Personal Privacy: Limited Disclosure using Cryptographic Techniques Mark Shaneck Karthikeyan 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 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 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.

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. *

Other Scenarios ISP Customer Information Airlines – Passenger Information Medical Databases Of Course “Big – Brother” is omnipotent Personal Privacy on the Internet – is a myth ( beware.html) 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 Other resourceful websites Electronic Frontier Foundation Center for Democracy and Technology

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 K p =  i=p to P k i (where P is some system parameter - length of storage agreement) Let h be a hash function: h:{0,1} * => {0,1} m {1} 1 k 0 = k k i = h(k i-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 K p odd. A stores m eK P mod n and K p, n with DB

Limited Disclosure Scheme AB DB rd mod  (n), (rK p ) -1 mod  (n) rd mod  (n) m rK p mod n Computes (m eK p ) rd mod n Computes: (m rK p ) (rK p ) -1 mod n

What everybody knows AB DB Everything, of course N, p, q,  (n), e, d, k, h c, k, n, rd mod  (n) n, rd mod  (n), (rK p ) -1 mod  (n)

Limited Disclosure - Key Update Every night, DB computes: (m eK p ) k p-1 A can now give authorization for some time in the future by computing the proper K p and K p -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 ?