Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 1 | /* |
| 2 | * Copyright (C) 2009 The Android Open Source Project |
| 3 | * |
| 4 | * Licensed under the Apache License, Version 2.0 (the "License"); |
| 5 | * you may not use this file except in compliance with the License. |
| 6 | * You may obtain a copy of the License at |
| 7 | * |
| 8 | * http://www.apache.org/licenses/LICENSE-2.0 |
| 9 | * |
| 10 | * Unless required by applicable law or agreed to in writing, software |
| 11 | * distributed under the License is distributed on an "AS IS" BASIS, |
| 12 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
| 13 | * See the License for the specific language governing permissions and |
| 14 | * limitations under the License. |
| 15 | */ |
| 16 | |
| 17 | package com.android.server; |
| 18 | |
| 19 | import java.io.File; |
Dianne Hackborn | 13579ed | 2012-11-28 18:05:36 -0800 | [diff] [blame] | 20 | import java.io.FileNotFoundException; |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 21 | import java.io.FileOutputStream; |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 22 | import java.io.IOException; |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 23 | import java.io.OutputStream; |
| 24 | import java.io.PrintWriter; |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 25 | |
Nick Kralevich | 79619dd | 2013-03-04 13:05:32 -0800 | [diff] [blame] | 26 | import android.content.BroadcastReceiver; |
| 27 | import android.content.Context; |
| 28 | import android.content.Intent; |
| 29 | import android.content.IntentFilter; |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 30 | import android.os.Binder; |
| 31 | import android.os.Environment; |
| 32 | import android.os.Handler; |
| 33 | import android.os.Message; |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 34 | import android.os.SystemProperties; |
Joe Onorato | 8a9b220 | 2010-02-26 18:56:32 -0800 | [diff] [blame] | 35 | import android.util.Slog; |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 36 | |
| 37 | /** |
| 38 | * A service designed to load and periodically save "randomness" |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 39 | * for the Linux kernel RNG and to mix in data from Hardware RNG (if present) |
| 40 | * into the Linux RNG. |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 41 | * |
| 42 | * <p>When a Linux system starts up, the entropy pool associated with |
| 43 | * {@code /dev/random} may be in a fairly predictable state. Applications which |
| 44 | * depend strongly on randomness may find {@code /dev/random} or |
| 45 | * {@code /dev/urandom} returning predictable data. In order to counteract |
| 46 | * this effect, it's helpful to carry the entropy pool information across |
| 47 | * shutdowns and startups. |
| 48 | * |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 49 | * <p>On systems with Hardware RNG (/dev/hw_random), a block of output from HW |
| 50 | * RNG is mixed into the Linux RNG on EntropyMixer's startup and whenever |
| 51 | * EntropyMixer periodically runs to save a block of output from Linux RNG on |
| 52 | * disk. This mixing is done in a way that does not increase the Linux RNG's |
| 53 | * entropy estimate is not increased. This is to avoid having to trust/verify |
| 54 | * the quality and authenticity of the "randomness" of the HW RNG. |
| 55 | * |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 56 | * <p>This class was modeled after the script in |
| 57 | * <a href="http://www.kernel.org/doc/man-pages/online/pages/man4/random.4.html">man |
| 58 | * 4 random</a>. |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 59 | */ |
Nick Kralevich | 6967cbc | 2011-11-17 13:24:32 -0800 | [diff] [blame] | 60 | public class EntropyMixer extends Binder { |
| 61 | private static final String TAG = "EntropyMixer"; |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 62 | private static final int ENTROPY_WHAT = 1; |
| 63 | private static final int ENTROPY_WRITE_PERIOD = 3 * 60 * 60 * 1000; // 3 hrs |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 64 | private static final long START_TIME = System.currentTimeMillis(); |
| 65 | private static final long START_NANOTIME = System.nanoTime(); |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 66 | |
