Data Sharing on Untrusted Storage with Attribute-Based Encryption

Storing data on untrusted storage makes secure data sharing a challenge issue. On one hand, data access policies should be enforced on these storage servers; on the other hand, confidentiality of sensitive data should be well protected against them. Cryptographic methods are usually applied to address this issue -- only encrypted data are stored on storage servers while retaining secret key(s) to the data owner herself; user access is granted by issuing the corresponding data decryption keys. The main challenges for cryptographic methods include simultaneously achieving system scalability and fine-grained data access control, efficient key/user management, user accountability and etc. To address these challenge issues, this dissertation studies and enhances a novel public-key cryptography -- attribute-based encryption (ABE), and applies it for fine-grained data access control on untrusted storage. The first part of this dissertation discusses the necessity of applying ABE to secure data sharing on untrusted storage and addresses several security issues for ABE. More specifically, we propose three enhancement schemes for ABE: In the first enhancement scheme, we focus on how to revoke users in ABE with the help of untrusted servers. In this work, we enable the data owner to delegate most computation-intensive tasks pertained to user revocation to untrusted servers without disclosing data content to them. In the second enhancement scheme, we address key abuse attacks in ABE, in which authorized but malicious users abuse their access privileges by sharing their decryption keys with unauthorized users. Our proposed scheme makes it possible for the data owner to efficiently disclose the original key owner\u27s identity merely by checking the input and output of a suspicious user\u27s decryption device. Our third enhancement schemes study the issue of privacy preservation in ABE. Specifically, our proposed schemes hide the data owner\u27s access policy not only to the untrusted servers but also to all the users. The second part presents our ABE-based secure data sharing solutions for two specific applications -- Cloud Computing and Wireless Sensor Networks (WSNs). In Cloud Computing cloud servers are usually operated by third-party providers, which are almost certain to be outside the trust domain of cloud users. To secure data storage and sharing for cloud users, our proposed scheme lets the data owner (also a cloud user) generate her own ABE keys for data encryption and take the full control on key distribution/revocation. The main challenge in this work is to make the computation load affordable to the data owner and data consumers (both are cloud users). We address this challenge by uniquely combining various computation delegation techniques with ABE and allow both the data owner and data consumers to securely mitigate most computation-intensive tasks to cloud servers which are envisaged to have unlimited resources. In WSNs, wireless sensor nodes are often unattendedly deployed in the field and vulnerable to strong attacks such as memory breach. For securing storage and sharing of data on distributed storage sensor nodes while retaining data confidentiality, sensor nodes encrypt their collected data using ABE public keys and store encrypted data on storage nodes. Authorized users are given corresponding decryption keys to read data. The main challenge in this case is that sensor nodes are extremely resource-constrained and can just afford limited computation/communication load. Taking this into account we divide the lifetime of sensor nodes into phases and distribute the computation tasks into each phase. We also revised the original ABE scheme to make the overhead pertained to user revocation minimal for sensor nodes. Feasibility of the scheme is demonstrated by experiments on real sensor platforms

Secure publish-subscribe protocols for heterogeneous medical wireless body area networks

Security and privacy issues in medical wireless body area networks (WBANs) constitute a major unsolved concern because of the challenges posed by the scarcity of resources in WBAN devices and the usability restrictions imposed by the healthcare domain. In this paper, we describe a WBAN architecture based on the well-known publish-subscribe paradigm. We present two protocols for publishing data and sending commands to a sensor that guarantee confidentiality and fine-grained access control. Both protocols are based on a recently proposed ciphertext policy attribute-based encryption (CP-ABE) scheme that is lightweight enough to be embedded into wearable sensors. We show how sensors can implement lattice-based access control (LBAC) policies using this scheme, which are highly appropriate for the eHealth domain. We report experimental results with a prototype implementation demonstrating the suitability of our proposed solution.This work was supported by the MINECO grant TIN2013-46469-R (SPINY: Security and Privacy in the Internet of You)

CDEdit: A Highly Applicable Redactable Blockchain with Controllable Editing Privilege and Diversified Editing Types

