Expressive, Efficient, and Revocable Data Access Control for Multi-Authority Cloud Storage(2014)

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Data access control is an effective way to ensure the data security in the cloud. Due to data outsourcing and untrusted cloud servers, the data access control becomes a challenging issue in cloud storage systems. Ciphertext-Policy Attributebased Encryption (CP-ABE) is regarded as one of the most suitable technologies for data access control in cloud storage, because it gives data owners more direct control on access policies. However, it is difficult to directly apply existing CP-ABE schemes to data access control for cloud storage systems because of the attribute revocation problem. In this paper, we design an expressive, efficient and revocable data access control scheme for multi-authority cloud storage systems, where there are multiple authorities co-exist and each authority is able to issue attributes independently. Specifically, we propose a revocable multi-authority CP-ABE scheme, and apply it as the underlying techniques to design the data access control scheme. Our attribute revocation method can efficiently achieve both forward security and backward security. The analysis and simulation results show that our proposed data access control scheme is secure in the random oracle model and is more efficient than previous works.


This new paradigm of data hosting and data access services introduces a great challenge to dataaccess control. Because the cloud server cannot be fully trusted by data owners, they can no longer rely on servers to do access control. Ciphertext-Policy Attribute-based Encryption (CP-ABE) is regarded as one of the most suitabletechnologies for data access control in cloud storage systems,because it gives the data owner more direct control on access policies. In CP-ABE scheme, there is an authority that is responsible for attribute management and key distribution.


 -  Chase’s multi-authority CP-ABE protocol allows the central authority to decrypt allthe ciphertexts, since it holds the               master key of the system.

 -  Chase’s protocol does not support sattribute revocation.


In this paper, we first propose a revocable multiauthority CP-ABE scheme, where an efficient and secure revocation method is proposed to solve the attribute revocation problem in the system. Our attribute revocation method is efficient in the sense that it incurs less communication cost and computation cost, and is secure in the sense that it can achieve both backward security (The revoked user cannot decrypt any new ciphertext that requires the revoked attribute to decrypt)and forward security (The newly joined user can also decrypt the previously published ciphertexts1, if it has sufficient.attributes). Our scheme does not require the server to be fully trusted, because the key update is enforced by each attribute authority not the server. Even if the server is not semitrusted in some scenarios, our scheme can still guarantee the backward security. Then, we apply our proposed revocable multi-authority CP-ABE scheme as the underlying techniques to construct the expressive and secure data access control scheme for multi-authority cloud storage systems.


  - We modify the framework of the scheme and make it more practical to cloud storage systems, in which data owners are         not involved in the key generation.

  - We greatly improve the efficiency of the attribute revocation method.

  -  We also highly improve the expressiveness of our access control scheme, where we remove the limitation that each             attribute can only appear at most once in a ciphertext.


1. Certificate Authority

2. Attribute Authorities

3. Data Owners

4. Cloud Server

5. Data Consumers


Certificate Authority:

The CA is a global trusted certificate authority in the system. It sets up the system and accepts the registration of all the users and AAs in the system. For each legal user in the system, the CA assigns a global unique user identity to it and also generates a global public key for this user. However, the CA is not involved in any attribute management and the creation of secret keys that are associated with attributes. For example, the CA can be the Social Security Administration, an independent agency of the United States government. Each user will be issued a Social Security Number (SSN) as its global identity.

Attribute Authorities:

Every AA is an independent attribute authority that is responsible for entitling and revoking user’s attributes according to their role or identity in its domain. In our scheme, every attribute is associated with a single AA, but each AA can manage an arbitrary number of attributes. Every AA has full control over the structure and semantics of its attributes. Each AA is responsible for generating a public attribute key for each attribute it manages and a secret key for each user reflecting his/her attributes.

Data Consumers:

Each user has a global identity in the system. A user may be entitled a set of attributes which may come from multiple attribute authorities. The user will receive a secret key associated with its attributes entitled by the corresponding attribute authorities.

Data Owners:

Each owner first divides the data into several components according to the logic granularities and encrypts each data component with different content keys by using symmetric encryption techniques. Then, the owner defines the access policies over attributes from multiple attribute authorities and encrypts the content keys under the policies.

Cloud Server:

Then, the owner sends the encrypted data to the cloud server together with the ciphertexts. They do not rely on the server to do data access control. But, the access control happens inside the cryptography. That is only when the user’s attributes satisfy the access policy defined in the cipher text; the user is able to decrypt the ciphertext. Thus, users with different attributes can decrypt different number of content keys and thus obtain different granularities of information from the same data



Ø System                          :         Pentium IV 2.4 GHz.

Ø Hard Disk                      :         40 GB.

Ø Floppy Drive                 :         1.44 Mb.

Ø Monitor                         :         15 VGA Colour.

Ø Mouse                            :         Logitech.

Ø Ram                               :         512 Mb.


Ø Operating system           :         Windows XP/7.

Ø Coding Language         :         JAVA/J2EE

Ø IDE                                   :         Netbeans 7.4

Ø Database                        :         MYSQL

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