Nick Kralevich | 93a6839 | 2010-03-19 16:57:21 -0700 | [diff] [blame] | 67 | private final String randomDevice; |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 68 | private final String hwRandomDevice; |
Nick Kralevich | 93a6839 | 2010-03-19 16:57:21 -0700 | [diff] [blame] | 69 | private final String entropyFile; |
| 70 | |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 71 | /** |
| 72 | * Handler that periodically updates the entropy on disk. |
| 73 | */ |
| 74 | private final Handler mHandler = new Handler() { |
| 75 | @Override |
| 76 | public void handleMessage(Message msg) { |
| 77 | if (msg.what != ENTROPY_WHAT) { |
Joe Onorato | 8a9b220 | 2010-02-26 18:56:32 -0800 | [diff] [blame] | 78 | Slog.e(TAG, "Will not process invalid message"); |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 79 | return; |
| 80 | } |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 81 | addHwRandomEntropy(); |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 82 | writeEntropy(); |
| 83 | scheduleEntropyWriter(); |
| 84 | } |
| 85 | }; |
| 86 | |
Nick Kralevich | 79619dd | 2013-03-04 13:05:32 -0800 | [diff] [blame] | 87 | private final BroadcastReceiver mBroadcastReceiver = new BroadcastReceiver() { |
| 88 | @Override |
| 89 | public void onReceive(Context context, Intent intent) { |
| 90 | writeEntropy(); |
| 91 | } |
| 92 | }; |
| 93 | |
| 94 | public EntropyMixer(Context context) { |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 95 | this(context, getSystemDir() + "/entropy.dat", "/dev/urandom", "/dev/hw_random"); |
Nick Kralevich | 93a6839 | 2010-03-19 16:57:21 -0700 | [diff] [blame] | 96 | } |
| 97 | |
| 98 | /** Test only interface, not for public use */ |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 99 | public EntropyMixer( |
| 100 | Context context, |
| 101 | String entropyFile, |
| 102 | String randomDevice, |
| 103 | String hwRandomDevice) { |
Nick Kralevich | 93a6839 | 2010-03-19 16:57:21 -0700 | [diff] [blame] | 104 | if (randomDevice == null) { throw new NullPointerException("randomDevice"); } |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 105 | if (hwRandomDevice == null) { throw new NullPointerException("hwRandomDevice"); } |
Nick Kralevich | 93a6839 | 2010-03-19 16:57:21 -0700 | [diff] [blame] | 106 | if (entropyFile == null) { throw new NullPointerException("entropyFile"); } |
| 107 | |
| 108 | this.randomDevice = randomDevice; |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 109 | this.hwRandomDevice = hwRandomDevice; |
Nick Kralevich | 93a6839 | 2010-03-19 16:57:21 -0700 | [diff] [blame] | 110 | this.entropyFile = entropyFile; |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 111 | loadInitialEntropy(); |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 112 | addDeviceSpecificEntropy(); |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 113 | addHwRandomEntropy(); |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 114 | writeEntropy(); |
| 115 | scheduleEntropyWriter(); |
Nick Kralevich | 79619dd | 2013-03-04 13:05:32 -0800 | [diff] [blame] | 116 | IntentFilter broadcastFilter = new IntentFilter(Intent.ACTION_SHUTDOWN); |
| 117 | broadcastFilter.addAction(Intent.ACTION_POWER_CONNECTED); |
| 118 | broadcastFilter.addAction(Intent.ACTION_REBOOT); |
| 119 | context.registerReceiver(mBroadcastReceiver, broadcastFilter); |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 120 | } |
| 121 | |
| 122 | private void scheduleEntropyWriter() { |
| 123 | mHandler.removeMessages(ENTROPY_WHAT); |
| 124 | mHandler.sendEmptyMessageDelayed(ENTROPY_WHAT, ENTROPY_WRITE_PERIOD); |
| 125 | } |
| 126 | |
| 127 | private void loadInitialEntropy() { |
| 128 | try { |
Elliott Hughes | 6907891 | 2011-04-04 12:15:34 -0700 | [diff] [blame] | 129 | RandomBlock.fromFile(entropyFile).toFile(randomDevice, false); |
Dianne Hackborn | 13579ed | 2012-11-28 18:05:36 -0800 | [diff] [blame] | 130 | } catch (FileNotFoundException e) { |
| 131 | Slog.w(TAG, "No existing entropy file -- first boot?"); |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 132 | } catch (IOException e) { |
