Efficient Search on Encrypted Data

1. Efficient Search on Encrypted Data

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

3. SWP Linear Scan • Ki = fk’(Li) • Xi = Ek’’(Wi)

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 keyword pointer document

5. Simple way • Simple way： • Operation： • B search E(W) ，return A encrypted list. • 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：Kw = Fk’’’(E(W))  pointer Ekw(Pi) • Search：send < E(W), Kw > to server

7. Goh Bloom Filter • Document D：S={s1,s2,…,sn} • n : the number of words chosen by client • S : m bit array

8. Methodology The motivations： • Have a method that allows the owner of the data to find the required data from a remote and untrusted storage • Supports any types of data • Allows Alice to choose just the required keywords describing the data • Preserve the keywords where the keywords can be retrieved if needed • Time complexity of 0(1) to search for a keyword • Easy integration with any existing indexing scheme • 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 Loc(Wi) = H( Ek’(W)+id ) HT 2 HT 1 HT n Loc(W1) c1 Loc(W1) c1 Loc(W1) c1 c2 c2 Loc(W2) c2 Loc(W2) Loc(W2) c3 c3 Loc(W3) c3 Loc(W3) Loc(W3) … … … cn cn cn Loc(Wn) Loc(Wn) Loc(Wn)

12. Search Phase：Single Document Searching Mode • 傳給server id // Loc(Wi) // Ek’(W) // ki

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