Android Security Model: Analysis and Improvements

A study of the Android security
model and what has been done to
improve it
David Armenteros Martı́nez
Fakulteta za elektrotehniko, računalništvo in informatiko, Univerza v Mariboru
Email: [email protected]
Smartphones are used by billions of people that means the applications of the
smartphone is increasing, it is out of control for applications market places to
completely validate if an application is malicious or legitimate. Furthermore, it
is up to users to choose for themselves whether an app is safe in terms of use or
not. It is important to say that there are some differences among mobile devices
and PC machines in resource management mechanisms, the security solutions
for computer malware are not compatible with mobile devices. So, it’s a fact
that the use of smartphones is on the rise. Day by day our dependence on
these devices is greater and therefore the information they store is increasingly
critically. As a consequence, security requirements are increasing and mobile
application development platforms must begin to offer certain guarantees. This
article is focused on studying the security guarantees offered by Android through
its security model. It is also shown a study of the works that identify some of the
shortcomings of this model and improve it in certain aspects.
Keywords: Android; Information Security; Smartphones; Operative Systems
1.
INTRODUCTION
Android is an operating system for mobile applications
created by Google that has had a great growth since
its launch in 2008. It is built on the Linux kernel
from which it inherits certain security capabilities, in
addition to implementing its own mechanisms that
facilitate the development of applications up to certain
point for sure. However, the fact that Android is an
open-source platform and that developing applications
for that operating system is so simple, makes building
malicious applications easy. Therefore, current security
mechanisms are not sufficient and user information
is vulnerable. There is currently a whole research
community dedicated to finding mechanisms to reduce
Android security vulnerabilities. Thanks to this, you
can find several research articles that study the security
model of this operating system, identifying its strengths
and weaknesses. In addition, there are other works
that go further and propose mechanisms to increase
the security levels of users’ information. In this article,
an analysis is done regarding to the Android security
model from a perspective not only of architecture but
also of the security risk mitigation program proposed by
the Android team. Subsequently, the article proposes a
study of related works that allows the reader to get an
idea of where we are in this particular research topic.
The rest of this article is organized like this: In
the section two there is a description of the Android
operating system in terms of its impact on the market
and its architecture. In the section 3 it is shown
what the Android security model is like and what its
strengths and limitations are. In the section 4 there
is a list of relevant related works and how they have
contributed to overcoming these security limitations.
Finally, in the section 5, the article is concluded.
2.
ANDROID OPERATING SYSTEM
Throughout this section there’s a description of
the Android operating system.
Initially, there
is an introduction about its developers and their
participation in the market. Later, it is shown its
architecture and there’s an analysis of the layers that
make it up.
2.1.
Android in the mobile operating system
market
Android is an operating system for mobile devices
initially created by Android Inc., a firm that was bought
by Google in 2005. Later, it was developed by the Open
Handset Alliance, which is also led by Google. Devices
with Android operating system have a high market
share. According to StatCounter Global Stats, Android
ranked first in sales with 70 percent of the market
followed by 28 percent of devices with Apple OS. The
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D. Armenteros
figure 1 presents the market share of the different mobile
operating systems in 2021, verifying the big potential in
sales in Android devices.
2.
3.
4.
SLIKA 1: 2021 OS Market in Smartphones
Android works with an Apache license (ASL), which
allows freely modifying the platform, adding new
functionalities and does not require sharing the code
or having to allow its use to third parties. Google
explains that the creation of Android was a response
to its own experiences with mobile applications. They
wanted to make sure that there was always an open
platform for operators, manufacturers and developers
that allowed them to implement innovative ideas. The
main objective is to ensure that there is not a monopoly
in the industry that restricts or controls the innovations
of others, for this same reason the platform is open.
Many developers have joined the Android community
so the quantity of new apps created and downloaded
per month in Play Store is increasing drastically. This
generates a great offer for all users of the platform and
a collaborative participation to improve the experience
with mobile devices. [1]
2.2.
