Decryption Privilege Research Articles

A Revocable Certificateless Encryption Scheme for Multi‐User

ABSTRACTCertificateless cryptography, which solves the key escrow problem and avoids the complexity of certificate management, is an important part of public key cryptography. In the multi‐user scenarios, broadcast encryption can improve computational efficiency and reduce communication cost. Moreover, there may be some malicious users in the above scenarios, and the decryption permissions of these users need an effective mechanism to revoke them. In this paper, a revocable certificateless encryption scheme for multi‐user (RCLE‐MU) is proposed to address this issue. In the scheme, the Cloud Server Provider (CSP) utilizes the master time key to periodically generate time keys for legitimate users. For illegitimate users, their decryption privileges are revoked since they are unable to obtain the time keys. Then this new scheme is proved to be ciphertext indistinguishable under selected identity and chosen‐ciphertext attacks (sID‐CCAs). Finally, compared with several other schemes, the new scheme has more efficiency advantage. So it is suitable for multi‐user scenarios.

Revocable and Fog-Enabled Proxy Re-Encryption Scheme for IoT Environments.

As technology advances rapidly, a diverse array of Internet of Things (IoT) devices finds widespread application across numerous fields. The intelligent nature of these devices not only gives people more convenience, but also introduces new challenges especially in security when transmitting data in fog-based cloud environments. In fog computing environments, data need to be transmitted across multiple devices, increasing the risk of data being intercepted or tampered with during transmission. To securely share cloud ciphertexts, an alleged proxy re-encryption approach is a commonly adopted solution. Without decrypting the original ciphertext, such a mechanism permits a ciphertext intended for user A to be easily converted into the one intended for user B. However, to revoke the decryption privilege of data users usually relies on the system authority to maintain a user revocation list which inevitably increases the storage space. In this research, the authors come up with a fog-based proxy re-encryption system with revocable identity. Without maintaining the traditional user revocation list, the proposed scheme introduces a time-updated key mechanism. The time-update key could be viewed as a partial private key and should be renewed with different time periods. A revoked user is unable to obtain the renewed time-update key and hence cannot share or decrypt cloud ciphertexts. We formally demonstrate that the introduced scheme satisfies the security of indistinguishability against adaptively chosen identity and chosen plaintext attacks (IND-PrID-CPA) assuming the hardness of the Decisional Bilinear Diffie-Hellman (DBDH) problem in the random oracle model. Furthermore, compared with similar systems, the proposed one also has lower computational complexity as a whole.

Efficient and accountable anti-leakage attribute-based encryption scheme for cloud storage

To ensure secure and flexible data sharing in cloud storage, attribute-based encryption (ABE) is introduced to meet the requirements of fine-grained access control and secure one-to-many data sharing. However, the computational burden imposed by attribute encryption renders it unsuitable for resource-constrained environments such as the Internet of Things (IoT) and edge computing. Furthermore, the issue of accountability for illegal keys is crucial, as authorized users may actively disclose or sell authorization keys for personal gain, and keys may also passively leak due to management negligence or hacking incidents. Additionally, since all authorization keys are generated by the attribute authorization center, there is a potential risk of unauthorized key forgery. In response to these challenges, this paper proposes an efficient and accountable leakage-resistant scheme based on attribute encryption. The scheme adopts more secure online/offline encryption mechanisms and cloud server-assisted decryption to alleviate the computational burden on resource-constrained devices. For illegal keys, the scheme supports accountability for both users and the authorization center, allowing the revocation of decryption privileges for malicious users. In the case of passively leaked keys, timely key updates and revocation of decryption capabilities for leaked keys are implemented. Finally, the paper provides selective security and accountability proofs for the scheme under standard models. Efficiency analysis and experimental results demonstrate that the proposed scheme enhances encryption/decryption efficiency, and the storage overhead for accountability is also extremely low.

A comparative analysis of public key cryptographic algorithms: RSA, ELGamal, and elliptic curve encryption

Cryptography stands as an indispensable and efficient facet within the expansive field of information security. It offers a reliable method for ensuring the confidentiality and integrity of data during the complex process of information transmission between a sender and a recipient. Beyond this, exclusive decryption privileges are meticulously reserved for the designated recipient. This individual holds the exclusive authority to decipher the transmitted information, which has been encrypted by the key holder beforehand. This scholarly investigation introduces and delves into three prevalent cryptographic algorithms: RSA, El-Gamal, and Elliptic Curve Cryptography. It offers a discerning examination and contrast of the underlying mathematical challenges associated with each sophisticated method. The discourse unfolds a detailed comparative analysis of these three pivotal algorithms, zeroing in on their crucial aspects such as key size length and operational running time. The in-depth exploration within this study aims to shed light on the intricate workings, strengths, and potential limitations of RSA, El-Gamal, and Elliptic Curve Cryptography. By unraveling these aspects, the study contributes to a richer understanding and more informed choices in the practical application of cryptographic algorithms, enhancing the overarching realm of information security in an increasingly digital and interconnected world.

