1. 1 Conjunctive Keyword Search on Encrypted Data with Completeness and Computational Privacy Author ： Radu Sion Bogdan Carbunar Presentered by Chia Jui Hsu Date ： 2008-10-07

2. 2 Outline Introduction Multiplicative Checksums Less Information Leaks Oblivious Search Analysis Conclusion

3. 3 Introduction(1/3) User Server Keyword returned correctness ？ 1.Maybe Hacker ？ 2.Maybe Program’s error ？

4. 4 Introduction(2/3) Using “d i ” to denote these identifiers and D = (d i ), i=1..n to denote the outsourced documents. Let K = (k i ), i>0 be the set of keyword Let X be the average number of keywords per document.

5. 5 Introduction(3/3) Query keywords q = {k i1, k i2,…, k iq } Keyword Document Sets (KDS) KDS set {d 1,…,d t }

6. 6 Multiplicative Checksums Let the client choose two secrets: a large prime p and x (1 < x <p, x is random integer).

7. 7 Less information Leaks(1/2) Let F be a pseudo-random function. Quadratic residues

8. 8 Less information Leaks(2/2) is provides an obfuscated version of the matrix.

9. 9 Oblivious Search

10. 10 Analysis Overheads, example n = 10000 e-mails, k = 1000 keywords and x = 50 keywords per document. a message of roughly 2KBytes and 500 multiplications at the client. ( d i + x ) ≡ 0 mod p we ignore this event for the analysis, as it only occurs with negligible probability.

11. 11 Conclusion Using Quadratic Residues(QR)