5.
application, by itself, tasks are a series of activities,
possibly from multiple applications. The concept
of task is useful in Android applications because
it allows the user to step-by-step undo or return
pop-up operations from a stack.
Application framework: Through this framework, APIs are provided to developers in various
areas such as graphical user interface, power management, network, multimedia, search, and data
access. This layer also provides mechanisms so that
the components can be replaced by the user and the
reuse of them is simple, the applications can publish their functionalities and others can use them
according to the security rules.
Libraries: In this layer are the set of libraries
that each version of Android provides (the number
changes between versions). The most common
libraries are the system, graphics, and media
libraries.
These are presented to developers
through the application framework and are written
in C and C ++.
Android runtime: The runtime environment is
made up of Dalvik and core libraries. Dalvik is
an Android virtual machine where applications are
run and it has been written so that devices can run
multiple virtual machines efficiently. Core libraries
basically provide the functions available in Java
libraries since the applications are written in this
language.
Linux kernel: Android uses a modification of
the 2.6 series of the Linux kernel for basic system
functions such as security, process management,
memory, and drivers. One of the most important
changes made to the original kernel is in the
improvement to the power management since this
is a crucial aspect for mobile devices. As it is usual
in Android system, the kernel is freely accessible.
Android Architecture
Android was developed on a modification of the Linux
kernel[2]. The figure 2 1 shows its architecture whose
components are written in Java, C, C ++ and XML:
1.
Application layer: In this layer are the operating
system applications written in Java language.
The native applications include a program for
text messages, calendar, contacts, browser, among
others. In Android, applications and tasks are
strictly related, a task can be seen as a user
1 taken
from: http://suniljoy.wordpress.com/2011/02/28/
SLIKA 2: Android Architecture
android/
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Paper Title
3.
3.1.
ANDROID SECURITY MODEL ANALYSIS
Security program
The Android team envisioned a security program in
its development cycle to address weaknesses in mobile
operating systems. [3]The main security activities
carried out in the program are:
1.
2.
3.
4.
3.2.
Design review: Android security was approached
from an early stage of the development cycle with
the creation and design of a robust and configurable
security model. Each of the main features of the
platform was revised to integrate the appropriate
controls into the system architecture.
Penetration testing and code review: During
the development of the platform, the Android
components and those with a free license that
it uses underwent detailed security reviews.
These reviews were conducted by the Android
security team, Google’s information security team,
and independent security consultants.
The
objective was to identify potential weaknesses and
vulnerabilities long before the platform was used
and to simulate the types of analysis that external
security experts will carry out after the platform is
launched.
Community review: Since Android is an opensource project, it allows extensive security review
from any interested party, which contributes to the
improvement of the platform.
Incident response: In order to address security
problems in production, Android created a
comprehensive process that includes two aspects,
to provide security answers.
First, there is
constant vigilance by the Android security team
of system components and the community to
identify potential vulnerabilities. Second, once
problems are discovered, the security team has
a response process that allows rapid attention
to vulnerabilities so that the potential risk for
Android users is minimized. These responses may
include platform updates and removal of apps from
Google Play and from devices.
Safety components
3.
SLIKA 3: Android OS Permission
4.
One of the goals of Android is to be the most secure and
useful operating system for mobile devices, providing
system security controls to: protect user data, protect
system resources (including the network), and provide
isolation from the applications[4]. To achieve these
three goals, Android provides key security features:
1.
2.
Security through the Linux kernel: At the
operating system security level, Android offers the
security of the Linux kernel, which has been used
for years and is used to secure millions of sensitive
environments. The Linux kernel has become a
stable kernel that offers security features such as
that which works with a permission-based model,
provides for sandboxing, has an extensible security
mechanism, and allows removing unnecessary and
potentially unsafe parts.
Security mechanism sandbox required for all
applications: In Linux each application runs as a
process with particular user and group identifiers.