Secure access control using updateable attribute keys.

In the era of cloud computing, the technique of access control is vital to protect the confidentiality and integrity of cloud data. From the perspective of servers, they should only allow authenticated clients to gain the access of data. Specifically, the server will share a communication channel with the client by generating a common session key. It is thus regarded as a symmetric key for encrypting data in the current channel. An access control mechanism using attribute-based encryptions is most flexible, since the decryption privilege can be granted to the ones who have sufficient attributes. In the paper, the authors propose a secure access control consisting of the attributed-based mutual authentication and the attribute-based encryption. The most appealing property of our system is that the attribute keys associated with each user is periodically updatable. Moreover, we will also show that our system fulfills the security of fuzzy selective-ID assuming the hardness of Decisional Modified Bilinear Diffie-Hellman (DMBDH) problem.

TRAK-CPABE: A novel Traceable, Revocable and Accountable Ciphertext-Policy Attribute-Based Encryption scheme in cloud computing

Ciphertext Policy Attribute Based Encryption (CPABE) offers fine-grained access control in Cloud Computing environment. It is considered as the most promising one-to-many encryption mechanism. However, a Cloud user can delegate decryption privileges to unauthorized users for profits. The key abuse issue is not the only limit with this model for the reason that when the malicious user has been caught, it cannot be revoked. To address these problems, we propose a Traceable, Revocable, Accountable and Key-escrow free CPABE scheme (TRAK-CPABE). This solution supports white-box traceability and direct revocation. The main idea of this work is to divide the original data after publishing in cloud server. In the case of user revocation, one single slice is affected. Data owner needs to retrieve, re-encrypt and re-publish it. In addition, shared keys will be traced and conflict scenario will be resolved. More, the traceability of TRAK-CPABE depends on the l-Strong Diffie–Hellman (l-SDH) and Indistinguishability under chosen-plaintext attack (IND-CPA. The security of the proposed scheme is proved formally by using the Scyther tool. Furthermore, the experimental results show the efficiency of the proposed solution.

Comments on “Attribute-Based Data Sharing Scheme Revisited in Cloud Computing”

In this letter, we discuss the security weakness of Wang et al. ’s attribute-based data sharing scheme, in IEEE TRANSACTIONS ON INFORMATION FORENSICS AND SECURITY (TIFS) (DOI: 10.1109/TIFS.2016.2549004). Through designing two concrete attacks, we identify two serious security flaws in their scheme. 1) First, we show that their scheme is insecure because in their scheme any authenticated user can freely tamper with the weight of his own attribute to gain higher level decryption privilege to arbitrarily decrypt the ciphertext belonging to another user with higher weight of attribute. 2) Second, we further demonstrate that their scheme is trivial insecure because in their scheme even any malicious authenticated user’s attribute does not match the access policy of a ciphertext, he/she still has the power to decrypt the ciphertext, i.e., the decryption power is independent of attributes, thus, their scheme is not a rigorous attribute-based scheme. The two weaknesses discovered may hinder their scheme infeasible for practical deployment. Accordingly, we present a remedy solution to the issues while preserving all the security features of the original scheme. We hope that our cryptoanalysis and remedy scheme may contribute to avoiding similar design flaws in future designs.

A Traceable and Revocable Multiauthority Attribute-Based Encryption Scheme with Fast Access

Multiauthority ciphertext-policy attribute-based encryption (MA-CP-ABE) is a promising technique for secure data sharing in cloud storage. As multiple users with same attributes have same decryption privilege in MA-CP-ABE, the identity of the decryption key owner cannot be accurately traced by the exposed decryption key. This will lead to the key abuse problem, for example, the malicious users may sell their decryption keys to others. In this paper, we first present a traceable MA-CP-ABE scheme supporting fast access and malicious users’ accountability. Then, we prove that the proposed scheme is adaptively secure under the symmetric external Diffie–Hellman assumption and fully traceable under the q -Strong Diffie–Hellman assumption. Finally, we design a traceable and revocable MA-CP-ABE system for secure and efficient cloud storage from the proposed scheme. When a malicious user leaks his decryption key, our proposed system can not only confirm his identity but also revoke his decryption privilege. Extensive efficiency analysis results indicate that our system requires only constant number of pairing operations for ciphertext data access.

