Server-Aided Revocable Predicate Encryption: Formalization and Lattice-Based Instantiation

Efficient user revocation is a necessary but challenging problem in many multi-user cryptosystems. Among known approaches, server-aided revocation yields a promising solution, because it allows to outsource the major workloads of system users to a computationally powerful third party, called the server, whose only requirement is to carry out the computations correctly. Such a revocation mechanism was considered in the settings of identity-based encryption and attribute-based encryption by Qin et al. (ESORICS 2015) and Cui et al. (ESORICS 2016), respectively. In this work, we consider the server-aided revocation mechanism in the more elaborate setting of predicate encryption (PE). The latter, introduced by Katz, Sahai, and Waters (EUROCRYPT 2008), provides fine-grained and role-based access to encrypted data and can be viewed as a generalization of identity-based and attribute-based encryption. Our contribution is two-fold. First, we formalize the model of server-aided revocable predicate encryption (SR-PE), with rigorous definitions and security notions. Our model can be seen as a non-trivial adaptation of Cui et al.'s work into the PE context. Second, we put forward a lattice-based instantiation of SR-PE. The scheme employs the PE scheme of Agrawal, Freeman and Vaikuntanathan (ASIACRYPT 2011) and the complete subtree method of Naor, Naor, and Lotspiech (CRYPTO 2001) as the two main ingredients, which work smoothly together thanks to a few additional techniques. Our scheme is proven secure in the standard model (in a selective manner), based on the hardness of the Learning With Errors (LWE) problem.Comment: 24 page

Server-Aided Revocable Identity-Based Encryption from Lattices

Server-aided revocable identity-based encryption (SR-IBE), recently proposed by Qin et al. at ESORICS 2015, offers significant advantages over previous user revocation mechanisms in the scope of IBE. In this new system model, almost all the workloads on users are delegated to an untrusted server, and users can compute decryption keys at any time period without having to communicate with either the key generation center or the server. In this paper, inspired by Qin et al.’s work, we design the first SR-IBE scheme from lattice assumptions. Our scheme is more efficient than existing constructions of lattice-based revocable IBE. We prove that the scheme is selectively secure in the standard model, based on the hardness of the Learning with Errors problem. At the heart of our design is a “double encryption” mechanism that enables smooth interactions between the message sender and the server, as well as between the server and the recipient, while ensuring the confidentiality of messages

A Generic Construction of Revocable Identity-Based Encryption

Revocable identity-based encryption (RIBE) is an extension of IBE that supports a key revocation mechanism, which is important when deployed an IBE system in practice. Boneh and Franklin presented the first generic construction of RIBE, however, their scheme is not scalable where the size of key update is linear in the number of users in the system. Then, Boldyreva, Goyal and Kumar presented the first scalable RIBE where the size of key update is logarithmic in the number of users and linear in the number of revoked users. In this paper, we present a generic construction of scalable RIBE from any IBE in a black-box way. Our construction has some merits both in theory and in practice. We obtain the first RIBE scheme based on quadratic residuosity problem and the first adaptively secure RIBE scheme based on lattices if we instantiate the underlying IBE with IBE schemes from quadratic residuosity assumption and adaptively secure IBE from lattices, respectively. In addition, the size of public parameters and secret keys are the same as that of the underlying IBE schemes. In server-aided model, the overheads of communication and computation for receivers are the same as those of underlying IBE schemes. Furthermore, the storage overhead for key update in our scheme is constant (in the number of users) while it was linear in the number of users in previous works

Anonymous and Adaptively Secure Revocable IBE with Constant Size Public Parameters

