Personal Privacy: Limited Disclosure using Cryptographic Techniques

Mark ShaneckKarthikeyan Mahadevan

SCLab

What is Privacy Privacy is the expectation that

confidential personal information disclosed in a private place will not be disclosed to third parties, when that disclosure would cause either embarrassment or emotional distress to a person of reasonable sensitivities.

Information is interpreted broadly to include facts, images (e.g., photographs, videotapes), and disparaging opinions.

Privacy Invasion – Grocery Store Using a credit card to pay for the

groceries The credit card information should be

used only for the payment What you buy should never be revealed

to anyone. This is a bird’s eye view of the problem.

Although not serious please visit http://www.rbs2.com/privacy.htm for more interesting problems

A quotation “The Home Office caused controversy last

year when it attempted to allow a long list of public authorities to access records of individuals' telephone and Internet usage. This "communications data" -- phone numbers and e-mail addresses contacted, web sites visited, locations of mobile phones, etc. -- would have been available without any judicial oversight, under the Regulation of Investigatory Powers Act 2000” - London

What is Limited Disclosure California passed a law, SB 27, requiring

disclosure to consumers of the kinds of information companies collect and shared about them. [Takes effect from 2005]

As the title suggests we want to limit disclosure of personal information

In other words I and only I should provide access to my personal information.

Misuse of Personal Information On average, 49% of victims did not know

how their information was obtained. Identity Theft

27.3 million Americans have been victims of identity theft in the last five years

67% of identity theft victims - more than 6.5 million victims in the last year - report that existing credit card accounts were misused.

www.idtheftcenter.com

Real Life Examples * Almost 10 months after the World Trade

Center attack, a widow found out that an identity clone had been living and working using her husband's information.

He had died during the attack. A mother keeps receiving collection

notices on her daughter's credit card accounts.

Her daughter died 17 years ago. * http://www.idtheftcenter.org/vg117.shtml

Other Scenarios ISP Customer Information Airlines – Passenger Information Medical Databases Of Course “Big – Brother” is

omnipotent Personal Privacy on the Internet – is

a myth (http://www.epic.org/reports/surfer-beware.html)

Privacy Policy

Yes there is enough literature, documents and other resources on Privacy Policy

But how many of us read the privacy agreements? (Has anyone really read EULA?)

Policies are really like traffic rules, but we still need a cop to enforce it.

Privacy… KYD’s example: AIDS website P3P (Platform for Privacy Preference) Privacy Tools

http://www.epic.org/privacy/tools.html Other resourceful websites

Electronic Frontier Foundation www.eff.org

Center for Democracy and Technology www.cdt.org

Security in Databases

Designing databases with privacy as a central concern – Hippocratic Databases

Secure Databases – Executing SQL Queries over Encrypted Databases

Encrypted Keyword Search There has a lot of good work done

in this area.

Why this talk? For our project we initially decided

that we will solve one part of the Hippocratic Databases – Limited Disclosure

There is a solution based on P3P for limited disclosure

Cryptographic Techniques to provide limited disclosure is the theme of our project

Definitions

Kp = i=p to P ki (where P is some system parameter - length of storage agreement)

Let h be a hash function: h:{0,1}* => {0,1}m{1}1

k0 = k ki = h(ki-1)

Limited Disclosure - Setup

A

DB

•Chooses n = pq (p,q large primes) where p = 2x+1, q = 2y+1 (x, y large primes)•Chooses e, d, such that ed = 1 mod (n)•Chooses Kp odd.•A stores meKP mod n and Kp, n with DB

Limited Disclosure Scheme

A B

DB

rd mod (n), (rKp)-1 mod (n)

rd mod (n)

mrKp mod n

Computes (meKp)rd mod n

Computes:(mrKp)(rKp)

-1

mod n

What everybody knows

A B

DB

Everything, of courseN, p, q, (n), e, d, k, h

c, k, n, rd mod (n)

n, rd mod (n), (rKp)-1 mod (n)

Limited Disclosure - Key Update Every night, DB computes:

(meKp)kp-1

A can now give authorization for some time in the future by computing the proper Kp and Kp

-1

A knows that the data will change, and does not want to give authorization until after the change, but wants to give the authorization token now)

Benefits A is mostly offline (only needed when giving

authorization, which can be done beforehand)

A keeps DB out of the loop when changing “access control lists”

Requires no authorization checking from DB. DB just responds to all queries with the encrypted data.

Disables B from checking if cached copy of A’s data is still valid (after expiration of authorization)

Lines of Thought

We think that e is used only by the owner of the data, can we keep this as a secret ?

Is this scheme secure ? Can we use a symmetric key

system ?

Future Work

Collaboration attack – Can we avoid this ?

Analyze the protocol for any security breaches

If possible provide a “Proof of security”

Tie this with P3P

Questions .. Suggestions ?