To improve the security of user-chosen Android screen lock patterns, we propose a novel system-guided pattern lock scheme called "SysPal" that mandates the use of a small number of randomly selected points while selecting a pattern. Users are given the freedom to use those mandated points at any position. We conducted a large-scale online study with 1,717 participants to evaluate the security and usability of three SysPal policies, varying the number of mandatory points that must be used (upon selecting a pattern) from one to three. Our results suggest that the two SysPal policies that mandate the use of one and two points can help users select significantly more secure patterns compared to the current Android policy: 22.58% and 23.19% fewer patterns were cracked. Those two SysPal policies, however, did not show any statistically significant inferiority in pattern recall success rate (the percentage of participants who correctly recalled their pattern after 24 hours). In our lab study, we asked participants to install our screen unlock application on their own Android device, and observed their real-life phone unlock behaviors for a day. Again, our lab study did not show any statistically significant difference in memorability for those two SysPal policies compared to the current Android policy.

System-generated random passwords have maximum password security and are highly resistant to guessing attacks. However, few systems use such passwords because they are difficult to remember. In this paper, we propose a system-initiated password scheme called "Surpass" that lets users replace few characters in a random password to make it more memorable. We conducted a large-scale online study to evaluate the usability and security of four Surpass policies, varying the number of character replacements allowed from 1 to 4 in randomly-generated 8-character passwords. The study results suggest that some Surpass policies (with 3 and 4 character replacements) outperform by 11% to 13% the original randomly-generated password policy in memorability, while showing a small increase in the percentage of cracked passwords. When compared to a user-generated password complexity policy (that mandates the use of numbers, symbols, and uppercase letters) the Surpass policy with 4-character replacements did not show statistically significant inferiority in memorability. Our qualitative lab study showed similar trends. This Surpass policy demonstrated significant superiority in security though, with 21% fewer cracked passwords than the user-generated password policy.

We propose an effective pattern lock strength meter to help users choose stronger pattern locks on Android devices. To evaluate the effectiveness of the proposed meter with a real world dataset (i.e., with complete ecological validity), we created an Android application called EnCloud that allows users to encrypt their Dropbox files. 101 pattern locks generated by real EnCloud users were collected and analyzed, where some portion of the users were provided with the meter support. Our statistical analysis indicates that about 10% of the pattern locks that were generated without the meter support could be compromised through just 16 guessing attempts. As for the pattern locks that were generated with the meter support, that number goes up to 48 guessing attempts, showing significant improvement in security. Our recommendation is to implement a strength meter in the next version of Android.

Electronic door locks must be carefully designed to allow valid users to open (or close) a door and prevent unauthorized people from opening (or closing) the door. However, lock manufacturers have often ignored the fact that door locks can be modified by attackers in the real world. In this paper, we demonstrate that the most popular electronic door locks can easily be compromised by inserting a malicious hardware backdoor to perform unauthorized operations on the door locks. Attackers can replay a valid DC voltage pulse to open (or close) the door in an unauthorized manner or capture the user's personal identification number (PIN) used for the door lock.