On Enabling Attribute-Based Encryption to Be Traceable Against Traitors

Abstract Attribute-based encryption (ABE) is a versatile one-to-many encryption primitive, which enables fine-grained access control over encrypted data. Due to its promising applications in practice, ABE schemes with high efficiency, security and expressivity have been continuously emerging. On the other hand, due to the nature of ABE, a malicious user may abuse its decryption privilege. Therefore, being able to identify such a malicious user is crucial towards the practicality of ABE. Although some specific ABE schemes in the literature enjoys the tracing function, they are only proceeded case by case. Most of the ABE schemes do not support traceability. It is thus meaningful and important to have a generic way of equipping any ABE scheme with traceability. In this work, we partially solve the aforementioned problem. Namely, we propose a way of transforming (non-traceable) ABE schemes satisfying certain requirements to fully collusion-resistant black-box traceable ABE schemes, which adds only $O(\sqrt{\mathcal{K}})$ elements to the ciphertext where ${\mathcal{K}}$ is the number of users in the system. And to demonstrate the practicability of our transformation, we show how to convert a couple of existing non-traceable ABE schemes to support traceability.

Cryptanalysis of RNZ, an identity-based fully anonymous broadcast encryption

Abstract An identity-based fully anonymous broadcast encryption ( IB-FAnoBE ) is a novel concept for transmitting confidential data to a group of users in which subscribed users’ outsider and insider anonymity are at primary concern. In this paper, we review one of the most efficient IB-FAnoBE , proposed by Ren, Niu and Zhang (RNZ), and show that their construction does not provide the main message indistinguishability security requirement of broadcast encryption. For this purpose, we exhibit that an unauthorized user can decrypt the encrypted content without having legitimate decryption privilege. Furthermore, we suggest some modifications to improve this scheme and construct a secure IB-FAnoBE .

Server-Aided Revocable Attribute-Based Encryption from Lattices

Attribute-based encryption (ABE) can support a fine-grained access control to encrypted data. When the user’s secret-key is compromised, the ABE system has to revoke its decryption privileges to prevent the leakage of encrypted data. Although there are many constructions about revocable ABE from bilinear maps, the situation with lattice-based constructions is less satisfactory, and a few efforts were made to close this gap. In this work, we propose the first lattice-based server-aided revocable attribute-based encryption (SR-ABE) scheme and thus the first such construction that is believed to be quantum resistant. In the standard model, our scheme is proved to be secure based on the hardness of the Learning With Errors (LWE) problem.

Practical traceable multi-authority CP-ABE with outsourcing decryption and access policy updation

Multi-authority ciphertext policy attribute-based encryption (CP-ABE) is one of the promising approaches where multiple authorities issue and manage various attributes to achieve fine-grained access control on stored data in cloud platforms. However, the practical use of multi-authority CP-ABE (MCP-ABE) requires satisfaction of different features. Firstly, in MCP-ABE, users having the same set of attributes must share the same decryption privileges. This may potentially lead to exposure of decryption keys by some malicious users. Thus, there is a need of designing MCP-ABE with traceability to overcome this problem. Secondly, as the cost of decryption increases with the complexity of access policy, it is preferred to provide the functionality of outsourcing decryption to reduce the computational burden on the user. Finally, the data owners must have flexibility to change the access policy. Hence, policy updation must be an integral part of MCP-ABE scheme. In this paper, we construct a new multi-authority CP-ABE scheme over large attribute universe with decentralization of authorities that supports white-box traceability along with policy updation and outsourcing decryption. Our proposed cryptosystem is built on prime order groups and supports monotonic access structures. These features improve efficiency and expressiveness of our system. We implemented our proposed cryptosystem in Charm cryptographic framework and analyzed its performance with a diverse set of test cases.

Black‐Box and Public Traceability in Multi‐authority Attribute Based Encryption

Ciphertext-policy Attribute-based encryption (CP-ABE) is a promising tool for implementing finegrained cryptographic access control. While the uniqueness of generating private keys brings extra security issues. The key escrow is inherent in CP-ABE systems because the trusted authority has the power to decrypt every ciphertext. The private keys are only associated with the attributes nor the user's identity. Some malicious users might be tempted to leak their decryption privileges for financial gain without the risk of being caught as the decryption privilege could be shared by multiple users who own the same set of attributes. We propose a new multiauthority CP-ABE with blackbox and public traceability, where the private keys are assigned by the cooperation between one central authority and multi-authorities. The performance and security analyses indicate that the proposed scheme is highly efficient and provably secure under the security model.

