am 07a5f126: Merge change 4754 into donut (92eef877) · Commits · e / os / android_frameworks_base

services/java/com/android/server/EntropyService.java

+48 −1

Original line number	Diff line number	Diff line
		@@ -17,12 +17,16 @@
		package com.android.server;

		import java.io.File;
		import java.io.FileOutputStream;
		import java.io.IOException;
		import java.io.OutputStream;
		import java.io.PrintWriter;

		import android.os.Binder;
		import android.os.Environment;
		import android.os.Handler;
		import android.os.Message;
		import android.os.SystemProperties;
		import android.util.Log;

		/**
		@@ -49,6 +53,8 @@ public class EntropyService extends Binder {
		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";
		private static final long START_TIME = System.currentTimeMillis();
		private static final long START_NANOTIME = System.nanoTime();

		/**
		* Handler that periodically updates the entropy on disk.
		@@ -67,6 +73,7 @@ public class EntropyService extends Binder {

		public EntropyService() {
		loadInitialEntropy();
		addDeviceSpecificEntropy();
		writeEntropy();
		scheduleEntropyWriter();
		}
		@@ -88,7 +95,47 @@ public class EntropyService extends Binder {
		try {
		RandomBlock.fromFile(RANDOM_DEV).toFile(ENTROPY_FILENAME);
		} catch (IOException e) {
		Log.e(TAG, "unable to write entropy", e);
		Log.w(TAG, "unable to write entropy", e);
		}
		}

		/**
		* Add additional information to the kernel entropy pool. The
		* information isn't necessarily "random", but that's ok. Even
		* sending non-random information to {@code /dev/urandom} is useful
		* because, while it doesn't increase the "quality" of the entropy pool,
		* it mixes more bits into the pool, which gives us a higher degree
		* of uncertainty in the generated randomness. Like nature, writes to
		* the random device can only cause the quality of the entropy in the
		* kernel to stay the same or increase.
		*
		* <p>For maximum effect, we try to target information which varies
		* on a per-device basis, and is not easily observable to an
		* attacker.
		*/
		private void addDeviceSpecificEntropy() {
		PrintWriter out = null;
		try {
		out = new PrintWriter(new FileOutputStream(RANDOM_DEV));
		out.println("Copyright (C) 2009 The Android Open Source Project");
		out.println("All Your Randomness Are Belong To Us");
		out.println(START_TIME);
		out.println(START_NANOTIME);
		out.println(SystemProperties.get("ro.serialno"));
		out.println(SystemProperties.get("ro.bootmode"));
		out.println(SystemProperties.get("ro.baseband"));
		out.println(SystemProperties.get("ro.carrier"));
		out.println(SystemProperties.get("ro.bootloader"));
		out.println(SystemProperties.get("ro.hardware"));
		out.println(SystemProperties.get("ro.revision"));
		out.println(System.currentTimeMillis());
		out.println(System.nanoTime());
		} catch (IOException e) {
		Log.w(TAG, "Unable to add device specific data to the entropy pool", e);
		} finally {
		if (out != null) {
		out.close();
		}
		}
		}