1. Efficient Search on Encrypted Data

2. Outline SWP Linear Scan SWP encrypted index Goh Bloom Filter Hybird scheme Discussion

3. SWP Linear Scan K i = f k’ (L i ) X i = E k’’ (W i )

4. SWP encrypted index motivation ：當文件量大時， sequential scan 不是一個有效率的方 法。 ex ：在大型資料庫上，用 pre-computed index 是加速搜尋最常 用的技巧。 ex ： index keywordpointerdocument

5. Simple way Simple way ： Operation ： 1)B search E(W) ， return A encrypted list. 2)A may decrypt the encrypted entries and send B another request to retrieve the documents advantage ： the request could be embedded in other retrievals disadvantage ： A has to spend round-trip time

6. Another way motivation ： save time Another way ： K w = F k’’’ (E(W))  pointer E kw (P i ) Search ： send to server

7. Goh Bloom Filter Document D ： S={s 1, s 2, …, s n } n : the number of words chosen by client S : m bit array

8. Methodology The motivations ： 1.Have a method that allows the owner of the data to find the required data from a remote and untrusted storage 2.Supports any types of data 3.Allows Alice to choose just the required keywords describing the data 4.Preserve the keywords where the keywords can be retrieved if needed 5.Time complexity of 0(1) to search for a keyword 6.Easy integration with any existing indexing scheme 7.Good performance time in terms of encryption, decryption and search

9. Scheme Setup/Encryption Phase Search Phase  Single Document Searching Mode  Multiple Documents Search Mode Decryption Phase

10. Setup/Encryption Phase

11. Hash Table c1 Loc(W i ) = H( E k’ (W)+id ) c2 c3 cn … Loc(W1) Loc(W2) Loc(W3) Loc(Wn) HT 1 c1 c2 c3 cn … Loc(W1) Loc(W2) Loc(W3) Loc(Wn) HT 2 c1 c2 c3 cn … Loc(W1) Loc(W2) Loc(W3) Loc(Wn) HT n

12. Search Phase ： Single Document Searching Mode 傳給 server id // Loc(W i ) // E k’ (W) // k i

13. Search Phase ： Multiple Documents Search Mode motivation ：  Document number is unknown  Find a certain word in multiple documents This allows server to do the hash function H on behalf of client

14. Multiple Documents Search Mode

15. Decryption Phase

16. Discussion

17. SWP Linear Scan disadvantage Long processing time The search time increases as with the number of word  not suitable for files with many words

18. SWP encrypted index The fastest processing time disadvantage ：  A single master index manages all the documents  Maintain a pool of keywords

19. Goh Bloom Filter High security disadvantage ：  Large index size  Long processing time  Not suitable for active file server where changes document occur frequently