Studies On Public-key Cryptosystems With Special Features

With the rapid development of information technology, cloud computing and big data have already attracted a huge amount of interest. Advances in cloud computing and big data inevitably bring a problem, that is, how to protect data privacy and integrity.Public-key cryptosystems are suitable solutions to this problem. While in many realistic scenarios, such as fair exchange of digital signatures and the verifiability requirement of outsourced computation results, meeting just the requirement of protecting data privacy and integrity is often not enough. Fortunately, public-key cryptosystems with special features are very flexible and are able to meet these complex requirements.In this work, we focus on public-key cryptosystems with special features, and achieve the following results:1. Digital signatures protect data integrity. We focus on two lattice-based signature schemes with special features. First, we analyze a lattice-based proxy signature scheme, and point out its drawback. Next, we propose a latticed-based proxy signature scheme in the standard model. Last, we analyze a lattice-based multiparty concurrent signature scheme.2. We revisit the notion of separable identity-based encryption(IBE) and the transformation from separable identity-based encryption to CCA-secure public-key encryption(PKE), and then give an instantiation of separable IBE, which cannot be transformed into a CCA-secure PKE scheme via this transformation. We then introduce a more accurate cryptographic primitive, verifiable partitioned IBE, and give a refined generic transformation to CCA-secure public-key encryption from verifiable partitioned IBE. The same situations happen to the generic transformation from separable tag-based encryption(TBE) to PKE. We also give a similar cryptographic primitive, verifiable partitioned TBE, and then give a generic transformation to CCA-secure PKE from verifiable partitioned TBE.3. In IBE systems, revocation mechanism is of great importance and should be provided in an efficient manner. We propose a new approach to constructing an efficient revocable IBE scheme, and construct a concrete IBE scheme with efficient revocation from multilinear maps, which supports exponentially many identities. In our revocable IBE scheme, both the public parameters and the private key are constant-size. Simultaneously, the size of the update key at some time is only proportional to the number of revoked users at the time. In most cases, the number of revoked users is dramatically less than the total number of system users.4. Usually, users wants to verify the correctness of outsourcing computation done by an untrusted proxy. We propose generic constructions of CPA-secure and RCCA-secure ABE systems with verifiable outsourced decryption from CPAsecure ABE with outsourced decryption, respectively. We then, compared with the existing scheme, our selectively CPA-secure construction has more compact ciphertext and less computational costs. Moreover, the techniques involved in the RCCA-secure construction can be applied in generally constructing CCA-secure ABE, which we believe to be of independent interest.