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Encrypt data within mobile apps

John Muchow, Author
John Muchow, an independent J2ME consultant, developer, and technical writer, is the author of Core J2ME Technology and MIDP. John is also one of several Subject Matter Experts who designed and developed Sun Microsystems' newest certification exam Sun Certified Mobile Application Developer (SCMAD) for J2ME. Visit Core J2ME for additional source code, articles, developer resources, and to learn more about the SCMAD certification exam. Always on the lookout for interesting J2ME projects (writing, consulting, training, or permanent opportunities), John welcomes your e-mail.

Summary:  This tutorial provides an overview of how to encrypt application-related data in a Java 2 Micro Edition (J2ME) application (MIDlet).

Date:  03 Feb 2004
Level:  Introductory
PDF:  A4 and Letter (536 KB | 31 pages)Get Adobe® Reader®

Activity:  6797 views
Comments:  

Before you start

About this tutorial

With the ever present concern over security, software applications must consider how to secure confidential data. A mobile application is not immune from privacy concerns. In fact, mobile devices and their software applications have special considerations given that most people carry these devices wherever they go.

This tutorial provides an overview of how to encrypt application-related data in a Java 2 Micro Edition (J2ME) application (MIDlet). The tutorial begins with a brief introduction to data encryption. As encryption is not a topic for the faint of heart, this section is rather brief, and focuses specifically on the open source encryption API written by the Legion of Bouncy Castle. The topic concludes by developing a MIDlet to demonstrate encrypting and decrypting of text strings.

One problem inherent to most mobile devices is the limited amount of memory. Although Bouncy Castle and other encryption libraries offer an abundance of functionality, there is a price. As with most any library you use, only a small portion of the code is typically needed by your application. One common way to eliminate unused code, and at the same time make it more challenging to reverse engineer an application, is to use a Java obfuscator. I'll introduce the open source obfuscator, ProGuard. This addresses everything from downloading and installing, to configuring the J2ME Wireless Toolkit to use ProGuard. The final section in this tutorial compares MIDlet JAR file sizes, with and without obfuscation.

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Prerequisites

To run the samples in this tutorial, you'll need the following software tools:

  • The Java Development Kit (JDK)
  • The Wireless Toolkit (WTK)
  • Bouncy Castle
  • ProGuard

See Software prerequisites for information on downloading, installing, and configuring these software tools.

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