Provably secure group key management scheme based on proxy re-encryption with constant public bulletin size and key derivation time

The group key management is for a group manager to maintain a consistent group key for a dynamic group of members through a broadcast channel. In this paper we propose a group key management scheme based on a meta proxy re-encryption (PRE) scheme. In particular, we propose an RSA-based PRE scheme with special properties. It is the first RSA-based PRE scheme for group key management and has the desired properties of uni-directionality and multi-hop. In our group key management scheme, each group member holds just one secret auxiliary key and logN public auxiliary keys. The size of rekey messages for each group key update remains O(logN). Additionally, our scheme has some distinct features. Firstly, the size of the key update history is a constant O(N) no matter how many times of group key updates occur. Secondly, the computation time of computing the newest group key from the key update history is always O(logN) no matter how many group key updates are missed. This feature provides a practical solution for group key update when members go offline from time to time. Finally, the proposed scheme is immune to the collusion attack of other members.

To ensure private message exchange among the group members, it is desirable to construct secure and efficient group key management schemes. Moreover, these schemes are more versatile if they could support dynamic join or leave of group members. In IET Information Security 2014, Vijayakumar et al. have introduced such a group key management scheme with lightweight overheads in both computation and communication. And this scheme has been used as a building block in many cryptographic protocols afterwards. In this paper, the authors demonstrate that Vijayakumar's scheme suffers some potential security weaknesses. First, after participating in the group communications for some sessions, a group member may still be able to obtain the group key after it leaves the group, and this violates the claimed security property of forward secrecy. Second, some colluding group members may derive another group member's long term secret key, and obviously, this has more serious consequences. One of the main reasons for the existence of these attacks is that the security analyses in Vijayakumar's scheme are informal and they cannot cover the dynamic environment. To address this issue, the authors’ suggestion is that heuristic arguments of security are not adequate in the design of cryptographic protocols, but formal security definitions and proofs are required.

Key management schemes for secure group communications should satisfy two basic security requirements, backward secrecy and forward secrecy. Most of the prominent secure group key management schemes are shown to satisfy the basic security requirements considering passive attack model. In this paper, we analyze secure group key management schemes under active outsider attack model. In active outsider attack model, an adversary can compromise a legitimate user of the group. We show that some of the efficient tree based, non-tree based and proxy re-encryption based group key management schemes are not secure under active attack model. We evaluate the cost involved in making these schemes secure under active attack model. Also, we construct a secure version of these schemes and show that the schemes are secure under active outsider attack model.

Proxy re-encryption (PRE) allows a proxy to transform one ciphertext to another under different encryption keys while keeping the underlying plaintext secret. Because of the ciphertext transformability of PRE, there are many potential private communicating applications of this feature. However, existing PRE schemes are not as full-fledged as expected. The lack of necessary features makes them hard to apply in real-world scenarios. So far, there does not exist a unidirectional multihop PRE scheme with constant decryption efficiency and constant ciphertext size without extensions. Impractical performance and weak scalability also hinder PRE from most real-world applications. In this work, we present a new PRE scheme with secure hardware enclave named <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hPRESS</monospace> (hardware-enhanced PRE scheme using secure enclave). To the best of our knowledge, <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hPRESS</monospace> is the first unidirectional multihop PRE scheme which achieves both constant decryption efficiency and constant ciphertext size without extensions. A detailed security analysis demonstrates that our proposal is CCA secure based on the security of the underlying encryption schemes and the secure enclave. We also implement a prototype based on Intel SGX, one of the most popular secure enclave techniques in recent years, and evaluate its performance. The experimental results show that, compared with previous PRE schemes, our <monospace xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">hPRESS</monospace> is almost one order of magnitude faster in terms of the decryption and transformation.

The Near-Space Network has gotten more and more attentions and become a new research focus with the rapidly development of space information system recently. It is a large network with characteristics of high exposure, dynamic topology, heterogeneous network, etc. The requirement of security for group communications system is much stronger. A group key management scheme based on the hierarchical and domain structure of Near-Space Network is proposed. The proxy re-cryptography algorithm is used in the rekeying process, which solves the problem of a single point of failure thoroughly. Rekeying algorithm for group members' switching between domains is designed and can efficaciously reduce the rekeying overhead caused by switch actions of high speed nodes. The performance analysis shows that the proposed scheme is a secure and reliable group key management scheme for near-space network.

