Java example source code file (SeedGenerator.java)
The SeedGenerator.java Java example source code/*
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*
* This code is distributed in the hope that it will be useful, but WITHOUT
* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
* version 2 for more details (a copy is included in the LICENSE file that
* accompanied this code).
*
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* 2 along with this work; if not, write to the Free Software Foundation,
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package sun.security.provider;
/**
* This class generates seeds for the SHA1PRNG cryptographically strong
* random number generator.
* <p>
* The seed is produced using one of two techniques, via a computation
* of current system activity or from an entropy gathering device.
* <p>
* In the default technique the seed is produced by counting the
* number of times the VM manages to loop in a given period. This number
* roughly reflects the machine load at that point in time.
* The samples are translated using a permutation (s-box)
* and then XORed together. This process is non linear and
* should prevent the samples from "averaging out". The s-box
* was designed to have even statistical distribution; it's specific
* values are not crucial for the security of the seed.
* We also create a number of sleeper threads which add entropy
* to the system by keeping the scheduler busy.
* Twenty such samples should give us roughly 160 bits of randomness.
* <p>
* These values are gathered in the background by a daemon thread
* thus allowing the system to continue performing it's different
* activites, which in turn add entropy to the random seed.
* <p>
* The class also gathers miscellaneous system information, some
* machine dependent, some not. This information is then hashed together
* with the 20 seed bytes.
* <p>
* The alternative to the above approach is to acquire seed material
* from an entropy gathering device, such as /dev/random. This can be
* accomplished by setting the value of the {@code securerandom.source}
* Security property to a URL specifying the location of the entropy
* gathering device, or by setting the {@code java.security.egd} System
* property.
* <p>
* In the event the specified URL cannot be accessed the default
* threading mechanism is used.
*
* @author Joshua Bloch
* @author Gadi Guy
*/
import java.security.*;
import java.io.*;
import java.util.Properties;
import java.util.Enumeration;
import java.net.*;
import java.nio.file.DirectoryStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.Random;
import sun.security.util.Debug;
abstract class SeedGenerator {
// Static instance is created at link time
private static SeedGenerator instance;
private static final Debug debug = Debug.getInstance("provider");
// Static initializer to hook in selected or best performing generator
static {
String egdSource = SunEntries.getSeedSource();
/*
* Try the URL specifying the source (e.g. file:/dev/random)
*
* The URLs "file:/dev/random" or "file:/dev/urandom" are used to
* indicate the SeedGenerator should use OS support, if available.
*
* On Windows, this causes the MS CryptoAPI seeder to be used.
*
* On Solaris/Linux/MacOS, this is identical to using
* URLSeedGenerator to read from /dev/[u]random
*/
if (egdSource.equals(SunEntries.URL_DEV_RANDOM) ||
egdSource.equals(SunEntries.URL_DEV_URANDOM)) {
try {
instance = new NativeSeedGenerator(egdSource);
if (debug != null) {
debug.println(
"Using operating system seed generator" + egdSource);
}
} catch (IOException e) {
if (debug != null) {
debug.println("Failed to use operating system seed "
+ "generator: " + e.toString());
}
}
} else if (egdSource.length() != 0) {
try {
instance = new URLSeedGenerator(egdSource);
if (debug != null) {
debug.println("Using URL seed generator reading from "
+ egdSource);
}
} catch (IOException e) {
if (debug != null) {
debug.println("Failed to create seed generator with "
+ egdSource + ": " + e.toString());
}
}
}
// Fall back to ThreadedSeedGenerator
if (instance == null) {
if (debug != null) {
debug.println("Using default threaded seed generator");
}
instance = new ThreadedSeedGenerator();
}
}
/**
* Fill result with bytes from the queue. Wait for it if it isn't ready.
*/
static public void generateSeed(byte[] result) {
instance.getSeedBytes(result);
}
abstract void getSeedBytes(byte[] result);
/**
* Retrieve some system information, hashed.
*/
static byte[] getSystemEntropy() {
byte[] ba;
final MessageDigest md;
try {
md = MessageDigest.getInstance("SHA");
} catch (NoSuchAlgorithmException nsae) {
throw new InternalError("internal error: SHA-1 not available."
