Attribute-based encryption for cloud computing access control: A survey

National Research Foundation (NRF) Singapore; AXA Research Fun

Longitude : a privacy-preserving location sharing protocol for mobile applications

Location sharing services are becoming increasingly popular. Although many location sharing services allow users to set up privacy policies to control who can access their location, the use made by service providers remains a source of concern. Ideally, location sharing providers and middleware should not be able to access users’ location data without their consent. In this paper, we propose a new location sharing protocol called Longitude that eases privacy concerns by making it possible to share a user’s location data blindly and allowing the user to control who can access her location, when and to what degree of precision. The underlying cryptographic algorithms are designed for GPS-enabled mobile phones. We describe and evaluate our implementation for the Nexus One Android mobile phone

Data security in cloud storage services

Cloud Computing is considered to be the next-generation architecture for ICT where it moves the application software and databases to the centralized large data centers. It aims to offer elastic IT services where clients can benefit from significant cost savings of the pay-per-use model and can easily scale up or down, and do not have to make large investments in new hardware. However, the management of the data and services in this cloud model is under the control of the provider. Consequently, the cloud clients have less control over their outsourced data and they have to trust cloud service provider to protect their data and infrastructure from both external and internal attacks. This is especially true with cloud storage services. Nowadays, users rely on cloud storage as it offers cheap and unlimited data storage that is available for use by multiple devices (e.g. smart phones, tablets, notebooks, etc.). Besides famous cloud storage providers, such as Amazon, Google, and Microsoft, more and more third-party cloud storage service providers are emerging. These services are dedicated to offering more accessible and user friendly storage services to cloud customers. Examples of these services include Dropbox, Box.net, Sparkleshare, UbuntuOne or JungleDisk. These cloud storage services deliver a very simple interface on top of the cloud storage provided by storage service providers. File and folder synchronization between different machines, sharing files and folders with other users, file versioning as well as automated backups are the key functionalities of these emerging cloud storage services. Cloud storage services have changed the way users manage and interact with data outsourced to public providers. With these services, multiple subscribers can collaboratively work and share data without concerns about their data consistency, availability and reliability. Although these cloud storage services offer attractive features, many customers have not adopted these services. Since data stored in these services is under the control of service providers resulting in confidentiality and security concerns and risks. Therefore, using cloud storage services for storing valuable data depends mainly on whether the service provider can offer sufficient security and assurance to meet client requirements. From the way most cloud storage services are constructed, we can notice that these storage services do not provide users with sufficient levels of security leading to an inherent risk on users\u27 data from external and internal attacks. These attacks take the form of: data exposure (lack of data confidentiality); data tampering (lack of data integrity); and denial of data (lack of data availability) by third parties on the cloud or by the cloud provider himself. Therefore, the cloud storage services should ensure the data confidentiality in the following state: data in motion (while transmitting over networks), data at rest (when stored at provider\u27s disks). To address the above concerns, confidentiality and access controllability of outsourced data with strong cryptographic guarantee should be maintained. To ensure data confidentiality