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Merge change 4754 into donut

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* changes:
  At boot time, add additional per-device information to the kernel randomness pool.  This helps increase the quality / uniqueness of the random numbers, and is especially important during the device's first boot, when insufficient randomness is available.
This commit is contained in:
Android (Google) Code Review
2009-06-22 10:55:25 -07:00
parent d6dd686bc7 b8cba95ffd
commit 07a5f126df
1 changed files with 48 additions and 1 deletions
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49
services/java/com/android/server/EntropyService.java
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@@ -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();
}
}
}