Redactable blockchains allow modifiers or voting committees with modification privileges to edit the data on the chain. Trapdoor holders in chameleon-based hash redactable blockchains can quickly compute hash collisions for arbitrary data, and without breaking the link of the hash-chain. However, chameleon-based hash redactable blockchain schemes have difficulty solving the problem of multi-level editing requests and competing for modification privileges. In this paper, we propose CDEdit, a highly applicable redactable blockchain with controllable editing privilege and diversified editing types. The proposed scheme increases the cost of invalid or malicious requests by paying the deposit on each edit request. At the same time, the editing privilege is subdivided into request, modification, and verification privileges, and the modification privilege token is distributed efficiently to prevent the abuse of the modification privilege and collusion attacks. We use chameleon hashes with ephemeral trapdoor (CHET) and ciphertext policy attribute-based encryption (CP-ABE) to implement two editing types of transaction-level and block-level, and present a practical instantiation and security analysis. Finally, the implementation and evaluation show that our scheme only costs low-performance overhead and is suitable for multi-level editing requests and modification privilege competition scenarios.Comment: 11 pages, 6 figure

SECURE, POLICY-BASED, MULTI-RECIPIENT DATA SHARING

In distributed systems users often need to share sensitive data with other users based on the latter's ability to satisfy various policies. In many cases the data owner may not even know the identities of the data recipients, but deems it crucial that they are legitimate; i.e., satisfy the policy. Enabling such data sharing over the Internet faces the challenge of (1) securely associating access policies with data and enforcing them, and (2) protecting data as it traverses untrusted proxies and intermediate repositories. Furthermore, it is desirable to achieve properties such as: (1) flexibility of access policies; (2) privacy of sensitive access policies; (3) minimal reliance on trusted third parties; and (4) efficiency of access policy enforcement. Often schemes enabling controlled data sharing need to trade one property for another. In this dissertation, we propose two complimentary policy-based data sharing schemes that achieve different subsets of the above desired properties. In the first part of this dissertation, we focus on CiphertextPolicy Attribute- Based Encryption (CP-ABE) schemes that specify and enforce access policies cryptographically and eliminate trusted mediators. We motivate the need for flexible attribute organization within user keys for efficient support of many practical applications. We then propose Ciphertext-Policy Attribute-Set Based Encryption (CP-ASBE) which is the first CP-ABE scheme to (1) efficiently support naturally occurring compound attributes, (2) support multiple numerical assignments for a given attribute in a single key and (3) provide efficient key management. While the CP-ASBE scheme minimizes reliance on trusted mediators, it can support neither context-based policies nor policy privacy. In the second part of this dissertation, we propose Policy Based Encryption System (PBES), which employs mediated decryption and supports both context-based policies and policy privacy. Finally, we integrate the proposed schemes into practical applications (i.e., CP-ASBE scheme with Attribute-Based Messaging (ABM) and PBES scheme with a conditional data sharing application in the Power Grid) and demonstrate their usefulness in practice

Data Access in Multiauthority Cloud Storage: Expressive and Revocable Data Control System

ABSTRACT Cloud computing is rising enormously due to its advantages and the adaptable storage services being provided by it. Because of this, the number of users has reached the top level. The users will share the sensitive data through the cloud. Furthermore, the user can\u27t trust the untrusted cloud server. Subsequently, the data access control has turned out to be extremely challenging in cloud storage framework. In existing work, revocable data access control scheme proposed for multi-authority cloud storage frameworks which supports the access control in light of the authority control. The authorized users who have desirable attributes given by various authorities can access the data. However, it couldn\u27t control the attacks which can happen to the authorized user who is not having desirable attributes. In this work, they propose a new algorithm named Improved Security Data Access Control which beats the issue exists in the existing work. And furthermore, incorporates the efficient attribute revocation strategy for multi-authority cloud storage. Keywords: Access control, multi-authority, attribute revocation, cloud storage

An Efficient Method for Realizing Contractions of Access Structures in Cloud Storage

In single-cloud storage, ciphertext-policy attribute-based encryption (CP-ABE) allows one to encrypt any data under an access structure to a cloud server, specifying what attributes are required to decrypt. In multi-cloud storage, a secret sharing scheme (SSS) allows one to split any data into multiple shares, one to a single server, and specify which subset of the servers are able to recover the data. It is an interesting problem to remove some attributes/servers but still enable the remaining attributes/servers in every authorized set to recover the data. The problem is related to the contraction problem of access structures for SSSs. In this paper, we propose a method that can efficiently transform a given SSS for an access structure to SSSs for contractions of the access structure. We show its applications in solving the attribute removal problem in the CP-ABE based single-cloud storage and the data relocating problem in multi-cloud storage. Our method results in solutions that require either less server storage or even no additional server storage.Comment: IEEE Transactions on Services Computin