14fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich/* 24fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * Copyright (C) 2009 The Android Open Source Project 34fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * 44fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * Licensed under the Apache License, Version 2.0 (the "License"); 54fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * you may not use this file except in compliance with the License. 64fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * You may obtain a copy of the License at 74fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * 84fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * http://www.apache.org/licenses/LICENSE-2.0 94fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * 104fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * Unless required by applicable law or agreed to in writing, software 114fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * distributed under the License is distributed on an "AS IS" BASIS, 124fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. 134fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * See the License for the specific language governing permissions and 144fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * limitations under the License. 154fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich */ 164fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 174fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevichpackage com.android.server; 184fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 194fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevichimport java.io.File; 20b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevichimport java.io.FileOutputStream; 214fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevichimport java.io.IOException; 22b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevichimport java.io.OutputStream; 23b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevichimport java.io.PrintWriter; 244fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 254fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevichimport android.os.Binder; 264fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevichimport android.os.Environment; 274fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevichimport android.os.Handler; 284fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevichimport android.os.Message; 29b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevichimport android.os.SystemProperties; 308a9b22056b13477f59df934928c00c58b5871c95Joe Onoratoimport android.util.Slog; 314fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 324fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich/** 334fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * A service designed to load and periodically save "randomness" 344fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * for the Linux kernel. 354fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * 364fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * <p>When a Linux system starts up, the entropy pool associated with 374fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * {@code /dev/random} may be in a fairly predictable state. Applications which 384fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * depend strongly on randomness may find {@code /dev/random} or 394fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * {@code /dev/urandom} returning predictable data. In order to counteract 404fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * this effect, it's helpful to carry the entropy pool information across 414fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * shutdowns and startups. 424fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * 434fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * <p>This class was modeled after the script in 444fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * <a href="http://www.kernel.org/doc/man-pages/online/pages/man4/random.4.html">man 454fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * 4 random</a>. 464fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * 474fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * <p>TODO: Investigate attempting to write entropy data at shutdown time 484fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * instead of periodically. 494fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich */ 506967cbc959b079fa7e4411360e40e2a0ed65da29Nick Kralevichpublic class EntropyMixer extends Binder { 516967cbc959b079fa7e4411360e40e2a0ed65da29Nick Kralevich private static final String TAG = "EntropyMixer"; 524fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich private static final int ENTROPY_WHAT = 1; 534fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich private static final int ENTROPY_WRITE_PERIOD = 3 * 60 * 60 * 1000; // 3 hrs 54b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich private static final long START_TIME = System.currentTimeMillis(); 55b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich private static final long START_NANOTIME = System.nanoTime(); 564fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 5793a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich private final String randomDevice; 5893a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich private final String entropyFile; 5993a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich 604fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich /** 614fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich * Handler that periodically updates the entropy on disk. 624fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich */ 634fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich private final Handler mHandler = new Handler() { 644fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich @Override 654fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich public void handleMessage(Message msg) { 664fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich if (msg.what != ENTROPY_WHAT) { 678a9b22056b13477f59df934928c00c58b5871c95Joe Onorato Slog.e(TAG, "Will not process invalid message"); 684fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich return; 694fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 704fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich writeEntropy(); 714fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich scheduleEntropyWriter(); 724fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 734fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich }; 744fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 756967cbc959b079fa7e4411360e40e2a0ed65da29Nick Kralevich public EntropyMixer() { 7693a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich this(getSystemDir() + "/entropy.dat", "/dev/urandom"); 7793a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich } 7893a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich 7993a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich /** Test only interface, not for public use */ 806967cbc959b079fa7e4411360e40e2a0ed65da29Nick Kralevich public EntropyMixer(String entropyFile, String