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Commit 07a5f126 authored by Android (Google) Code Review's avatar Android (Google) Code Review
Browse files

Merge change 4754 into donut 

* 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.
parents d6dd686b b8cba95f

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();

            }

        }

    }