Semi-trusted Proxy Research Articles

Non-transferable Proxy Re-encryption

The traditional security notion of proxy re-encryption (PRE) focuses on preventing the proxy learning anything about the encrypted messages. However, such a basic security requirement is clearly not enough for scenarios where the proxy can collude with Bob. A desirable security goal is, therefore, to prevent a malicious proxy colluding with Bob to re-delegate Alice's decryption right. In 2005, Ateniese et al. first proposed this intriguing problem called non-transferability, in the sense that the only way for Bob to transfer Alice's decryption capability is to expose his own secret key. However, no solutions have achieved this property. In this paper, we positively resolve this open problem. In particular, we give the first construction of non-transferable PRE where the attacker is allowed to obtain one pair of keys consisting of Bob's secret key and the corresponding re-encryption key. Using indistinguishability obfuscation and k-unforgeable authentication as main tools, our scheme is provably secure in the standard model. The essential idea behind our approach is to allow Bob's secret key to be evoked in the process of decrypting Alice's ciphertext while hiding the fact that only Bob could decrypt it by the obfuscated program. In addition, we also show a negative result: a CPA secure PRE scheme with ‘error-freeness’ property cannot be non-transferable.

Revocable attribute-based access control in mutli-autority systems

Multi-authority attribute-based encryption is an encryption method which provides a distributed, flexible and fine-grained access control in untrustworthy environments. However, this method suffers from some shortcoming as revocation which is one of its major challenges. The revocation consists of banishing users from the system or some of their attributes to prevent them from getting access to the data. In literature, the most known solutions, as time-based solutions and proxy solutions, suggest to attribute an expiration time to users' keys or to naively rely on a semi-trusted proxy to revoke users. In the time-based solutions, the revocation is not immediate and the revoked users might continue to access the data until the next key regeneration phase, while proxy-based solutions do not achieve fine-grained access and the users cannot get access if the proxy goes offline. In this paper, we propose a novel and efficient revocation solution for decentralized attribute-based scheme. Our solution ensures flexible and fine-grained access control and prevents security degradations. Moreover, it performs immediate users or attributes revocation without any key regeneration or any changes on the users’ side, as well as it provides collusion resistance and supports scalability. Finally, we show through experimentation that our solution outperforms existing ones.

Secure sharing of mobile personal healthcare records using certificateless proxy re‐encryption in cloud

AbstractThe ubiquitous and timely access to personal health records help physicians to take critical decisions and save lives. Cloud computing has a potential to provide ubiquitous and on‐demand instant access to common pool of shared resources and services to various stakeholders involved in electronic healthcare industry such as patients, healthcare professionals, insurance companies, etc. The speedy evolution and adoption of cloud computing in electronic healthcare systems have inevitably raised concerns enveloping outsourced data in a myriad of safety issues. In this paper, cryptanalysis of Qin's scheme is performed breaching confidentiality of their scheme. We further proposed a lightweight and pairing free single‐hop unidirectional certificateless proxy re‐encryption scheme based on elliptic curves for secure sharing of mobile personal health records with public cloud competent for low‐power mobile devices. In certificateless proxy re‐encryption, patients encrypt the data with their public keys before outsourcing to the cloud and cloud resident semitrusted proxy further re‐encrypts into ciphertext under intended recipient's public key without learning anything about encrypted message. We prove its security through formal analysis against chosen ciphertext attack in the random oracle model. Our proposed scheme is more efficient and suitable for low‐power mobile devices in comparison with existing schemes.

Revocable identity-based proxy re-signature against signing key exposure.

Identity-based proxy re-signature (IDPRS) is a novel cryptographic primitive that allows a semi-trusted proxy to convert a signature under one identity into another signature under another identity on the same message by using a re-signature key. Due to this transformation function, IDPRS is very useful in constructing privacy-preserving schemes for various information systems. Key revocation functionality is important in practical IDPRS for managing users dynamically; however, the existing IDPRS schemes do not provide revocation mechanisms that allow the removal of misbehaving or compromised users from the system. In this paper, we first introduce a notion called revocable identity-based proxy re-signature (RIDPRS) to achieve the revocation functionality. We provide a formal definition of RIDPRS as well as its security model. Then, we present a concrete RIDPRS scheme that can resist signing key exposure and prove that the proposed scheme is existentially unforgeable against adaptive chosen identity and message attacks in the standard model. To further improve the performance of signature verification in RIDPRS, we introduce a notion called server-aided revocable identity-based proxy re-signature (SA-RIDPRS). Moreover, we extend the proposed RIDPRS scheme to the SA-RIDPRS scheme and prove that this extended scheme is secure against adaptive chosen message and collusion attacks. The analysis results show that our two schemes remain efficient in terms of computational complexity when implementing user revocation procedures. In particular, in the SA-RIDPRS scheme, the verifier needs to perform only a bilinear pairing and four exponentiation operations to verify the validity of the signature. Compared with other IDPRS schemes in the standard model, our SA-RIDPRS scheme greatly reduces the computation overhead of verification.

