Survey on Revocation in Ciphertext-Policy Attribute-Based Encryption <s> Full expressive <s> Cloud computing, as an emerging computing paradigm, enables users to remotely store their data into a cloud so as to enjoy scalable services on-demand. Especially for small and medium-sized enterprises with limited budgets, they can achieve cost savings and productivity enhancements by using cloud-based services to manage projects, to make collaborations, and the like. However, allowing cloud service providers (CSPs), which are not in the same trusted domains as enterprise users, to take care of confidential data, may raise potential security and privacy issues. To keep the sensitive user data confidential against untrusted CSPs, a natural way is to apply cryptographic approaches, by disclosing decryption keys only to authorized users. However, when enterprise users outsource confidential data for sharing on cloud servers, the adopted encryption system should not only support fine-grained access control, but also provide high performance, full delegation, and scalability, so as to best serve the needs of accessing data anytime and anywhere, delegating within enterprises, and achieving a dynamic set of users. In this paper, we propose a scheme to help enterprises to efficiently share confidential data on cloud servers. We achieve this goal by first combining the hierarchical identity-based encryption (HIBE) system and the ciphertext-policy attribute-based encryption (CP-ABE) system, and then making a performance-expressivity tradeoff, finally applying proxy re-encryption and lazy re-encryption to our scheme. <s> BIB001 </s> Survey on Revocation in Ciphertext-Policy Attribute-Based Encryption <s> Full expressive <s> We present a new methodology for realizing Ciphertext-Policy Attribute Encryption (CP-ABE) under concrete and noninteractive cryptographic assumptions in the standard model. Our solutions allow any encryptor to specify access control in terms of any access formula over the attributes in the system. In our most efficient system, ciphertext size, encryption, and decryption time scales linearly with the complexity of the access formula. The only previous work to achieve these parameters was limited to a proof in the generic group model. ::: ::: We present three constructions within our framework. Our first system is proven selectively secure under a assumption that we call the decisional Parallel Bilinear Diffie-Hellman Exponent (PBDHE) assumption which can be viewed as a generalization of the BDHE assumption. Our next two constructions provide performance tradeoffs to achieve provable security respectively under the (weaker) decisional Bilinear-Diffie-Hellman Exponent and decisional Bilinear Diffie-Hellman assumptions. <s> BIB002 </s> Survey on Revocation in Ciphertext-Policy Attribute-Based Encryption <s> Full expressive <s> In Attribute-based Encryption (ABE) scheme, attributes play a very important role. Attributes have been exploited to generate a public key for encrypting data and have been used as an access policy to control users' access. The access policy can be categorized as either key-policy or ciphertext-policy. The key-policy is the access structure on the user's private key, and the ciphertext-policy is the access structure on the ciphertext. And the access structure can also be categorized as either monotonic or non-monotonic one. Using ABE schemes can have the advantages: (1) to reduce the communication overhead of the Internet, and (2) to provide a fine-grained access control. In this paper, we survey a basic attribute-based encryption scheme, two various access policy attribute-based encryption schemes, and two various access structures, which are analyzed for cloud environments. Finally, we list the comparisons of these schemes by some criteria for cloud environments. <s> BIB003 </s> Survey on Revocation in Ciphertext-Policy Attribute-Based Encryption <s> Full expressive <s> One method which is effective and also ensures security in cloud storage is data access control. Now-a-days this method faces lot of challenges from data out sourcing as well as un-trusted cloud servers. In this case data owners should get direct controls on access policies, which is provided by Cipher text-Policy Attribute-based Encryption (CP-ABE).Due to attribute revocation it is not easy for applying existing CP-ABE schemes to data in cloud storage. This design gives an efficient, expressive and revocation in data access control scheme in multi-authority storage cloud systems, in which there is co-existence of multiple authorities and each will be able to issue independently attributes. Specifically, this implemented system has a revocable multi-authority CP-ABE scheme, which gives the underlying techniques that helps to design schemes in data access control. This efficient revocation method achieves forward security as well as backward security. The screenshots show results in the data access control scheme which is secure and efficient. <s> BIB004 </s> Survey on Revocation in Ciphertext-Policy Attribute-Based Encryption <s> Full expressive <s> In this work, we aim to make attribute-based encryption ABE more suitable for access control to data stored in the cloud. For this purpose, we concentrate on giving to the encryptor full control over the access rights, providing feasible key management even in case of multiple independent authorities, and enabling viable user revocation, which is