The ISC International Journal of Information Security

Abstract The potential of Attribute-Based Encryption (ABE) in the context of IoT has driven researchers to propose pairing-free ABE schemes that are suitable for resource-constrained devices. Unfortunately, many of these schemes turned out to be insecure. This fact reinforces the view of some researchers according to which instantiating an Identity-Based Encryption (IBE) in plain Decisional Diffie-Hellman (DDH) groups is impossible. In this paper, we provide a generic Ciphertext-Policy ABE (CP-ABE) scheme supporting secret AND-gate policy using Inner-Product Functional Encryption (IPFE). We also propose an instantiation of our generic CP-ABE scheme based on the DDH assumption. From our generic CP-ABE scheme, we derive an IBE scheme by introducing the concept of Clustered Identity-Based Encryption (CIBE). Our schemes show that it is possible to construct secure IBE and ABE schemes based on the classical DDH assumption. An implementation of our CIBE in Python using the Charm framework is available on GitHub. 

Abstract Public key encryption with keyword search (PEKS) is a cryptographic primitive designed for performing secure search operations over encrypted data stored on untrusted cloud servers. However, in some applications of cloud computing, there is a hierarchical access-privilege setup among users so that upper-level users should be able to monitor data used by lower-level ones in the hierarchy. To support such situations, Wang et al. introduced the notion of hierarchical ID-based searchable encryption. However, Wang et al.'s construction suffers from a serious security problem. To provide a PEKS scheme that securely supports hierarchical structures, Li et al. introduced the notion of hierarchical public key encryption with keyword search (HPEKS). However, Li et al.'s HPEKS scheme is established on traditional public key infrastructure (PKI) which suffers from costly certificate management problem. To address these issues, in this paper, we consider designated-server HPEKS in identity-based setting. We introduce the notion of designated-server hierarchical identity-based searchable encryption (dHIBSE) and provide a formal definition of its security model. We then propose a dHIBSE scheme and prove its security under our model. Finally, we provide performance analysis as well as comparisons with related schemes to show the overall superiority of our dHIBSE scheme.

Abstract In the last two decades bilinear pairings have found many applications in cryptography. Meanwhile identity-based cryptosystems based on bilinear pairings have received particular attention. The IEEE, IETF, and ISO organizations have been working on standardization of pairing-based cryptographic schemes. The Boneh-Franklin identity-based encryption and Sakai-Kasahara identity-based signature are the most well-known identity-based schemes that have been standardized. So far, various schemes have been proposed to reduce the computational overhead of pairing operations. All these schemes are trying to outsource pairing operations in a secure manner. But besides pairing operations, there are other basic and costly operations in pairing-based cryptography and identity-based schemes, including scalar multiplication on elliptic curves. In this research, we outsource the Boneh-Franklin encryption in a more secure and efficient (in terms of computational and communication complexity) way than existing schemes. Also we outsource the BLMQ signature (based on Sakai-Kasahara) scheme for the first time. The proposed schemes are secure in the OMTUP model. Also, unlike previous schemes, we considered communication channels insecure. Moreover, compared with the trivial solution which outsources every single operation (such as pairing, scalar multiplication and modular exponentiation) as a separate subroutine, our schemes offer less complexity by seamlessly outsourcing the whole encryption scheme for the first time.