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\section*{Handout 7 (Privacy)}

The first motor car was invented around 1886. For ten years,

until 1896, the law in the UK and elsewhere required a person

to walk in front of any moving car waving a red flag. Cars

were such a novelty that most people did not know what to make

of them. The person with the red flag was intended to warn the

public, for example horse owners, about the impending

novelty---a car. In my humble opinion, we are at the same

stage of development with privacy. Nobody really knows what it

is about or what it is good for. All seems very hazy. There

are a few laws (cookie law, right-to-be-forgotten) which

address problems with privacy, but even if they are well

intentioned, they either back-fire or are already obsolete

because of newer technologies. The result is that the world of

``privacy'' looks a little bit like the old Wild West.

For example, UCAS, a charity set up to help students to apply

to universities, has a commercial unit that happily sells your

email addresses to anybody who forks out enough money in order

to be able to bombard you with spam. Yes, you can opt out very

often in such ``schemes'', but in case of UCAS any opt-out

will limit also legit emails you might actually be interested

in.\footnote{The main objectionable point, in my opinion, is

that the \emph{charity} everybody has to use for HE

applications has actually very honourable goals (e.g.~assist

applicants in gaining access to universities), but in their

small print (or better under the link ``About us'') reveals

they set up their organisation so that they can also

shamelessly sell email addresses they ``harvest''. Everything

is of course very legal\ldots{}moral?\ldots{}well that is in

the eye of the beholder. See:

\url{http://www.ucas.com/about-us/inside-ucas/advertising-opportunities} 

or

\url{http://www.theguardian.com/uk-news/2014/mar/12/ucas-sells-marketing-access-student-data-advertisers}}

Another example: Verizon, an ISP who is supposed to provide

you just with connectivity, has found a ``nice'' side-business

too: When you have enabled all privacy guards in your browser

(the few you have at your disposal) Verizon happily adds a

kind of cookie to your

HTTP-requests.\footnote{\url{http://webpolicy.org/2014/10/24/how-verizons-advertising-header-works/}}

As shown in the picture below, this cookie will be sent to

every web-site you visit. The web-sites then can forward the

cookie to advertisers who in turn pay Verizon to tell them

everything they want to know about the person who just made

this request, that is you.

\begin{center}

\includegraphics[scale=0.19]{../pics/verizon.png}

\end{center}

\noindent How disgusting? Even worse, Verizon is not known for

being the cheapest ISP on the planet (completely the

contrary), and also not known for providing the fastest

possible speeds, but rather for being among the few ISPs in

the US with a quasi-monopolistic ``market distribution''.

Well, we could go on and on\ldots{}and that has not even

started us yet with all the naughty things NSA \& Friends are

up to. Why does privacy actually matter? Nobody, I think, has

a conclusive answer to this question yet. Maybe the following

four notions help with clarifying the overall picture

somewhat: 

\begin{itemize}

\item \textbf{Secrecy} is the mechanism used to limit the

      number of principals with access to information (e.g.,

      cryptography or access controls). For example I better

      keep my password secret, otherwise people from the wrong

      side of the law might impersonate me.

\item \textbf{Confidentiality} is the obligation to protect

      the secrets of other people or organisations (secrecy

      for the benefit of an organisation). For example as a

      staff member at King's I have access to data, even

      private data, I am allowed to use in my work but not

      allowed to disclose to anyone else.

\item \textbf{Anonymity} is the ability to leave no evidence of

      an activity (e.g., sharing a secret). This is not equal

        with privacy---anonymity is required in many 

        circumstances, for example for whistle-blowers, 

        voting, exam marking and so on.

\item \textbf{Privacy} is the ability or right to protect your

      personal secrets (secrecy for the benefit of an

      individual). For example, in a job interview, I might

      not like to disclose that I am pregnant, if I were

      a woman, or that I am a father. Similarly, I might not

      like to disclose my location data, because thieves might

      break into my house if they know I am away at work. 

      Privacy is essentially everything which `shouldn't be

      anybody's business'.

