Allow offline manual time sync about google-authenticator-android

[ThomasHabets]

Does it not have that? Why do you need it to be manual? It seems that it gets the time drift from Google.

Also, why not just set the system time manually, then?

And I can't speak for the validity window for Google services, but surely the window of acceptable codes is larger than 30 seconds?

[ocdtrekkie]

This would be nice as an option, if it got contributed back to the open source. (Noting, of course, that the current Play Store version of Google Authenticator is closed source.)

Part of the reason to allow a manual option to set time drift is in the case of the reason I forked the app: I wanted to remove the INTERNET permission, as I don't think 2FA apps should have the INTERNET permission. (Especially since you no longer have any idea what Google might be sending back and forth with the closed source versions going forward.)

[ThomasHabets]

Ah. For the open source app you'll know what is being sent, because you have the source.

But I still don't understand the use case. If you fork the code and remove network sync, then you can also add manual time sync. But this (opensource) version will continue to have internet permissions, so why would it require or even want the user to have to manually sync the time?

And if the time is wrong and requires manual intervention, then why set the time in GA when it can be fixed globally on the device?

In any case, it's not me you have to convince. I'm merely an owner on github, and not an Android developer.

[baffo32]

The following patch exposes the time correction as a preference. This resolved my personal issue of having an offline device with a skewed clock.

diff --git a/res/xml/preferences_time_correction.xml b/res/xml/preferences_time_correction.xml
index cd9337d..6e7d60d 100644
--- a/res/xml/preferences_time_correction.xml
+++ b/res/xml/preferences_time_correction.xml
@@ -25,6 +25,11 @@
       android:targetClass="com.google.android.apps.authenticator.timesync.SyncNowActivity">
     </intent>
   </PreferenceScreen>
+  <EditTextPreference
+      android:defaultValue="0"
+      android:inputType="numberSigned"
+      android:key="timeCorrectionMinutes"
+      android:title="Adjustment in minutes" />
   <PreferenceScreen
     android:key="about"
     android:title="@string/timesync_about_feature_preference_title"
diff --git a/src/com/google/android/apps/authenticator/TotpClock.java b/src/com/google/android/apps/authenticator/TotpClock.java
index ee9add4..0b6586c 100644
--- a/src/com/google/android/apps/authenticator/TotpClock.java
+++ b/src/com/google/android/apps/authenticator/TotpClock.java
@@ -26,7 +26,7 @@ import android.preference.PreferenceManager;
  *
  * @author [email protected] (Alex Klyubin)
  */
-public class TotpClock {
+public class TotpClock implements SharedPreferences.OnSharedPreferenceChangeListener {

   // @VisibleForTesting
   static final String PREFERENCE_KEY_OFFSET_MINUTES = "timeCorrectionMinutes";
@@ -45,6 +45,7 @@ public class TotpClock {

   public TotpClock(Context context) {
     mPreferences = PreferenceManager.getDefaultSharedPreferences(context);
+    mPreferences.registerOnSharedPreferenceChangeListener(this);
   }

   /**
@@ -62,7 +63,11 @@ public class TotpClock {
   public int getTimeCorrectionMinutes() {
     synchronized (mLock) {
       if (mCachedCorrectionMinutes == null) {
-        mCachedCorrectionMinutes = mPreferences.getInt(PREFERENCE_KEY_OFFSET_MINUTES, 0);
+       try {
+           mCachedCorrectionMinutes = mPreferences.getInt(PREFERENCE_KEY_OFFSET_MINUTES, 0);
+       } catch(ClassCastException e) {
+           mCachedCorrectionMinutes = Integer.valueOf(mPreferences.getString(PREFERENCE_KEY_OFFSET_MINUTES,"0"));
+       }
       }
       return mCachedCorrectionMinutes;
     }
@@ -80,4 +85,11 @@ public class TotpClock {
       mCachedCorrectionMinutes = null;
     }
   }
+  
+  public void onSharedPreferenceChanged(SharedPreferences sharedPreferences, String key) {
+    if (key.equals(PREFERENCE_KEY_OFFSET_MINUTES)) {
+      // Invalidate the cache
+      mCachedCorrectionMinutes = null;
+    }
+  }
 }

[baffo32]

Sorry, I hadn't seen the new comments.

• Not all devices (mine does not) allow setting the system time.
• The device is not always online. It may be in an area of no service without wifi for an extended period of time, or may be old and damaged. Personally I would like the option of airgapping my device -- if it has a network connection it may be hacked over that network connection and is then no longer a secure token.

[ThomasHabets]

Would you mind setting that in a pull request?