In Identity-Based Encryption (IBE) systems, key revocation is non-trivial. This is because a user's identity is itself a public key. Moreover, the private key corresponding to the identity needs to be obtained from a trusted key authority through an authenticated and secrecy protected channel. So far, there exist only a very small number of revocable IBE (RIBE) schemes that support non-interactive key revocation, in the sense that the user is not required to interact with the key authority or some kind of trusted hardware to renew her private key without changing her public key (or identity). These schemes are either proven to be only selectively secure or have public parameters which grow linearly in a given security parameter. In this paper, we present two constructions of non-interactive RIBE that satisfy all the following three attractive properties: (i) proven to be adaptively secure under the Symmetric External Diffie-Hellman (SXDH) and the Decisional Linear (DLIN) assumptions; (ii) have constant-size public parameters; and (iii) preserve the anonymity of ciphertexts---a property that has not yet been achieved in all the current schemes

Revocable Identity-based Encryption from Codes with Rank Metric

In this paper, we present an identity-based encryption scheme from codes with efficient key revocation. Recently, in Crypto 2017, Gaborit et al. proposed a first identity-based encryption scheme from codes with rank metric, called RankIBE. To extract the decryption key from any public identity, they constructed a trapdoor function which relies on RankSign, a signature scheme proposed by Gaborit et al. in PQCrypto 2014. We adopt the same trapdoor function to add efficient key revocation functionality in the RankIBE scheme. Our revocable IBE scheme from codes with rank metric makes use of a binary tree data structure to reduce the amount of work in terms of key updates for the key authority. The total size of key updates requires logarithmic complexity in the maximum number of users and linear in the number of revoked users. We prove that our revocable IBE scheme is selective-ID secure in the random oracle model, under the hardness of three problems: the Rank Syndrome Decoding (RSD) problem, the Augmented Low-Rank Parity Check Code (LRPC+) problem, and the Rank Support Learning (RSL) problem

On Cryptographic Building Blocks and Transformations

Cryptographic building blocks play a central role in cryptography, e.g., encryption or digital signatures with their security notions. Further, cryptographic building blocks might be constructed modularly, i.e., emerge out of other cryptographic building blocks. Essentially, one cryptographically transforms the underlying block(s) and their (security) properties into the emerged block and its properties. This thesis considers cryptographic building blocks and new cryptographic transformations

Revocable Identity-Based Encryption from Lattices

In this paper, we present an identity-based encryption (IBE) scheme from lattices with efficient key revocation. We adopt multiple trapdoors from the Agrawal-Boneh-Boyen and Gentry-Peikerty-Vaikuntanathan lattice IBE schemes to realize key revocation, which in turn, makes use of binary-tree data structure. Using our scheme, key update requires logarithmic complexity in the maximal number of users and linear in the number of revoked users for the relevant key authority. We prove that our scheme is selective secure in the standard model and under the LWE assumption, which is as hard as the worst-case approximating short vectors on arbitrary lattices. Moreover, our key revocation techniques from lattices can be applied to obtain revocable functional encryption schemes in the similar setting

Revocable Hierarchical Attribute-based Signatures from Lattices

Attribute-based Signatures (ABS) allow users to obtain attributes from issuing authorities, and sign messages whilst simultaneously proving compliance of their attributes with a verification policy. ABS demands that both the signer and the set of attributes used to satisfy a policy remain hidden to the verifier. Hierarchical ABS (HABS) supporting roots of trust and delegation were recently proposed to alleviate scalability issues in centralised ABS schemes. An important yet challenging property for privacy-preserving ABS is revocation, which may be applied to signers or some of the attributes they possess. Existing ABS schemes lack efficient revocation of either signers or their attributes, relying on generic costly proofs.Moreover, in HABS there is a further need to support revocation of authorities on the delegation paths, which is not provided by existing HABS constructions. This paper proposes a direct HABS scheme with a Verifier-Local Revocation (VLR) property. We extend the original HABS security model to address revocation and develop a new attribute delegation technique with appropriate VLR mechanism for HABS, which also implies the first ABS scheme to support VLR. Moreover, our scheme supports inner-product signing policies, offering a wider class of attribute relations than previous HABS schemes, and is the first to be based on lattices, which are thought to offer post-quantum security