

D( E(p, k+), k- ) = p

D( E(p, k-), k+ ) = p

  • Public keys are distributed (typically) through public key certificates
    • Anyone can communicate secretly with you if they have your certificate
    • E.g., SSL-base web commerce
mixes chaum81














kX = encrypted with public key of Mix X

Mixes [Chaum81]



Mix C

Mix A

Mix B

Sender routes message randomly through network

of “Mixes”, using layered public-key encryption.

  • Users join a Crowd of other users
  • Web requests from the crowd cannot be linked to any individual
  • Protection from
    • end servers
    • other crowd members
    • system administrators
    • eavesdroppers
  • First system to hide data shadow on the web without trusting a central authority


Crowd members

Web servers













anonymous e mail
Anonymous email
  • Anonymous remailers allow people to send email anonymously
  • Similar to anonymous web proxies
    • Send mail to remailer, which strips out any identifying information (very controversial)
    • Johan (Julf) Helsingius ~ Penet
  • Some can be chained and work like mixes