30-10-2012, 04:28 PM
A New Graphical Password Scheme Resistant to Shoulder-Surfing
A New Graphical Password.pdf (Size: 381.99 KB / Downloads: 36)
A Shoulder- Resistant.pdf (Size: 175.53 KB / Downloads: 87)
Abstract
Shoulder-surfing is a known risk where an attacker
can capture a password by direct observation or by recording
the authentication session. Due to the visual interface, this
problem has become exacerbated in graphical passwords.
There have been some graphical schemes resistant or immune
to shoulder-surfing, but they have significant usability
drawbacks, usually in the time and effort to log in. In this
paper, we propose and evaluate a new shoulder-surfing
resistant scheme which has a desirable usability for PDAs. Our
inspiration comes from the drawing input method in DAS and
the association mnemonics in Story for sequence retrieval. The
new scheme requires users to draw a curve across their
password images orderly rather than click directly on them.
The drawing input trick along with the complementary
measures, such as erasing the drawing trace, displaying
degraded images, and starting and ending with randomly
designated images provide a good resistance to shouldersurfing.
A preliminary user study showed that users were able
to enter their passwords accurately and to remember them
over time.
INTRODUCTION
Graphical passwords have been proposed as a useful
authentication method for Personal Digital Assistants (PDAs)
which are increasingly used with their small size, compact
deployment and low cost [1]. Given the fact that pictures are
generally easier to remember than words [2, 3] and that
humans are the ‘weakest link’ in any password
authentication mechanism [4-6], it is conceivable that
graphical passwords would be able to provide a good tradeoff
between usability and security.
However, most of the current graphical password
schemes are vulnerable to shoulder-surfing [7-10], a known
risk where an attacker can capture a password by direct
observation or by recording the authentication session. Due
to the visual interface, shoulder-surfing becomes an
exacerbated problem in graphical passwords. Several
approaches have been developed to deal with this problem,
but they have significant usability drawbacks, usually in the
time and effort to log in, making them less suitable for
everyday authentication [11-13]. For example
RELATED WORKS
The trend toward a highly mobile workforce and the
ubiquity of graphical interfaces (such as the stylus and touchscreen)
has enabled the emergence of graphical
authentications in PDAs. According to the memory task
involved in remembering and entering the password,
graphical passwords can be divided into three general
categories: recall-based systems, cued-recall systems and
recognition-based systems [13, 14].
DAS is the first recall-based graphical password scheme
in which the password is a free-form picture drawn on a 2D
grid [7]. This scheme releases users from remembering
complex text string and has a large theoretical password
space. But the drawing rules are difficult to follow, resulting
in a usability problem. For example, users cannot locate
strokes too close to a grid-line or cross a corner. To solve
this issue, Pass-Go (named after an ancient board game Go)
is proposed which allows users to draw their password using
grid intersection points instead of grid cells in DAS [15].
Another modification to DAS is YAGP [24] where
approximately correct drawing can be accepted by dividing
“trend quadrants” and adopting Levenshtein distance string
matching.
Cued-recall systems typically require users to remember
and target specific locations within a presented image. A
well-known scheme in this category is PassPoints which has
attracted great attention [10]. In this scheme, users should
choose several points on an image and click orderly on them
within a tolerance for authentication. Security analyses find
it vulnerable to hotspots and simple patterns within images
[13, 17, 18]. A commercial version of PassPoints for the
PocketPC is available from visKey for screen-unlock [16].
OUR SCHEME
The proposed shoulder-surfing resistant scheme can be
considered as an improvement of Story, as it keeps most of
the advantage of Story and achieves stronger security. Like
Story, our scheme is based on recognition, an easier memory
task than recall [21, 22], and suggests users to create a story
for sequence retrieval. Instead of direct input, it depends on
users drawing a curve across their password images (passimages)
in order. The curve containing both pass-images and
decoys guards against shoulder-surfing attacks by human
observation. Using a drawing input method, our scheme is
designed to empower users to log in their mobile devices
quickly. The following paragraphs describe the design and
present a prototype.
Methodology
To discuss the usability of CDS, we invited twenty
university students (10 males and 10 females) to our lab.
They were in the age range of 20 to 30 and none of them
were familiar with graphical password schemes. We
conducted a between-subjects design to benchmark the
usability against that of Story [9]. So, half of the subjects
were assigned to the CDS group (using the prototype of CDS)
and half to the control group (using Story with the identical
deployment in Figure 3). For both group, each participant
was required to select five images as his/her pass-images.
Participants carried out the usability study individually in
two sessions, an initial session (session 1) and a follow-up
session (session 2) one week later.
CONCLUSION
In this paper, a new shoulder-surfing resistant scheme
CDS was proposed. It adopts a visual login technique that
matches the capabilities and limitations of most handheld
devices and provides a simple and intuitive way for users to
authenticate. As such, it is an example of “usable security”.
The main contribution is that it overcomes a drawback of
recall-based systems by erasing the drawing trace and
introduces the drawing method to a variant of Story to resist
shoulder-surfing. Usability testing of the CDS scheme
showed that users were able to enter their passwords
accurately and to remember them over time. In the first ten
successful login, it took participants about 13.7 seconds to
log in CDS at average and there was a gentle downward
trend in time to input the password. One week later, all the
participants recalled their CDS passwords correctly and
spent approximately 19.8 seconds recalling and logging in.