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Fuzzy Keyword Search overEncrypted Data inCloud Computing
Jin Li, Qian Wang, Cong Wang,Ning Cao, Kui Ren, and Wenjing Lou
IEEE 29th International Conference on Computer CommunicationsINFOCOM 2010
San Diego, CA - USA - 2010
Presentation by Mateus Cruz
Introduction Preliminaries Proposal Conclusion
OUTLINE
1 Introduction
2 Preliminaries
3 Proposal
4 Conclusion
Introduction Preliminaries Proposal Conclusion
OUTLINE
1 Introduction
2 Preliminaries
3 Proposal
4 Conclusion
Introduction Preliminaries Proposal Conclusion
SCENARIO
Outsourcing dataPrivacy concernsEncryption as a solutionSearch encrypted data
I Only considers exact matching
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Introduction Preliminaries Proposal Conclusion
PROPOSAL
Fuzzy keyword search over encrypted dataUse of edit distanceEfficient construction of fuzzy sets
I Smaller sets
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RELATED WORK
Plaintext fuzzy keyword searchI Dictionary and statistical attacks
Searchable encryptionI Only supports exact search
Secure multiparty computationI High complexity and slow execution
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Introduction Preliminaries Proposal Conclusion
OUTLINE
1 Introduction
2 Preliminaries
3 Proposal
4 Conclusion
Introduction Preliminaries Proposal Conclusion
ARCHITECTURE
RolesI Data owner, data users and cloud server
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SYSTEM MODEL
Collection of N encrypted filesI C = {F1,F2, ...,FN}
Predefined set of p distinct keywordsI W = {w1,w2, ...,wp}
Each file is indexed by an IDI And it is linked to a set of keywords
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Introduction Preliminaries Proposal Conclusion
THREAT MODEL
Semi-trusted serverNothing should be leaked
I Except the result and search patterns
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EDIT DISTANCE
Number of operations to transform onestring into another
I SubstitutionI DeletionI Insertion
Sw ,dI Set of words that satisfy ed(w ,w ′) ≤ d
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FUZZY KEYWORD SEARCH
InputI Encrypted files C = (F1,F2, ...,FN)I Set of distinct keywords W = {w1,w2, ...,wp}I Query (w , k) (edit distance threshold k )
OutputI If w = wi ∈W , return FIDwI If w /∈W , return {FIDwi}
– ed(w ,wi) ≤ k
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Introduction Preliminaries Proposal Conclusion
OUTLINE
1 Introduction
2 Preliminaries
3 Proposal
4 Conclusion
Introduction Preliminaries Proposal Conclusion
PROPOSED APPROACHES
Straightforward approachWildcard-based approach
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STRAIGHTFORWARD APPROACH
Symmetric encryption schemeI Setup(λ)
– Receives security parameter λ– Outputs a secret key sk
I Enc(sk , ·)I Dec(sk , ·)
Tw is a trapdoor of keyword wI Twi = f(sk ,wi)
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FUZZY SETS CONSTRUCTION
Swi ,d for each wi ∈W (1 ≤ i ≤ p)I Edit distance d
Straightforward constructionI Enumerate all possible words w ′
i such thated(wi ,w ′
i ) ≤ d
Examplewi = CASTLEPossibilities for one substitution:{AASTLE , . . . ,ZASTLE}Still have to consider deletion and insertion!
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Introduction Preliminaries Proposal Conclusion
INDEX CONSTRUCTION
Computation of trapdoorsI Tw ′
i= f foreachw ′
i ∈ Swi ,d
Encryption of FIDwiI Set of file IDs whose files contain wiI Enc(sk ,FIDwi ||wi)
Creates and uploads index tableI {({Tw ′
i}w ′
i ∈Swi ,d,Enc(sk ,FIDwi ||wi))}wi∈W
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Introduction Preliminaries Proposal Conclusion
FUZZY SEARCH
An authorized user...I Computes TwI Sends Tw to the server
The server...I Look for the trapdoor in the index tableI Returns {Enc(sk ,FIDwi ||wi)}
The user...I Decrypts the resultsI Retrieve relevant files
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PROBLEMS
Large fuzzy setsHigh storage costThree edit operations
I Substitution, deletion, insertion
Demand for smaller fuzzy sets
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WILDCARD-BASED APPROACHTry to generate smaller fuzzy setsWildcards
I Denote operations at the same positionWildcard-based fuzzy set
I Swi ,d = {S′wi ,0,S
′wi ,1, . . . ,S
′wi ,d}
I S′wi , τ is the set of words w ′i with τ wildcards
Examplew = CASTLE , τ = 1SCASTLE ,1 = {CASTLE , ∗CASTLE , ∗ASTLE ,
C ∗ ASTLE ,C ∗ STLE , . . . ,CASTL ∗ E ,CAST ∗ E ,CASTLE∗}
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EFFICIENT FUZZY KEYWORD SEARCH
The data owner...I Constructs fuzzy keyword set Swi ,d
– Using the wildcard-based techniqueI Computes trapdoor set {T ′
wi}
– For each w ′i ∈ Swi ,d
I Encrypts FIDwi as Enc(sk ,FIDwi ||wi)
An authorized user...I Computes the trapdoor set {Tw ′}w ′∈Sw,k
The server...I Receives the trapdoor set {Tw ′}w ′∈Sw,kI Returns all possible identifiers{Enc(sk ,FIDwi ||wi)}
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ANALYSIS
Keyword wi with length `Straightforward approach
I Size of Swi ,1 will be (2`+ 1)× 26 + 1Wildcard-based approach
I Size of Swi ,1 will be 2`+ 1 + 1Reduced storage requirements
I O(`d)
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OUTLINE
1 Introduction
2 Preliminaries
3 Proposal
4 Conclusion