in public cloud storage services, data should be encrypted data before it is outsourced to these services. Although, users can rely on client side cloud storage services or software encryption tools for encrypting user\u27s data; however, many of these services fail to achieve data confidentiality. Box, for example, does not encrypt user files via SSL and within Box servers. Client side cloud storage services can intentionally/unintentionally disclose user decryption keys to its provider. In addition, some cloud storage services support convergent encryption for encrypting users\u27 data exposing it to “confirmation of a file attack. On the other hand, software encryption tools use full-disk encryption (FDE) which is not feasible for cloud-based file sharing services, because it encrypts the data as virtual hard disks. Although encryption can ensure data confidentiality; however, it fails to achieve fine-grained access control over outsourced data. Since, public cloud storage services are managed by un-trusted cloud service provider, secure and efficient fine-grained access control cannot be realized through these services as these policies are managed by storage services that have full control over the sharing process. Therefore, there is not any guarantee that they will provide good means for efficient and secure sharing and they can also deduce confidential information about the outsourced data and users\u27 personal information. In this work, we would like to improve the currently employed security measures for securing data in cloud store services. To achieve better data confidentiality for data stored in the cloud without relying on cloud service providers (CSPs) or putting any burden on users, in this thesis, we designed a secure cloud storage system framework that simultaneously achieves data confidentiality, fine-grained access control on encrypted data and scalable user revocation. This framework is built on a third part trusted (TTP) service that can be employed either locally on users\u27 machine or premises, or remotely on top of cloud storage services. This service shall encrypts users data before uploading it to the cloud and decrypts it after downloading from the cloud; therefore, it remove the burden of storing, managing and maintaining encryption/decryption keys from data owner\u27s. In addition, this service only retains user\u27s secret key(s) not data. Moreover, to ensure high security for these keys, it stores them on hardware device. Furthermore, this service combines multi-authority ciphertext policy attribute-based encryption (CP-ABE) and attribute-based Signature (ABS) for achieving many-read-many-write fine-grained data access control on storage services. Moreover, it efficiently revokes users\u27 privileges without relying on the data owner for re-encrypting massive amounts of data and re-distributing the new keys to the authorized users. It removes the heavy computation of re-encryption from users and delegates this task to the cloud service provider (CSP) proxy servers. These proxy servers achieve flexible and efficient re-encryption without revealing underlying data to the cloud. In our designed architecture, we addressed the problem of ensuring data confidentiality against cloud and against accesses beyond authorized rights. To resolve these issues, we designed a trusted third party (TTP) service that is in charge of storing data in an encrypted format in the cloud. To improve the efficiency of the designed architecture, the service allows the users to choose the level of severity of the data and according to this level different encryption algorithms are employed. To achieve many-read-many-write fine grained access control, we merge two algorithms (multi-authority ciphertext policy attribute-based encryption (MA- CP-ABE) and attribute-based Signature (ABS)). Moreover, we support two levels of revocation: user and attribute revocation so that we can comply with the collaborative environment. Last but not least, we validate the effectiveness of our design by carrying out a detailed security analysis. This analysis shall prove the correctness of our design in terms of data confidentiality each stage of user interaction with the cloud

