Oblivious keyword search

The rapid development of information and communication technology has enabled more people to outsource and store their data on the networked databases. However, it brings challenges related to the data privacy and security. Our research focuses on the privacy in which the party who requests for a service discloses the minimum amount of personal information, whereas the party that offers data is able to ensure that only the requested data are revealed. Particularly, we focus on the mechanism searching for keywords on encrypted data. There are numbers of techniques that can be applied in the keyword search, such as public encryption with keyword search (PEKS), oblivious transfer (OT), private information retrieval (PIR), symmetric key encryption and homomorphic encryption. In this work, we consider PEKS, symmetric key encryptions and OT to perform oblivious keyword search. Our work can be summarized as follows. • Keyword search in designated senders. Most of current keyword search schemes only consider the keyword stored in the email gateway or database service providers. Hence, an off-line keyword guessing attack was developed to perform brute force attacks on a limited keyword space. An efficient solution is providing another element, for example, the sender’s identity, in the cipher-text in order to improve the security of encrypted keywords. This allows us to achieve a new cryptography primitive namely keyword search with designated signers. • Symmetric key encryption that provides a better security level than the other ones. The underlying principle of a symmetric key encryption is that the sender and the receiver must share the same secret key. We propose a construction based on the public key infrastructure that allows the sender and the receiver to exchange their public keys and construct a secret key. This scheme is based on a computable assumption that is more secure than the one based on decisional assumption. • Oblivious keyword search. The idea of oblivious keyword search is from the oblivious transfer (OT). The security of OT requires that both sender’s and receiver’s privacy are preserved. Therefore, from the privacy point of view, OT is suitable for enabling privacy of outsourced data. • Public key encryption with oblivious keyword search. Combining the notions of PEKS and OT, we propose an oblivious keyword search scheme. The new scheme achieves the properties of both PEKS and OT. We note that the combination is done in a non-trivial manner in order to ensure the security of the system

Provably secure proxy signature scheme from factorization

Proxy signature is a cryptographic primitive used for delegating the signing rights. The security of most existing proxy signature schemes is based on the complexity assumptions of discrete logarithms and the intractable problems of elliptic curves. While several proxy signature schemes from integer factorization were proposed, unfortunately they cannot resist against the attacks lunched by a malicious original signer or a malicious proxy signer. Hence, it is an interesting research problem on how to construct a provably secure proxy signature scheme based on factorization. In this paper, we propose a new construction of proxy signature whose security is reduced to the integer factorization problem in the random oracle model. We demonstrate that our scheme outperforms the other existing schemes in terms of security, computational efficiency and the length of the public key. Our scheme is the first provably secure proxy signature scheme from integer factorization

Risk Factors for Post-Transplant Death in Donation after Circulatory Death Liver Transplantation

Purpose: In spite of the increasing success of liver transplantation, there remains inevitable risk of postoperative complications, re-operations, and even death. Risk factors that correlate with post-transplant death have not been fully identified. Materials and Methods: We performed a retrospective analysis of 65 adults that received donation after circulatory death liver transplantation. Binary logistic regression and Cox's proportional hazards regression were employed to identify risk factors that associate with postoperative death and the length of survival period. Results: Twenty-two recipients (33.8%) deceased during 392.3 ± 45.6 days. The higher preoperative Child–Pugh score (p = .007), prolonged postoperative ICU stay (p = .02), and more postoperative complications (p = .0005) were observed in deceased patients. Advanced pathological staging (p = .02) with more common nerve invasion (p = .03), lymph node invasion (p = .02), and para-tumor satellite lesion (p = .01) were found in deceased group. The higher pre-transplant Child–Pugh score was a risk factor for post-transplant death (OR = 4.38, p = .011), and was correlated with reduced post-transplant survival period (OR = 0.35, p = .009). Nerve invasion was also a risk factor for post-transplant death (OR = 13.85, p = .014), although it failed to affect survival period. Conclusions: Our study emphasizes the impact of recipient's pre-transplant liver function as well as pre-transplant nerve invasion by recipient's liver cancer cells on postoperative outcome and survival period in patients receiving liver transplantation