src/com/android/settings/UserCredentialsSettings.java - LeafOS-Project/android_packages_apps_Settings - Gitiles

 /*
  * Copyright (C) 2015 The Android Open Source Project
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
  * You may obtain a copy of the License at
  *
  *      http://www.apache.org/licenses/LICENSE-2.0
  *
  * Unless required by applicable law or agreed to in writing, software
  * distributed under the License is distributed on an "AS IS" BASIS,
  * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  * See the License for the specific language governing permissions and
  * limitations under the License.
  */

 package com.android.settings;

 import android.annotation.LayoutRes;
 import android.annotation.Nullable;
 import android.app.Dialog;
 import android.app.settings.SettingsEnums;
 import android.content.Context;
 import android.content.DialogInterface;
 import android.os.AsyncTask;
 import android.os.Bundle;
 import android.os.Parcel;
 import android.os.Parcelable;
 import android.os.Process;
 import android.os.RemoteException;
 import android.os.UserHandle;
 import android.os.UserManager;
 import android.security.Credentials;
 import android.security.IKeyChainService;
 import android.security.KeyChain;
 import android.security.KeyChain.KeyChainConnection;
 import android.security.keystore.KeyProperties;
 import android.security.keystore2.AndroidKeyStoreLoadStoreParameter;
 import android.util.Log;
 import android.util.SparseArray;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
 import android.widget.TextView;

 import androidx.annotation.VisibleForTesting;
 import androidx.appcompat.app.AlertDialog;
 import androidx.fragment.app.DialogFragment;
 import androidx.fragment.app.Fragment;
 import androidx.recyclerview.widget.RecyclerView;

 import com.android.settings.core.instrumentation.InstrumentedDialogFragment;
 import com.android.settings.wifi.helper.SavedWifiHelper;
 import com.android.settingslib.RestrictedLockUtils;
 import com.android.settingslib.RestrictedLockUtils.EnforcedAdmin;
 import com.android.settingslib.RestrictedLockUtilsInternal;

 import java.security.Key;
 import java.security.KeyStore;
 import java.security.KeyStoreException;
 import java.security.NoSuchAlgorithmException;
 import java.security.UnrecoverableKeyException;
 import java.security.cert.Certificate;
 import java.util.ArrayList;
 import java.util.EnumSet;
 import java.util.Enumeration;
 import java.util.List;
 import java.util.SortedMap;
 import java.util.TreeMap;

 import javax.crypto.SecretKey;

 public class UserCredentialsSettings extends SettingsPreferenceFragment
         implements View.OnClickListener {
     private static final String TAG = "UserCredentialsSettings";

     private static final String KEYSTORE_PROVIDER = "AndroidKeyStore";

     @VisibleForTesting
     protected SavedWifiHelper mSavedWifiHelper;

     @Override
     public int getMetricsCategory() {
         return SettingsEnums.USER_CREDENTIALS;
     }

     @Override
     public void onResume() {
         super.onResume();
         refreshItems();
     }

     @Override
     public void onClick(final View view) {
         final Credential item = (Credential) view.getTag();
         if (item == null) return;
         if (item.isInUse()) {
             item.setUsedByNames(mSavedWifiHelper.getCertificateNetworkNames(item.alias));
         }
         showCredentialDialogFragment(item);
     }

     @Override
     public void onCreate(@Nullable Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         getActivity().setTitle(R.string.user_credentials);
         mSavedWifiHelper = SavedWifiHelper.getInstance(getContext(), getSettingsLifecycle());
     }

     @VisibleForTesting
     protected void showCredentialDialogFragment(Credential item) {
         CredentialDialogFragment.show(this, item);
     }

     protected void announceRemoval(String alias) {
         if (!isAdded()) {
             return;
         }
         getListView().announceForAccessibility(getString(R.string.user_credential_removed, alias));
     }

     protected void refreshItems() {
         if (isAdded()) {
             new AliasLoader().execute();
         }
     }

     /** The fragment to show the credential information. */
     public static class CredentialDialogFragment extends InstrumentedDialogFragment
             implements DialogInterface.OnShowListener {
         private static final String TAG = "CredentialDialogFragment";
         private static final String ARG_CREDENTIAL = "credential";

         public static void show(Fragment target, Credential item) {
             final Bundle args = new Bundle();
             args.putParcelable(ARG_CREDENTIAL, item);

             if (target.getFragmentManager().findFragmentByTag(TAG) == null) {
                 final DialogFragment frag = new CredentialDialogFragment();
                 frag.setTargetFragment(target, /* requestCode */ -1);
                 frag.setArguments(args);
                 frag.show(target.getFragmentManager(), TAG);
             }
         }

         @Override
         public Dialog onCreateDialog(Bundle savedInstanceState) {
             final Credential item = (Credential) getArguments().getParcelable(ARG_CREDENTIAL);

             View root = getActivity().getLayoutInflater()
                     .inflate(R.layout.user_credential_dialog, null);
             ViewGroup infoContainer = (ViewGroup) root.findViewById(R.id.credential_container);
             View contentView = getCredentialView(item, R.layout.user_credential, null,
                     infoContainer, /* expanded */ true);
             infoContainer.addView(contentView);