This allows access policies to be defined for each
application depending on its requirements and
purpose. Said permissions are approved by the user
at installation time by accepting the manifest. In
some operating systems memory corruption errors
compromise the complete security of the device;
These errors are minimized in Android because
all the applications and their resources are in an
isolated space, so a memory corruption will only
allow the execution of the code in the context of the
application and with the permissions established
for it.
System partition and safe mode: The system
partition is the one shown in the figure ??
,that is, the one that contains the Linux kernel,
the libraries, the execution time, the application
framework and the applications. This partition is
read-only. When a user starts the computer in
safe mode, only the system partition is started,
so only the basic Android applications will be
available, which ensures that the user can start
their phone with an environment free of third-party
applications and by both in a safe mode.
5.
File system permissions: Permissions on
the Linux file system ensure that one user
cannot read or write another user’s files. Since
Android applications run as their own user, an
application cannot read or write files created
by another application, unless the application
developer explicitly exposes them.
Password protection:
Android can be
configured to ask for a user password before
providing access to the device, this facilitates the
prevention of unauthorized use of the device and
the password as explained above is used by the
encryption algorithm.
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6.
3.3.
1.
2.
3.
4.
D. Armenteros
Permissions ”root”on devices: On Android
only the kernel and a small subset of the main
applications run with root permissions. Root
permissions can modify the operating system,
kernel, and any other application, plus you have
full access to application data. If a user changes
device permissions and grants root permissions
to applications, he is increasing the security risk
of malicious applications. Android has allowed
root permissions to be configured since this is
an important property for developers and for
those users who, for example, want to allow the
installation of an alternative operating system.
Limitations
Malicious software detection is difficult: Given the ingenuity of malicious software developers,
and that ultimately it is the phone user who decides which applications they use and therefore
which applications they grant the permissions they
request over their resources, it is difficult to detect malicious applications in a preventive manner.
Usually, the user discovers that the security of his
phone has been compromised when he realizes that
something is wrong.
Malicious software detection is slow:
Although Google Play contains a considerable number of applications that offer Android users a diverse range of functionalities and features, many of
them are malicious software, so proactive detection
of them is a pressing need to protect the majority.
number of users possible. However, according to
the Symantec report[twenty] the detection of these
malicious software is insecure and delayed, so by
the time they are detected, many users have already downloaded it and, worse still, removal from
Google Play is also delayed.
Little control in the interaction between
applications:
Despite the Android sandbox
security mechanism, there are no mechanisms to
regulate communication between applications. In
other words, an application with few permissions
can take advantage (for malicious purposes) of
the permissions of a more privileged application.
Suppose, for example, that a user installs two
applications A and B. on his phone. Application
A has limited permissions and application B has
privileged permissions. Since A can invoke B via
its respective API, it could use the operations
provided by B to breach the security of the system.
Difficulty in the definition process of access
policies:
Due to the large number of factors
that must be taken into account when defining an
access policy, it is difficult even for an experienced
developer to create them. As a consequence, and to
avoid errors at the functionality level, the developer
usually ends up granting more permissions than an
5.
4.
application needs to function.
Delay in posting updates: Although Android
indicates that it addresses the security flaws found
as quickly as possible, the history shows that
the patches are delayed and users are not able
to protect their mobile devices while the updates
arrive, and even worse, many of them never install
them and they continue to be victims of security
problems already identified [5].
RELATED WORK
Throughout this section it will be presented a study
of related work. Initially, it is shown some research
articles that also analyse the Android security model.
Subsequently, the are some works whose purpose is to
improve the Android security model by strengthening
some of its limitations.
4.1.
1.
2.
Android security model improvements
Proposals for detecting malicious software:
There are some proposals that focus on detecting
malicious applications. One of these is the one
presented in [6]. There, the authors show what
they call a ”distance model”that makes it possible
to measure the level of danger that a particular
combination of permits represents.
