This paper provide a brief survey of semantic similarity including semantic similarity between concepts and semantic textual similarity. We classify methods of semantic similarity between into four categories based on background information resource used and classify methods of semantic textual similarity into four categories too. As a basic methodology of text related research and applications, semantic similarity measure is often used in online social network analysis. This survey introduces how similarity computation methods assist in many aspects of social network analysis.

Mobile agent and its security are first introduced in this paper. Fundamental to the mentioned communication security properties are issues relating to the identification and authentication of sending and receiving parties. A security authentication scheme for mobile agent of multi domain is provided and a detail description is given in the paper. The scheme is based on identity-based public key cryptography, so as to overcome some shortage posed by traditional authentication model based on PKI. The security of the scheme is also analyzed and it shows that the proposed scheme is secure and effective.

In order to improve the accuracy of trust evaluation of subscribers (or key holders) from relying parties' point of view, a new model of trust degrees for PKI is proposed. By analyzing the security risks during the applying and using process of certificates and private keys, we introduce non-trust factor (NTF); then based on NTF, a method for trust degrees of keys is presented. Comparing with the existing work, the model integrates several critical factors which influence trust degrees of keys into one formula, thus improving the accuracy of trust evaluation for PKI and being applicable to a variety of PKI trust models.