\end{itemize}

\noindent While this might provide us with some rough

definitions, the problem with privacy is that it is an

extremely fine line what should stay private and what should

not. For example, since I am working in academia, I am every

so often very happy to be a digital exhibitionist: I am very

happy to disclose all `trivia' related to my work on my

personal web-page. This is a kind of bragging that is normal

in academia (at least in the field of CS), even expected if

you look for a job. I am even happy that Google maintains a

profile about all my academic papers and their citations. 

On the other hand I would be very irritated if anybody I do

not know had a too close look on my private live---it

shouldn't be anybody's business. The reason is that knowledge

about my private life usually is used against me. As mentioned

above, public location data might mean I get robbed. If

supermarkets build a profile of my shopping habits, they will

use it to \emph{their} advantage---surely not to \emph{my}

advantage. Also whatever might be collected about my life will

always be an incomplete, or even misleading, picture---for

example I am sure my creditworthiness score was temporarily(?)

destroyed by not having a regular income in this country

(before coming to King's I worked in Munich for five years).

To correct such incomplete or flawed credit history data there

is, since recently, a law that allows you to check what

information is held about you for determining your

creditworthiness. But this concerns only a very small part of

the data that is held about me/you.

To see how private matter can lead really to the wrong

conclusions, take the example of Stephen Hawking: When he was

diagnosed with his disease, he was given a life expectancy of

two years. If employers would know about such problems, would

they have employed Hawking? Now, he is enjoying his 70+

birthday. Clearly personal medical data needs to stay private.

A movie which has this topic as its main focus is Gattaca from

1997.\footnote{\url{http://www.imdb.com/title/tt0119177/}}

To cut a long story short, I let you ponder about the two

statements that often voiced in discussions about privacy:

\begin{itemize}

\item \textit{``You have zero privacy anyway. Get over it.''}\\

\mbox{}\hfill{}{\small{}by Scott Mcnealy (CEO of Sun)}

\item \textit{``If you have nothing to hide, you have nothing 

to fear.''}

\end{itemize}

\noindent If you want to read up further on this topic, I can

recommend the following article that appeared in 2011 in the

Chronicle of Higher Education

\begin{center} 

\url{http://chronicle.com/article/Why-Privacy-Matters-Even-if/127461/} 

\end{center} 

\noindent Funnily, or maybe not so funnily, the author of this

article carefully tries to construct an argument that does not

only attack the nothing-to-hide statement in cases where

governments \& Co collect people's deepest secrets, or

pictures of people's naked bodies, but an argument that

applies also in cases where governments ``only'' collect data

relevant to, say, preventing terrorism. The fun is of course

that in 2011 we could just not imagine that respected

governments would do such infantile things as intercepting

people's nude photos. Well, since Snowden we know some people

at the NSA did exactly that and then shared such photos among

colleagues as ``fringe benefit''.  

\subsubsection*{Re-Identification Attacks} 

Apart from philosophical musings, there are fortunately also

some real technical problems with privacy. The problem I want

to focus on in this handout is how to safely disclose datasets

containing very potentially private data, say health data. What can

go wrong with such disclosures can be illustrated with four

well-known examples:

\begin{itemize}

\item In 2006, a then young company called Netflix offered a 1

      Mio \$ prize to anybody who could improve their movie

      rating algorithm. For this they disclosed a dataset

      containing 10\% of all Netflix users at the time

      (appr.~500K). They removed names, but included numerical

      ratings of movies as well as times of ratings. Though

      some information was perturbed (i.e., slightly

      modified).

      Two researchers had a closer look at this anonymised

      data and compared it with public data available from the

      International Movie Database (IMDb). They found that

      98\% of the entries could be re-identified in the

      Netflix dataset: either by their ratings or by the dates

      the ratings were uploaded. The result was a class-action

      suit against Netflix, which was only recently resolved

      involving a lot of money.