             AlertDialog.Builder builder = new AlertDialog.Builder(getActivity())
                     .setView(root)
                     .setTitle(R.string.user_credential_title)
                     .setPositiveButton(R.string.done, null);

             final String restriction = UserManager.DISALLOW_CONFIG_CREDENTIALS;
             final int myUserId = UserHandle.myUserId();
             if (!RestrictedLockUtilsInternal.hasBaseUserRestriction(getContext(), restriction,
                     myUserId)) {
                 DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener() {
                     @Override public void onClick(DialogInterface dialog, int id) {
                         final EnforcedAdmin admin = RestrictedLockUtilsInternal
                                 .checkIfRestrictionEnforced(getContext(), restriction, myUserId);
                         if (admin != null) {
                             RestrictedLockUtils.sendShowAdminSupportDetailsIntent(getContext(),
                                     admin);
                         } else {
                             new RemoveCredentialsTask(getContext(), getTargetFragment())
                                     .execute(item);
                         }
                         dialog.dismiss();
                     }
                 };
                 builder.setNegativeButton(R.string.trusted_credentials_remove_label, listener);
             }
             AlertDialog dialog = builder.create();
             dialog.setOnShowListener(this);
             return dialog;
         }

         /**
          * Override for the negative button enablement on demand.
          */
         @Override
         public void onShow(DialogInterface dialogInterface) {
             final Credential item = (Credential) getArguments().getParcelable(ARG_CREDENTIAL);
             if (item.isInUse()) {
                 ((AlertDialog) getDialog()).getButton(AlertDialog.BUTTON_NEGATIVE)
                         .setEnabled(false);
             }
         }

         @Override
         public int getMetricsCategory() {
             return SettingsEnums.DIALOG_USER_CREDENTIAL;
         }

         /**
          * Deletes all certificates and keys under a given alias.
          *
          * If the {@link Credential} is for a system alias, all active grants to the alias will be
          * removed using {@link KeyChain}. If the {@link Credential} is for Wi-Fi alias, all
          * credentials and keys will be removed using {@link KeyStore}.
          */
         private class RemoveCredentialsTask extends AsyncTask<Credential, Void, Credential[]> {
             private Context context;
             private Fragment targetFragment;

             public RemoveCredentialsTask(Context context, Fragment targetFragment) {
                 this.context = context;
                 this.targetFragment = targetFragment;
             }

             @Override
             protected Credential[] doInBackground(Credential... credentials) {
                 for (final Credential credential : credentials) {
                     if (credential.isSystem()) {
                         removeGrantsAndDelete(credential);
                     } else {
                         deleteWifiCredential(credential);
                     }
                 }
                 return credentials;
             }

             private void deleteWifiCredential(final Credential credential) {
                 try {
                     final KeyStore keyStore = KeyStore.getInstance(KEYSTORE_PROVIDER);
                     keyStore.load(
                             new AndroidKeyStoreLoadStoreParameter(
                                     KeyProperties.NAMESPACE_WIFI));
                     keyStore.deleteEntry(credential.getAlias());
                 } catch (Exception e) {
                     throw new RuntimeException("Failed to delete keys from keystore.");
                 }
             }

             private void removeGrantsAndDelete(final Credential credential) {
                 final KeyChainConnection conn;
                 try {
                     conn = KeyChain.bind(getContext());
                 } catch (InterruptedException e) {
                     Log.w(TAG, "Connecting to KeyChain", e);
                     return;
                 }

                 try {
                     IKeyChainService keyChain = conn.getService();
                     keyChain.removeKeyPair(credential.alias);
                 } catch (RemoteException e) {
                     Log.w(TAG, "Removing credentials", e);
                 } finally {
                     conn.close();
                 }
             }

             @Override
             protected void onPostExecute(Credential... credentials) {
                 if (targetFragment instanceof UserCredentialsSettings && targetFragment.isAdded()) {
                     final UserCredentialsSettings target = (UserCredentialsSettings) targetFragment;
                     for (final Credential credential : credentials) {
                         target.announceRemoval(credential.alias);
                     }
                     target.refreshItems();
                 }
             }
         }
     }

     /**
      * Opens a background connection to KeyStore to list user credentials.
      * The credentials are stored in a {@link CredentialAdapter} attached to the main
      * {@link ListView} in the fragment.
      */
     private class AliasLoader extends AsyncTask<Void, Void, List<Credential>> {
         /**
          * @return a list of credentials ordered:
          * <ol>
          *   <li>first by purpose;</li>
          *   <li>then by alias.</li>
          * </ol>
          */
         @Override
         protected List<Credential> doInBackground(Void... params) {
             // Certificates can be installed into SYSTEM_UID or WIFI_UID through CertInstaller.
             final int myUserId = UserHandle.myUserId();
             final int systemUid = UserHandle.getUid(myUserId, Process.SYSTEM_UID);
             final int wifiUid = UserHandle.getUid(myUserId, Process.WIFI_UID);

             try {
                 KeyStore processKeystore = KeyStore.getInstance(KEYSTORE_PROVIDER);
                 processKeystore.load(null);
                 KeyStore wifiKeystore = null;
                 if (myUserId == 0) {
                     wifiKeystore = KeyStore.getInstance(KEYSTORE_PROVIDER);
                     wifiKeystore.load(new AndroidKeyStoreLoadStoreParameter(
                             KeyProperties.NAMESPACE_WIFI));
                 }

