[Android] SecureStorage: Rework logic to delete shared prefs when key is corrupt

src/Essentials/src/SecureStorage/SecureStorage.android.cs

@@ -3,6 +3,7 @@
 using Android.Content;
 using AndroidX.Security.Crypto;
 using Java.Security;
+using Javax.Crypto;
 using Xamarin.Google.Crypto.Tink.Shaded.Protobuf;
 
 namespace Microsoft.Maui.Storage
@@ -80,31 +81,62 @@ void PlatformRemoveAll()
 			editor?.Clear()?.Apply();
 		}
 
+		static void DeleteSharedPreferences()
+		{
+			// Open an editor to the preferences we can clear, using the alias for storing encrypted values
+			var editPreferences = Application.Context.GetSharedPreferences(Alias, FileCreationMode.Private).Edit();
+			// Commit is synchronous here so we can be sure it's done before trying to create the encrypted preferences again
+			editPreferences?.Clear()?.Commit();
+		}
+
 		ISharedPreferences GetEncryptedSharedPreferences()
 		{
 			try
 			{
-				var context = Application.Context;
-
-				var prefsMainKey = new MasterKey.Builder(context, Alias)
-					.SetKeyScheme(MasterKey.KeyScheme.Aes256Gcm)
-					.Build();
-
-				return EncryptedSharedPreferences.Create(
-					context,
-					Alias,
-					prefsMainKey,
-					EncryptedSharedPreferences.PrefKeyEncryptionScheme.Aes256Siv,
-					EncryptedSharedPreferences.PrefValueEncryptionScheme.Aes256Gcm);
+				return CreateEncryptedSharedPreferences();
 			}
-			catch (InvalidProtocolBufferException)
+			catch (System.Exception ex) 
+			when (ex is InvalidProtocolBufferException or Android.Security.KeyStoreException or KeyStoreException or BadPaddingException)
 			{
-				// TODO: Use Logger here?
-				System.Diagnostics.Debug.WriteLine(
-					"Unable get encrypted shared preferences, which is likely due to an app uninstall. Removing all keys and returning null.");
-				PlatformRemoveAll();
+				// If we encounter any of these exceptions, it's likely due to a corrupt key or bad migration between devices
+				// There isn't much to do at this point except try to delete the shared preferences so we can recreate them
+				try
+				{
+					System.Diagnostics.Debug.WriteLine(
+						"Unable get encrypted shared preferences, which is likely due to corrupt encryption key or bad app cache backup/restore. Removing all keys and returning null.");
+					System.Diagnostics.Debug.WriteLine(ex);
+
+					// Delete the shared preferences
+					DeleteSharedPreferences();
+
+					// Try to return a new instance now that we've deleted the old
+					return CreateEncryptedSharedPreferences();
+				}
+				catch (System.Exception ex2)
+				{
+					// If we still can't create things, we'll have to give up and return null
+					// TODO: Use Logger here?
+					System.Diagnostics.Debug.WriteLine("Still unable to create encrypted shared preferences after attempting to deleting them. Returning null.");
+					System.Diagnostics.Debug.WriteLine(ex2);
+				}
 				return null;
 			}
 		}
+
+		ISharedPreferences CreateEncryptedSharedPreferences()
+		{
+			var context = Application.Context;
+
+			var prefsMainKey = new MasterKey.Builder(context, Alias)
+				.SetKeyScheme(MasterKey.KeyScheme.Aes256Gcm)
+				.Build();
+
+			return EncryptedSharedPreferences.Create(
+				context,
+				Alias,
+				prefsMainKey,
+				EncryptedSharedPreferences.PrefKeyEncryptionScheme.Aes256Siv,
+				EncryptedSharedPreferences.PrefValueEncryptionScheme.Aes256Gcm);
+		}
 	}
 }