, nsae);
}
// The current time in millis
byte b =(byte)System.currentTimeMillis();
md.update(b);
java.security.AccessController.doPrivileged
(new java.security.PrivilegedAction<Void>() {
@Override
public Void run() {
try {
// System properties can change from machine to machine
String s;
Properties p = System.getProperties();
Enumeration<?> e = p.propertyNames();
while (e.hasMoreElements()) {
s =(String)e.nextElement();
md.update(s.getBytes());
md.update(p.getProperty(s).getBytes());
}
md.update
(InetAddress.getLocalHost().toString().getBytes());
// The temporary dir
File f = new File(p.getProperty("java.io.tmpdir"));
int count = 0;
try (
DirectoryStream<Path> stream =
Files.newDirectoryStream(f.toPath())) {
// We use a Random object to choose what file names
// should be used. Otherwise on a machine with too
// many files, the same first 1024 files always get
// used. Any, We make sure the first 512 files are
// always used.
Random r = new Random();
for (Path entry: stream) {
if (count < 512 || r.nextBoolean()) {
md.update(entry.getFileName()
.toString().getBytes());
}
if (count++ > 1024) {
break;
}
}
}
} catch (Exception ex) {
md.update((byte)ex.hashCode());
}
// get Runtime memory stats
Runtime rt = Runtime.getRuntime();
byte[] memBytes = longToByteArray(rt.totalMemory());
md.update(memBytes, 0, memBytes.length);
memBytes = longToByteArray(rt.freeMemory());
md.update(memBytes, 0, memBytes.length);
return null;
}
});
return md.digest();
}
/**
* Helper function to convert a long into a byte array (least significant
* byte first).
*/
private static byte[] longToByteArray(long l) {
byte[] retVal = new byte[8];
for (int i=0; i<8; i++) {
retVal[i] = (byte) l;
l >>= 8;
}
return retVal;
}
/*
// This method helps the test utility receive unprocessed seed bytes.
public static int genTestSeed() {
return myself.getByte();
}
*/
private static class ThreadedSeedGenerator extends SeedGenerator
implements Runnable {
// Queue is used to collect seed bytes
private byte[] pool;
private int start, end, count;
// Thread group for our threads
ThreadGroup seedGroup;
/**
* The constructor is only called once to construct the one
* instance we actually use. It instantiates the message digest
* and starts the thread going.
*/
ThreadedSeedGenerator() {
pool = new byte[20];
start = end = 0;
MessageDigest digest;
try {
digest = MessageDigest.getInstance("SHA");
} catch (NoSuchAlgorithmException e) {
throw new InternalError("internal error: SHA-1 not available."
, e);
}
final ThreadGroup[] finalsg = new ThreadGroup[1];
Thread t = java.security.AccessController.doPrivileged
(new java.security.PrivilegedAction<Thread>() {
@Override
public Thread run() {
ThreadGroup parent, group =
Thread.currentThread().getThreadGroup();
while ((parent = group.getParent()) != null) {
group = parent;
}
finalsg[0] = new ThreadGroup
(group, "SeedGenerator ThreadGroup");
Thread newT = new Thread(finalsg[0],
ThreadedSeedGenerator.this,
"SeedGenerator Thread");
newT.setPriority(Thread.MIN_PRIORITY);
newT.setDaemon(true);
return newT;
}
});
seedGroup = finalsg[0];
t.start();
}
/**
* This method does the actual work. It collects random bytes and
* pushes them into the queue.
*/
@Override
final public void run() {
try {
while (true) {
// Queue full? Wait till there's room.
synchronized(this) {
while (count >= pool.length) {
wait();
}
}
int counter, quanta;
byte v = 0;
// Spin count must not be under 64000
for (counter = quanta = 0;
(counter < 64000) && (quanta < 6); quanta++) {
// Start some noisy threads
try {
BogusThread bt = new BogusThread();
Thread t = new Thread
(seedGroup, bt, "SeedGenerator Thread");
t.start();
} catch (Exception e) {
throw new InternalError("internal error: " +
"SeedGenerator thread creation error.", e);
}
// We wait 250milli quanta, so the minimum wait time
// cannot be under 250milli.
int latch = 0;
long l = System.currentTimeMillis() + 250;
while (System.currentTimeMillis() < l) {
synchronized(this){};
latch++;
}
// Translate the value using the permutation, and xor
// it with previous values gathered.
v ^= rndTab[latch % 255];
counter += latch;
}
// Push it into the queue and notify anybody who might
// be waiting for it.
synchronized(this) {
pool[end] = v;
end++;
count++;
if (end >= pool.length) {
end = 0;
}
notifyAll();
}
}
} catch (Exception e) {
throw new InternalError("internal error: " +
"SeedGenerator thread generated an exception.", e);
}
}
@Override
void getSeedBytes(byte[] result) {
for (int i = 0; i < result.length; i++) {
result[i] = getSeedByte();
}
}
byte getSeedByte() {
byte b;
try {
// Wait for it...
synchronized(this) {
while (count <= 0) {
wait();
}
}
} catch (Exception e) {
if (count <= 0) {
throw new InternalError("internal error: " +
"SeedGenerator thread generated an exception.", e);
}
}
synchronized(this) {
// Get it from the queue
b = pool[start];
pool[start] = 0;
start++;
count--;
if (start == pool.length) {
start = 0;
}
// Notify the daemon thread, just in case it is
// waiting for us to make room in the queue.
notifyAll();
}
return b;
}
// The permutation was calculated by generating 64k of random
// data and using it to mix the trivial permutation.