\item In the 1990ies, medical datasets were often made public

      for research purposes. This was done in anonymised form

      with names removed, but birth dates, gender and ZIP-code

      were retained. In one case where such data about

      hospital visits of state employees in Massachusetts was

      made public, the then governor assured the public that

      the released dataset protected patient privacy by

      deleting identifiers. 

      A graduate student could not resist cross-referencing

      public voter data with the released data including birth

      dates, gender and ZIP-code. The result was that she

      could send the governor his own hospital record. It

      turns out that birth dates, gender and ZIP-code uniquely

      identify 87\% of people in the US. This work resulted

      in a number of laws prescribing which private data

      cannot be released in such datasets.

\item In 2006, AOL published 20 million Web search queries

      collected from 650,000 users (names had been deleted).

      This was again done for research purposes. However,

      within days an old lady, Thelma Arnold, from Lilburn,

      Georgia, (11,596 inhabitants) was identified as user

      No.~4417749 in this dataset. It turned out that search

      engine queries are deep windows into people's private

      lives. 

\item Genome-Wide Association Studies (GWAS) was a public

      database of gene-frequency studies linked to diseases.

      It would essentially record that people who have a

      disease, say diabetes, have also these genes. In order

      to maintain privacy, the dataset would only include

      aggregate information. In case of DNA data this was 

      achieved by mixing the DNA of many individuals (having

      a disease) into a single solution. Then this mixture 

      was sequenced and included in the dataset. The idea

      was that the agregate information would still be helpful

      to researchers, but would protect the DNA data of 

      individuals. 

      In 2007 a forensic computer scientist showed that 

      individuals can be still identified. For this he used

      the DNA data from a comparison group (people from the

      general public) and ``subtracted'' this data from the

      published data. He was left with data that included

      all ``special'' DNA-markers of the individuals

      present in the original mixture. He essentially deleted

      the ``background noise''. Now the problem with

      DNA data is that it is of such a high resolution that

      even if the mixture contained maybe 100 individuals,

      you can now detect whether an individual was included

      in the mixture or not.

      This result changed completely how DNA data is nowadays

      published for research purposes. After the success of 

      the human-genome project with a very open culture of

      exchanging data, it became much more difficult to 

      anonymise datasuch that patient's privacy is preserved.

      The public GWAS database was taken offline in 2008.

\end{itemize}

\noindent There are many lessons that can be learned from

these examples. One is that when making data public in 

anonymised form you want to achieve \emph{forward privacy}.

This means, no matter of what other data that is also available

or will be released later, the data does not compromise

an individual's privacy. This principle was violated by the 

data in the Netflix and governor of Massachusetts cases. There

additional data allowed one to re-identify individuals in the

dataset. In case of GWAS a new technique of re-identification 

compromised the privacy of people on the list.

The case of the AOL dataset shows clearly how incomplete such 

data can be: Although the queries uniquely identified the

old lady, she also looked up diseases that her friends had,

which had nothing to do with her. Any rational analysis of her

query data must have concluded, the lady is on her deathbed, 

while she was actually very much alive and kicking.

\subsubsection*{Differential Privacy}

Differential privacy is one of the few methods, that tries to 

achieve forward privacy with large datasets. The basic idea

is to add appropriate noise, or errors, to any query of the

dataset. The intention is to make the result of a query 

insensitive to individual entries in the database. The hope is

that the added error does not eliminate the ``signal'' one is 

looking for by querying the dataset.

\begin{center}

User\;\;\;\;    

\begin{tabular}{c}

tell me $f(x)$ $\Rightarrow$\\

$\Leftarrow$ $f(x) + \text{noise}$

\end{tabular}

\;\;\;\;\begin{tabular}{@{}c}

Database\\

$x_1, \ldots, x_n$

\end{tabular}

\end{center}

\end{document}

http://randomwalker.info/teaching/fall-2012-privacy-technologies/?

http://chronicle.com/article/Why-Privacy-Matters-Even-if/127461/

http://repository.cmu.edu/cgi/viewcontent.cgi?article=1077&context=hcii

https://josephhall.org/papers/NYU-MCC-1303-S2012_privacy_syllabus.pdf

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