Biblio

Cloud computing is a remarkable model for permitting on-demand network access to an elastic collection of configurable adaptive resources and features including storage, software, infrastructure, and platform. However, there are major concerns about security-related issues. A very critical security function is user authentication using passwords. Although many flaws have been discovered in password-based authentication, it remains the most convenient approach that people continue to utilize. Several schemes have been proposed to strengthen its effectiveness such as salted hashes, one-time password (OTP), single-sign-on (SSO) and multi-factor authentication (MFA). This study proposes a new authentication mechanism by combining user's password and modified characters of CAPTCHA to generate a passkey. The modification of the CAPTCHA depends on a secret agreed upon between the cloud provider and the user to employ different characters for some characters in the CAPTCHA. This scheme prevents various attacks including short-password attack, dictionary attack, keylogger, phishing, and social engineering. Moreover, it can resolve the issue of password guessing and the use of a single password for different cloud providers.

User authentication is an important security mechanism that allows mobile users to be granted access to roaming service offered by the foreign agent with assistance of the home agent in mobile networks. While security-related issues have been well studied, how to preserve user privacy in this type of protocols still remains an open problem. In this paper, we revisit the privacy-preserving two-factor authentication scheme presented by Li et al. at WCNC 2013. We show that, despite being armed with a formal security proof, this scheme actually cannot achieve the claimed feature of user anonymity and is insecure against offline password guessing attacks, and thus, it is not recommended for practical applications. Then, we figure out how to fix these identified drawbacks, and suggest an enhanced scheme with better security and reasonable efficiency. Further, we conjecture that under the non-tamper-resistant assumption of the smart cards, only symmetric-key techniques are intrinsically insufficient to attain user anonymity.