How to check if APK is signed or "debug build"?

There are different way to check if the application is build using debug or release certificate, but the following way seems best to me.

According to the info in Android documentation Signing Your Application, debug key contain following subject distinguished name: "CN=Android Debug,O=Android,C=US". We can use this information to test if package is signed with debug key without hardcoding debug key signature into our code.

Given:

import android.content.pm.Signature;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;

You can implement an isDebuggable method this way:

private static final X500Principal DEBUG_DN = new X500Principal("CN=Android Debug,O=Android,C=US");
private boolean isDebuggable(Context ctx)
{
    boolean debuggable = false;

    try
    {
        PackageInfo pinfo = ctx.getPackageManager().getPackageInfo(ctx.getPackageName(),PackageManager.GET_SIGNATURES);
        Signature signatures[] = pinfo.signatures;

        CertificateFactory cf = CertificateFactory.getInstance("X.509");

        for ( int i = 0; i < signatures.length;i++)
        {   
            ByteArrayInputStream stream = new ByteArrayInputStream(signatures[i].toByteArray());
            X509Certificate cert = (X509Certificate) cf.generateCertificate(stream);       
            debuggable = cert.getSubjectX500Principal().equals(DEBUG_DN);
            if (debuggable)
                break;
        }
    }
    catch (NameNotFoundException e)
    {
        //debuggable variable will remain false
    }
    catch (CertificateException e)
    {
        //debuggable variable will remain false
    }
    return debuggable;
}

To check the debuggable flag, you can use this code:

boolean isDebuggable =  ( 0 != ( getApplicationInfo().flags & ApplicationInfo.FLAG_DEBUGGABLE ) );

Kotlin:

val isDebuggable = 0 != applicationInfo.flags and ApplicationInfo.FLAG_DEBUGGABLE

For more information, please see Securing Android LVL Applications.

Alternatively, if you're using Gradle correctly, you can check if BuildConfig.DEBUG is true or false.

Answered by Mark Murphy

The simplest, and best long-term solution, is to use BuildConfig.DEBUG. This is a boolean value that will be true for a debug build, false otherwise:

if (BuildConfig.DEBUG) {
  // do something for a debug build
}