CWAC Security: Helping You Help Your Users Defend Their Data

This project contains utility code related to Android security measures.

At present, it contains:

• a PermissionUtils class with a checkCustomPermissions() static method, to help you detect if another app has defined your custom permissions before your app was installed

This Android library project is available as a JAR or as an artifact for use with Gradle. To use that, add the following blocks to your build.gradle file:

repositories {
    maven {
        url "https://repo.commonsware.com.s3.amazonaws.com"
    }
}

dependencies {
    compile 'com.commonsware.cwac:security:0.1.+'
}

Or, if you cannot use SSL, use http://repo.commonsware.com for the repository URL.

Usage: checkCustomPermissions()

Custom permissions in Android are "first one in wins". In other words, whatever app first has a <permission> element for a given android:name gets to define, for all subsequent apps, what the details are for that permission. And, courtesy of Android's rules for informing users about permissions, the app that defined the permission can hold the permission without the user's knowledge.

This has some security implications, which are covered in greater detail in this paper.

The checkCustomPermissions() method is designed to help you detect if another app has defined the same custom permissions that you are defining. Typically, developers expect to be the first one to define the custom permission, but that may not be true, with consequences for the developers and their users.

Calling checkCustomPermissions() is easy: just pass it a Context, such as your launcher Activity.

What it returns is a HashMap<PackageInfo, ArrayList<PermissionLint>>, which will require some explanation.

What checkCustomPermissions() does is find all of the custom permissions in your app that you have declared via <permission> elements. Then, it scans all other apps on the device, finding all their custom permissions, and sees if there is a match on the permission name (android:name attribute).

Each entry in the HashMap represents one app that has redefined one or more of your custom permissions, keyed by the PackageInfo object describing that application. Each permission that has been so redefined will be in the ArrayList. So, if you define two custom permissions, but some other app only redefined one, there will only be one entry in the ArrayList.

Each PermissionLint in the ArrayList contains the following public fields:

• PermissionInfo perm providing details of the permission as declared in the other app

• boolean wasDowngraded, which will be true if you declared the permisison to be signature, but the other app declared it to be normal or dangerous

• boolean wasUpgraded, which will be true if you declared the permission to be normal or dangerous, but the other app declared it to be signature

• boolean proseDiffers, which will be true if, for the user's configured device locale, the label or description of the other app's edition of this permission differs from your edition of this permission

Hence, if all three boolean fields are false, the permission in the other app is functionally identical to your own definition, at least for this user and this locale.

The expectation is that you would call checkCustomPermissions() on the first run of your app after installation. If you get back an empty HashMap, then you can continue your first run normally. If you get back a non-empty HashMap, you can decide what to do with the information, including:

• warning the user about possible data leakage to other apps

• sending information about the pre-defined permission to your servers, so you can track possible malware attacks targeting your application and users

Dependencies

This project has no dependencies and should work on most versions of Android, though it is only being tested on API Level 15+. If you determine that the library (not the demos) do not work on an older-yet-relevant version of Android, please file an issue.

Version

This is version v0.1.0 of this module, meaning it is rather new.

Demo

In the demoA/ sub-project you will find an application that uses checkCustomPermissions() to see if some other app has already defined a custom permission. The demoB/ sub-project does not use CWAC-Security, but defines that permission, so that you can verify that demoA works as expected.

License

The code in this project is licensed under the Apache Software License 2.0, per the terms of the included LICENSE file.

Questions

If you have questions regarding the use of this code, please post a question on StackOverflow tagged with commonsware and android. Be sure to indicate what CWAC module you are having issues with, and be sure to include source code and stack traces if you are encountering crashes.

If you have encountered what is clearly a bug, or if you have a feature request, please post an issue. Be certain to include complete steps for reproducing the issue.

Do not ask for help via Twitter.

Also, if you plan on hacking on the code with an eye for contributing something back, please open an issue that we can use for discussing implementation details. Just lobbing a pull request over the fence may work, but it may not.

Release Notes

• v0.1.0: initial release

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