PRIAM: PR ivate I nformation A ccess M anagement on Outsourced Storage Service Providers

1. PRIAM: PRivate Information Access Management on Outsourced Storage Service Providers Mark Shaneck Karthikeyan Mahadevan Jeff Yongdae Kim

2. Collection of Personal Information on the Internet * • A survey by www.epic.org on the hot 100 websites (www.100hot.com) suggested that 49 of these collect private information • “For example America Online is matching its subscribers to demographic and psychographic data obtained from Donnelley Marketing” *Source: http://www.epic.org/reports/surfer-beware.html

3. Privacy – do we have it on the Internet ? • Privacy is a right that every individual should possess • Apparently this concept is not true in the Internet • "You have zero privacy now. Get over it“ - Sun CEO Scott McNealy • Conclusion: Protecting privacy will be one the greatest challenges for the Internet

4. Outline • Motivation • Existing Approaches • Overview of PRIAM • Challenge • Details • Conclusion and Future Work

5. Problem Setting • Alice wants to have control over her private information • She wants to store it with a highly available storage provider, which she could access from anywhere • Storage provider should not know what she is storing • Alice - Minimal computation • Alice should be able to let the people she like access some information for a limited period of time

6. Basic Architecture

7. Existing Approaches - ACL • Access Control List: Owner defines an ACL and gives it to the PIP • Problems • PIP should be trusted. • Else encrypt the data – implies more key management issues

8. Existing Approaches - Kerberos • Kerberos : Owner has to play AS • Problems • Owner has to online • Also PIP should be trusted • Else encrypt files – key management problems (similar to ACL approach)

9. Existing Approaches - Lockbox • Idea – encrypt the file with symmetric key and encrypt the symmetric key with public key of users who will be granted access (used in Storage Security) • Problem owner has to be online to provide access to new user! • Once the authorization expires – update the lockbox, has to contact PIP!

10. PRIAM • PRIAM is a suite of protocols: • Private Information Storage Protocol • Private Information Evolution Protocol • Private Information Authorization Protocol • Private Information Retrieval Protocol

11. Challenge • How can the PIP do updation without owner interference? • There exists a function f such that:

12. Building Blocks • Safe Prime: A prime p is called a safe prime if it is of the form p = 2p’+1, where p’is a prime • Odd hash function • Key Chain

13. Set up • Owner does the following • Choose two safe primes p, q and compute n=pq • Pick random odd number r (blinding factor) which is co prime to φ(n) • Public value : n • Private values: p, q, p’, q’, φ(n), r

14. Private Information Storage • Alice wants to store t items {m(0), m(1),…,m(t)} – after initial setup • For each i, 1≤i≤t, generate an odd random number such that • Compute: • To store the information with PIP, Alice will send encrypted message, along with initial value of k, index i:

15. Private Information Evolution • PIP updates the encryption key every night (whenever appropriate) as follows: • Note, that for day j :

16. Private Information Authorization • Bob wants to know some information about Alice, he must get Alice’s consent. Alice -> Bob : • This message is sent over a secure channel, where r is a fixed odd random. • Alice could give Bob authorization for over a period of time

17. Temporal Private Information Retrieval Querier can now recover the message as

18. Performance Evaluation

19. Security Analysis • Confidentiality • Our scheme is secure against an outside attack • Our scheme is secure against an inside attacker under the hardness of finding φ(n) from n • Integrity: RSA guarantees this property

20. Security Analysis – Cont’d • Collusion • The advantage of any number of collusion is not better that that of an inside attacker with several transcripts • Knowing the values of encryption keys without the knowledge of φ(n) does not help finding the inverse of a future key

21. Application – (1) • Private Information on the Internet • We will be able to realize privacy on the Internet using our approach. • For example Alice purchasing products from a website could provide authorization to some information, with which the website could contact a PIP

22. Application – (2) • Disclosure of Medical History Information • Any doctor would be able to access the required medical information about a patient with his/her authorization

23. Conclusions • We have proposed a scheme to achieve control over one’s private information • Provide dynamic authorization • No necessity to contact the PIP for key updates • PIP is minimally trusted !

24. Future Work • Applying to Storage Area Networks • Symmetric Key Version of this scheme • Supporting multiple owners • Digital watermarking or traitor tracing to prevent information dissemination from an authorized querier.

25. Questions ?