Certificate-based encryption was introduced in Eurocrypt'03 to solve the certificate management problem in public key encryption. Recently, this idea was extended to certificate-based signatures. Several new schemes and security models of certificate-based signatures have been proposed. In this paper, we first take a closer look at the certificate-based signature by comparing it with digital signatures in other popular public key systems. We introduce a new security model of certificate-based signature, which defines several new types of adversaries against certificate-based signatures, along with the security model of certificate-based signatures against them. The new model is clearer and more elaborated compared with other existing ones. We then investigate the relationship between certificate-based signatures and certificateless signatures, and propose a generic construction of certificate-based signatures. We prove that the generic construction is secure (in the random oracle model) against all types of adversaries defined in this paper, assuming the underlying certificateless signatures satisfying certain security notions. Based on our generic construction, we are able to construct new certificate-based signature schemes, which are more efficient in comparison with other schemes with similar security levels.

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Whale shark Rhincodon typus is a globally distributed species, but there is a lack of knowledge pertaining to their biology, seasonal occurrence, and distribution in the northern Gulf of Mexico (NGOM). Understanding critical habitat for whale sharks is essential on both a regional and global basis for proper management because of their large migratory range. The goal of the present study was to describe the regional distribution of whale shark feeding aggregations in the NGOM by exploiting a presence-only dataset collected as a part of a volunteer sighting survey. Whale shark aggregations have been documented in large numbers in the NGOM since 2003, and species distribution models provide a unique approach to analyzing these presence data. We used maximum entropy and ecological niche factor analysis, 2 algorithms designed for predicting species distribution based only on presence data, to analyze data for the summer period in 2008 and 2009. Cohen's kappa (kappa) and the 'area under the receiver operating characteristic curve' (AUC) were used to evaluate model performance with an external testing dataset. Kappa values ranged from 0.28 to 0.69, and AUC values ranged from 0.73 to 0.80, indicating that the predicted distribution had a fair to substantial agreement with the testing data. Distance to continental shelf edge, distance to adjacent petroleum platforms, and chlorophyll a were the variables most strongly related to whale shark sightings, likely due to an association of these variables with high food availability. Suitable habitat was predicted along the continental shelf edge, with the most suitable habitat predicted south of the Mississippi River Delta. The spatial distribution of suitable habitat is dynamic; therefore, a multi-year study is underway to better delineate temporal trends in regional whale shark distribution and to identify consistent areas of high suitability. Presenceonly habitat models are a powerful tool for delineating important regional habitat for a vulnerable, highly migratory species.

We present a study of security in certificateless signatures. We divide potential adversaries according to their attack power, and for the first time, three new kinds of adversaries are introduced into certificateless signatures. They are Normal Adversary, Strong Adversary and Super Adversary (ordered by their attack power). Combined with the known Type IAdversary and Type IIAdversary in certificateless cryptography, we then define the security of certificateless signatures in different attack scenarios. Our new security models, together with others in the literature, provide a clear definition of the security in certificateless signatures. Two concrete schemes with different security levels are also proposed in this paper. The first scheme, which is proven secure (in the random oracle model) against Normal Type I and Super Type II adversaries, has the shortest signature length among all known certificateless signature schemes. The second scheme is secure (in the random oracle model) against Super Type I and Type II adversaries. Compared with another scheme that has a similar security level, our second scheme requires less operational cost but a little longer signature length. Two server-aided verification protocols are also proposed to reduce the verification cost on the verifier.