                 List<Credential> credentials = new ArrayList<>();
                 credentials.addAll(getCredentialsForUid(processKeystore, systemUid).values());
                 if (wifiKeystore != null) {
                     credentials.addAll(getCredentialsForUid(wifiKeystore, wifiUid).values());
                 }
                 return credentials;
             } catch (Exception e) {
                 throw new RuntimeException("Failed to load credentials from Keystore.", e);
             }
         }

         private SortedMap<String, Credential> getCredentialsForUid(KeyStore keyStore, int uid) {
             try {
                 final SortedMap<String, Credential> aliasMap = new TreeMap<>();
                 Enumeration<String> aliases = keyStore.aliases();
                 while (aliases.hasMoreElements()) {
                     String alias = aliases.nextElement();
                     Credential c = new Credential(alias, uid);
                     if (!c.isSystem()) {
                         c.setInUse(mSavedWifiHelper.isCertificateInUse(alias));
                     }
                     Key key = null;
                     try {
                         key = keyStore.getKey(alias, null);
                     } catch (NoSuchAlgorithmException | UnrecoverableKeyException e) {
                         Log.e(TAG, "Error tying to retrieve key: " + alias, e);
                         continue;
                     }
                     if (key != null) {
                         // So we have a key
                         if (key instanceof SecretKey) {
                             // We don't display any symmetric key entries.
                             continue;
                         }
                         // At this point we have determined that we have an asymmetric key.
                         // so we have at least a USER_KEY and USER_CERTIFICATE.
                         c.storedTypes.add(Credential.Type.USER_KEY);

                         Certificate[] certs =  keyStore.getCertificateChain(alias);
                         if (certs != null) {
                             c.storedTypes.add(Credential.Type.USER_CERTIFICATE);
                             if (certs.length > 1) {
                                 c.storedTypes.add(Credential.Type.CA_CERTIFICATE);
                             }
                         }
                     } else {
                         // So there is no key but we have an alias. This must mean that we have
                         // some certificate.
                         if (keyStore.isCertificateEntry(alias)) {
                             c.storedTypes.add(Credential.Type.CA_CERTIFICATE);
                         } else {
                             // This is a weired inconsistent case that should not exist.
                             // Pure trusted certificate entries should be stored in CA_CERTIFICATE,
                             // but if isCErtificateEntry returns null this means that only the
                             // USER_CERTIFICATE is populated which should never be the case without
                             // a private key. It can still be retrieved with
                             // keystore.getCertificate().
                             c.storedTypes.add(Credential.Type.USER_CERTIFICATE);
                         }
                     }
                     aliasMap.put(alias, c);
                 }
                 return aliasMap;
             } catch (KeyStoreException e) {
                 throw new RuntimeException("Failed to load credential from Android Keystore.", e);
             }
         }

         @Override
         protected void onPostExecute(List<Credential> credentials) {
             if (!isAdded()) {
                 return;
             }

             if (credentials == null || credentials.size() == 0) {
                 // Create a "no credentials installed" message for the empty case.
                 TextView emptyTextView = (TextView) getActivity().findViewById(android.R.id.empty);
                 emptyTextView.setText(R.string.user_credential_none_installed);
                 setEmptyView(emptyTextView);
             } else {
                 setEmptyView(null);
             }

             getListView().setAdapter(
                     new CredentialAdapter(credentials, UserCredentialsSettings.this));
         }
     }

     /**
      * Helper class to display {@link Credential}s in a list.
      */
     private static class CredentialAdapter extends RecyclerView.Adapter<ViewHolder> {
         private static final int LAYOUT_RESOURCE = R.layout.user_credential_preference;

         private final List<Credential> mItems;
         private final View.OnClickListener mListener;

         public CredentialAdapter(List<Credential> items, @Nullable View.OnClickListener listener) {
             mItems = items;
             mListener = listener;
         }

         @Override
         public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
             final LayoutInflater inflater = LayoutInflater.from(parent.getContext());
             return new ViewHolder(inflater.inflate(LAYOUT_RESOURCE, parent, false));
         }

         @Override
         public void onBindViewHolder(ViewHolder h, int position) {
             getCredentialView(mItems.get(position), LAYOUT_RESOURCE, h.itemView, null, false);
             h.itemView.setTag(mItems.get(position));
             h.itemView.setOnClickListener(mListener);
         }

         @Override
         public int getItemCount() {
             return mItems.size();
         }
     }

     private static class ViewHolder extends RecyclerView.ViewHolder {
         public ViewHolder(View item) {
             super(item);
         }
     }