A New Kind of Conditional Proxy Re-Encryption for Secure Cloud Storage

Secure cloud storage has important applications in our big data-driven society, and to achieve secure cloud storage, we need to enforce strong access control mechanism. Proxy re-encryption (PRE) has been shown to be an effective tool of constructing cryptographically enforced access control schemes. In a traditional PRE scheme, a semi-trusted proxy can convert all ciphertexts for a delegator to ciphertexts for a delegatee once the proxy obtains the relevant re-encryption key from the delegator. In many practical applications, however, a fine-grained delegation of decryption abilities may be demanded, and thus, the notion of conditional PRE (C-PRE) is introduced, which allows only the ciphertexts satisfying a concrete condition to be converted by the proxy. In this paper, we introduce a special kind of C-PRE, sender-specified PRE (SS-PRE), which enables the delegator to delegate the decryption right of the ciphertexts from a specified sender to his/her delegatee. We give a formal definition of SS-PRE and its security model. We also provide the concrete constructions of an IND-CPA secure SS-PRE scheme and an IND-CCA secure SS-PRE scheme with the properties of unidirectionality and single-use and prove the security of both schemes in the standard model. The detailed analysis shows that our new IND-CCA secure SS-PRE scheme achieves a higher efficiency in computation cost and ciphertext size than the conventional C-PRE schemes.

Delegation of Decryption Rights With Revocability From Learning With Errors

The notion of decryption rights delegation was initially introduced by Blaze et al. in EUROCRYPT 1998. It, defined as proxy re-encryption , allows a semi-trusted proxy to convert a ciphertext intended for a party to another ciphertext of the same plaintext, without knowledge of the underlying plaintext and decryption key. It has been explored to many real-world applications, e.g., encrypted email forwarding. However, the intrinsic all-or-nothing share feature of proxy re-encryption yields a limitation that the share cannot be revoked. This may hinder the scalability of its applications in practice. In this paper, for the first time, we define the concept of revocability in terms of decryption rights delegation. The novel concept enables data owner to revoke the shared decryption rights when needed. Inspired by the seminal lattice-based proxy re-encryption proposed in PKC 2014, we design a concrete lattice-based construction which satisfies the notion. In our construction, we make use of binary-tree structure to implement the revocation of decryption rights, so that the update of re-encryption key is reduced to $O(logN)$ (instead of $O(N)$ ), where $N$ is the maximum number of delegatee. Furthermore, the security of our scheme is based on the standard learning with errors problem (LWE problem), which could be reduced to the worst-case hard problems (such as GapSVP and SIVP) in the context of lattices. The scheme is chosen ciphertext secure in the standard model. As of independent interest, our scheme achieves both backward and forward security, which means that once a user is revoked after a time period $\mathbf {t}$ , it cannot gain access to all encrypted files before and after $\mathbf {t}$ .

A proxy broadcast re-encryption for cloud data sharing

Proxy re-encryption (PRE) enables a semi-trusted proxy to automatically convert a delegator’s ciphertext to a delegate’s ciphertext without learning anything about the underlying plaintext. PRE schemes have broad applications, such as cloud data sharing systems, distributed file systems, email forward systems and DRM systems. In this paper, we introduced a new notion of proxy broadcast re-encryption (PBRE). In a PBRE scheme, a delegator, Alice, can delegate the decryption right to a set of users at a time, which means that Alice’s ciphertext can be broadcast re-encrypted. We propose a PBRE scheme and prove its security against a chosen-ciphertext attack (CCA) in the random oracle model under the decisional n-BDHE assumption. Furthermore, our scheme is collusion-resistant, which means the proxy cannot collude with a set of delegates to reveal the delegator’s private key.

Identity-based conditional proxy re-encryption with fine grain policy

An identity-based conditional proxy re-encryption scheme (IB-CPRE) allows a semi-trusted proxy to convert a ciphertext satisfying one condition, which is set by the delegator, under one identity to another without the necessity to reveal the underlying message. In ICISC 2012, Liang, Liu, Tan, Wong and Tang proposed an IB-CPRE scheme, and left an open problem on how to construct chosen-ciphertext secure IB-CPRE supporting OR gates on conditions. In this work, we answer this aforementioned problem by constructing an identity-based conditional proxy re-encryption scheme with fine grain policy (IB-CPRE-FG). In an IB-CPRE-FG scheme, each ciphertext is labeled with a set of descriptive conditions and each re-encryption key is associated with an access tree that specifies which type of ciphertexts the proxy can re-encrypt. Furthermore, our scheme can be proved secure against adaptive access tree and adaptive identity chosen-ciphertext attack.

