efficient similarity search over encrypted datamuratk/courses/cloud13s_files/efficie… ·...
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UT DALLASUT DALLAS Erik Jonsson School of Engineering & Computer Science
FEARLESS engineering
Efficient Similarity Search over Encrypted Data
Mehmet Kuzu, Saiful Islam, Murat Kantarcioglu
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FEARLESS engineering
Introduction
Client
Similarity Search over Encrypted Data
Selected Encrypted Items
Untrusted Server
Requires: Requires: Requires: Requires: Efficient and Secure Efficient and Secure Efficient and Secure Efficient and Secure
Similarity Searchable Encryption ProtocolsSimilarity Searchable Encryption ProtocolsSimilarity Searchable Encryption ProtocolsSimilarity Searchable Encryption Protocols
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FEARLESS engineering
Problem Formulation
• BuildIndex(K, D): Extract feature set for each data item in D and form secure index I with key K.
• Trapdoor (K, f): Generate a trapdoor for a specific feature f with key K and output T.
• Search(I,T): Perform search on I with trapdoor of feature f (T) and output encrypted collection C:
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FEARLESS engineering
Locality Sensitive Hashing
• Family of functions is said to be (r1, r2, p1,p2)-sensitive if for any x, y ∈ F and for any h ∈ H.
• A composite function g: (g1, …, gλ) can be formed
to push p1 closer to 1 and p2 closer to 0 by adjusting the LSH parameters (k, λ).
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FEARLESS engineering
Security Goals
• Access Pattern (Ap): Identifiers of data items that are in the result set of a specific query.
• Similarity Pattern (Sp): Relative similarity among distinct queries.
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FEARLESS engineering
Secure LSH Index
• Content of any bucket Bk is a bit vector (VBk):
• [Encid(Bk), Encpayload(VBk )] ϵ I.
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FEARLESS engineering
Secure Search Scheme
Shared Information
• Kcoll: Secret key of data collection encryption
• K id, Kpayload: Secret keys of index construction
• ρ: Metric space translation function
• g: Locality sensitive function
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FEARLESS engineering
Secure Search Scheme
• Trapdoor Construction for feature fi :
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FEARLESS engineering
Multi-Server Setting
• Basic search scheme reveals similarity and access patterns.
• It is desirable to separate leaked information to mitigate potential attacks.
• Multi-server setting enables lighter clients.
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FEARLESS engineering
One Round Search Scheme
• This scheme is built on Paillier encryption that is semantically secure and additive homomorphic.
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FEARLESS engineering
One Round Search Scheme
• Bob performs homomorphic addition on the payloads of trapdoor components.
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FEARLESS engineering
Error Aware Keyword Search
• Typographical errors are common both in the queries and data sources.
• In this context, data items be the documents, features be the words in the document and query feature be a keyword.
• Bloom filter encoding enables efficient space translation for approximate string matching.
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FEARLESS engineering
Error Aware Keyword Search
• Elegant locality sensitive family has been designed for Jaccard distance (MinHash) that is [r1, r2 ,1-r1, 1-r2] sensitive.
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FEARLESS engineering
Experimental Setup
• A sample corpus of 5000 emails is constructed from publicly available Enron e-mail dataset.
• Words in e-mails are embedded into 500 bit Bloom filter with 15 hash functions.
• (0.45, 0.8, 0.85, 0.01)-sensitive family is formed from MinHash to tolerate typos. Common typos are introduced into the queries %25 of the time.
• Default Parameters: (Number of documents: 5000, Number of features: 5000, k:5, λ: 37).
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FEARLESS engineering
Retrieval Evaluation
• Ranking limits retrieval of irrelevant items.
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FEARLESS engineering
Performance Evaluation (Single Server)
• Increase in k and decrease in λ have similar effects. Decrease in λ leads smaller trapdoors.
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FEARLESS engineering
Performance Evaluation (Single Server)
• With increasing nd, matching documents and the size of transferred bit vectors becomes larger.
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FEARLESS engineering
Performance Evaluation (Multi-Server)
• Transfer of homomorphic addition results between servers is the main bottleneck.
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FEARLESS engineering
Conclusion
• We proposed LSH based secure index and search scheme to enable fast similarity search over encrypted data.
• We provided a rigorous security definition and proved the security of the scheme to ensure confidentiality of the sensitive data.
• Efficiency of the proposed scheme is verified with empirical analysis.
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FEARLESS engineering
Conclusion
THANKS …!
QUESTIONS?