Secure in-app keyboard

      Technique summary
    Technique Secure keyboard
    Against Screen recording, malicious keyboard, and UI injection attacks
    Limitations None
    Side effects May reduce user's functionality compared to the standard keyboard
    Recommendations Recommended for use on Android API Level ≤ 30 (Android ≤ 11)

    A secure in-app keyboard for Android apps is a specialized keyboard designed to enhance security and privacy when users input sensitive information within an application. Unlike standard keyboards, which might be susceptible to various forms of interception, secure in-app keyboards are specifically engineered to mitigate these risks.

    Keypress leaks


    Left: Unprotected view. Right: Protected view leaking information through the keyboard.

    In Android ≤11 the standard keyboard may leak information about keypresses:

    The solution would be to use a dedicated keyboard for the application, and setting FLAG_SECURE on the keyboard. As a result, every time the user is typing, the keyboard would appear, and the screen would become black. However, this might not be convenient to happen everywhere in terms of UX.

    A better solution could be to apply FLAG_SECURE only on specific edit text views. This can be done by filtering by a particular field ID, which can be obtained from the symbol list. For example:

    public class MyKeyboard extends InputMethodService { // (...) @Override public void onStartInputView(EditorInfo info, boolean restarting) { // (...) String packageName = info.packageName; int fieldId = info.fieldId; if (packageName.equals("")) { if (fieldId == 0x7f070054) { Objects.requireNonNull( getWindow().getWindow()). addFlags(WindowManager.LayoutParams.FLAG_SECURE); } } // (...)

    Malicious keyboards

    Malicious keyboards can replace the user's default keyboard entirely, leading to continuous keylogging. A dedicated secure in-app keyboard helps mitigate the risk.


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