| /* |
| * Copyright (C) 2009 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.server; |
| |
| import java.io.File; |
| import java.io.IOException; |
| |
| import android.os.Binder; |
| import android.os.Environment; |
| import android.os.Handler; |
| import android.os.Message; |
| import android.util.Log; |
| |
| /** |
| * A service designed to load and periodically save "randomness" |
| * for the Linux kernel. |
| * |
| * <p>When a Linux system starts up, the entropy pool associated with |
| * {@code /dev/random} may be in a fairly predictable state. Applications which |
| * depend strongly on randomness may find {@code /dev/random} or |
| * {@code /dev/urandom} returning predictable data. In order to counteract |
| * this effect, it's helpful to carry the entropy pool information across |
| * shutdowns and startups. |
| * |
| * <p>This class was modeled after the script in |
| * <a href="http://www.kernel.org/doc/man-pages/online/pages/man4/random.4.html">man |
| * 4 random</a>. |
| * |
| * <p>TODO: Investigate attempting to write entropy data at shutdown time |
| * instead of periodically. |
| */ |
| public class EntropyService extends Binder { |
| private static final String ENTROPY_FILENAME = getSystemDir() + "/entropy.dat"; |
| private static final String TAG = "EntropyService"; |
| private static final int ENTROPY_WHAT = 1; |
| private static final int ENTROPY_WRITE_PERIOD = 3 * 60 * 60 * 1000; // 3 hrs |
| private static final String RANDOM_DEV = "/dev/urandom"; |
| |
| /** |
| * Handler that periodically updates the entropy on disk. |
| */ |
| private final Handler mHandler = new Handler() { |
| @Override |
| public void handleMessage(Message msg) { |
| if (msg.what != ENTROPY_WHAT) { |
| Log.e(TAG, "Will not process invalid message"); |
| return; |
| } |
| writeEntropy(); |
| scheduleEntropyWriter(); |
| } |
| }; |
| |
| public EntropyService() { |
| loadInitialEntropy(); |
| writeEntropy(); |
| scheduleEntropyWriter(); |
| } |
| |
| private void scheduleEntropyWriter() { |
| mHandler.removeMessages(ENTROPY_WHAT); |
| mHandler.sendEmptyMessageDelayed(ENTROPY_WHAT, ENTROPY_WRITE_PERIOD); |
| } |
| |
| private void loadInitialEntropy() { |
| try { |
| RandomBlock.fromFile(ENTROPY_FILENAME).toFile(RANDOM_DEV); |
| } catch (IOException e) { |
| Log.w(TAG, "unable to load initial entropy (first boot?)", e); |
| } |
| } |
| |
| private void writeEntropy() { |
| try { |
| RandomBlock.fromFile(RANDOM_DEV).toFile(ENTROPY_FILENAME); |
| } catch (IOException e) { |
| Log.e(TAG, "unable to write entropy", e); |
| } |
| } |
| |
| private static String getSystemDir() { |
| File dataDir = Environment.getDataDirectory(); |
| File systemDir = new File(dataDir, "system"); |
| systemDir.mkdirs(); |
| return systemDir.toString(); |
| } |
| } |