essential in practice. Our main result is an extension of the decentralized CP-ABE scheme of Lewko and Waters [6] with identity-based user revocation. Our revocation system is made feasible by removing the computational burden of a revocation event from the cloud service provider, at the expense of some permanent, yet acceptable overhead of the encryption and decryption algorithms run by the users. Thus, the computation overhead is distributed over a potentially large number of users, instead of putting it on a single party e.g., a proxy server, which would easily lead to a performance bottleneck. The formal security proof of our scheme is given in the generic bilinear group and random oracle models. <s> BIB005 </s> Survey on Revocation in Ciphertext-Policy Attribute-Based Encryption <s> Full expressive <s> In several distributed systems a user should only be able to access data if a user possesses a certain set of credentials or attributes. Currently, the only method for enforcing such polices is to employ a trusted server store the data and mediate confidentiality of the data will be compromised. In this paper we present a system for realizing complex access control on encrypted data that we call cipher text-policy attribute-based encryption. By using our techniques encrypted data can be secure against collusion attacks. Previous attribute-based encryption systems used attributes to describe the encrypted data and built policies into user's key; while in our system attributes are used to describe a user's credentials, and a party encrypting data determines a policy for who can decrypt. Thus, out methods are conceptually closer to traditional access control methods such as role-based access control(RBAC).In addition, we provide an implementation of our system and five performance measurements. In cloud computing the data security is achieved by Data Access Control Scheme. Cipher text-Policy Attribute-based Encryption (CP-ABE) is considered as one of the most suitable scheme for data access control in cloud storage. This scheme provides data owners more direct control on access policies. However, CP-ABE schemes to data access control for cloud storage systems are difficult because of the attribute revocation problem. So This paper produce survey on efficient and revocable data access control scheme for multi-authority cloud storage systems, where there are multiple authorities cooperate and each authority is able to issue attributes independently. Specifically, this paper surveys a revocable multi-authority CP-ABE scheme. The attribute revocation method can efficiently achieve both forward security and backward security. This survey shows that revocable multi-authority CP-ABE scheme is secure in the random oracle model and is more efficient than previous multi-authority CP-ABE. Key Words —Access control; multi-authority; CP-ABE; attribute revocation; cloud storage. <s> BIB006
Wang et al. BIB001 The first hierarchical ABE scheme with a disjunctive normal form (DNF) policy Addressing revocation Wang et al. BIB001 The first hierarchical ABE scheme with a disjunctive normal form (DNF) policy The most popular variant of ABE techniques is CP-ABE. Four entities are responsible for running this scheme. These entities are attribute authority, data owner, data user, and cloud server. The role of the attribute authority is to generate secret keys for users according to their attributes to decrypt data. In addition, it is responsible for generating a public key and a master key. The data owner's role is to define an access policy that describes who can access to its data as well as encrypting those data under this access policy. Firstly, a data owner uses a symmetric encryption technique (e.g., AES) to encrypt its data. After that, the owner encrypts the symmetric key under its access policy using CP-ABE by selecting a random value as a secret which is shared using the linear secret sharing scheme technique to generate some values associated with each corresponding attribute in the ciphertext according to the owner's access policy. This policy is determined over a set of attributes by the data owner, and can be demonstrated as a Boolean function with (AND, OR) gates between attributes (e.g., (lecturer AND experience ≥ 2 years) OR Professor). Then the encrypted data is sent to the designated cloud for storage including the data ciphertext, the CP-ABE ciphertext and the access policy. Associating the access policy with the ciphertext means that the ciphertext chooses which key can recover the plaintext, giving the data owner more control of its outsourced data BIB003 . The eligible users who possess the required attributes in a right combination (i.e., satisfy the access policy) can successfully decrypt the encrypted data. As a result, the main benefit from CP-ABE is that sensitive data can be stored on an untrusted server without performing authentication checks for the data access  . A common framework of a CP-ABE scheme includes four algorithms, as demonstrated in Figure 3 : Setup, Encryption, Key Generation, and Decryption BIB002 , which are defined below. • Setup(λ, U) → (MSK, PK) : Takes a set of attributes U in the system and an implicit security parameter λ (such as the type of the elliptic curve group used and the base finite field) as inputs to generate a public key PK and a master key MSK as outputs. Takes as inputs a public key PK, an access structure A, and a message M to be encrypted. The