Biblio

Order-revealing encryption (ORE) is a basic cryptographic primitive for ciphertext comparisons based on the order relationship of plaintexts while maintaining the privacy of them. In the data era we are experiencing, cross-dataset transactions become ubiquitous in practice. However, almost all the previous ORE schemes can only support comparisons on ciphertexts from the same user, which does not meet the requirement for the multi-user environment. In this work, we introduce and design ORE schemes with delegation functionality, which is referred to as delegatable ORE (DORE). The "delegation" here is an authorization that allows for efficient ciphertext comparisons among different users. To the best of our knowledge, it is the first ORE that allows an user to delegate the comparison privilege for his ciphertexts, which also opens the door for future explorations. At the heart of the construction and analysis of DORE is a new building tool proposed in this work, named delegatable equality-revealing encoding (DERE), which might be of independent interest.

With the widespread of cloud computing, the delegation of storage and computing is becoming a popular trend. Concerns on data integrity, security, user privacy as well as the correctness of execution are highlighted due to the untrusted remote data manipulation. Most of existing proposals solve the integrity checking and verifiable computation problems by challenge-response model, but are lack of scalability and reusability. Via blockchain, we achieve efficient and transparent public verifiable delegation for both storage and computing. Meanwhile, the smart contract provides API for request handling and secure data query. The security and privacy issues of data opening are settled by applying cryptographic algorithms all through the delegations. Additionally, any access to the outsourced data requires the owner's authentication, so that the dat transference and utilization are under control.

Certification of keys and attributes is in practice typically realized by a hierarchy of issuers. Revealing the full chain of issuers for certificate verification, however, can be a privacy issue since it can leak sensitive information about the issuer's organizational structure or about the certificate owner. Delegatable anonymous credentials solve this problem and allow one to hide the full delegation (issuance) chain, providing privacy during both delegation and presentation of certificates. However, the existing delegatable credentials schemes are not efficient enough for practical use. In this paper, we present the first hierarchical (or delegatable) anonymous credential system that is practical. To this end, we provide a surprisingly simple ideal functionality for delegatable credentials and present a generic construction that we prove secure in the UC model. We then give a concrete instantiation using a recent pairing-based signature scheme by Groth and describe a number of optimizations and efficiency improvements that can be made when implementing our concrete scheme. The latter might be of independent interest for other pairing-based schemes as well. Finally, we report on an implementation of our scheme in the context of transaction authentication for blockchain, and provide concrete performance figures.

We construct the first fully succinct garbling scheme for RAM programs, assuming the existence of indistinguishability obfuscation for circuits and one-way functions. That is, the size, space requirements, and runtime of the garbled program are the same as those of the input program, up to poly-logarithmic factors and a polynomial in the security parameter. The scheme can be used to construct indistinguishability obfuscators for RAM programs with comparable efficiency, at the price of requiring sub-exponential security of the underlying primitives. In particular, this opens the door to obfuscated computations that are sublinear in the length of their inputs. The scheme builds on the recent schemes of Koppula-Lewko-Waters and Canetti-Holmgren-Jain-Vaikuntanathan [STOC 15]. A key technical challenge here is how to combine the fixed-prefix technique of KLW, which was developed for deterministic programs, with randomized Oblivious RAM techniques. To overcome that, we develop a method for arguing about the indistinguishability of two obfuscated randomized programs that use correlated randomness. Along the way, we also define and construct garbling schemes that offer only partial protection. These may be of independent interest.

In recent years, the issues of RFID security and privacy are a concern. To prevent the tag is cloned, physically unclonable function (PUF) has been proposed. In each PUF-enabled tag, the responses of PUF depend on the structural disorder that cannot be cloned or reproduced. Therefore, many responses need to store in the database in the initial phase of many authentication protocols. In the supply chain, the owners of the PUF-enabled Tags change frequently, many authentication and delegation protocols are proposed. In this paper, a new lightweight authentication and delegation protocol for RFID tags (LADP) is proposed. The new protocol does not require pre-stored many PUF's responses in the database. When the authentication messages are exchanged, the next response of PUF is passed to the reader secretly. In the transfer process of ownership, the new owner will not get the information of the interaction of the original owner. It can protect the privacy of the original owner. Meanwhile, the original owner cannot continue to access or track the tag. It can protect the privacy of the new owner. In terms of efficiency, the new protocol replaces the pseudorandom number generator with the randomness of PUF that suitable for use in the low-cost tags. The cost of computation and communication are reduced and superior to other protocols.

When a user accesses a resource, the accounting process at the server side does the job of keeping track of the resource usage so as to charge the user. In cloud computing, a user may use more than one service provider and need two independent service providers to work together. In this user-centric context, the user is the owner of the information and has the right to authorize to a third party application to access the protected resource on the user's behalf. Therefore, the user also needs to monitor the authorized resource usage he granted to third party applications. However, the existing accounting protocols were proposed to monitor the resource usage in terms of how the user uses the resource from the service provider. This paper proposed the user-centric accounting model called AccAuth which designs an accounting layer to an OAuth protocol. Then the prototype was implemented, and the proposed model was evaluated against the standard requirements. The result showed that AccAuth passed all the requirements.