Updatable Ciphertext-Policy Attribute-Based Encryption Scheme With Traceability and Revocability

Ciphertext-policy attribute-based encryption (CP-ABE) can offer fine-grained access control over encrypted data, which is suitable for complex commercial applications. However, since the same decryption privileges could be shared by multiple users in the one-to-many encryption mechanism, it is dangerous that a malicious user misuses his secret key but cannot be traced. In addition to further security, when the malicious user has been caught, it is required to revoke him from the system. To address these problems, we propose a novel updatable CP-ABE scheme supporting white-box traceability and traitor revocation. In the proposed scheme, a “fixed point” is embedded into the user's secret key to achieving the traceability and each user is assigned with a unique identifier for revocation. Moreover, the secret exponent used to encrypt a message is divided into two parts: one is assigned to access policy and the other to the revocation list. Therefore, only a part of the ciphertext components needs to be updated when the revocation list is changed, which greatly simplifies the process of ciphertext update. Compared to the previous works, our scheme is more efficient, and can achieve valid revocation and ciphertext update. In addition, the traceability of the proposed scheme is depended on the l-Strong Difffie-Hellman assumption, and the indistinguishability security under selective access policy and chosen-plaintext attacks in the standard model is reduced to the Decisional q-Bilinear Diffie-Hellman assumption. Furthermore, the experimental results show that the proposed scheme is efficient.

Flexible Wildcard Searchable Encryption System

Searchable encryption is an important technique for public cloud storage service to provide user data confidentiality protection and at the same time allow users performing keyword search over their encrypted data. Previous schemes only deal with exact or fuzzy keyword search to correct some spelling errors. In this paper, we propose a new wildcard searchable encryption system to support wildcard keyword queries which has several highly desirable features. First, our system allows multiple keywords search in which any queried keyword may contain zero, one or two wildcards, and a wildcard may appear in any position of a keyword and represent any number of symbols. Second, it supports simultaneous search on multiple data owner's data using only one trapdoor. Third, it provides flexible user authorization and revocation to effectively manage search and decryption privileges. Fourth, it is constructed based on homomorphic encryption rather than Bloom filter and hence completely eliminates the false probability caused by Bloom filter. Finally, it achieves a high level of privacy protection since matching results are unknown to the cloud server in the test phase. The proposed system is thoroughly analyzed and is proved secure. Extensive experimental results indicate that our system is efficient compared with other existing wildcard searchable encryption schemes in the public key setting.

White-Box Traceable CP-ABE for Cloud Storage Service: How to Catch People Leaking Their Access Credentials Effectively

Ciphertext-policy attribute-based encryption (CP-ABE) has been proposed to enable fine-grained access control on encrypted data for cloud storage service. In the context of CP-ABE, since the decryption privilege is shared by multiple users who have the same attributes, it is difficult to identify the original key owner when given an exposed key. This leaves the malicious cloud users a chance to leak their access credentials to outsourced data in clouds for profits without the risk of being caught, which severely damages data security. To address this problem, we add the property of traceability to the conventional CP-ABE. To catch people leaking their access credentials to outsourced data in clouds for profits effectively, in this paper, we first propose two kinds of non-interactive commitments for traitor tracing. Then we present a fully secure traceable CP-ABE system for cloud storage service from the proposed commitment. Our proposed commitments for traitor tracing may be of independent interest, as they are both pairing-friendly and homomorphic. We also provide extensive experimental results to confirm the feasibility and efficiency of the proposed solution.

Traceable-then-revocable ciphertext-policy attribute-based encryption scheme

A traceable ciphertext-policy attribute-based encryption (T-CPABE) scheme can trace a malicious user, who may leak her/his decryption privilege to a third party for some benefits. However, even if the malicious user is traced, the existing schemes cannot revoke her/him from the cryptosystems. Thus, it is necessary to embed a revocation mechanism into a T-CPABE scheme in practice. In this paper, we propose a ciphertext-policy attribute-based encryption scheme with white-box traceability and direct user revocation. In the proposed scheme, the ciphertext is related to an access structure and a revocation list R. The secret key is associated with an attribute set and a user’s identity assigned a leaf node in a binary tree. The value of a leaf node is used to trace a malicious user. Once a malicious user is caught, her/his identity is added in the revocation list R. Only the ciphertext components associated with the revocation list R are updated according to the new revocation list R′, and the updated ciphertext can provide forward security. Therefore, a user can decrypt a ciphertext if and only if she/he is not in the revocation list and her/his attribute set satisfies the access policy, simultaneously. Furthermore, our scheme is proved to be secure under selective access policy and chosen-plaintext attacks based on the decisional q-bilinear Diffie–Hellman exponent hardness assumption in the standard model.

