A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> Cloud computing is revolutionizing how information technology resources and services are used and managed but the revolution comes with new security problems. Among these is the problem of securely managing the virtual-machine images that encapsulate each application of the cloud. These images must have high integrity because the initial state of every virtual machine in the cloud is determined by some image. However, as some of the enefits of the cloud depend on users employing images built by third parties, users must also be able to share images safely. This paper explains the new risks that face administrators and users (both image publishers and image retrievers) of a cloud's image repository. To address those risks, we propose an image management system that controls access to images, tracks the provenance of images, and provides users and administrators with efficient image filters and scanners that detect and repair security violations. Filters and scanners achieve efficiency by exploiting redundancy among images; an early implementation of the system shows that this approach scales better than a naive approach that treats each image independently. <s> BIB001 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> More and more companies begin to provide different kinds of cloud computing services for Internet users at the same time these services also bring some security problems. Currently the majority of cloud computing systems provide digital identity for users to access their services, this will bring some inconvenience for a hybrid cloud that includes multiple private clouds and/or public clouds. Today most cloud computing system use asymmetric and traditional public key cryptography to provide data security and mutual authentication. Identity-based cryptography has some attraction characteristics that seem to fit well the requirements of cloud computing. In this paper, by adopting federated identity management together with hierarchical identity-based cryptography (HIBC), not only the key distribution but also the mutual authentication can be simplified in the cloud. <s> BIB002 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> In the following years, the desktop-based applications will be changed to cloud computing gradually. Since all users' profile and context data will be stored on the service supplier side based on their ID. ID is becoming a security bottleneck: attackers can trace all other information via user ID. Increasingly, a simple service may be involved in a chain of service clouds; each cloud is able to access data in its cloud without the control of any technology. With ID and password cross utilization in clear text, leakage of ID profile and password in one cloud may propagate to the whole cloud chain. Without proper protection, the success of cloud computing will be threatened by ID privacy leakage. In this paper, privacy preserved ID profile utilizing protocol (PPID) is proposed to prevent this privacy flaw. PPID together with its extension ID anonymity protocol (IDA) separate ID and services. With these two protocols, threaten from crash of whole cloud chain caused by ID privacy leakage is minimized. <s> BIB003 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> With the popular use of service-oriented technologies, Database as a Service(DaaS) as a new paradigm is becoming a more practical and useful model for those enterprises who can't afford the expensive DBMS products. However access control management by the database service provider ($DSP$) in the DaaS context is challenging because the $DSP$ may be untrusted for the delegated data contents. In thispaper, we first present an approach to implement the flexible accesscontrol enforcement management by applying a $DSP$ re-encryption mechanism. Our approach not only can implement the selective accesscontrol of the encrypted data by the $DSP$, but also can relieve the users from the complex key derivation procedure. The underlying idea of our approach is that the $DSP$ uses different re-encryption keys for users of the system to implement flexible access control enforcement management under the $DSP$ re-encryption mechanism. We demonstrate the usefulness and security property of our flexible access control enforcement management, finally we analyze and resolve the possible attacks and information disclosure. <s> BIB004 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> Large distributed systems such as clouds are increasingly becoming targets of attacks. Virtualization can be leveraged to increase the security of such systems by protecting the integrity of guest components. This paper discusses the integrity protection problem in the clouds and sketches a novel architecture, Transparent Cloud Protection System (TCPS) for increased security of cloud resources. TCPS can be tailored to different cloud flavors to monitor the integrity of guests and infrastructure components while remaining transparent to virtual machines. <s> BIB005 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> Cloud computing is a model for enabling convenient, on-demand network access to a shared pool of configurable computing resources that can be rapidly provisioned and released with minimal management effort or service provider interaction. With this pay-as-you-go model of computing, cloud solutions are seen as having the potential to both dramatically reduce costs and increase the rapidity of development of applications. <s> BIB006 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> Cloud Computing is becoming one of the most important topics in the IT world. Several challenges are being raised from the adoption of this computational paradigm including security, privacy, and federation. This paper aims to introduce new concepts in cloud computing and security, focusing on heterogeneous and federated scenarios. We present a reference architecture able to address the Identity Management (IdM) problem in the InterCloud context and show how it can be successfully applied to manage the authentication needed among clouds for the federation establishment. <s> BIB007 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> Cloud computing allows the use of Internet-based services to support business processes and rental of IT-services on a utility-like basis. It offers a concentration of resources but also poses risks for data privacy. A single breach can cause significant loss. The heterogeneity of “users” represents a danger of multiple, collaborative threats. In cloud computing, entities may have multiple accounts associated with a single or multiple