Email spam is a critical problem to the Internet for a long time. The average amount of spam mail reached 72.1% of all email traffic in the world in 2012. The greatest threat to the email service providers was the spam mail sent from botnet, because the spam mail sent from botnet was accounting for more than 78% in 2011; therefore appeared many anti-spam solutions and techniques that were focus on the botnet. Owing to these anti-spam techniques, botnet spam is not effective as before. Spammers are finding new way to send the spam mail. One of the effective methods is using compromised accounts (or bot accounts) to send the spam mail because compromised accounts have good reputation IP addresses and compromised accounts send the spam mail with complete SMTP implemented server, such as Gmail, Yahoo!Mail, and Microsoft Live Mail. The spam mail send form compromised accounts are very difficult to be detected by any anti-spam techniques. Hence, we focus on the features spammers cannot easily hide. According to our research we find that normal users usually do not reply to the spam mail. Moreover, our empirical analysis reveals that the compromised account actually have low reply rate. We develop a system called “Hawkeye” that can find the compromised accounts effectively by checking the account's reply rate.

Text passwords have been used in authentication systems for many decades. Users must recall the textual strings selected during registration to pass authentication. However, there are some serious problems with text passwords---recollection and security. Hence, various graphical-password authentication systems have been proposed to solve the problems of text passwords. Previous studies indicate that humans are better at recognizing and recalling images than texts. In 2005, Wiedenbeck et al. proposed PassPoints in which a password consists of a sequence of click-points (5 to 8) that a user chooses on an image. In the paper, we proposed an alternative system in which users can memorize fewer points while providing more security than PassPoints. Based on the idea of using an extremely large image as the password space, we propose a novel world map based graphical-password authentication system called PassMap in which a password consists of a sequence of 2 click-points that a user selects on an large world map. We also conducted a user study for evaluation. The result shows that the passwords of PassMap are easy to memorize for humans and PassMap is friendly to use in practice. Furthermore, PassMap provides higher entropy than PassPoints and also increases the cost of attacks.

Text password is the most popular form of user authentication on websites due to its convenience and simplicity. However, users' passwords are prone to be stolen and compromised under different threats and vulnerabilities. Firstly, users often select weak passwords and reuse the same passwords across different websites. Routinely reusing passwords causes a domino effect; when an adversary compromises one password, she will exploit it to gain access to more websites. Second, typing passwords into untrusted computers suffers password thief threat. An adversary can launch several password stealing attacks to snatch passwords, such as phishing, keyloggers and malware. In this paper, we design a user authentication protocol named oPass which leverages a user's cellphone and short message service to thwart password stealing and password reuse attacks. oPass only requires each participating website possesses a unique phone number, and involves a telecommunication service provider in registration and recovery phases. Through oPass, users only need to remember a long-term password for login on all websites. After evaluating the oPass prototype, we believe oPass is efficient and affordable compared with the conventional web authentication mechanisms.

Establishing trust between a group of individuals remains a difficult problem. Prior works assume trusted infrastructure, require an individual to trust unknown entities, or provide relatively low probabilistic guarantees of authenticity (95 percent for realistic settings). This work presents SPATE, a primitive that allows users to establish trust via mobile devices and physical interaction. Once the SPATE protocol runs to completion, its participants' mobile devices have authentic data that their applications can use to interact securely (i.e., the probability of a successful attack is 2-24). For this work, we leverage SPATE as part of a larger system to facilitate efficient, secure, and user-friendly collaboration via e-mail, file-sharing, and text messaging services. Our implementation of SPATE on Nokia N70 smartphones allows users to establish trust in small groups of up to eight users in less than one minute. The example SPATE applications provide increased security with little overhead noticeable to users once keys are established.

With the rapid development of wireless communication, mobile users are able to manually switch their network interfaces to different types of networks. The IEEE 802.21 Draft Standard was proposed to integrate the Media Independent Handover (MIHs) between the wireless network interfaces, such as WiFi, WiMAX, 3GPP, and 3GPP2. However, it may not hold the seamless roaming character and does not provide the security mechanism.In this paper, we propose an efficient handover mechanism among WiFi and WiMAX networks to meet the seamless roaming character by reducing the authentication processes. In addition, the proposed scheme involves security mechanisms that guarantee the handover messages to be secure and maintain the authenticity for the reduced steps.