Outsourcing private data and heavy computation tasks to the cloud may lead to privacy breach as attackers (e.g., malicious outsiders or cloud administrators) may correlate any relevant information to penetrate information of their interests. Therefore, how to preserve cloud users' privacy has been a top concern when adopting cloud solutions. In this paper, we investigate the identity privacy problem for the proxy re-encryption, which allows any third party (e.g., cloud) to re-encrypt ciphertexts in order to delegate the decryption right from one to another user. The relevant identity information, e.g., whose ciphertext was re-encrypted to the ciphertext under whose public key, may leak because re-encryption keys and ciphertexts (before and after re-encryption) are known to the third party. We review prior anonymity (identity privacy) notions, and find that these notions are either impractical or too weak. To address this problem thoroughly, we rigorously define the anonymity notion that not only embraces the prior anonymity notions but also captures the necessary anonymity requirement for practical applications. In addition, we propose a new and efficient proxy re-encryption scheme. The scheme satisfies the proposed anonymity notion under the Squared Decisional Bilinear Diffie-Hellman assumption and achieves security against chosen ciphertext attack under the Decisional Bilinear Diffie-Hellman assumption in the random oracle model. To the best of our knowledge, it is the first proxy re-encryption scheme attaining both chosen-ciphertext security and anonymity simultaneously.We implement a prototype based on the proposed proxy re-encryption scheme and the performance study shows that it is efficient.

Proxy re-encryption is a cryptographic primitive proposed by Blaze, Bleumer and Strauss in 1998. It allows a user, Alice, to decide that in case of unavailability, one (or several) particular user, the delegatee, Bob, will be able to read her confidential messages. This is made possible thanks to a semi-trusted third party, the proxy, which is given by Alice a re-encryption key, computed with Alice’s secret key and Bob’s public key. This information allows the proxy to transform a ciphertext intended to Alice into a ciphertext intended to Bob. Very few constructions of proxy re-encryption scheme actually handle the concern that the original sender may not want his message to be read by Bob instead of Alice. In this article, we adapt the primitive of proxy re-encryption to allow a sender to choose who among the potential delegatees will be able to decrypt his messages, and propose a simple and efficient scheme which is secure under chosen plaintext attack under standard algorithmic assumptions in a bilinear setting. We also add to our scheme a traceability of the proxy so that Alice can detect if it has leaked some re-encryption keys.

With the proliferation of Internet of Things (IoT) devices that collect sensitive data, access control is more crucial than ever to safeguard IoT data from unauthorized use. To enforce access control policies without trusted online entity, one promising approach is to maintain a group key shared between a device and its current subscribers, such that the device can encrypt its data and only the subscribers can decrypt it. However, prior group key management (GKM) schemes fail to efficiently address new challenges introduced by the massive scale of IoT devices, dynamic memberships of users, and changes in the number of devices. This paper explores efficient GKM to accommodate multiple devices (in addition to multiple users) and to handle frequent membership and device number changes. Inspired by the observation that devices with similar functionalities often have similar access permissions, we propose a two-tier GKM architecture called GroupIt, in which each device is assigned to one of many predefined groups, and key management is performed within each group as well as between groups to improve efficiency. Despite being conceptually simple, GroupIt addresses technical challenges including: 1) preventing a malicious device from obtaining extra information about other devices in the same group and 2) ensuring forward/backward secrecy and preventing collusion attacks when gluing two existing GKMs together. The probability of a successful collusion attack quickly drops to 0.3% after five membership changes even in a small device group (e.g., 8). This paper provides both theoretical analysis and a proof-of-concept implementation based on Alljoyn, an opensource IoT communication framework to demonstrate the feasibility of GroupIt.

In this paper, an identity-based conditional proxy re-encryption (PRE) scheme is proposed, where a delegator provides a re-encryption key satisfying one condition to a semi-trusted proxy who can convert a ciphertext encrypted under the delegator’s public key into one that can be decrypted using the delegatee’s private key. We address the identity-based proxy re-encryption scheme, where the delegator and the delegatee request keys from a trusted party known as a key generator center (KGC), who generates private keys for delegator and delegatee based on their identities. Meanwhile, the identity-based conditional proxy re-encryption scheme satisfies the properties of PRE including unidirectionality, non-interactivity and multi-hop. Additionally, the identity-based conditional proxy re-encryption scheme is efficient in terms of both the communication cost and the computing cost, and can realize security secret sharing in cloud computing environments.