A Searchable Hierarchical Conditional Proxy Re-encryption Scheme for Cloud Storage Services

As cloud technologies thrive, researches in the field of cloud storage have switched their focus from encryption-decryption techniques that help data owners protect their privacy and data confidentiality to the application of searching techniques on encrypted data while maintaining high level security and privacy of outsource data. To begin with, Song et al. offered some practical techniques for searches on encrypted data. After that, Weng et al. presented their conditional proxy re-encryption scheme where the data owner can decide which ciphertext satisfies a certain keyword condition set and then can have the retrieved data re-encrypted by the semi-trusted proxy server. The basic concepts of the above schemes are indeed quite innovative and do lead the way towards the solutions to the major practical cloud storage application problems; however, of all the researches that follow, none has had both searching on encrypted data and conditional proxy re-encryption combined. In this paper, we propose a new scheme for cloud storage services that integrates keyword search with conditional proxy re-encryption. This say, with a newly added keyword or new proxy, the cloud service provider is able to generate a hierarchical key. As far as data security is concerned, our scheme provides proven data owner authentication, re-delegation, and chosen-ciphertext security. The superior performance of the proposed scheme has been established by comparing it with related works, and our security analysis as well as BAN logic correctness check also offered solid proof that the new scheme is both secure and practical.DOI: http://dx.doi.org/10.5755/j01.itc.45.3.13224

On the security of two identity-based conditional proxy re-encryption schemes

Proxy re-encryption allows a semi-trusted proxy with a re-encryption key to convert a delegator's ciphertext into a delegatee's ciphertext, and the semi-trusted proxy cannot learn anything about the underlying plaintext. If a proxy re-encryption scheme is indistinguishable against chosen-ciphertext attacks, its initialized ciphertext should be non-malleable. Otherwise, there might exist an adversary who can break the chosen-ciphertext security of the scheme. Recently, Liang et al. proposed two proxy re-encryption schemes. They claimed that their schemes were chosen-ciphertext secure in the standard model. However, we find that the original ciphertext in their schemes are malleable. Thus, we present some concrete attacks and indicate their schemes fail to achieve chosen-ciphertext security in the standard model.

Efficient and Adaptively Secure Attribute-Based Proxy Reencryption Scheme

Ciphertext-Policy Attribute-Based Proxy Reencryption (CP-ABPRE) has found many practical applications in the real world, because it extends the traditional Proxy Reencryption (PRE) and allows a semitrusted proxy to transform a ciphertext under an access policy to the one with the same plaintext under another access policy. The existing CP-ABPRE schemes were proven secure only in the selective security model, a limited model, which is an unnatural constraint on the attacker. The scheme proved in this model can only be called selectively secure one. However, from a security perspective, the adaptively secure CP-ABPRE scheme is more desirable. In this paper, an adaptively secure CP-ABPRE scheme is proposed, which is based on Waters’ dual system encryption technology. The proposed scheme is constructed in composite order bilinear groups and proven secure under the complexity assumptions of the subgroup decision problem for 3 primes (3P-SDP). Analyses show that our proposal provides higher computational efficiency compared with the existing schemes.

Research on Non-interactive Construction based on Fuzzy Conditional Proxy Re-encryption

In a conditional proxy re-encryption (C-PRE) scheme, a semi-trusted proxy can transform Alice’s ciphertext into Bob’s ciphertext without learning the underlying plaintext, if the ciphertext satisfies a certain condition. To achieve more fine-grained delegation on conditions, Fang, Wang and Ge introduced the notion of fuzzy conditional proxy re-encryption (FC-PRE), whereby the conditions is viewed a set of descriptive

Collusion-Resistant Identity-Based Proxy Re-Encryption Without Random Oracles

In an identity-based proxy re-encryption scheme, a semi-trusted proxy can convert a ciphertext under Alice’s public identity into a ciphertext for Bob. The proxy does not know the secret key of Alice or Bob, and also does not know the plaintext during the conversion. In identity-based proxy re-encryption, the collusion of the proxy and a delegatee may result in the decryption of ciphertext for delegator. In this paper, we present a new scheme which can avoid the collusion of proxy and delegatee. Our scheme improves the scheme of Chu and Tzeng while inheriting all useful properties such as unidirectionality and non-interactivity. In our scheme, we get the security by using added secret parameter and change the secret key and re-encryption key. Our sheme is secure against ChosenCiphertext Attack (CCA) and collusion attack in the standard model.