service providers (SPs). Sharing sensitive identity information (that is, Personally Identifiable information or PII) along with associated attributes of the same entity across services can lead to mapping of the identities to the entity, tantamount to privacy loss. Identity management (IDM) is one of the core components in cloud privacy and security and can help alleviate some of the problems associated with cloud computing. Available solutions use trusted third party (TTP) in identifying entities to SPs. The solution providers do not recommend the usage of their solutions on untrusted hosts. We propose an approach for IDM, which is independent of TTP and has the ability to use identity data on untrusted hosts. The approach is based on the use of predicates over encrypted data and multi-party computing for negotiating a use of a cloud service. It uses active bundle—which is a middleware agent that includes PII data, privacy policies, a virtual machine that enforces the policies, and has a set of protection mechanisms to protect itself. An active bundle interacts on behalf of a user to authenticate to cloud services using user’s privacy policies. <s> BIB008 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> One of the challenging problems cloud computing is facing today is the security of data in the cloud. Since the physical location of user data in the cloud is unknown and the data are often distributed across multiple cloud services, a user controllable and privacy preserving access control mechanism is necessary for the success of cloud computing in general and for the protection of user data in specific. In this paper, we discuss a novel approach to controlling access to user data in the cloud; the concept is called Permission as a Service (PaaS). Specifically, PaaS separates access control from other services to provide a separate service in the cloud. This allows users to set permissions for all data in a single location. In PaaS, user data are encrypted to maintain confidentiality and permissions are managed via decryption keys. As a proof-of-concept, we discuss the design and implementation of our prototype leveraging attribute based encryption (ABE). <s> BIB009 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> Cloud is a relatively new concept and so it is unsurprising that the information assurance, data protection, network security and privacy concerns have yet to be fully addressed. The cloud allows users to avoid upfront hardware and software investments, gain flexibility, collaborate with others, and take advantage of the sophisticated services. However, security is a huge issue for cloud users especially access control, user profile management and accessing services offered by the private cloud environment. A privacy enhancement system on Academic-based private cloud system using Eucalyptus open source cloud infrastructure has been proposed in this paper. This system provides the cloud users to improve the privacy and security of the private personal data. Two approaches (Role-based Access Control and Attribute-based Access Control model) are combined as a new approach (ARBAC). This means that they are applied to improve the privacy which supports both mandatory and discretionary access control needs on the target private cloud system. <s> BIB010 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> In this paper we are interested in privacy preserving discretionary access control (DAC) for outsourced storage such as increasingly popular cloud storage services. Our main goal is to enable clients, who outsource data items, to delegate permissions (read, write, delete) to other clients such that clients are able to unlinkably and anonymously perform operations on outsourced data items when holding adequate permission. In contrast to recent approaches based on oblivious RAM, oblivious transfer combined with anonymous credentials or attribute based encryption, we propose a solution based on dynamic accumulators. In doing so, our approach naturally reflects the concept of access control lists (ACLs), which are a popular means to implement DAC. <s> BIB011 </s> A survey on security issues and solutions at different layers of Cloud computing <s> Authentication and access control level security issues <s> Traditional access control models often assume that the entity enforcing access control policies is also the owner of data and resources. This assumption no longer holds when data is outsourced to a third-party storage provider, such as the cloud. Existing access control solutions mainly focus on preserving confidentiality of stored data from unauthorized access and the storage provider. However, in this setting, access control policies as well as users’ access patterns also become privacy sensitive information that should be protected from the cloud. We propose a two-level access control scheme that combines coarse-grained access control enforced at the cloud, which provides acceptable communication overhead and at the same time limits the information that the cloud learns from his partial view of the access rules and the access patterns, and fine-grained cryptographic access control enforced at the user’s side, which provides the desired expressiveness of the access control policies. Our solution handles both read and write access control. <s> BIB012
In Cloud computing, the client's information is transmitted over the Internet, which poses data ownership issues BIB005 . As this information is processed outside the enterprise, it brings an inherent level of risk. This issue is addressed by providing support for security assertion markup language (SAML) federation protocol (which contains authentication credentials in the form of SAML assertions) with their own authentication protocol BIB006 . SAML is issued to exchange information, such as assertions related to a subject or authentication Fig. 7 Securing virtual image repository and access control BIB001 information between the cooperating domains. The request and response messages of it are mapped over Simple Object Access Protocol (SOAP) relying on XML. As discussed in Sect. 3.1, using a Signature Wrapping Attack, it is possible to modify an eavesdropped message despite of it being digitally signed. Thus, an attacker may be able to execute arbitrary machine commands on behalf of a legitimate user. To address such issues, data should be transmitted via secured channel and fine-grained authentication and authorization techniques can be used for preventing data from unauthorized access. Yan et al. BIB002 proposed an authentication approach that uses federated identity management together with hierarchical