Large Universe CP-ABE With Whitebox Traceability

In a ciphertext-policy attribute-based encryption (CP-ABE) system, decryption keys are defined over attributes shared by multiple users. Traceability is the ability of ABE to trace the malicious users or traitors who intentionally leak the partial or modified decryption keys for profits. Nevertheless, due to the nature of CP-ABE, it is difficult to identify the original key owner from an exposed key since the decryption privilege is shared by multiple users who have the same attributes. In this paper, we propose a new CPABE system that supportstraceability of malicious users who leaked their decryption privileges.Thistraceable CP-ABE does not weaken the expressivenessor efficiency when compared with the most efficient conventional(non-traceable) CP-ABE systems. In our newsystems attributes need not be fixed at system setup,the attributes’ size is not polynomially bounded and thepublic parameters’ size does not grow linearly with thenumber of attributes.

White-Box Traceable Ciphertext-Policy Attribute-Based Encryption Supporting Flexible Attributes

Ciphertext-policy attribute-based encryption (CP-ABE) enables fine-grained access control to the encrypted data for commercial applications. There has been significant progress in CP-ABE over the recent years because of two properties called traceability and large universe, greatly enriching the commercial applications of CP-ABE. Traceability is the ability of ABE to trace the malicious users or traitors who intentionally leak the partial or modified decryption keys for profits. Nevertheless, due to the nature of CP-ABE, it is difficult to identify the original key owner from an exposed key since the decryption privilege is shared by multiple users who have the same attributes. On the other hand, the property of large universe in ABE enlarges the practical applications by supporting flexible number of attributes. Several systems have been proposed to obtain either of the above properties. However, none of them achieve the two properties simultaneously in practice, which limits the commercial applications of CP-ABE to a certain extent. In this paper, we propose two practical large universe CP-ABE systems supporting white-box traceability. Compared with existing systems, both the two proposed systems have two advantages: 1) the number of attributes is not polynomially bounded and 2) malicious users who leak their decryption keys could be traced. Moreover, another remarkable advantage of the second proposed system is that the storage overhead for traitor tracing is constant, which are suitable for commercial applications.

Traceable CP-ABE: How to Trace Decryption Devices Found in the Wild

In Ciphertext-policy attribute-based encrypt- ion (CP-ABE), ciphertexts are associated with access policies, which do not have to contain the identities of eligible receivers, and attributes are shared by multiple users. CP-ABE is useful for providing fine-grained access control on encrypted data. However, it also has a practicality concern that a malicious user, with his attributes shared with other users, might leak his decryption privilege as a decryption blackbox, for some financial gain or other incentives, as there is little risk of getting caught. There are two types of decryption blackboxes that reflect different practical scenarios. A key-like decryption blackbox is associated with an attribute set $S_{\cal D}$ and can decrypt ciphertexts with access policies satisfied by $S_{\cal D}$ . A policy-specific decryption blackbox is associated with an access policy $\mathbb {A}_{\cal D}$ and can decrypt ciphertexts with ${\mathbb {A}}_{\cal D}$ . Policy-specific decryption blackbox has weaker decryption capacity than key-like decryption blackbox, but tracing it is deemed to be more difficult. In the preliminary version (in CCS 2013) of this paper, we proposed a new CP-ABE scheme which is adaptively traceable against key-like decryption blackbox. The scheme has sublinear overhead, which is the most efficient one to date supporting fully collusion-resistant blackbox traceability. The scheme is fully secure in the standard model, and supports any monotonic access structures. In this paper, we further show that the scheme is also selectively traceable against policy-specific decryption blackbox. Furthermore, and more importantly, we prove a general statement that if a CP-ABE scheme is (selectively) traceable against policy-specific decryption blackbox, it is also (selectively) traceable against key-like decryption blackbox, which implies that we now only need to focus on building CP-ABE schemes which are traceable against policy-specific decryption blackbox.