Efficient Certificate-Based Proxy Re-encryption Scheme for Data Sharing in Public Clouds

Nowadays, public cloud storage is gaining popularity and a growing number of users are beginning to use the public cloud storage for online data storing and sharing. However, how the encrypted data stored in public clouds can be effectively shared becomes a new challenge. Proxy re-encryption is a public-key primitive that can delegate the decryption right from one user to another. In a proxy re-encryption system, a semi-trusted proxy authorized by a data owner is allowed to transform an encrypted data under the data owner’s public key into a re-encrypted data under an authorized recipient’s public key without seeing the underlying plaintext. Hence, the paradigm of proxy re-encryption provides a promising solution to effectively share encrypted data. In this paper, we propose a new certificate-based proxy re-encryption scheme for encrypted data sharing in public clouds. In the random oracle model, we formally prove that the proposed scheme achieves chosen-ciphertext security. The simulation results show that it is more efficient than the previous certificate-based proxy re-encryption schemes.

Secure bidirectional proxy re-encryption for cryptographic cloud storage

Bidirectional proxy re-encryption allows ciphertext transformation between Alice and Bob via a semi-trusted proxy, who however cannot obtain the corresponding plaintext. Due to this special property, bidirectional proxy re-encryption has become a flexible tool in many dynamic environments, such as cryptographic cloud storage. Nonetheless, how to design a secure and efficient bidirectional proxy re-encryption is still challenging. In this paper, we propose a new bidirectional proxy re-encryption scheme that holds the following properties: (1) constant ciphertext size no matter how many times the transformation is performed; (2) master secret security in the random oracle model, i.e., Alice (resp. Bob) colluding with the proxy cannot obtain Bob’s (resp. Alice’s) private key; (3) replayable chosen ciphertext (RCCA) security in the random oracle model. The above three properties are usually required in the cryptographic cloud storage. Furthermore, the proposed new master secret security may be of independent interest, as it is closer to the original desire: delegate the decryption rights while keeping the signing rights.

Secure Content Distribution Using Multi-hop Proxy Re-encryption

A proxy re-encryption (PRE) scheme allows a semi-trusted proxy to convert a ciphertext intended for some recipient, say Alice, into another ciphertext which can only be decrypted by the other desig...

Identity-based proxy re-signatures from lattices

Proxy re-signature is an important cryptographic primitive in which a semi-trusted proxy is able to transform a delegatee's signature on some message into a delegator's signature on the same message, while the proxy itself cannot generate any signatures for either the delegatee or the delegator. The existing proxy re-signature schemes in the literature all rely on the hardness assumptions that can be easily solved by quantum algorithms. In this paper we present an identity-based proxy re-signature scheme from lattice assumptions. The scheme supports multi-use bidirectional conversion, and is provably secure in the random oracle model under conventional small integer solution assumption that is as hard as approximating several standard lattice problems. As the underlying lattice problems are intractable even for quantum computers, our scheme would work well in the quantum age.

A Novel Proxy Re-Encryption with Keyword Search

In this paper, a novel proxy re-encryption (PRE) scheme with keyword search is proposed, where only the ciphertext containing the keyword set by the delegator can be transformed by the semi-trusted proxy and then decrypted by delegatee. In the proposed scheme, the semi-trusted proxy can convert the ciphertext encrypted under the delegator’s public key into the ciphertext encrypted under the delegatee’s public key. In addition, only the delegatee’s email gateway with a trapdoor can test whether or not a given cipheretext containing some keyword, but can learn nothing else about the sensitive data of email. We proposed an identity-based proxy re-encryption with keyword search scheme, where the delegator and the delegatee extract keys from a trusted party called the key generator center (KGC), who generates public-private key pair for delegator and delegatee based on their identities. Meanwhile, the identity-based proxy re-encryption with keyword search scheme satisfies the properties of PRE including unidirectionality, multi-use and transparency. Additionally, the proposed scheme is efficient in terms of both computation and communication, and can realize security privacy preserving in cloud computing environments.

Efficient and provably-secure certificateless proxy re-encryption scheme for secure cloud data sharing

In current cloud computing system, large amounts of sensitive data are shared to other cloud users. To keep these data confidentiality, data owners should encrypt their data before outsourcing. We choose proxy reencryption (PRE) as the cloud data encryption technique. In a PRE system, a semi-trusted proxy can transform a ciphertext under one public key into a ciphertext of the same message under another public key, but the proxy cannot gain any information about the message. In this paper, we propose a certificateless PRE (CL-PRE) scheme without pairings. The security of the proposed scheme can be proved to be equivalent to the computational Diffie-Hellman (CDH) problem in the random oracle model. Compared with other existing CL-PRE schemes, our scheme requires less computation cost and is significantly more efficient. The new scheme does not need the public key certificates to guarantee validity of public keys and solves the key escrow problem in identity-based public key cryptography.

An Identity-Based Conditional Proxy Re-Encryption in Cloud Computing Environments

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.