output will be a ciphertext CT. In this algorithm, a master key MSK and a set of attributes S are taken as inputs. A user's secret key SK is generated as output. This algorithm takes as inputs a user's secret key SK and a ciphertext CT. It returns a message M when the user's attributes satisfy the access structure. There are some appealing merits of the CP-ABE technique over other one-to-one traditional encryption techniques that enable coarse-grained access control. First, CP-ABE is to enable fine-grained access control in an encrypted form. This is desirable for many access control applications that run some cloud services such as storage and sharing services. Secondly, it supports highly expressive policies representing any access structures. Thirdly, it offers a good solution to data confidentiality. As generating a secret key for a user happens only once but it can be used to decrypt all the subsequent ciphertexts, CP-ABE reduces communication overhead BIB003 . Fourthly, it is collusion-resistant against misbehaving authorized users, which is achieved by associating a random number or polynomial with each attribute of a user's secret key so that only the attributes with the same random value can be used for decryption, leading to preventing different legitimate users from colluding with each other  . Finally, it is possible to integrate CP-ABE with a proxy re-encryption technique in cloud in order to increase security by re-encrypting ciphertexts without disclosing the plaintexts to the cloud BIB003 . There are some appealing merits of the CP-ABE technique over other one-to-one traditional encryption techniques that enable coarse-grained access control. First, CP-ABE is to enable fine-grained access control in an encrypted form. This is desirable for many access control applications that run some cloud services such as storage and sharing services. Secondly, it supports highly expressive policies representing any access structures. Thirdly, it offers a good solution to data confidentiality. As generating a secret key for a user happens only once but can be used to decrypt all the subsequent ciphertexts, CP-ABE reduces communication overhead BIB003 . Fourthly, it is collusion-resistant against misbehaving authorized users, which is achieved by associating a random number or polynomial with each attribute of a user's secret key so that only the attributes with the same random value can be used for decryption, leading to preventing different legitimate users from colluding with each other  . Finally, it is possible to integrate CP-ABE with a proxy re-encryption technique in cloud in order to increase security by re-encrypting ciphertexts without disclosing the plaintexts to the cloud BIB003 . However, there are some weaknesses related to CP-ABE. These include the fact that CP-ABE only works fine when attributes are descriptive. In other words, temporal attributes are not well handled by CP-ABE. In addition, this technique is difficult to handle the attribute/user revocation problem  without trusting the cloud service provider that has already hosted the data, particularly in dynamic environments where users' attributes can change over time. Trusting a cloud server raises another issue which is a collusion attack. This attack involves revoked users colluding with the cloud server to combine their information together to gain access to unauthorized data. Therefore, the adoption of CP-ABE requires additional refinements. Based on the entities that a user can obtain authorization from, CP-ABE is classified into two different categories BIB004 . They are single authority CP-ABE, where all attributes are handled by a single authority, and multiauthority CP-ABE, in which different authorities manage the attributes in a distributed manner. However, in multiauthority systems, many complicated issues can be experienced when the CP-ABE systems are built. For example, to tie the work of all authorities together, some existing systems use either a central authority, which can cause a bottleneck problem and is contradictory to the distributed control principle BIB006 , or coordination between the authorities, which increases communication and computational costs. In addition, each authority needs to be aware of each other, running the risk of collusion by combining their information to figure out unauthorized information. In addition, the revocation process is more complicated to manage in this type of system BIB005 BIB006 . On the other hand, some issues can be encountered in any single authority systems. The first one is the key escrow problem that happens due to the ability of the authority to gain access to all users' keys. This ability is obtained by the authority as it possesses the master key from which the users' keys are derived. The second issue is the limited ability of any single authority system to handle a wide range of different attributes. Moreover, it represents a single-point bottleneck on security. Once an adversary compromises the system, the authority's master key is easy to obtain. To efficiently exploit the advantages of CP-ABE and avoid most of its drawbacks, we need to construct a new scheme of CP-ABE that mitigates the difficulties in the existing schemes and use sufficient, alternative solutions that dynamically change users' privileges without entrusting information to a cloud server and build a collusion resistant system. The main issues that we are concerned about are