Personal Privacy: Limited Disclosure using Cryptographic Techniques

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Personal Privacy Limited Disclosure using
Cryptographic Techniques

• Mark Shaneck
• Karthikeyan Mahadevan
• SCLab

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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.

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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 birds eye view of the problem.
  Although not serious please visit
  http//www.rbs2.com/privacy.htm for more
  interesting problems

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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

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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.

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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

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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
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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)

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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.

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Privacy

• KYDs 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

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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.

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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

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Definitions

• Kp Pip to P ki (where P is some system
  parameter - length of storage agreement)
• Let h be a hash function h0,1 gt
  0,1m11
• k0 k
• ki h(ki-1)

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Limited Disclosure - Setup

• Chooses n pq (p,q large primes) where p
  2x1, q 2y1 (x, y large primes)
• Chooses e, d, such that ed 1 mod f(n)
• Chooses Kp odd.
• A stores meKP mod n and Kp, n with DB

A
DB
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Limited Disclosure Scheme
Computes (mrKp)(rKp)-1 mod n
A
B
DB
Computes (meKp)rd mod n
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What everybody knows
Everything, of course N, p, q, f(n), e, d, k, h
n, rd mod f(n), (rKp)-1 mod f(n)
A
B
DB
c, k, n, rd mod f(n)
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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)

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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 As
  data is still valid (after expiration of
  authorization)

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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 ?

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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

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Questions .. Suggestions ?