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SECURE DATABASE OUTSOURCING

ALLA LANOVENKOADVISIOR: DR. HUIPING GUO

CALIFORNIA STATE UNIVERSITY LOS ANGELES03-19-2007

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Outline

• Database-As-A-Service Model (DAS)

– Overview of the DAS Model

– Advantages and Disadvantages of DAS Model

• Related Work on Secure Database Outsourcing

• Suggested Dynamic Group Key Management

Schema for Outsourced Databases

• Conclusion

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Database-As-A-Service Model (DAS)

• Data owner: an organization that produces data to be made available for controlled external release.

• User: an organization or human entity that presents requests (queries) to the system and transforms this queries into queries on the encrypted data stored on the server .

• Server: an organization that receives the encrypted data from a data owner and makes them available for distribution to users.

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Advantages of DAS Model

• Saves organizations hardware and software

resources

• Reduce database cost

• A way for organizations to share the expertise of

the database professionals

• Promises higher availability and more effective

disaster protection plan.

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Disadvantages of the DAS Model

• Security

– Data confidentiality: outsiders and the server cannot see the owner’s database contents in any case. Users of the database have only partial access to the outsourced data, they can only access the permitted data by the owner.

– Owner privacy: database owner does not want the server to know about the queries and the returned results.

– Authentication and data integrity: users must be ensured that data returned from the untrusted server is originated from the data owner and has not been tampered with.

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Outline

• Database-As-A-Service Model

• Related Work on Secure Database Outsourcing

– Query Execution Techniques for Outsourced

Databases

– Access Control Mechanism for Outsourced

Databases

• Suggested Dynamic Group Key Management Schema

for Outsourced Databases

• Conclusion

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Query Execution Techniques for Outsourced Databases

• To store only encrypted data do not work because it would

enable external service provider to support selective

access. Since confidentiality demands that data decryption

must be possible only at the client side different

techniques were presented to enable external servers to

execute queries on encrypted data.

• Proposed query execution techniques to select the data to

be return in responds to a query without the need of

decrypting the data themselves based on storing together

with the encrypted data additional indexing information [1,

2,13, 16, 17].

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Query Execution Techniques for Outsourced Databases

• index of range technique proposed by Mehrotra, Li and Iyer for both equality and range predicate query.

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Query Execution Techniques for Outsourced Databases

• Basic idea of how index of range technique works:– Employee(eid, ename, salary, addr, did)

– EmployeeS(etuple, eidS, enameS, salaryS, addrS, didS) on server side

– Partition of attribute eid Employee [0, 200] = 2, [200, 400] = 7, [400, 600] = 5, [600, 800] = 1 and [800, 1000] = 4

– To retrieve record of the employee whose employee id = 320 SELECT * from Employee map to SELECT * from Employee

WHERE eid = “320” WHERE eid = 7

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Query Execution Techniques for Outsourced Databases

• The Other Query Execution Techniques :– in [1, 13] proposed a hash-based method suitable for

selection queries– in [3] order preserving encryption schema (OPES) is

presented to support equality and range query. This approach operates only on integer value

– in [10] proposed techniques for performing arithmetic operations ( +, -, *, / ) on encrypted data and do not consider comparison operations.

– [4, 5] proposed execution of aggregation queries over encrypted data

Limitation of the proposed techniques: they are protecting data at the server side, and provides complete access to the database contents on the client side.

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Access Control Mechanism for Outsourced Databases

• Proposed by Damiani, Foresti, Samarati and others prof. of University of Milan, access control mechanism exploit data encryption by including authorization in the encrypted data themselves. In this way it is enforce access restriction to deferent users, sets of users, or applications.

• Access Control Mechanism for outsourced databases proposed a different method that consists in grouping users with the same access privileges and in encrypting each groupof tuples with the key associated with the set of users that can access it.

• Mechnism limited to the static groups.

• Can not be directly applied to the dynamic groups. In this case outsourced database has to be re-encrypted each time group membership changes.

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Outline

• Database-As-A-Service Model

• Related Work on Secure Database Outsourcing

• Suggested Dynamic Group Key Management Schema for Outsourced

Databases

– System Description

– System Architecture

– Group Key Distribution Model

– Query Processing

– Experiment

• Conclusion

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Suggested Dynamic Group Key Management Schema for Outsourced Databases

• The thesis proposes a dynamic group key management schema for

outsourced databases.

