# Enhancing the Security of Pattern Unlock with Surface EMG-Based Biometrics
## 2 Related Work  
### Improving the Security of Pattern Unlock  
There are a number of schemes which have been proposed up to now to improve the security of pattern unlock. To defend against smudge attacks, [PERSON] et al. [9] proposed TinyLock, an affordable defense against smudge attacks. They made the size of the pattern grid very small and introduced a virtual wheel to wipe off the actual smudge. However, due to the tiny size grid, it has several drawbacks. Because the grid dots are not visible to the users, the error rate is very high, and it is very difficult to draw complex patterns. Concepts where the position of the pattern grid is translated to a different position, scale, and rotation on the screen for each unlock attempt have been explored by [PERSON] et al. [10] and [PERSON] et al. [11]. However, they reported that users experienced difficulty in locating the grid due to its varying location. M-Pattern is a scheme which was proposed in [12] that employs multiple patterns to unlock the screen. The system randomly pick a pattern that can be inferred by the user from a visual cue, such as a background image. Since the smudges created by M-Pattern overlapped with each other, it was much harder for the attackers to recover the patterns compared with pattern unlock. The usability of the M-Pattern is compromised due to the memorization of multiple patterns by the user.  
Besides smudge attacks, there are schemes proposed to defend against other attacks. [PERSON] et al. [13] proposed a shoulder-surfing-resistant scheme that uses a pass pattern of pattern unlock. The scheme utilizes challenge-and-response authentication and the user's short-term memory. In [14], a scheme called Pass-O was proposed, which employs a circular layout of the grid. Pass-O has a pattern space almost 2.5 times larger than pattern unlock, which makes it harder for guessing attacks. [PERSON] et al. [15] proposed a multi-layered drawing lock mechanism which greatly increases the pattern space compared with pattern unlock. Warp cells at the corners of the grid enable more complex patterns by using multiple layers. For example, when a warp cell is touched as part of pattern entry, a second empty grid layer is displayed, obscuring the original grid layer, on which the pattern entry can continue.  
Some other schemes were also proposed to improve the security by encouraging users to create more complex patterns. [PERSON] et al. [16] proposed a formula to calculate the pattern strength quantitatively.  
The quantitative strength score is displayed through a pattern strength meter when the user creates a pattern. Their study showed that users created more complex patterns with the help of a pattern strength meter. TinyPal is an enhanced interface proposed in [17] for pattern unlock, which highlights the set of available dots that can be connected from the currently connected dot. TinyPal helps users create patterns containing more visual features, like overlaps and knight moves, to resist attacks. Their experimental results showed that users created more secure patterns using TinyPal than those using the original interface.