Application Security for the Android Platform: Processes, Permissions, and Other Safeguards

112 Pages·2011·5.51 MB·English

by  Jeff Six

Application Security for the Android
Platform
Jeff Six
Beijing • Cambridge • Farnham • Köln • Sebastopol • Tokyo
Application Security for the Android Platform
by Jeff Six
Copyright © 2012 Jeff Six. All rights reserved.
Printed in the United States of America.
Published by O’Reilly Media, Inc., 1005 Gravenstein Highway North, Sebastopol, CA 95472.
O’Reilly books may be purchased for educational, business, or sales promotional use. Online editions
are also available for most titles (http://my.safaribooksonline.com). For more information, contact our
corporate/institutional sales department: [phone] or [email protected].
Editors: Andy Oram and Mike Hendrickson Cover Designer: Karen Montgomery
Production Editor: Melanie Yarbrough Interior Designer: David Futato
Proofreader: Melanie Yarbrough Illustrator: Robert Romano
Revision History for the First Edition:
2011-12-02 First release
See http://oreilly.com/catalog/errata.csp?isbn=9781449315078 for release details.
Nutshell Handbook, the Nutshell Handbook logo, and the O’Reilly logo are registered trademarks of
O’Reilly Media, Inc., Application Security for the Android Platform, the image of a red gunard, and related
trade dress are trademarks of O’Reilly Media, Inc.
Many of the designations used by manufacturers and sellers to distinguish their products are claimed as
trademarks. Where those designations appear in this book, and O’Reilly Media, Inc. was aware of a
trademark claim, the designations have been printed in caps or initial caps.
While every precaution has been taken in the preparation of this book, the publisher and authors assume
no responsibility for errors or omissions, or for damages resulting from the use of the information con-
tained herein.
ISBN: 978-1-449-31507-8
[LSI]
1322594274
Table of Contents
Preface ..................................................................... vii
1. Introduction ........................................................... 1
Application Security: Why You Should Care 2
The Current State of Mobile Application Security on Android 3
Security: Risk = Vulnerability + Threat + Consequences 4
Evolution of Information Security: Why Applications Matter the Most 7
Your Role: Protect the Data 8
Secure Software Development Techniques 9
Unique Characteristics of Android 10
Moving On 12
2. Android Architecture ................................................... 13
Introduction to the Android Architecture 14
The Linux Security Model 15
The Resulting Android Security Model 15
Application Signing, Attribution, and Attestation 16
Process Design 18
Android Filesystem Isolation 21
Android Preferences and Database Isolation 22
Moving up the Layers to System API and Component Permissions 24
3. Application Permissions ................................................. 25
Android Permission Basics 27
Using Restricted System APIs and the User Experience 29
Custom Permissions 32
4. Component Security and Permissions ..................................... 37
The Types of Android Components 37
Intercomponent Signaling Using Intents 38
Public and Private Components 41
iii
Imposing Restrictions on Access to Components 42
Securing Activities 42
Securing Services 42
Securing Content Providers 44
Securing Broadcast Intents 49
Putting It All Together: Securing Communications in a Multi-Tier App 51
5. Protecting Stored Data ................................................. 53
The Threats and Vulnerabilities Against Stored Data 53
Vulnerabilities of Stored Data 53
Threats to, and Mitigations for, Stored Data 54
Protection Principles 55
Cryptography Primer: Encryption 56
Symmetric Encryption 56
Asymmetric Key Encryption 57
Cryptography Primer: Hashing 58
Cryptographic Practicalities 60
Computational Infeasibility 60
Algorithm Choice and Key Size 61
Cipher Operation Modes, Initialization Vectors, and Salt 61
Public Keys and Their Management 62
Key Derivation and Management 63
Motivation 64
Key Derivation 64
Encryption Without User-Supplied Key Derivation 67
Practical Cryptography: Applying a Technique Against a Threat 68
6. Securing Server Interactions ............................................. 73
Confidentiality and Authentication 73
SSL/TLS: The Industry Standard 74
Authentication of the Entities 74
Encryption of Data 76
Protecting Data En Route to Public Services 76
Introducing the Android SSL/TLS Environment 77
Server Verification 78
Handling SSL/TLS Connection Errors 80
Protecting Data En Route to Private Services 81
Using Only Specific Certificates for SSL/TLS 81
One Step Further: Using Client-Side Authentication SSL/TLS 85
Threats Against Devices Using Data in Transit 87
Input Validation: The Central Tenant of Application Security 90
Reject-Known-Bad 90
Accept-Known-Good 90
iv | Table of Contents
Wrapping It Up: Input Validation 91
Preventing Command Injection 91
7. Summary ............................................................. 95
Key Themes 95
It’s All About Risk 95
The Principle of Least Privilege 96
Use the Permissions System 96
Android Is an Open Architecture 96
Get the Cryptography Right 96
Never Trust User Input 97
Wrapping It Up 97
Table of Contents | v

Preface
The purpose of this book is to convey vital knowledge about application security to
developers working on the Android platform, to enable the development of robust,
rugged, and more secure applications.
While application security knowledge and skills have matured rapidly over the past
couple of years, that knowledge is still scattered in a huge number of diverse locations.
As of now, no single resource has existed that a developer with some experience in
developing Android applications could turn to in order to understand the more im-
portant topics within the application security space and to find guidance on how to
make their applications more secure. If you are such a developer, you’ll find the key
points of application security that you need to know to develop secure applications laid
out in a succinct and actionable manner. If you are an experienced security engineer or
practitioner, you’ll find a summary of the unique characteristics of Android that you
need to know to work within this environment. In short, this book enables the devel-
opment of secure applications for the Android platform, whatever your background.
Organization of the Book
Although the chapters cover different topics, they have been arranged so that the con-
cepts and techniques in earlier chapters form a foundation for the others.
Chapter 1, Introduction
Lays out the importance of this topic, and perhaps scares you a bit, so as to motivate
you to read the book.
Chapter 2, Android Architecture
Describes the way Android differs from other common systems, notably desktop
systems, and how its architecture both enables security and requires you to work
with its unique structure.
Chapter 3, Application Permissions
Looks behind the familiar list of permissions that users see when adding applica-
tions to their devices, and shows how to use the system robustly without over-
whelming the user.
vii
Chapter 4, Component Security and Permissions
Takes the permissions system to a finer granularity by showing how components
such as Content Providers and Services can grant limited access to their data and
functions.
Chapter 5, Protecting Stored Data
Treats the critical topic of encrypting data so that it is secure even if the user or a
thief can bypass other application security controls provided by Android (or when
such controls do not apply).
Chapter 6, Securing Server Interactions
Shows how you can protect the interactions between your application and the
servers it communicates with.
Chapter 7, Summary
Focuses on the key take-aways from the book.
Conventions Used in This Book
The following typographical conventions are used in this book:
Italic
Indicates new terms, URLs, email addresses, filenames, and file extensions.
Constant width
Used for program listings, as well as within paragraphs to refer to program elements
such as variable or function names, databases, data types, and environment vari-
ables.
Constant width bold
Shows commands or other text that should be typed literally by the user.
Constant width italic
Shows text that should be replaced with user-supplied values or by values deter-
mined by context.
This icon signifies a tip, suggestion, or general note.
This icon indicates a warning or caution.
viii | Preface