Secure data sharing in cloud and IoT by leveraging attribute-based encryption and blockchain

“Data sharing is very important to enable different types of cloud and IoT-based services. For example, organizations migrate their data to the cloud and share it with employees and customers in order to enjoy better fault-tolerance, high-availability, and scalability offered by the cloud. Wearable devices such as smart watch share user’s activity, location, and health data (e.g., heart rate, ECG) with the service provider for smart analytic. However, data can be sensitive, and the cloud and IoT service providers cannot be fully trusted with maintaining the security, privacy, and confidentiality of the data. Hence, new schemes and protocols are required to enable secure data sharing in the cloud and IoT. This work outlines our research contribution towards secure data sharing in the cloud and IoT. For secure data sharing in the cloud, this work proposes several novel attribute-based encryption schemes. The core contributions to this end are efficient revocation, prevention of collusion attacks, and multi-group support. On the other hand, for secure data sharing in IoT, a permissioned blockchain-based access control system has been proposed. The system can be used to enforce fine-grained access control on IoT data where the access control decision is made by the blockchain-based on the consensus of the participating nodes”--Abstract, page iv

Efficient Ciphertext-policy Attribute Based Encryption for Cloud-Based Access Control

Outsourcing data to some cloud servers enables a massive, flexible usage of cloud computing resources and it is typically held by different organizations and data owners. However, various security concerns have been raised due to hosting sensitive data on an untrusted cloud environment, and the control over such data by their owners is lost after uploading to the cloud. Access control is the first defensive line that forbids unauthorized access to the stored data. Moreover, fine-grained access control on the untrusted cloud can be enforced using advanced cryptographic mechanisms. Some schemes have been proposed to deliver such access control using Ciphertext-policy attribute based encryption (CP-ABE) that can enforce data owners’ access policies to achieve such cryptographic access control and tackle the majority of those concerns. However, some challenges are still outstanding due to the complexity of frequently changing the cryptographic enforcements of the owners’ access policies in the hosted cloud data files, which poses computational and communicational overheads to data owners. These challenges are: 1) making dynamic decisions to grant access rights to the cloud resources, 2) solving the issue of the revocation process that is considered as a performance killer, and 3) building a collusion resistant system. The aim of our work is to construct an access control scheme that provides secure storing and sharing sensitive data on the cloud and suits limited-resources devices. In this thesis, we analyse some of the existing, related issues and propose a scheme that extends the relevant existing techniques to resolve the inherent problems in CP-ABE without incurring heavy computation overhead. In particular, most existing revocation techniques require re-issuing many private keys for all non-revoked users as well as re-encrypting the related ciphertexts. Our proposed scheme offers a solution to perform a novel technique that dynamically changes the access privileges of legitimate users. The scheme drives the access privileges in a specific way by updating the access policy and activating a user revocation property. Our technique assigns processing-intensive tasks to cloud servers without any information leakage to reduce the computation cost on resource-limited computing devices. Our analytical theoretical and experimental findings and comparisons of our work with related existing systems indicate that our scheme is efficient, secure and more practical compared to the current related systems, particularly in terms of policy updating and ciphertext re-encryption. Therefore, our proposed scheme is suited to Internet of Things (IoT) applications that need a practical, secure access control scheme. Moreover, to achieve secure, public cloud storage and minimise the limitations of CP-ABE which mainly supports storing data only on a private cloud storage system managed by only one single authority, our proposed access control scheme is extended to a secure, critical access control scheme with multiple authorities. This scheme ought to be carefully designed to achieve fine-grained access control and support outsourced-data confidentiality. In addition, most existing multi-authority access control schemes do not properly consider the revocation issue due to the difficulty of addressing it in distributed settings. Therefore, building a multi-authority CP-ABE scheme along with addressing changes to policy attributes and users, have motivated many researchers to develop more suitable schemes with limited success. By leveraging the existing work, in this thesis, we propose a second CP-ABE scheme that tackles most of the existing work’s limitations and allows storing data securely on a public cloud storage system by employing multiple authorities which manage a joint set of attributes. Furthermore, the proposed scheme efficiently maintains the revocation by adapting the two techniques used in the first proposed single authority access control scheme to allow dynamic policy update and invalidate a revoked user’s secret key that eliminates collusion attacks. In terms of computation overhead, the proposed multi-authority scheme outsources expensive operations of encryption and decryption to a cloud server to mitigate the burden on a data owner and data users, respectively. Our scheme analysis and the theoretical and implemented results demonstrate that our scheme is scalable and efficient

Fine-Grained Access Control with User Revocation in Smart Manufacturing

This research has been founded by the European Union’s Horizon 2020 Research and Innovation program under grant agreement No. 871518, a project named COLLABS [19].Collaborative manufacturing is a key enabler of Industry 4.0 that requires secure data sharing among multiple parties. However, intercompany data-sharing raises important privacy and security concerns, particularly given intellectual property and business-sensitive information collected by many devices. In this paper, we propose a solution that combines four technologies to address these challenges: Attribute-Based Encryption for data access control, blockchain for data integrity and non-repudiation, Hardware Security Modules for authenticity, and the Interplanetary File System for data scalability. We also use OpenID for dynamic client identification and propose a new method for user revocation in Attribute-Based Encryption. Our evaluation shows that the solution can scale up to 2,000,000 clients while maintaining all security guarantees.European Union’s Horizon 2020, 87151