     /**
      * Mapping from View IDs in {@link R} to the types of credentials they describe.
      */
     private static final SparseArray<Credential.Type> credentialViewTypes = new SparseArray<>();
     static {
         credentialViewTypes.put(R.id.contents_userkey, Credential.Type.USER_KEY);
         credentialViewTypes.put(R.id.contents_usercrt, Credential.Type.USER_CERTIFICATE);
         credentialViewTypes.put(R.id.contents_cacrt, Credential.Type.CA_CERTIFICATE);
     }

     protected static View getCredentialView(Credential item, @LayoutRes int layoutResource,
             @Nullable View view, ViewGroup parent, boolean expanded) {
         if (view == null) {
             view = LayoutInflater.from(parent.getContext()).inflate(layoutResource, parent, false);
         }

         ((TextView) view.findViewById(R.id.alias)).setText(item.alias);
         updatePurposeView(view.findViewById(R.id.purpose), item);

         view.findViewById(R.id.contents).setVisibility(expanded ? View.VISIBLE : View.GONE);
         if (expanded) {
             updateUsedByViews(view.findViewById(R.id.credential_being_used_by_title),
                     view.findViewById(R.id.credential_being_used_by_content), item);

             for (int i = 0; i < credentialViewTypes.size(); i++) {
                 final View detail = view.findViewById(credentialViewTypes.keyAt(i));
                 detail.setVisibility(item.storedTypes.contains(credentialViewTypes.valueAt(i))
                         ? View.VISIBLE : View.GONE);
             }
         }
         return view;
     }

     @VisibleForTesting
     protected static void updatePurposeView(TextView purpose, Credential item) {
         int subTextResId = R.string.credential_for_vpn_and_apps;
         if (!item.isSystem()) {
             subTextResId = (item.isInUse())
                     ? R.string.credential_for_wifi_in_use
                     : R.string.credential_for_wifi;
         }
         purpose.setText(subTextResId);
     }

     @VisibleForTesting
     protected static void updateUsedByViews(TextView title, TextView content, Credential item) {
         List<String> usedByNames = item.getUsedByNames();
         if (usedByNames.size() > 0) {
             title.setVisibility(View.VISIBLE);
             content.setText(String.join("\n", usedByNames));
             content.setVisibility(View.VISIBLE);
         } else {
             title.setVisibility(View.GONE);
             content.setVisibility(View.GONE);
         }
     }

     static class AliasEntry {
         public String alias;
         public int uid;
     }

     static class Credential implements Parcelable {
         static enum Type {
             CA_CERTIFICATE (Credentials.CA_CERTIFICATE),
             USER_CERTIFICATE (Credentials.USER_CERTIFICATE),
             USER_KEY(Credentials.USER_PRIVATE_KEY, Credentials.USER_SECRET_KEY);

             final String[] prefix;

             Type(String... prefix) {
                 this.prefix = prefix;
             }
         }

         /**
          * Main part of the credential's alias. To fetch an item from KeyStore, prepend one of the
          * prefixes from {@link CredentialItem.storedTypes}.
          */
         final String alias;

         /**
          * UID under which this credential is stored. Typically {@link Process#SYSTEM_UID} but can
          * also be {@link Process#WIFI_UID} for credentials installed as wifi certificates.
          */
         final int uid;

         /**
          * Indicate whether or not this credential is in use.
          */
         boolean mIsInUse;

         /**
          * The list of networks which use this credential.
          */
         List<String> mUsedByNames = new ArrayList<>();

         /**
          * Should contain some non-empty subset of:
          * <ul>
          *   <li>{@link Credentials.CA_CERTIFICATE}</li>
          *   <li>{@link Credentials.USER_CERTIFICATE}</li>
          *   <li>{@link Credentials.USER_KEY}</li>
          * </ul>
          */
         final EnumSet<Type> storedTypes = EnumSet.noneOf(Type.class);

         Credential(final String alias, final int uid) {
             this.alias = alias;
             this.uid = uid;
         }

         Credential(Parcel in) {
             this(in.readString(), in.readInt());

             long typeBits = in.readLong();
             for (Type i : Type.values()) {
                 if ((typeBits & (1L << i.ordinal())) != 0L) {
                     storedTypes.add(i);
                 }
             }
         }

         public void writeToParcel(Parcel out, int flags) {
             out.writeString(alias);
             out.writeInt(uid);

             long typeBits = 0;
             for (Type i : storedTypes) {
                 typeBits |= 1L << i.ordinal();
             }
             out.writeLong(typeBits);
         }

         public int describeContents() {
             return 0;
         }

         public static final Parcelable.Creator<Credential> CREATOR
                 = new Parcelable.Creator<Credential>() {
             public Credential createFromParcel(Parcel in) {
                 return new Credential(in);
             }

             public Credential[] newArray(int size) {
                 return new Credential[size];
             }
         };

         public boolean isSystem() {
             return UserHandle.getAppId(uid) == Process.SYSTEM_UID;
         }

         public String getAlias() {
             return alias;
         }

         public EnumSet<Type> getStoredTypes() {
             return storedTypes;
         }

         public void setInUse(boolean inUse) {
             mIsInUse = inUse;
         }

         public boolean isInUse() {
             return mIsInUse;
         }

         public void setUsedByNames(List<String> names) {
             mUsedByNames = new ArrayList<>(names);
         }

