Decentralized access control with anonymous authentication of data stored in clouds

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DECENTRALIZED ACCESS CONTROL WITH ANONYMOUS AUTHENTICATION OF
DATA STORED IN CLOUDS
ABSTRACT
A new decentralized access control scheme is proposed for secure data storage in
clouds that supports anonymous authentication. In the proposed scheme, the
cloud verifies the authenticity of the series without knowing the user’s identity
before storing data. Access control is enabled, in which only valid users are able
to decrypt the stored information. The scheme prevents replay attacks and
supports creation, modification, and reading data stored in the cloud.
Authentication and access control scheme is decentralized and robust, unlike
other access control schemes designed for clouds which are centralized. The
communication, computation, and storage overheads are comparable to
centralized approaches.
AIM
The problems of access control, authentication, and privacy protection should be
solved simultaneously.

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INTRODUCTION
Research in cloud computing is receiving a lot of attention from both academic
and industrial worlds. In cloud computing, users can outsource their computation
and storage to servers (also called clouds) using Internet. This frees users from the
hassles of maintaining resources on-site. Clouds can provide several types of
services like applications, infrastructures, 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.

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SCOPE OF WORK
Access control in clouds is gaining attention because it is important that only
authorized users have access to valid service. A huge amount of information is
being stored in the cloud, and much of this is sensitive information. Care should
be taken to ensure access control of this sensitive information which can often be
related to health, important documents or even personal information. There are
broadly three types of access control: user-based access control (UBAC), role-based
access control (RBAC), and attribute-based access control (ABAC). In UBAC,
the access control list contains the list of users who are authorized to access data.
This is not feasible in clouds where there are many users. In RBAC, users are
classified based on their individual roles. Data can be accessed by users who have
matching roles. The roles are defined by the system. ABAC is more extended in
scope, in which users are given attributes, and the data has attached access
policy.

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EXISTING SYSTEM
Secure and dependable cloud storage
 Cloud servers prone to Byzantine failure, where a storage server can fail in
arbitrary ways. The cloud is also prone to data modification and server
colluding attacks.
 In server colluding attack, the adversary can compromise storage servers,
so that it can modify data files as long as they are internally consistent.
 To provide secure data storage, the data needs to be encrypted. However,
the data is often modified and this dynamic property needs to be taken into
account while designing efficient secure storage techniques.
Privacy preserving search
 The clouds should not know the query but should be able to return the
records that satisfy the query.
 This is achieved by means of searchable encryption. The keywords are sent
to the cloud encrypted, and the cloud returns the result without knowing
the actual keyword for the search.
 The problem here is that the data records should have keywords associated
with them to enable the search.

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Drawbacks
 The correct records are returned only when searched with the exact
keywords.
Storage security
 Reed-Solomon erasure-correcting codes were used.
 Many homomorphic encryption techniques have been suggested to ensure
that the cloud is not able to read the data while performing computations
on them. Using homomorphic encryption, the cloud receives ciphertext of
the data and performs computations on the ciphertext and returns the
encoded value of the result. The user is able to decode the result, but the
cloud does not know what data it has operated on.
 In such circumstances, it must be possible for the user to verify that the
cloud returns correct results.
Disadvantages
 Accountability of clouds is a very challenging task and involves technical
issues and law enforcement.
 Neither clouds nor users should deny any operations performed or
requested.

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Proposed system
 To propose ABS scheme to achieve authenticity and privacy.
 This is resistant to replay attacks, in which a user can replace fresh data
with stale data from a previous write, even if it no longer has valid claim
policy.
 This is an important property because a user, revoked of its attributes,
might no longer be able to write to the cloud.
 This scheme also allows writing multiple times which was not permitted in
earlier work.
Advantages
 Distributed access control of data stored in cloud so that only authorized
users with valid attributes can access them.
 Authentication of users who store and modify their data on the cloud.
 The identity of the user is protected from the cloud during authentication.
 The architecture is decentralized, meaning that there can be several KDCs
for key management.

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 The access control and authentication are both collusion resistant, meaning
that no two users can collude and access data or authenticate themselves,
if they are individually not authorized.
 Revoked users cannot access data after they have been revoked.
 The proposed scheme is resilient to replay attacks. A writer whose
attributes and keys have been revoked cannot write back stale information.
 The protocol supports multiple read and write on the data stored in the
cloud.
 The costs are comparable to the existing centralized approaches, and the
expensive operations are mostly done by the cloud.

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LITERATURE SUMMARY
ABE was proposed by Sahai and Waters. In ABE, a user has a set of attributes in
addition to its unique ID.
There are two classes of ABEs.
 Key-policy ABE (KP-ABE)
o Sender has an access policy to encrypt data. A writer whose
attributes and keys have been revoked cannot write back stale
information. The receiver receives attributes and secret keys from
the attribute authority and is able to decrypt information if it has
matching attributes.
 Ciphertext-policy (CP-ABE)
o 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.
 Chase proposed a multiauthority ABE, in which there are several KDC
authorities which distribute attributes and secret keys to users.
Multiauthority ABE protocol was studied, which required no trusted
authority which requires every user to have attributes from at all the KDCs.

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 Lewko and Waters proposed a fully decentralized ABE where users could
have zero or more attributes from each authority and did not require a
trusted server. In all these cases, decryption at user’s end is computation
intensive.
 Green et al. proposed to outsource the decryption task to a proxy server, so
that the user can compute with minimum resources. However, the
presence of one proxy and one KDC makes it less robust than decentralized
approaches. Both these approaches had no way to authenticate users,
anonymously.
 Yang et al. presented a modification, authenticate users, who want to
remain anonymous while accessing the cloud.
 To ensure anonymous user authentication ABSs were introduced by Maji et
al. This was also a centralized approach. A recent scheme by Maji et al.
takes a decentralized approach and provides authentication without
disclosing the identity of the users. However, as mentioned earlier in the
previous section it is prone to replay attack.

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Decentralized access control with anonymous authentication of data stored in clouds

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