Abstract:- Cloud computing has is a popular design in managing world to back up large volumetric details using cluster of commodity computer systems. It is the newest effort in offering and managing computing as a service. The decentralized access control scheme distributes the data stored in cloud to user. Valid user can only access the stored information. The valid users attribute satisfies the access policy that attached to the cipher text. In the proposed decentralized approach, the technique does not authenticate users. When the users have matching set of attributes, can they decrypt the information stored in the cloud the set of attributes possessed by the revoked user. This provides user revocation and prevents replay attacks. Decentralized access control scheme can distribute secret keys for valid user in set of attribute. If the user is not authorized individually decentralized access control distribute authorized secret keys to user in set of attribute such that only that user can encrypt the stored data using its secret key. The proposed algorithm is Token Verification algorithm. Using this algorithm the creator or author of the data can verify who are all modifying the document. The algorithm provides more security in access control and authentication. Moreover, our authentication and access management theme is suburbanized and sturdy, in contrast to different access management schemes designed for clouds that square measure centralized.
Keywords: Decentralized Access Control Authentication
Cloud computing is set of services offered through the internet. Cloud computing is receiving a lot of attention from both academic and industrial worlds. Cloud services are delivered from data centers located throughout the world. The boom in cloud computing has brought lots of security challenges for the consumers and service providers. In cloud computing, users can outsource storage and infrastructure to servers using Internet .
Clouds can provide several types of services like applications (e.g., Google Apps, Microsoft online), infrastructures (e.g., Amazon’s EC2, Eucalyptus, Nimbus), and platforms to help developers write applications. Much of the data stored in clouds is highly sensitive, for example, medical records and social networks. Security and privacy are, thus, very important issues in cloud computing. In one hand, the user should authenticate itself before initiating any transaction, and on the other hand, it must be ensured that the cloud does not tamper with the data that is outsourced . User privacy is also required so that the cloud or other users do not know the identity of the user. The cloud can hold the user accountable for the data it outsources, and likewise, the cloud is itself accountable for the services it provides. The validity of the user who stores the data is also verified. Apart from the technical solutions to ensure security and privacy, there is also a need for law enforcement .
The cloud can hold the user accountable for the data it outsources, and likewise, the cloud is itself accountable for the services it provides. To provide secure data storage the data stored in cloud should be in an encrypted format. There are many types of access control is there in cloud User Based Access Control (UBAC), Role Based Access Control (RBAC)  And Attribute Based Access Control (ABAC). In User based Access control scheme there is a list of user that who can access the data. Only those users can access the data that stored in cloud. In Role Based Access Control Scheme the users who having matching set of roles they can access the data and in Attribute Based Access Control the users can access the data only if they having matching set off attributes. According to the access policy the user who satisfies certain conditions only can access the data that stored in cloud . It prevents replay attacks and support creation, modification and reading data stored in cloud.
Cipher text Policy Attribute Based Encryption is a type of ABAC it provides a secure access control. Authentication and access control scheme is decentralized and robust. The valid user in set of attribute that satisfies the access policy attached with the attribute of cipher text means they can modify and store data in cloud. The validity of the user who stores the data is also verified. Using ABE, the records area unit encrypted below some access policy and keep within the cloud [4, 5]. User’s area unit given sets of attributes and corresponding keys. Only if the users have matching set of attributes, will they rewrite the data keep within the cloud . Access management in health care has been studied. Access management is additionally gaining importance in on-line social networking where users (members) store their personal info, pictures, and videos and share them with selected teams of users or communities they belong to. Access management in on-line social networking has been studied in . Such information area unit being keeps in clouds. Data stored in clouds is highly sensitive, for example, medical records and social networks. Providing security and privacy are important issues in cloud computing .
Two main things are firstly, the user should authenticate itself before initiating any transaction, and on the second one is that, it must be ensured that the cloud does not tamper or interfere with the data that is outsourced or the data which is sent to the user. The wide acceptance of www has raised security risks along with the uncountable benefits so is the case with cloud computing. Also user privacy  is required so that the cloud or other users do not know the identity of the user. The cloud can hold the user accountable for the data it outsources to the client, and likewise, the cloud is itself accountable for the services it provides to the client or the user who is accessing the cloud. The validity of the user who stores the data is also verified (by the admin). Apart from the technical solutions to ensure security and privacy in cloud, there is also a need for law enforcement such as access policies provided to the client or the users.
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