         public List<String> getUsedByNames() {
             return new ArrayList<String>(mUsedByNames);
         }
     }
 }
	/*
	* Copyright (C) 2015 The Android Open Source Project
	*
	* Licensed under the Apache License, Version 2.0 (the "License");
	* you may not use this file except in compliance with the License.
	* You may obtain a copy of the License at
	*
	* http://www.apache.org/licenses/LICENSE-2.0
	*
	* Unless required by applicable law or agreed to in writing, software
	* distributed under the License is distributed on an "AS IS" BASIS,
	* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	* See the License for the specific language governing permissions and
	* limitations under the License.
	*/

	package com.android.settings;

	import android.annotation.LayoutRes;
	import android.annotation.Nullable;
	import android.app.Dialog;
	import android.app.settings.SettingsEnums;
	import android.content.Context;
	import android.content.DialogInterface;
	import android.os.AsyncTask;
	import android.os.Bundle;
	import android.os.Parcel;
	import android.os.Parcelable;
	import android.os.Process;
	import android.os.RemoteException;
	import android.os.UserHandle;
	import android.os.UserManager;
	import android.security.Credentials;
	import android.security.IKeyChainService;
	import android.security.KeyChain;
	import android.security.KeyChain.KeyChainConnection;
	import android.security.keystore.KeyProperties;
	import android.security.keystore2.AndroidKeyStoreLoadStoreParameter;
	import android.util.Log;
	import android.util.SparseArray;
	import android.view.LayoutInflater;
	import android.view.View;
	import android.view.ViewGroup;
	import android.widget.TextView;

	import androidx.annotation.VisibleForTesting;
	import androidx.appcompat.app.AlertDialog;
	import androidx.fragment.app.DialogFragment;
	import androidx.fragment.app.Fragment;
	import androidx.recyclerview.widget.RecyclerView;

	import com.android.settings.core.instrumentation.InstrumentedDialogFragment;
	import com.android.settings.wifi.helper.SavedWifiHelper;
	import com.android.settingslib.RestrictedLockUtils;
	import com.android.settingslib.RestrictedLockUtils.EnforcedAdmin;
	import com.android.settingslib.RestrictedLockUtilsInternal;

	import java.security.Key;
	import java.security.KeyStore;
	import java.security.KeyStoreException;
	import java.security.NoSuchAlgorithmException;
	import java.security.UnrecoverableKeyException;
	import java.security.cert.Certificate;
	import java.util.ArrayList;
	import java.util.EnumSet;
	import java.util.Enumeration;
	import java.util.List;
	import java.util.SortedMap;
	import java.util.TreeMap;

	import javax.crypto.SecretKey;

	public class UserCredentialsSettings extends SettingsPreferenceFragment
	implements View.OnClickListener {
	private static final String TAG = "UserCredentialsSettings";

	private static final String KEYSTORE_PROVIDER = "AndroidKeyStore";

	@VisibleForTesting
	protected SavedWifiHelper mSavedWifiHelper;

	@Override
	public int getMetricsCategory() {
	return SettingsEnums.USER_CREDENTIALS;
	}

	@Override
	public void onResume() {
	super.onResume();
	refreshItems();
	}

	@Override
	public void onClick(final View view) {
	final Credential item = (Credential) view.getTag();
	if (item == null) return;
	if (item.isInUse()) {
	item.setUsedByNames(mSavedWifiHelper.getCertificateNetworkNames(item.alias));
	}
	showCredentialDialogFragment(item);
	}

	@Override
	public void onCreate(@Nullable Bundle savedInstanceState) {
	super.onCreate(savedInstanceState);
	getActivity().setTitle(R.string.user_credentials);
	mSavedWifiHelper = SavedWifiHelper.getInstance(getContext(), getSettingsLifecycle());
	}

	@VisibleForTesting
	protected void showCredentialDialogFragment(Credential item) {
	CredentialDialogFragment.show(this, item);
	}

	protected void announceRemoval(String alias) {
	if (!isAdded()) {
	return;
	}
	getListView().announceForAccessibility(getString(R.string.user_credential_removed, alias));
	}

	protected void refreshItems() {
	if (isAdded()) {
	new AliasLoader().execute();
	}
	}

	/** The fragment to show the credential information. */
	public static class CredentialDialogFragment extends InstrumentedDialogFragment
	implements DialogInterface.OnShowListener {
	private static final String TAG = "CredentialDialogFragment";
	private static final String ARG_CREDENTIAL = "credential";

	public static void show(Fragment target, Credential item) {
	final Bundle args = new Bundle();
	args.putParcelable(ARG_CREDENTIAL, item);

	if (target.getFragmentManager().findFragmentByTag(TAG) == null) {
	final DialogFragment frag = new CredentialDialogFragment();
	frag.setTargetFragment(target, /* requestCode */ -1);
	frag.setArguments(args);
	frag.show(target.getFragmentManager(), TAG);
	}
	}

	@Override
	public Dialog onCreateDialog(Bundle savedInstanceState) {
	final Credential item = (Credential) getArguments().getParcelable(ARG_CREDENTIAL);