Dianne Hackborn | 13579ed | 2012-11-28 18:05:36 -0800 | [diff] [blame] | 133 | Slog.w(TAG, "Failure loading existing entropy file", e); |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 134 | } |
| 135 | } |
| 136 | |
| 137 | private void writeEntropy() { |
| 138 | try { |
Nick Kralevich | 79619dd | 2013-03-04 13:05:32 -0800 | [diff] [blame] | 139 | Slog.i(TAG, "Writing entropy..."); |
Elliott Hughes | 6907891 | 2011-04-04 12:15:34 -0700 | [diff] [blame] | 140 | RandomBlock.fromFile(randomDevice).toFile(entropyFile, true); |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 141 | } catch (IOException e) { |
Dianne Hackborn | 13579ed | 2012-11-28 18:05:36 -0800 | [diff] [blame] | 142 | Slog.w(TAG, "Unable to write entropy", e); |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 143 | } |
| 144 | } |
| 145 | |
| 146 | /** |
| 147 | * Add additional information to the kernel entropy pool. The |
| 148 | * information isn't necessarily "random", but that's ok. Even |
| 149 | * sending non-random information to {@code /dev/urandom} is useful |
| 150 | * because, while it doesn't increase the "quality" of the entropy pool, |
| 151 | * it mixes more bits into the pool, which gives us a higher degree |
| 152 | * of uncertainty in the generated randomness. Like nature, writes to |
| 153 | * the random device can only cause the quality of the entropy in the |
| 154 | * kernel to stay the same or increase. |
| 155 | * |
| 156 | * <p>For maximum effect, we try to target information which varies |
| 157 | * on a per-device basis, and is not easily observable to an |
| 158 | * attacker. |
| 159 | */ |
| 160 | private void addDeviceSpecificEntropy() { |
| 161 | PrintWriter out = null; |
| 162 | try { |
Nick Kralevich | 93a6839 | 2010-03-19 16:57:21 -0700 | [diff] [blame] | 163 | out = new PrintWriter(new FileOutputStream(randomDevice)); |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 164 | out.println("Copyright (C) 2009 The Android Open Source Project"); |
| 165 | out.println("All Your Randomness Are Belong To Us"); |
| 166 | out.println(START_TIME); |
| 167 | out.println(START_NANOTIME); |
| 168 | out.println(SystemProperties.get("ro.serialno")); |
| 169 | out.println(SystemProperties.get("ro.bootmode")); |
| 170 | out.println(SystemProperties.get("ro.baseband")); |
| 171 | out.println(SystemProperties.get("ro.carrier")); |
| 172 | out.println(SystemProperties.get("ro.bootloader")); |
| 173 | out.println(SystemProperties.get("ro.hardware")); |
| 174 | out.println(SystemProperties.get("ro.revision")); |
Nick Kralevich | 03ce760 | 2013-02-01 15:21:50 -0800 | [diff] [blame] | 175 | out.println(SystemProperties.get("ro.build.fingerprint")); |
Nick Kralevich | b91ec41 | 2010-09-27 14:49:00 -0700 | [diff] [blame] | 176 | out.println(new Object().hashCode()); |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 177 | out.println(System.currentTimeMillis()); |
| 178 | out.println(System.nanoTime()); |
| 179 | } catch (IOException e) { |
Joe Onorato | 8a9b220 | 2010-02-26 18:56:32 -0800 | [diff] [blame] | 180 | Slog.w(TAG, "Unable to add device specific data to the entropy pool", e); |
Nick Kralevich | b8cba95 | 2009-06-19 09:45:35 -0700 | [diff] [blame] | 181 | } finally { |
| 182 | if (out != null) { |
| 183 | out.close(); |
| 184 | } |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 185 | } |
| 186 | } |
| 187 | |
Alex Klyubin | 6ab3d20 | 2013-10-03 13:23:13 -0700 | [diff] [blame] | 188 | /** |
| 189 | * Mixes in the output from HW RNG (if present) into the Linux RNG. |
| 190 | */ |
| 191 | private void addHwRandomEntropy() { |
| 192 | try { |
| 193 | RandomBlock.fromFile(hwRandomDevice).toFile(randomDevice, false); |
| 194 | Slog.i(TAG, "Added HW RNG output to entropy pool"); |
| 195 | } catch (FileNotFoundException ignored) { |
| 196 | // HW RNG not present/exposed -- ignore |
| 197 | } catch (IOException e) { |
| 198 | Slog.w(TAG, "Failed to add HW RNG output to entropy pool", e); |
| 199 | } |
| 200 | } |
| 201 | |
Nick Kralevich | 4fb2561 | 2009-06-17 16:03:22 -0700 | [diff] [blame] | 202 | private static String getSystemDir() { |
| 203 | File dataDir = Environment.getDataDirectory(); |
| 204 | File systemDir = new File(dataDir, "system"); |
| 205 | systemDir.mkdirs(); |
| 206 | return systemDir.toString(); |
| 207 | } |
| 208 | } |