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.

Cloud storage services such as Dropbox [1] and Google Drive [2] are becoming more and more popular. On the one hand, they provide users with mobility, scalability, and convenience. However, privacy issues arise when the storage becomes not fully controlled by users. Although modern encryption schemes are effective at protecting content of data, there are two drawbacks of the encryption-before-outsourcing approach: First, one kind of sensitive information, Access Pattern of the data is left unprotected. Moreover, encryption usually makes the data difficult to use. In this paper, we propose AIS (Access Indistinguishable Storage), the first client-side system that can partially conceal access pattern of the cloud storage in constant time. Besides data content, AIS can conceal information about the number of initial files, and length of each initial file. When it comes to the access phase after initiation, AIS can effectively conceal the behavior (read or write) and target file of the current access. Moreover, the existence and length of each file will remain confidential as long as there is no access after initiation. One application of AIS is SSE (Searchable Symmetric Encryption), which makes the encrypted data searchable. Based on AIS, we propose SBA (SSE Built on AIS). To the best of our knowledge, SBA is safer than any other SSE systems of the same complexity, and SBA is the first to conceal whether current keyword was queried before, the first to conceal whether current operation is an addition or deletion, and the first to support direct modification of files.

Identity concealment and zero-round trip time (0-RTT) connection are two of current research focuses in the design and analysis of secure transport protocols, like TLS1.3 and Google's QUIC, in the client-server setting. In this work, we introduce a new primitive for identity-concealed authenticated encryption in the public-key setting, referred to as higncryption, which can be viewed as a novel monolithic integration of public-key encryption, digital signature, and identity concealment. We then present the security definitional framework for higncryption, and a conceptually simple (yet carefully designed) protocol construction. As a new primitive, higncryption can have many applications. In this work, we focus on its applications to 0-RTT authentication, showing higncryption is well suitable to and compatible with QUIC and OPTLS, and on its applications to identity-concealed authenticated key exchange (CAKE) and unilateral CAKE (UCAKE). Of independent interest is a new concise security definitional framework for CAKE and UCAKE proposed in this work, which unifies the traditional BR and (post-ID) frameworks, enjoys composability, and ensures very strong security guarantee. Along the way, we make a systematically comparative study with related protocols and mechanisms including Zheng's signcryption, one-pass HMQV, QUIC, TLS1.3 and OPTLS, most of which are widely standardized or in use.