• The proposed schema is performing scalable encryption/decryption

algorithm at the server side and the client side using key pair generated

from the group keys based on most widely used Rivest-Shamir-Adelman

(RSA) cryptographic algorithm.

• In case of dynamic group, proposed schema solves database re-

encryption problem in the event when group membership changes

dynamically. It efficiently solves the security problems: data

confidentiality and owner privacy.

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System Description

• All the users of the outsourced database are divided into different groups based on access privilege.

• Users with the same access privilege can access the same part of the outsourced data.

• Each group of database users has pair of keys:

– Encryption key KGRe

– Decryption key key KGRd

– Mod n• which are generated by the database owner using

RSA algorithm, KGRe and KGRd are secret to the group members.

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System Description

• Group encryption key KGRe is used by the database owner to encrypt tuples in the database.

– C = EKGRe [ Data ] mod n

• Group decryption key KGRd is used by the owner to randomly generate a pair of group subkeys KGRd1

and KGRd2 such that

– Data = DKGRd [ C ] mod n

– Data’ = DKGRd1 [ DKGRd2 [ C ] ] mod n

Data = Data’

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System Architecture• Proposed group key distribution schema uses centralized setting.• Includes tree entities:

– Database owner: is responsible for producing, distributing, managing and updating group keys.

– Group User: decrypts the result from the server using the first part of the group decryption subkey KGRd1 in the decryption algorithm in order to get the plaintext result.

– Server: is responsible for producing the query result on the encrypted database, decrypting the result with the second part of the group decryption subkey KGRd2 and sending encrypted result to the group user.

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Group Key Distribution Model

• Three phases in the system: initialization, adding new group member, and evicting existing group member.

• Initialization Phase:– Establishes group keys. – Performed by the database owner:

• uses RSA cryptographic algorithm to generate two keys: group encryption key (KGRe , mod n) and group decryption key (KGRd , mod n).

• splits decryption key KGRd on two parts and produces two group subkeys KGRd1 and KGRd2.

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Group Key Distribution Model

• db owner sends to each user Ui GRi a subkey KGRd1 and modulus n. Group members hold a group subkey KGRd1

and mod n as their secret key.

• db owner sends to the server a group subkey KGRd2. The Server holds a group subkey KGRd2 as group GRi secret key.

• db owner encrypts set of tuples with group GRi encryption key (KGRe, mod n) and store them in the outsourced database.

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Group Key Distribution Model

• Adding a Group Member

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Group Key Distribution Model

• Evicting a Group Member

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Query Processing

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Experiment • For the experiment we used the programming language Java with the

following characteristics: java version 1.4.2 Java(TM) 2 Runtime Environment, Standard Edition (build 1.5.0_02-b09).

• We also used Microsoft Access database for the data storage.

• Customerk {etuple, CustomerInd, AccountInd, AmountInd, Subkey}

Customer

Account Amount$

Alice 5678 3

Bob 2190 95

Donna 3456 740

Elvis 9017 56

Alla 8324 10,712

Sal 0153 839

Original data

Encrypted table

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Experiment• Key distribution schema

• Group 1 member retrieve the Customer table – Select * from the Customer map to Select etuple from the

Customer

• Group 2 member query result

Group number

Encryption key Decryption key

Subkey 1(user side)

Subkey 2(server side)

Modulus

1 905 44825 8965 5 11021

2 593 10769 979 11 23701

Query Result Received by the Group 1 Member

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Experiment• Group 1 Member Eviction

Group number Encryption key

Decryption key

Subkey 1(user side)

Subkey 2(server side)

Modulus

1(before member eviction)

 905

 44825

 8965

 5

 11021

1(after member

eviction)

 905

 44825

 4075

 11

 11021

•The test shows that on the select query existing group 1 users receive the same result as it shown in previous slide. However, evicted member can not access the tuples. Since Data = CKGRd mod n and Data’ = (C KGRd1’) KGRd2 mod n , Data Data’

Evicted Group 1 Member Query Result

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Conclusion

• Thesis investigates a solution for implementing

through cryptography a selective access policy.

Based on the modification of the RSA

cryptographic algorithm, the thesis proposed key

management schema for outsourced databases.

• This schema is suitable for the dynamic

environment where authorizations, users, and

objects can dynamically change. We also

performed implementation of our schema and

presented experimental result .

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Thank you!!