Efficient and Secure Data Sharing Using Attribute-based Cryptography

La crescita incontrollata di dati prodotti da molte sorgenti, eterogenee e di- namiche, spinge molti possessori di tali dati a immagazzinarli su server nel cloud, anche al fine di condividerli con terze parti. La condivisione di dati su server (possibilmente) non fidati fonte di importanti e non banali questioni riguardanti sicurezza, privacy, confidenzialit e controllo degli accessi. Al fine di prevenire accessi incontrollati ai dati, una tipica soluzione consiste nel cifrare i dati stessi. Seguendo tale strada, la progettazione e la realizzazione di politiche di accesso ai dati cifrati da parte di terze parti (che possono avere differenti diritti sui dati stessi) un compito complesso, che impone la presenza di un controllore fidato delle politiche. Una possibile soluzione l\u2019impiego di un meccanismo per il controllo degli accessi basato su schemi di cifratura attribute-base (ABE ), che permette al possessore dei dati di cifrare i dati in funzione delle politiche di accesso dei dati stessi. Di contro, l\u2019adozione di tali meccanismi di controllo degli accessi presentano due problemi (i) privacy debole: le politiche di accesso sono pubbliche e (ii) inefficienza: le politiche di accesso sono statiche e una loro modifica richiede la ricifratura (o la cifratura multipla) di tutti i dati. Al fine di porre rimedio a tali problemi, il lavoro proposto in questa tesi prende in con- siderazione un particolare schema di cifratura attribute-based, chiamato inner product encryption (IPE, che gode della propriet attribute-hiding e pertanto riesce a proteggere la privatezza delle politiche di accesso) e lo combina con le tecniche di proxy re-encryption, che introducono una maggiore flessibilit ed efficienza. La prima parte di questa tesi discute l\u2019adeguatezza dell\u2019introduzione di un meccanismo di controllo degli accessi fondato su schema basato su inner product e proxy re-encryption (IPPRE ) al fine di garantire la condivisione sicura di dati immagazzinati su cloud server non fidati. Pi specificamente, proponiamo due proponiamo due versioni di IPE : in prima istanza, presentiamo una versione es- tesa con proxy re-encryption di un noto schema basato su inner product [1]. In seguito, usiamo tale schema in uno scenario in cui vengono raccolti e gestiti dati medici. In tale scenario, una volta che i dati sono stati raccolti, le politiche di ac- cesso possono variare al variare delle necessit dei diversi staff medici. Lo schema proposto delega il compito della ricifratura dei dati a un server proxy parzial- mente fidato, che pu trasformare la cifratura dei dati (che dipende da una polit- ica di accesso) in un\u2019altra cifratura (che dipende da un\u2019altra politica di accesso) senza per questo avere accesso ai dati in chiaro o alla chiave segreta utilizzata dal possessore dei dati. In tal modo, il possessore di una chiave di decifratura corrispondente alla seconda politica di accesso pu accedere ai dati senza intera- gire con il possessore dei dati (richiedendo cio una chiave di decifratura associata alla propria politica di accesso). Presentiamo un\u2019analisi relativa alle prestazioni di tale schema implementato su curve ellittiche appartenenti alle classi SS, MNT e BN e otteniamo incoraggianti risultati sperimentali. Dimostriamo inoltre che lo schema proposto sicuro contro attacchi chosen plaintext sotto la nota ipotesi DLIN. In seconda istanza, presentiamo una versione ottimizzata dello schema proposto in precedenza (E-IPPRE ), basata su un ben noto schema basato suinner product, proposto da Kim [2]. Lo schema E-IPPRE proposto richiede un numero costante di operazioni di calcolo di pairing e ci garantisce che gli oggetti prodotti dall esecuzione dello schema (chiavi di decifratura, chiavi pubbliche e le cifrature stesse) sono di piccole rispetto ai parametri di sicurezza e sono efficientemente calcolabili. Testiamo sperimentalmente l\u2019efficienza dello schema proposto e lo proviamo (selettivamente nei confronti degli attributi) sicuro nei confronti di attacchi chosen plaintext sotto la nota ipotesi BDH. In altri termini, lo schema proposto non rivela alcuna informazione riguardante le politiche di accesso. La seconda parte di questa tesi presenta uno schema crittografico per la condivisione sicura dei dati basato su crittografia attribute-based e adatto per scenari basati su IoT. Come noto, il problema principale in tale ambito riguarda le limitate risorse computazionali dei device IoT coinvolti. A tal proposito, proponiamo uno schema che combina la flessibilit di E-IPPRE con l\u2019efficienza di uno schema di cifratura simmetrico quale AES, ottenendo uno schema di cifratura basato su inner product, proxy-based leggero (L-IPPRE ). I risultati sperimentali confermano l\u2019adeguatezza di tale schema in scenari IoT.Riferimenti [1] Jong Hwan Park. Inner-product encryption under standard assumptions. Des. Codes Cryptography, 58(3):235\u2013257, March 2011. [2] Intae Kim, Seong Oun Hwang, Jong Hwan Park, and Chanil Park. An effi- cient predicate encryption with constant pairing computations and minimum costs. IEEE Trans. Comput., 65(10):2947\u20132958, October 2016.With the ever-growing production of data coming from multiple, scattered, and highly dynamical