	View root = getActivity().getLayoutInflater()
	.inflate(R.layout.user_credential_dialog, null);
	ViewGroup infoContainer = (ViewGroup) root.findViewById(R.id.credential_container);
	View contentView = getCredentialView(item, R.layout.user_credential, null,
	infoContainer, /* expanded */ true);
	infoContainer.addView(contentView);

	AlertDialog.Builder builder = new AlertDialog.Builder(getActivity())
	.setView(root)
	.setTitle(R.string.user_credential_title)
	.setPositiveButton(R.string.done, null);

	final String restriction = UserManager.DISALLOW_CONFIG_CREDENTIALS;
	final int myUserId = UserHandle.myUserId();
	if (!RestrictedLockUtilsInternal.hasBaseUserRestriction(getContext(), restriction,
	myUserId)) {
	DialogInterface.OnClickListener listener = new DialogInterface.OnClickListener() {
	@Override public void onClick(DialogInterface dialog, int id) {
	final EnforcedAdmin admin = RestrictedLockUtilsInternal
	.checkIfRestrictionEnforced(getContext(), restriction, myUserId);
	if (admin != null) {
	RestrictedLockUtils.sendShowAdminSupportDetailsIntent(getContext(),
	admin);
	} else {
	new RemoveCredentialsTask(getContext(), getTargetFragment())
	.execute(item);
	}
	dialog.dismiss();
	}
	};
	builder.setNegativeButton(R.string.trusted_credentials_remove_label, listener);
	}
	AlertDialog dialog = builder.create();
	dialog.setOnShowListener(this);
	return dialog;
	}

	/**
	* Override for the negative button enablement on demand.
	*/
	@Override
	public void onShow(DialogInterface dialogInterface) {
	final Credential item = (Credential) getArguments().getParcelable(ARG_CREDENTIAL);
	if (item.isInUse()) {
	((AlertDialog) getDialog()).getButton(AlertDialog.BUTTON_NEGATIVE)
	.setEnabled(false);
	}
	}

	@Override
	public int getMetricsCategory() {
	return SettingsEnums.DIALOG_USER_CREDENTIAL;
	}

	/**
	* Deletes all certificates and keys under a given alias.
	*
	* If the {@link Credential} is for a system alias, all active grants to the alias will be
	* removed using {@link KeyChain}. If the {@link Credential} is for Wi-Fi alias, all
	* credentials and keys will be removed using {@link KeyStore}.
	*/
	private class RemoveCredentialsTask extends AsyncTask<Credential, Void, Credential[]> {
	private Context context;
	private Fragment targetFragment;

	public RemoveCredentialsTask(Context context, Fragment targetFragment) {
	this.context = context;
	this.targetFragment = targetFragment;
	}

	@Override
	protected Credential[] doInBackground(Credential... credentials) {
	for (final Credential credential : credentials) {
	if (credential.isSystem()) {
	removeGrantsAndDelete(credential);
	} else {
	deleteWifiCredential(credential);
	}
	}
	return credentials;
	}

	private void deleteWifiCredential(final Credential credential) {
	try {
	final KeyStore keyStore = KeyStore.getInstance(KEYSTORE_PROVIDER);
	keyStore.load(
	new AndroidKeyStoreLoadStoreParameter(
	KeyProperties.NAMESPACE_WIFI));
	keyStore.deleteEntry(credential.getAlias());
	} catch (Exception e) {
	throw new RuntimeException("Failed to delete keys from keystore.");
	}
	}

	private void removeGrantsAndDelete(final Credential credential) {
	final KeyChainConnection conn;
	try {
	conn = KeyChain.bind(getContext());
	} catch (InterruptedException e) {
	Log.w(TAG, "Connecting to KeyChain", e);
	return;
	}

	try {
	IKeyChainService keyChain = conn.getService();
	keyChain.removeKeyPair(credential.alias);
	} catch (RemoteException e) {
	Log.w(TAG, "Removing credentials", e);
	} finally {
	conn.close();
	}
	}

	@Override
	protected void onPostExecute(Credential... credentials) {
	if (targetFragment instanceof UserCredentialsSettings && targetFragment.isAdded()) {
	final UserCredentialsSettings target = (UserCredentialsSettings) targetFragment;
	for (final Credential credential : credentials) {
	target.announceRemoval(credential.alias);
	}
	target.refreshItems();
	}
	}
	}
	}

	/**
	* Opens a background connection to KeyStore to list user credentials.
	* The credentials are stored in a {@link CredentialAdapter} attached to the main
	* {@link ListView} in the fragment.
	*/
	private class AliasLoader extends AsyncTask<Void, Void, List<Credential>> {
	/**
	* @return a list of credentials ordered:
	* <ol>
	* <li>first by purpose;</li>
	* <li>then by alias.</li>
	* </ol>
	*/
	@Override
	protected List<Credential> doInBackground(Void... params) {
	// Certificates can be installed into SYSTEM_UID or WIFI_UID through CertInstaller.
	final int myUserId = UserHandle.myUserId();
	final int systemUid = UserHandle.getUid(myUserId, Process.SYSTEM_UID);
	final int wifiUid = UserHandle.getUid(myUserId, Process.WIFI_UID);

	try {
	KeyStore processKeystore = KeyStore.getInstance(KEYSTORE_PROVIDER);
	processKeystore.load(null);
	KeyStore wifiKeystore = null;
	if (myUserId == 0) {
	wifiKeystore = KeyStore.getInstance(KEYSTORE_PROVIDER);
	wifiKeystore.load(new AndroidKeyStoreLoadStoreParameter(
	KeyProperties.NAMESPACE_WIFI));
	}

