Because of the evolution of mobile devices and networks, users can now access a network at any moment, in whatever place with a smart card. User authentication using smart card is a technique in which server checks the legality of a user between insecure channel, which avoid the peril of eavesdropping. Today, the user authentication schemes are proposed several ways. As schemes are proposed and analyzed for several years, way to authentication is also diversifying such as chaotic map and elliptic curve discrete logarithm problem. Recently, new authentication scheme is proposed which uses Markov Chain. The proposed scheme is explained that can resist several hazard of security such as reflection attack, forgery attack, parallel-session attack. However, we refer that existing scheme is still insecure to protect some several security attack such as user impersonation attack, off-line password guessing attack, and so on, so the existing scheme is unsuitable for real implementation. To fix these security flaws, we recommend an efficient and robust authentication scheme, which protects all the identified flaws of existent scheme. Furthermore, our propose scheme is more efficient and covers the identified vulnerability of existing scheme; therefore, our proposed scheme is more suitable to apply real-life application. Copyright

Cloud computing is an emerging computing paradigm in which resources of the computing infrastructure are provided as outsourcing services through the Internet. With cloud computing technique, the users are able to outsource their computing and storage tasks to the cloud servers. In cloud computing environments, the user authentication is very important issue because it provides the authorization while users access their data and cloud services. In 2014, Chen et al. improved Choudhury et al.'s scheme, and claimed that their scheme is more secure and practical remote user authentication scheme for cloud computing. However, we find that Chen et al.'s scheme is still insecure against outsider attack, server impersonation attack, smart card stolen attack and off-line password guessing attack. To overcome this drawback, we propose a robust and more secure user authentication scheme. Finally, we show that our proposed scheme is more secure and supports security properties than Chen et al.'s scheme.

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The QR-Code authentication system using mobile application is easily implemented in a mobile device with high recognition rate without short distance wireless communication support such as NFC. This system has been widely used for physical authentication system does not require a strong level of security. The system also can be implemented at a low cost. However, the system has a vulnerability of tampering or counterfeiting, because of the nature of the mobile application that should be installed on the user's smart device. In this paper we analyze the vulnerabilities about each type of architectures of the system and discuss the concerns about the implementation aspect to reduce these vulnerabilities.

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