Access control in decentralized online social networks applying a policy hiding cryptographi

Access Control in Decentralized Online SocialNetworks: Applying a Policy-Hiding Cryptographic

Scheme and Evaluating Its Performance

ABSTRACT

Privacy concerns in online social networking services have prompted a number of

proposals for decentralized online social networks (DOSN) that remove the central provider and

aim at giving the users control over their data and who can access it. This is usually done by

cryptographic means. Existing DOSNs use cryptographic primitives that hide the data but reveal

the access policies. At the same time, there are privacy-preserving variants of these

cryptographic primitives that do not reveal access policies. They are, however, not suitable for

usage in the DOSN context because of performance or storage constraints. A DOSN needs to

achieve both privacy and performance to be useful. We analyze predicate encryption (PE) and

adapt it to the DOSN context. We propose a univariate polynomial construction for access

policies in PE that drastically increases performance of the scheme but leaks some part of the

access policy to users with access rights. We utilize Bloom filters as a means of decreasing

decryption time and indicate objects that can be decrypted by a particular user. We evaluate the

performance of the adapted scheme in the concrete scenario of a news feed. Our PE scheme is

best suited for encrypting for groups or small sets of separate identities.

We develops Computer Engineering Projects for BE/ME students. For any kind of support you may live chat with us at www.ocularsystems.in or call us on 020 30858066 or

Mail Us: [email protected] Address: Swagat Corner Building, Near Narayani Dham Temple, Katraj, Pune-46 (Maharashtra)

mailto:[email protected]

http://www.ocularsystems.in/

Existing System

Existing DOSNs use cryptographic primitives that hide the data but reveal the access

policies. At the same time, there are privacy-preserving variants of these cryptographic

primitives that do not reveal access policies. They are, however, not suitable for usage in the

DOSN context because of performance or storage constraints.

Disadvantage:

Hide the data but reveal the access policies.

Proposed System:

proposed a Predicate encryption (PE) is a cryptographic primitive that provides access

control of encrypted data using attribute based policies. When creating a ciphertext, the encrypt

or specifies an access policy and only those users whose keys satisfy the policy can decrypt. The

decryption keys are generated by the encrypt or using a master secret.

Advantages:

provides access control of encrypted data using attribute based policies.





Architecture:

MODULES”

1. System Initialization.

2. User Registration.





3. KDC setup.

4. Attribute generation.

5. Sign.

6. Verify.

7. Bloom filters.

Modules Description

1. System Initialization

Select a prime q, and groups G1 and G2, which are of order q. We define the mapping ê

: G1 ×G1 → G2. Let g1, g2 be generators of G1 and hj be generators of G2, for j ∈ [tmax], for

arbitrary tmax. Let H be a hash function. Let A0 = ha0 0 , where a0 ∈ Z ∗ q is chosen at random.

(TSig,TV er) mean TSig is the private key with which a message is signed and TV er is the

public key used for verification. The secret key for the trustee is TSK = (a0, TSig) and public key

is TPK = (G1,G2,H, g1,A0, h0, h1, . . . , htmax, g2, TV er).

2. User Registration

For a user with identity Uu the KDC draws at random Kbase ∈ G. Let K0 = K1/a0 base .

The following token γ is output γ = (u,Kbase,K0, ρ), where ρ is signature on u||Kbase using the

signing key TSig.





3. KDC setup

We emphasize that clouds should take a decentralized approach while distributing secret

keys and attributes to users. It is also quite natural for clouds to have many KDCs in different

locations in the world. The architecture is decentralized, meaning that there can be several KDCs

for key management.

4. Attribute generation

The token verification algorithm verifies the signature contained in γ using the signature

verification key TV er in TPK. This algorithm extracts Kbase from γ using (a, b) from ASK[i]

and computes Kx = K1/(a+bx) base , x ∈ J[i, u]. The key Kx can be checked for consistency

using algorithm ABS.KeyCheck(TPK,APK[i], γ,Kx), which checks ê(Kx,AijBx ij) = ê(Kbase,

hj), for all x ∈ J[i, u] and j ∈ [tmax].

5. Sign

The access policy decides who can access the data stored in the cloud. The creator

decides on a claim policy Y, to prove her authenticity and signs the message under this claim.

The ciphertext C with signature is c, and is sent to the cloud. The cloud verifies the signature and

stores the ciphertext C. When a reader wants to read, the cloud sends C. If the user has attributes

matching with access policy, it can decrypt and get back original message.

6. Verify





The verification process to the cloud, it relieves the individual users from time consuming

verifications. When a reader wants to read some data stored in the cloud, it tries to decrypt it

using the secret keys it receives from the KDCs.

7. Bloom filters

A profile in the DOSN contains multiple objects encrypted for different users. It is

impossible for a user to determine if an object is encrypted for him without trying to decrypt it

since the ciphertexts do not reveal access policies. The user could use a trial-and-error approach

(sequentially trying to decrypt objects) for rendering the profile, but this becomes prohibitively

expensive with the large number of objects. Therefore, we utilize Bloom filters to speed up

rendering and to show users in a privacy-preserving manner whether they can decrypt objects.

System Configuration:-

H/W System Configuration:-

Processor - Pentium –III

Speed - 1.1 Ghz

RAM - 256 MB (min)

Hard Disk - 20 GB

Floppy Drive - 1.44 MB

Key Board - Standard Windows KeyboardWe develops Computer Engineering Projects for BE/ME students. For any kind of support you may live

chat with us at www.ocularsystems.in or call us on 020 30858066 or Mail Us: [email protected]

Our Address: Swagat Corner Building, Near Narayani Dham Temple, Katraj, Pune-46 (Maharashtra)



Mouse - Two or Three Button Mouse

Monitor - SVGA

S/W System Configuration:-

Operating System :Windows95/98/2000/XP

Application Server : Tomcat5.0/6.X

Front End : HTML, Java, Jsp

Scripts : JavaScript.

Server side Script : Java Server Pages.

Database : Mysql

Database Connectivity : JDBC.

CONCLUSION

We have proposed to apply a privacy preserving scheme to the DOSN context: inner-

product predicate encryption (PE). It is too expensive to use out of the box. Therefore for PE we

proposed a construction for access policies that drastically increases performance, but introduces

some trade-offs: it allows encrypting for a bounded set of groups/users; this bound is a trade-off

between between efficiency and functionality of the scheme; the number of groups in the system

is unlimited; a user has 2g different decryption keys, where g is the number of groups a user is a

member of; having multiple keys leaks some information about access policies. PE is most

suitable for encrypting for groups or small sets of separate identities. We designed an experiment





that showed that for newsfeed assembly from all friends our scheme shows good performance

and thus user experience. For schemes that do not reveal access policies and have relatively slow

decryption, we proposed to use Bloom filters to indicate to users which files they can decrypt.

Bloom filters are both performant and space-efficient, and thus are suitable for DOSNs.

In this paper, we focused the evaluation on performance to see if PE is even feasible

under the constraints of decentralized online social networks, starting from the security and

privacy properties of the original scheme. The next steps are to focus on security and privacy, as

well as semantics of access policies of our modifications.