sources, many providers are motivated to upload their data to the cloud servers and share them with other persons for different purposes. However, storing data on untrusted cloud servers imposes serious concerns in terms of security, privacy, data confidentiality, and access control. In order to prevent privacy and security breaches, it is vital that data is encrypted first before it is outsourced to the cloud. However, designing access control mod- els that enable different users to have various access rights to the shared data is the main challenge. To tackle this issue, a possible solution is to employ a cryptographic-based data access control mechanism such as attribute-based encryption (ABE ) scheme, which enables a data owner to take full control over data access. However, access control mechanisms based on ABE raise two chal- lenges: (i) weak privacy: they do not conceal the attributes associated with the ciphertexts, and therefore they do not satisfy attribute-hiding security, and (ii) inefficiency: they do not support efficient access policy change when data is required to be shared among multiple users with different access policies. To address these issues, this thesis studies and enhances inner-product encryption (IPE ), a type of public-key cryptosystem, which supports the attribute-hiding property as well as the flexible fine-grained access control based payload-hiding property, and combines it with an advanced cryptographic technique known as proxy re-encryption (PRE ). The first part of this thesis discusses the necessity of applying the inner- product proxy re-encryption (IPPRE ) scheme to guarantee secure data sharing on untrusted cloud servers. More specifically, we propose two extended schemes of IPE : in the first extended scheme, we propose an inner-product proxy re- encryption (IPPRE ) protocol derived from a well-known inner-product encryp- tion scheme [1]. We deploy this technique in the healthcare scenario where data, collected by medical devices according to some access policy, has to be changed afterwards for sharing with other medical staffs. The proposed scheme delegates the re-encryption capability to a semi-trusted proxy who can transform a dele- gator\u2019s ciphertext associated with an attribute vector to a new ciphertext associ- ated with delegatee\u2019s attribute vector set, without knowing the underlying data and private key. Our proposed policy updating scheme enables the delegatee to decrypt the shared data with its own key without requesting a new decryption key. We analyze the proposed protocol in terms of its performance on three dif- ferent types of elliptic curves such as the SS curve, the MNT curve, and the BN curve, respectively. Hereby, we achieve some encouraging experimental results. We show that our scheme is adaptive attribute-secure against chosen-plaintext under standard Decisional Linear (D-Linear ) assumption. To improve the per- formance of this scheme in terms of storage, communication, and computation costs, we propose an efficient inner-product proxy re-encryption (E-IPPRE ) scheme using the transformation of Kim\u2019s inner-product encryption method [2]. The proposed E-IPPRE scheme requires constant pairing operations for its al- gorithms and ensures a short size of the public key, private key, and ciphertext,making it the most efficient and practical compared to state of the art schemes in terms of computation and communication overhead. We experimentally as- sess the efficiency of our protocol and show that it is selective attribute-secure against chosen-plaintext attacks in the standard model under Asymmetric De- cisional Bilinear Diffie-Hellman assumption. Specifically, our proposed schemes do not reveal any information about the data owner\u2019s access policy to not only the untrusted servers (e.g, cloud and proxy) but also to the other users. The second part of this thesis presents a new lightweight secure data sharing scheme based on attribute-based cryptography for a specific IoT -based health- care application. To achieve secure data sharing on IoT devices while preserving data confidentiality, the IoT devices encrypt data before it is outsourced to the cloud and authorized users, who have corresponding decryption keys, can ac- cess the data. The main challenge, in this case, is on the one hand that IoT devices are resource-constrained in terms of energy, CPU, and memory. On the other hand, the existing public-key encryption mechanisms (e.g., ABE ) require expensive computation. We address this issue by combining the flexibility and expressiveness of the proposed E-IPPRE scheme with the efficiency of symmet- ric key encryption technique (AES ) and propose a light inner-product proxy re-encryption (L-IPPRE ) scheme to guarantee secure data sharing between dif- ferent entities in the IoT environment. The experimental results confirm that the proposed L-IPPRE scheme is suitable for resource-constrained IoT scenar- ios.References [1] Jong Hwan Park. Inner-product encryption under standard assumptions. Des. Codes Cryptography, 58(3):235\u2013257, March 2011. [2] Intae Kim, Seong Oun Hwang, Jong Hwan Park, and Chanil Park. An effi- cient predicate encryption with constant pairing computations and minimum costs. IEEE Trans. Comput., 65(10):2947\u20132958, October 2016

