Get checksum of the source codes in Android library

Question

I am developing an android library and I want to apply a tamper-detection mechanism to my code, since it calls some sensitive financial web services.

What I'm going to implement is to calculate the checksum of the apk ( or important parts of it), programmatically on the runtime, so I can prevent a repackaged or recompiled apk from being able to do any harm (tamper prevention).

What I have come up with so far, is to calculate the checksum of the applicationInfo.publicSourceDir . but I'm not sure what happens with the apps that have multiple dex files or multiple splitApks.

What is the most reliable way to calculate checksum based on the code-base of an application in Android, programmatically?

Answer 1

如果您通过游戏分发，您可以查看SafetyNet： https ： //developer.android.com/training/safetynet/index.html

Answer 2

The checksum approach can be applied to single file or zip files. It will be a lengthy process to check the checksum of all files. I think you are in the wrong direction.

Firstly, There is no clear solution to this problem. Any app can be hacked - you can just make it hard to hack.

This is what is done to make it hard -

1. Encrypt the your apk - so that its hard to get to your source code. refer - APK to protect apk from reverse engineering - Check obfuscating tools.

2. Use data encryption while sending/receiving data from WebService. You can use HMAC to protect the data. Make sure your server is smart enough to block user/requesting-apps in case there are multiple bad calls. HMAC is easy to implement and there are libraries to generate HMAC keys.

Answer 3

Get the app signature which is tied to the certificate used to sign the APK

public static String getAppSignature(Context context) {
    try {
        for (Signature signature : context.getPackageManager().getPackageInfo(context.getPackageName(),
                PackageManager.GET_SIGNATURES).signatures) {
            MessageDigest md = MessageDigest.getInstance("SHA");
            md.update(signature.toByteArray());
            return Base64.encodeToString(md.digest(), Base64.DEFAULT);
        }
    } catch (Exception e) { /* Do nothing */ }
    return null;
}

This can be compared with a stored value to check if the signing certificate is the original or not.