Check if OpenKeychain is installed

app/src/main/java/eu/faircode/email/FragmentCompose.java

@@ -3377,7 +3377,7 @@ public class FragmentCompose extends FragmentBase {
 
                         // Encryption
                         if (ref.ui_encrypt != null && !EntityMessage.ENCRYPT_NONE.equals(ref.ui_encrypt)) {
-                            if (ActivityBilling.isPro(context))
+                            if (ActivityBilling.isPro(context) && Helper.isOpenKeychainInstalled(context))
                                 data.draft.ui_encrypt = ref.ui_encrypt;
                         }
 

app/src/main/java/eu/faircode/email/Helper.java

@@ -92,6 +92,7 @@ import androidx.recyclerview.widget.RecyclerView;
 import com.google.android.material.bottomnavigation.BottomNavigationView;
 
 import org.jetbrains.annotations.NotNull;
+import org.openintents.openpgp.util.OpenPgpApi;
 
 import java.io.ByteArrayOutputStream;
 import java.io.File;
@@ -408,6 +409,18 @@ public class Helper {
         return (biometrics || !TextUtils.isEmpty(pin));
     }
 
+    static boolean isOpenKeychainInstalled(Context context) {
+        SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
+        String provider = prefs.getString("openpgp_provider", "org.sufficientlysecure.keychain");
+
+        PackageManager pm = context.getPackageManager();
+        Intent intent = new Intent(OpenPgpApi.SERVICE_INTENT_2);
+        intent.setPackage(provider);
+        List<ResolveInfo> ris = pm.queryIntentServices(intent, 0);
+
+        return (ris.size() > 0);
+    }
+
     // View
 
     static Intent getChooser(Context context, Intent intent) {