DACC: Distributed Access Control in Clouds
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Transcript of DACC: Distributed Access Control in Clouds
DACC: Distributed Access Control in Clouds
2011 IEEE TrustCom-11Sushmita Ruj
Amiya Nayak and Ivan Stojmenovic
2013.04.29 Regular Seminar
Tae Hoon Kim
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Contents
1. Introduction2. Related work3. Background
A. Model and assumptionsB. Formats of access policiesC. Mathmatical backgroundD. Lewko-Waters ABE Scheme
4. Proposed scheme: DACC5. Security of DACC6. Performance7. Conclusion and Future work
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Introduction
Cloud is emerging technology User only require a terminal, a smart phone, table con-
nected internet User can rent the storage, computing resources of a
server provided by a company Application services
e.g) Google Apps, Microsoft online Infrastructural support
e.g)Amazon’s EC2, Eucalyptus, Nimbus Platform
e.g)Amazon’s S3, Windows Azure
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Introduction
Two important to preserve security of data
In cloud, Users trying to access data privacy of users
Only services are authorized user Using public key cryptographic techniques
User should ensure that The cloud is not tampering with user’s data and
computational results
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Introduction
Method of not tampering user data & com-putational results Hide the data from the clouds Use of homomorphic encryption techniques[9][10] Code obfuscation[11]
Important problem : Anonymously search data in Cloud(range, multidimensional, complex queries) Is achieved searchable encryption[12][13]
Takes keywords in encrypted form and return resultsWithout knowing the keyword or the retrieved records
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Introduction
Consider following scenarios Patients store their medical records in cloud Different users can access different data field The same data fields might be accessed by a se-
lective group of people(authorized set)Example)the patient’s medical history and drug admin-
istration can be accessed by doctors and nurses, but not by hospital management staff
Access Control : Granting access rights to certain users and forbidding other users to access data
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Introduction
Method of granting access To attach list of all valid users to data
problem : 1. Each time the list has to be checked to see if user is valid -> huge computation and storage cost
To encrypt data is by using public keys of valid usersProblem : 1. The same data then must be en-
crypted several times -> may result in huge storage cost
ABE(Attribute Based Encryption) : owners en-crypted data with attributes that they possess and store the information in the clouds
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Introduction
KDC(Key Distributed Center) Users are given attributes and secret keys by KDC
Set of attributes are able to decrypt the information E.g)(A, doctor, Key), (B, doctor, Key), (A, staff, Key) (A, patient, Key) (C,
doctor, Key)
Earlier work[17] : owners encrypt data with at-tributes(Not requried KDC)
Problem : increase the total number of secret keys given to users->in-creases storage and communication overhead
In this paper, proposes DACC is Cloud has cipher text(unable to decrypt cipher text) Owner decide on attributes that users should have and users
receive decryption keys KDC distributes secret keys to user
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Related work
Sahai and Waters[19] ABE A user has a set of attributes in addition to its
unique ID Shamir[20] IBE(Identity-based-encryp-
tion) Each user in IBE scheme has a unique identity
Bethencourt et al,. [21] Ciphertext-policy Receiver has the access policy in the form of
a tree, with attributes as leaves and monotonic access structure with AND, OR and other threshold gates.
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Related work
KDC(attribute authority) is assumed to be honest May not hold; a distributed system, authori-
ties can fail or be corrupt Chase[23] multi-authority ABE
Distribute attribute, and secret keys to users Wang et al[26],. Hierarchical access con-
trol mechanism Relies on Bethencoure et al[21], and Hierarchical
IBE[27]
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Background A. Model and assumptions
KDCs which may be even servers scattered in different countries, that generate secret keys for the users
Assume that the cloud is honest but curious
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Background :B. Format of access policies Two format of access policies
Boolean functions of attribute ( (a1a2 a3) (a4 a5) (a6 a7) )
(a1, a2.. A7) : attributesBe represented by access tree with attributes at the
leaves and AND and OR Linear Secret Sharing Scheme(LSSS)
Let V[x] be parent’s vector, If node x = AND then the left child is (V[x]|1), and the
right child is (0,…-1). If x= OR then both children also have unchanged vector
V[x]
∧∨
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Background : C. D.
C. Mathematical background Use bilinear pairings on elliptic curves
D. Lewko-Waters ABE scheme Consist of four steps
1)System Initialization2)Key and attribute distribution to users by KDCs3)Encryption of message by sender4)Decryption by receiver
∧∨
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Proposed Scheme:DACC
A. Sketch of DACC 1. Initially the parameters of the scheme and the
size of group are decided(232+1) 2. KDC Aj selects the set of attributes Lj
3. An owner Uu who wants to store information in cloud, chooses a set of attributes Iu which are specific to the data it wants to encrypt’
4. convert the access tree to a Matrix R
Aj = j 번째 KDC, Lj = KDC Aj 가 소유한 attribute 의 잡합I[j,u] Uu 가 준 attribute 의 집합
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Proposed Scheme:DACC
An Example; professional n/w J1:Engineering, J2(CS Research), J3(Faculty posi-
tions) P1:Canada P2:US
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Security of DACC, Performance
Security of DACC Show that only authorized users can decrypt the data in clouds Theorem : Our access control scheme is secure, collusion resistant
and allows access only to authorized users Proof
Performance Calculate the computation and communication overhead of DACC
scheme and DACC with revocation
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Conclusion
In DACC, the cloud is assumed to be honest
If not possible to satisfy, care should be taken The authenticity of the data must be verified
by the user hide the identity of the users and owners at
the same time provide their authentication Future work
Hide the access structure from the cloud, by scrambling the matrix in some way
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Thank you for listening my presenta-tion Q/A
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Appendix : Method
Method 1 : One way to hide the data from clouds
Method 2 : Use of homomorphic encryp-tion techniques(4 generation)
data
dataSends msg
: Homomorphicly encrypted data
Return re-sult
: Return en-crypted data
http://www2.readersnews.com/sub_read.html?uid=34467§ion=sc1
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Appendix : Method
Method 3 : Code obfuscation
Method 4 : Searchable encryption
: Obfuscation
Code
: Return data
?Provide re-sult
??
encrypted data
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Appendix : DACC
KDC2
posses KDC of list(HospitalA, doctor, SK 2,1), (HospitalB, doctor, SK 2,2), (HospitalA, Staff, SK2,3)
A2 A2 of attribute set Lj
Owner
Uu
Access treeUser n1User n2
IuUser n1 User
n2
Matrix R
• SSH:Secure Shell protocol
: Using SSH
1
2
3Cyper text
cc c
Matrix R
C1 C2