identity-based cryptography (HIBC). It provides keys (public key and private key) distribution along with mutual authentication between parties in the Cloud. It allows users to access services from other Clouds with a single digital identity. For web services, this approach can be used to distribute public keys, while reducing SOAP header size. It is used to create a session between two parties without any message exchange. However, it creates trust issues since third party key distribution is involved. Celesti et al. BIB007 addressed the identity management problem in inter-Cloud. In this approach, the third party is used as an identity provider (IDP). In order to communicate, each Cloud has to create an account using ID provided by IDP. Each Cloud performs authentication tasks on the provided ID to establish trust and gains the access to needed resources. Trust of foreign Cloud is accomplished by the IDP. The BIB003 limitation of this approach is that each Cloud has to trust and rely on the identity provider. To solve third party issues, Ranchal et al. BIB008 proposed an approach to protect identity information without including trusted third party and using an active bundle scheme. In this approach, Samir's multi-party secrete sharing scheme is used to encrypt data. In this scheme, encrypted data and keys are shared among multiple hosts. By computing predicate over encrypted data and multi-party computing, active bundle based authentication can be done without decrypting the data. Fine-grained access controls should be available for controlling access to sensitive data or the application code. Security officers are able to define a set of controls applied to applications depending on the data. For controlling access to Cloud resources, standards like eXtensible Access Control Markup Language (XACML) expressing access policies can be used. Service providers like Salesforce and Google Apps are using XACML for authorization decision and access control. Authors in  presented a security model for restricting access to information through covert channels in the Cloud. The solution for identity management among Clouds is presented in BIB003 . According to the proposed protocol in BIB003 , Cloud user registers his/her ID with the service provider and gets a certificate with a public key. Then third party service Cloud and service providers send their certificates to each other. While requesting to third party service Cloud, the user can verify its certificate. After which, messages for third party service Cloud and service provider Cloud are produced. In produced messages, service level information is hidden for service provider, whereas ID and privileges (IOMD as shown in Fig. 8 ) are hidden for third party service Cloud. For hiding such information, dual signatures (produced by hash function and encryption using user's private key) are used. Thus, disclosure of the user's ID and privileges can be protected from service providers. A re-encryption approach (as shown in Fig. 9 [60]) provides flexible access control mechanism in Cloud data storage. Here, data owner (Down) (who provides data to a service provider) generates private key and public key using a private key generator (PKG) for each user of these data. Then re-encryption keys corresponding to private Fig. 9 Re-encryption based approach BIB004 key for each user are generated using a key generator (REKG) and stored in authentication table. After which access control policies are stored in the access control matrix. Using the public key of each user, each tuple of owned database is encrypted. The authorization table is encrypted using the public key of database service provider (DSP). Encrypted database and authorization table are transferred to the DSP. By using re-encryption keys, DSP re-encrypts tuples of the database. Produced re-cipher text is decrypted only by the legal user's private key. Thus, DSP can authorize data users without seeing the data. Echeverria et al. BIB009 proposed an idea to control an access of user data in the Cloud; that is called Permission-as-a-Service. It separates access control from other services to provide a separate service in the cloud. This allows users to set permissions for all data in a single location. This approach provides confidentiality of user's by encrypting them using attribute based encryption (ABE) to provide data confidentiality. When any user wants to access this data, permissions to access this data are managed via decryption keys. However, this approach is applied only for PaaS. Mon et al. BIB010 combined Role-based Access Control (RBAC) and Attribute-based Access Control (ABAC) to provide the privacy and security of sensitive data of cloud users. In this approach, Cloud clients store their data based on privacy laws according to their user levels. With the use of RBAC and ABAC, the privacy manager defines the privacy policies, privacy laws, user levels, and security levels to control the data access. Using an access control list (ACL), users are granted or denied permission to access the data. In this approach, security and privacy policies are defined by the service providers, which restrict users to store all types of data since service providers are not fully trusted. Slamanig BIB011 presented a dynamic accumulator based approach for privacy preserving access control to outsourced data. In this approach, the concept of access control lists (ACLs) is used to provide permissions (read, write, delete) to other users who are able to unlinkably and anonymously perform operations on outsourced data items when having these permissions. Using this approach, it can be decided that whether the users are granted or denied access. The data user can give/get access rights to/from other users, whereas the Cloud provider will not be able to identify such users and linked operations done by users. The limitation of this approach is that if the data owner wants to revoke permission from a user, then that user must have to revoke granted permission from other users. This makes it computationally complex to maintain chain of users. Raykova et al. BIB012 proposed privacy enhanced access control for outsourced data. In this approach, the authors combine coarse-grained access control and fine-grained cryptographic access control. The coarse-grained access control offers an affordable communication overhead and provides privacy of information against view of the access rules and the access patterns, whereas fine-grained cryptographic access control is used at the user's side, which provides the desired access control policies. This approach offers read and write access control to the user's data.