	List<Credential> credentials = new ArrayList<>();
	credentials.addAll(getCredentialsForUid(processKeystore, systemUid).values());
	if (wifiKeystore != null) {
	credentials.addAll(getCredentialsForUid(wifiKeystore, wifiUid).values());
	}
	return credentials;
	} catch (Exception e) {
	throw new RuntimeException("Failed to load credentials from Keystore.", e);
	}
	}

	private SortedMap<String, Credential> getCredentialsForUid(KeyStore keyStore, int uid) {
	try {
	final SortedMap<String, Credential> aliasMap = new TreeMap<>();
	Enumeration<String> aliases = keyStore.aliases();
	while (aliases.hasMoreElements()) {
	String alias = aliases.nextElement();
	Credential c = new Credential(alias, uid);
	if (!c.isSystem()) {
	c.setInUse(mSavedWifiHelper.isCertificateInUse(alias));
	}
	Key key = null;
	try {
	key = keyStore.getKey(alias, null);
	} catch (NoSuchAlgorithmException \| UnrecoverableKeyException e) {
	Log.e(TAG, "Error tying to retrieve key: " + alias, e);
	continue;
	}
	if (key != null) {
	// So we have a key
	if (key instanceof SecretKey) {
	// We don't display any symmetric key entries.
	continue;
	}
	// At this point we have determined that we have an asymmetric key.
	// so we have at least a USER_KEY and USER_CERTIFICATE.
	c.storedTypes.add(Credential.Type.USER_KEY);

	Certificate[] certs = keyStore.getCertificateChain(alias);
	if (certs != null) {
	c.storedTypes.add(Credential.Type.USER_CERTIFICATE);
	if (certs.length > 1) {
	c.storedTypes.add(Credential.Type.CA_CERTIFICATE);
	}
	}
	} else {
	// So there is no key but we have an alias. This must mean that we have
	// some certificate.
	if (keyStore.isCertificateEntry(alias)) {
	c.storedTypes.add(Credential.Type.CA_CERTIFICATE);
	} else {
	// This is a weired inconsistent case that should not exist.
	// Pure trusted certificate entries should be stored in CA_CERTIFICATE,
	// but if isCErtificateEntry returns null this means that only the
	// USER_CERTIFICATE is populated which should never be the case without
	// a private key. It can still be retrieved with
	// keystore.getCertificate().
	c.storedTypes.add(Credential.Type.USER_CERTIFICATE);
	}
	}
	aliasMap.put(alias, c);
	}
	return aliasMap;
	} catch (KeyStoreException e) {
	throw new RuntimeException("Failed to load credential from Android Keystore.", e);
	}
	}

	@Override
	protected void onPostExecute(List<Credential> credentials) {
	if (!isAdded()) {
	return;
	}

	if (credentials == null \|\| credentials.size() == 0) {
	// Create a "no credentials installed" message for the empty case.
	TextView emptyTextView = (TextView) getActivity().findViewById(android.R.id.empty);
	emptyTextView.setText(R.string.user_credential_none_installed);
	setEmptyView(emptyTextView);
	} else {
	setEmptyView(null);
	}

	getListView().setAdapter(
	new CredentialAdapter(credentials, UserCredentialsSettings.this));
	}
	}

	/**
	* Helper class to display {@link Credential}s in a list.
	*/
	private static class CredentialAdapter extends RecyclerView.Adapter<ViewHolder> {
	private static final int LAYOUT_RESOURCE = R.layout.user_credential_preference;

	private final List<Credential> mItems;
	private final View.OnClickListener mListener;

	public CredentialAdapter(List<Credential> items, @Nullable View.OnClickListener listener) {
	mItems = items;
	mListener = listener;
	}

	@Override
	public ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
	final LayoutInflater inflater = LayoutInflater.from(parent.getContext());
	return new ViewHolder(inflater.inflate(LAYOUT_RESOURCE, parent, false));
	}

	@Override
	public void onBindViewHolder(ViewHolder h, int position) {
	getCredentialView(mItems.get(position), LAYOUT_RESOURCE, h.itemView, null, false);
	h.itemView.setTag(mItems.get(position));
	h.itemView.setOnClickListener(mListener);
	}

	@Override
	public int getItemCount() {
	return mItems.size();
	}
	}

	private static class ViewHolder extends RecyclerView.ViewHolder {
	public ViewHolder(View item) {
	super(item);
	}
	}