Granular Data Access Control with a Patient-Centric Policy Update for Healthcare

Healthcare is a multi-actor environment that requires independent actors to have a different view of the same data, hence leading to different access rights. Ciphertext Policy-Attribute-based Encryption (CP-ABE) provides a one-to-many access control mechanism by defining an attribute’s policy over ciphertext. Although, all users satisfying the policy are given access to the same data, this limits its usage in the provision of hierarchical access control and in situations where different users/actors need to have granular access of the data. Moreover, most of the existing CP-ABE schemes either provide static access control or in certain cases the policy update is computationally intensive involving all non-revoked users to actively participate. Aiming to tackle both the challenges, this paper proposes a patient-centric multi message CP-ABE scheme with efficient policy update. Firstly, a general overview of the system architecture implementing the proposed access control mechanism is presented. Thereafter, for enforcing access control a concrete cryptographic construction is proposed and implemented/tested over the physiological data gathered from a healthcare sensor: shimmer sensor. The experiment results reveal that the proposed construction has constant computational cost in both encryption and decryption operations and generates constant size ciphertext for both the original policy and its update parameters. Moreover, the scheme is proven to be selectively secure in the random oracle model under the q-Bilinear Diffie Hellman Exponent (q-BDHE) assumption. Performance analysis of the scheme depicts promising results for practical real-world healthcare applications

Revocable Key-Aggregate Cryptosystem for Data Sharing in Cloud

With the rapid development of network and storage technology, cloud storage has become a new service mode, while data sharing and user revocation are important functions in the cloud storage. Therefore, according to the characteristics of cloud storage, a revocable key-aggregate encryption scheme is put forward based on subset-cover framework. The proposed scheme not only has the key-aggregate characteristics, which greatly simplifies the user’s key management, but also can revoke user access permissions, realizing the flexible and effective access control. When user revocation occurs, it allows cloud server to update the ciphertext so that revoked users can not have access to the new ciphertext, while nonrevoked users do not need to update their private keys. In addition, a verification mechanism is provided in the proposed scheme, which can verify the updated ciphertext and ensure that the user revocation is performed correctly. Compared with the existing schemes, this scheme can not only reduce the cost of key management and storage, but also realize user revocation and achieve user’s access control efficiently. Finally, the proposed scheme can be proved to be selective chosen-plaintext security in the standard model