A string inverter converts the low voltage direct current coming from the string of its Photovoltaic (PV) panels into alternating current to be exported to the grid. In today Smart Grid’s context, PV plants feature clusters of cooperating smart string inverters that exchange information in a multicast fashion (typically) over the Internet Protocol (IP). However, IP multicast does not provide any mechanism to limit the access to multicast data to authorized subjects only. A security infringement may cause a cluster either into exporting no energy into the grid (zero energy attack) or more energy than the limit set (energy overflow attack). Both the attacks can lead to potential severe consequences. In this regard, we are the first addressing those issues. Particularly, we propose a Key Management Service (KMS) for group key generation and distribution. The KMS provides forward secrecy and periodic refresh. We implement a prototype on a cluster of Power-One Italy S.p.A. a member of FIMER Group smart string inverters and evaluate the performance. Experimental results indicate that the scheme scales up to clusters composed of 50 inverters with an efficiency of 90.5% in terms of latency for group key distribution and 99% in terms of memory overhead.

This paper reports on applicability of the Chinese Remainder Theorem (CRT) based Group Key Management (CRTGKM) for cloud environment. The results of our experiments confirm that the cloud environment group key management schemes known as ACV-BGKM and AB-GKM require high computation time for key update and key recovery processes. Therefore, to reduce the computational cost, a CRTGKM algorithm of multimedia multicast environment is applied to cloud environment based on applicability criteria. JAVA-based testbed was developed for simulation of performance of various group key management schemes and for estimation of the computation time for key update and key recovery processes.

HRA-secure attribute-based threshold proxy re-encryption from lattices

In a proxy re-encryption (PRE) scheme, a semi-trusted proxy is given special information that allows it to transform cipher texts encrypted under Alice's public key into the different cipher texts that can be decrypted by Bob's secret key. In 2006, Green and Ateniese proposed identity-based proxy re-encryption schemes, in which cipher texts are transformed from one identity to another. Based on this, we propose a new construction for certificate less proxy re-encryption scheme and the corresponding security model in this paper. The scheme is proved secure against chosen-plaintext attack in the random oracle model assuming that an underlying problem related to the Decisional Bilinear Diffie-Hellman problem is computationally hard.

Outsourcing heavy storage and computation to the cloud servers now becomes more and more popular. How to secure share the cloud storage is an important problem for many mobile users. Proxy re-encryption is such a cryptographic primitive which can be used to secure share cloud data. Until now there are many kinds of proxy re-encryption schemes with various properties, such as conditional proxy re-encryption, proxy re-encryption with keyword search etc. However until now there exists no work focus on proxy re-encryption for mobile cloud storage sharing. In mobile cloud storage, almost all the users are mobile ones, they only have resource-restricted equipments. In this paper we try to initialize this research, we give a very basic outsourced online/offline proxy re-encryption scheme for mobile cloud storage sharing and leave many interesting open problems as the future work.

The migration from wired network to wireless network has been a global trend in the past few decades because they provide anytime-anywhere networking services. The wireless networks are rapidly deployed in the future, secure wireless environment will be mandatory. As well, The mobility and scalability brought by wireless network made it possible in many applications. Among all the contemporary wireless networks,Mobile Ad hoc Networks (MANET) is one of the most important and unique applications. MANET is a collection of autonomous nodes or terminals which communicate with each other by forming a multihop radio network and maintaining connectivity in a decentralized manner. Due to the nature of unreliable wireless medium data transfer is a major problem in MANET and it lacks security and reliability of data. The most suitable solution to provide the expected level of security to these services is the provision of a key management protocol. A Key management is vital part of security. This issue is even bigger in wireless network compared to wired network. The distribution of keys in an authenticated manner is a difficult task in MANET. When a member leaves or joins the group, it needs to generate a new key to maintain forward and backward secrecy. In this paper, we propose a new group key management schemes namely a Hierarchical, Simple, Efficient and Scalable Group Key (HSESGK) based on clustering management scheme for MANETs and different other schemes are classified. Group members deduce the group key in a distributed manner.