In other
words, from an analysis of the permissions that
an application requests, it is possible to detect
whether or not it represents a danger to the
security of the system. Another of the proposals is
explained in [7], in which the detection mechanism
is based on analysis of the behaviour of the Linux
kernel during the execution of the application.
It is important to note that one of the biggest
challenges that these types of malware detection
applications have is that they finally run on a phone
that has limited memory and processing resources.
As a consequence, having a malware detection
application usually has undesirable effects for the
end user (for example, reducing battery life).
In response to this, proposals such as the one
presented in[fifteen] where the detection analysis
is done on a PC. For this, there is a mechanism by
which the files are downloaded from the phone to a
computer when the user connects it. Subsequently,
an analysis is made on said files, taking advantage
of the computational power of the PC and the
results are displayed.
Proposals to increase the integrity and
availability of information on Android
devices: Although most of the security proposals
on mobile devices focus on the protection of
information against unauthorized access, there
are proposals whose objective is to protect the
information from damage or loss, thus favouring
its integrity and availability. This is the case of
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what is presented by Changhao et al in[two],where
the authors are based on the idea that all the
information that is stored in the phone (even
the scores of the games) is of great value to
the user. They present the problem that the
information is sensitive in situations such as
software update processes or uninstallation of
applications and propose a strategy based on
effective synchronization mechanisms that allow
the storage of copies of the information in safe
places.still, removal from Google Play is also
delayed.
Proposals to increase Android security
based on the Linux kernel: So far, the
proposals presented are focused on reinforcing the
Android security model itself. However, they do
not take into account that since Android is running
on the Linux kernel, all its security weaknesses are
inherited, it can become the weakest link. This
problem is the main concern of Park et al in
[8], where it is proposed to improve Linux kernel
security according to Android needs and thus
improve Android security. Its strategy is based on
strengthening the mandatory access control system
for Linux.
5.
CONCLUSIONS
5
distance model. 2011 International Conference on
Internet Technology and Applications, pp. 1–4.
[7] Isohara, T., Takemori, K., and Kubota, A. (2011)
Kernel-based behavior analysis for android malware
detection. 2011 Seventh International Conference on
Computational Intelligence and Security, pp. 1011–
1015.
[8] Park, J., Kim, B., Kim, S.-R., Yoon, J. H., and Cho,
Y. (2011) Performance analysis of security enforcement
on android operating system. Proceedings of the 2011
ACM Symposium on Research in Applied Computation,
New York, NY, USA RACS ’11 282–286. Association
for Computing Machinery.
In this article I present an analysis of the Android
security model and the proposals that have been made
recently to improve it. To do this, I started with a
description of the operating system itself in terms of its
impact on the market and its architecture. Later, I show
the system’s security model and its main limitations.
Finally, I mention some of the works that I consider to
be the most relevant that have been done on the subject.
I divide them into those that do a security analysis of
Android and those that go further and show strategies
to improve some of its limitations.
LITERATURE
[1] Báez, M., Borrego, Á., Cordero, J., Cruz, L., González,
M., Hernández, F., Palomero, D., de Llera, J. R., Sanz,
D., Saucedo, M., et al. (2019). Introducción a android.
[2] Brahler, S. (2010) Analysis of the android architecture.
Karlsruhe institute for technology, 7.
[3] Schlöglhofer, R. and Sametinger, J. (2012) Secure and
usable authentication on mobile devices. Proceedings
of the 10th International Conference on Advances
in Mobile Computing Multimedia, New York, NY,
USA MoMM ’12 257–262. Association for Computing
Machinery.
[4] Felt, A. P., Chin, E., Hanna, S., Song, D. X., and
Wagner, D. A. (2011) Android permissions demystified.
CCS ’11.
[5] Bing, H. (2012). Analysis and research of system
security based on android.
[6] Tang, W., Jin, G., He, J., and Jiang, X. (2011)
Extending android security enforcement with a security
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