randomDevice) { 8193a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich if (randomDevice == null) { throw new NullPointerException("randomDevice"); } 8293a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich if (entropyFile == null) { throw new NullPointerException("entropyFile"); } 8393a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich 8493a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich this.randomDevice = randomDevice; 8593a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich this.entropyFile = entropyFile; 864fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich loadInitialEntropy(); 87b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich addDeviceSpecificEntropy(); 884fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich writeEntropy(); 894fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich scheduleEntropyWriter(); 904fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 914fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 924fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich private void scheduleEntropyWriter() { 934fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich mHandler.removeMessages(ENTROPY_WHAT); 944fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich mHandler.sendEmptyMessageDelayed(ENTROPY_WHAT, ENTROPY_WRITE_PERIOD); 954fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 964fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 974fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich private void loadInitialEntropy() { 984fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich try { 996907891b1f2d706fa2bd6c40b986f73e5666e00eElliott Hughes RandomBlock.fromFile(entropyFile).toFile(randomDevice, false); 1004fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } catch (IOException e) { 1018a9b22056b13477f59df934928c00c58b5871c95Joe Onorato Slog.w(TAG, "unable to load initial entropy (first boot?)", e); 1024fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 1034fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 1044fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 1054fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich private void writeEntropy() { 1064fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich try { 1076907891b1f2d706fa2bd6c40b986f73e5666e00eElliott Hughes RandomBlock.fromFile(randomDevice).toFile(entropyFile, true); 1084fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } catch (IOException e) { 1098a9b22056b13477f59df934928c00c58b5871c95Joe Onorato Slog.w(TAG, "unable to write entropy", e); 110b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich } 111b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich } 112b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich 113b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich /** 114b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * Add additional information to the kernel entropy pool. The 115b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * information isn't necessarily "random", but that's ok. Even 116b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * sending non-random information to {@code /dev/urandom} is useful 117b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * because, while it doesn't increase the "quality" of the entropy pool, 118b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * it mixes more bits into the pool, which gives us a higher degree 119b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * of uncertainty in the generated randomness. Like nature, writes to 120b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * the random device can only cause the quality of the entropy in the 121b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * kernel to stay the same or increase. 122b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * 123b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * <p>For maximum effect, we try to target information which varies 124b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * on a per-device basis, and is not easily observable to an 125b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich * attacker. 126b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich */ 127b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich private void addDeviceSpecificEntropy() { 128b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich PrintWriter out = null; 129b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich try { 13093a68398b661c02d6c417a2a04e64a6750a9a119Nick Kralevich out = new PrintWriter(new FileOutputStream(randomDevice)); 131b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println("Copyright (C) 2009 The Android Open Source Project"); 132b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println("All Your Randomness Are Belong To Us"); 133b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(START_TIME); 134b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(START_NANOTIME); 135b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(SystemProperties.get("ro.serialno")); 136b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(SystemProperties.get("ro.bootmode")); 137b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(SystemProperties.get("ro.baseband")); 138b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(SystemProperties.get("ro.carrier")); 139b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(SystemProperties.get("ro.bootloader")); 140b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(SystemProperties.get("ro.hardware")); 141b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(SystemProperties.get("ro.revision")); 142b91ec410c8ecd09390e7122115e2ab6b7aafefb8Nick Kralevich out.println(new Object().hashCode()); 143b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(System.currentTimeMillis()); 144b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.println(System.nanoTime()); 145b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich } catch (IOException e) { 1468a9b22056b13477f59df934928c00c58b5871c95Joe Onorato Slog.w(TAG, "Unable to add device specific data to the entropy pool", e); 147b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich } finally { 148b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich if (out != null) { 149b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich out.close(); 150b8cba95ffd4d9be0edace7a9eb42286e668ef3e3Nick Kralevich } 1514fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 1524fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 1534fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich 1544fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich private static String getSystemDir() { 1554fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich File dataDir = Environment.getDataDirectory(); 1564fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich File systemDir = new File(dataDir, "system"); 1574fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich systemDir.mkdirs(); 1584fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich return systemDir.toString(); 1594fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich } 1604fb256117ca271e3e37284a19b663d116f6ec20cNick Kralevich} 161