	/**
	* Mapping from View IDs in {@link R} to the types of credentials they describe.
	*/
	private static final SparseArray<Credential.Type> credentialViewTypes = new SparseArray<>();
	static {
	credentialViewTypes.put(R.id.contents_userkey, Credential.Type.USER_KEY);
	credentialViewTypes.put(R.id.contents_usercrt, Credential.Type.USER_CERTIFICATE);
	credentialViewTypes.put(R.id.contents_cacrt, Credential.Type.CA_CERTIFICATE);
	}

	protected static View getCredentialView(Credential item, @LayoutRes int layoutResource,
	@Nullable View view, ViewGroup parent, boolean expanded) {
	if (view == null) {
	view = LayoutInflater.from(parent.getContext()).inflate(layoutResource, parent, false);
	}

	((TextView) view.findViewById(R.id.alias)).setText(item.alias);
	updatePurposeView(view.findViewById(R.id.purpose), item);

	view.findViewById(R.id.contents).setVisibility(expanded ? View.VISIBLE : View.GONE);
	if (expanded) {
	updateUsedByViews(view.findViewById(R.id.credential_being_used_by_title),
	view.findViewById(R.id.credential_being_used_by_content), item);

	for (int i = 0; i < credentialViewTypes.size(); i++) {
	final View detail = view.findViewById(credentialViewTypes.keyAt(i));
	detail.setVisibility(item.storedTypes.contains(credentialViewTypes.valueAt(i))
	? View.VISIBLE : View.GONE);
	}
	}
	return view;
	}

	@VisibleForTesting
	protected static void updatePurposeView(TextView purpose, Credential item) {
	int subTextResId = R.string.credential_for_vpn_and_apps;
	if (!item.isSystem()) {
	subTextResId = (item.isInUse())
	? R.string.credential_for_wifi_in_use
	: R.string.credential_for_wifi;
	}
	purpose.setText(subTextResId);
	}

	@VisibleForTesting
	protected static void updateUsedByViews(TextView title, TextView content, Credential item) {
	List<String> usedByNames = item.getUsedByNames();
	if (usedByNames.size() > 0) {
	title.setVisibility(View.VISIBLE);
	content.setText(String.join("\n", usedByNames));
	content.setVisibility(View.VISIBLE);
	} else {
	title.setVisibility(View.GONE);
	content.setVisibility(View.GONE);
	}
	}

	static class AliasEntry {
	public String alias;
	public int uid;
	}

	static class Credential implements Parcelable {
	static enum Type {
	CA_CERTIFICATE (Credentials.CA_CERTIFICATE),
	USER_CERTIFICATE (Credentials.USER_CERTIFICATE),
	USER_KEY(Credentials.USER_PRIVATE_KEY, Credentials.USER_SECRET_KEY);

	final String[] prefix;

	Type(String... prefix) {
	this.prefix = prefix;
	}
	}

	/**
	* Main part of the credential's alias. To fetch an item from KeyStore, prepend one of the
	* prefixes from {@link CredentialItem.storedTypes}.
	*/
	final String alias;

	/**
	* UID under which this credential is stored. Typically {@link Process#SYSTEM_UID} but can
	* also be {@link Process#WIFI_UID} for credentials installed as wifi certificates.
	*/
	final int uid;

	/**
	* Indicate whether or not this credential is in use.
	*/
	boolean mIsInUse;

	/**
	* The list of networks which use this credential.
	*/
	List<String> mUsedByNames = new ArrayList<>();

	/**
	* Should contain some non-empty subset of:
	* <ul>
	* <li>{@link Credentials.CA_CERTIFICATE}</li>
	* <li>{@link Credentials.USER_CERTIFICATE}</li>
	* <li>{@link Credentials.USER_KEY}</li>
	* </ul>
	*/
	final EnumSet<Type> storedTypes = EnumSet.noneOf(Type.class);

	Credential(final String alias, final int uid) {
	this.alias = alias;
	this.uid = uid;
	}

	Credential(Parcel in) {
	this(in.readString(), in.readInt());

	long typeBits = in.readLong();
	for (Type i : Type.values()) {
	if ((typeBits & (1L << i.ordinal())) != 0L) {
	storedTypes.add(i);
	}
	}
	}

	public void writeToParcel(Parcel out, int flags) {
	out.writeString(alias);
	out.writeInt(uid);

	long typeBits = 0;
	for (Type i : storedTypes) {
	typeBits \|= 1L << i.ordinal();
	}
	out.writeLong(typeBits);
	}

	public int describeContents() {
	return 0;
	}

	public static final Parcelable.Creator<Credential> CREATOR
	= new Parcelable.Creator<Credential>() {
	public Credential createFromParcel(Parcel in) {
	return new Credential(in);
	}

	public Credential[] newArray(int size) {
	return new Credential[size];
	}
	};

	public boolean isSystem() {
	return UserHandle.getAppId(uid) == Process.SYSTEM_UID;
	}

	public String getAlias() {
	return alias;
	}

	public EnumSet<Type> getStoredTypes() {
	return storedTypes;
	}

	public void setInUse(boolean inUse) {
	mIsInUse = inUse;
	}

	public boolean isInUse() {
	return mIsInUse;
	}

	public void setUsedByNames(List<String> names) {
	mUsedByNames = new ArrayList<>(names);
	}

	public List<String> getUsedByNames() {
	return new ArrayList<String>(mUsedByNames);
	}
	}
	}