1 Efficient Conjunctive Keyword Search on Encrypted Data Storage System Author ： Jin Wook Byun Dong Hoon Lee Jongin Lim Presentered by Chia Jui Hsu Date ：

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3 Outline Introduction Related Works Example Contribution Security Definition Formal Security Proof Conclusion References

4 Introduction Encryption of sensitive data Management of encryption/decryption keys. But, it makes data be random and unreadable to anyone other than the users holding the encrypted keys.

5 Related Works (1/3) Web-based personal storage systems Two entities are involved Data supplier uploads encrypted data, then searches data containing keywords Song et al. [13] In 2000, they first suggest efficient and provably secure keyword search scheme by block cipher Goh[8] Goh suggested a secure search scheme using a Bloom filter Chang and Mitzenmacher[6] They suggested a practical keyword search protocol in terms of communication and storage overheads.

6 Related Works (2/3) Conjunctive keyword search Golle et al.’s work [7] They suggested two conjunctive keyword search protocols enabling users to search conjunctively. Golle I Communication and storage costs It requires O(n) Golle II Unverifiable computational assumption Is it really secure ?

7 Related Works (3/3) We assume structured documents where keywords are organized by fields From To Date Status m fields n docs D1D1 D2D2 DnDn The documents are the rows of the matrix D i = (W i, 1, …, W i, m ) AliceBob06/01/2004Urgent AliceCharlie05/28/2004Secret ………… DaveAlice06/04/2004Non-urgent

8 Example Capability for s from Alice to Bob is Let s = f k (alice) + f k (Bob) From To Status √ X Problem: the size of capabilities is linear in n

9 Contribution Comparison Table Efficiency + Provable Security ECKS-PS : Efficient Conjunctive Keyword Search in the Personal Storage Systems

10 Security Definition (1/3) Database n row and m column

11 Security Definition (2/3) Conjunctive Keyword Search

12 Security Definition (3/3) SS-CTA security in the PS setting

13 Formal Security Proof Multi decisional bilinear Diffie-Hellman (MDBDH) = DBDH Reducing the security to the assumption of MDBDH DBDH problem DBDH assumption If no polynomial algorithm has non-negligible advantage e in solving DBDH problem

14 Conclusion Analysis of Some Keyword Search Schemes in Encrypted Data, 2008 IK Rae Jeong and Jeong Ok Kwon Conjunctive Keyword Search scheme do not provide semantic security.

15 References Efficient Conjunctive Keyword Search on Encrypted Data Storage System, l.pdf l.pdf Analysis of Some Keyword Search Schemes in Encrypted Data, 2008