// It should be evenly distributed. The specific values
// are not crucial to the security of this class.
private static byte[] rndTab = {
56, 30, -107, -6, -86, 25, -83, 75, -12, -64,
5, -128, 78, 21, 16, 32, 70, -81, 37, -51,
-43, -46, -108, 87, 29, 17, -55, 22, -11, -111,
-115, 84, -100, 108, -45, -15, -98, 72, -33, -28,
31, -52, -37, -117, -97, -27, 93, -123, 47, 126,
-80, -62, -93, -79, 61, -96, -65, -5, -47, -119,
14, 89, 81, -118, -88, 20, 67, -126, -113, 60,
-102, 55, 110, 28, 85, 121, 122, -58, 2, 45,
43, 24, -9, 103, -13, 102, -68, -54, -101, -104,
19, 13, -39, -26, -103, 62, 77, 51, 44, 111,
73, 18, -127, -82, 4, -30, 11, -99, -74, 40,
-89, 42, -76, -77, -94, -35, -69, 35, 120, 76,
33, -73, -7, 82, -25, -10, 88, 125, -112, 58,
83, 95, 6, 10, 98, -34, 80, 15, -91, 86,
-19, 52, -17, 117, 49, -63, 118, -90, 36, -116,
-40, -71, 97, -53, -109, -85, 109, -16, -3, 104,
-95, 68, 54, 34, 26, 114, -1, 106, -121, 3,
66, 0, 100, -84, 57, 107, 119, -42, 112, -61,
1, 48, 38, 12, -56, -57, 39, -106, -72, 41,
7, 71, -29, -59, -8, -38, 79, -31, 124, -124,
8, 91, 116, 99, -4, 9, -36, -78, 63, -49,
-67, -87, 59, 101, -32, 92, 94, 53, -41, 115,
-66, -70, -122, 50, -50, -22, -20, -18, -21, 23,
-2, -48, 96, 65, -105, 123, -14, -110, 69, -24,
-120, -75, 74, 127, -60, 113, 90, -114, 105, 46,
27, -125, -23, -44, 64
};
/**
* This inner thread causes the thread scheduler to become 'noisy',
* thus adding entropy to the system load.
* At least one instance of this class is generated for every seed byte.
*/
private static class BogusThread implements Runnable {
@Override
final public void run() {
try {
for (int i = 0; i < 5; i++) {
Thread.sleep(50);
}
// System.gc();
} catch (Exception e) {
}
}
}
}
static class URLSeedGenerator extends SeedGenerator {
private String deviceName;
private InputStream seedStream;
/**
* The constructor is only called once to construct the one
* instance we actually use. It opens the entropy gathering device
* which will supply the randomness.
*/
URLSeedGenerator(String egdurl) throws IOException {
if (egdurl == null) {
throw new IOException("No random source specified");
}
deviceName = egdurl;
init();
}
private void init() throws IOException {
final URL device = new URL(deviceName);
try {
seedStream = java.security.AccessController.doPrivileged
(new java.security.PrivilegedExceptionAction<InputStream>() {
@Override
public InputStream run() throws IOException {
/*
* return a FileInputStream for file URLs and
* avoid buffering. The openStream() call wraps
* InputStream in a BufferedInputStream which
* can buffer up to 8K bytes. This read is a
* performance issue for entropy sources which
* can be slow to replenish.
*/
if (device.getProtocol().equalsIgnoreCase("file")) {
File deviceFile =
SunEntries.getDeviceFile(device);
return new FileInputStream(deviceFile);
} else {
return device.openStream();
}
}
});
} catch (Exception e) {
throw new IOException(
"Failed to open " + deviceName, e.getCause());
}
}
@Override
void getSeedBytes(byte[] result) {
int len = result.length;
int read = 0;
try {
while (read < len) {
int count = seedStream.read(result, read, len - read);
// /dev/random blocks - should never have EOF
if (count < 0) {
throw new InternalError(
"URLSeedGenerator " + deviceName +
" reached end of file");
}
read += count;
}
} catch (IOException ioe) {
throw new InternalError("URLSeedGenerator " + deviceName +
" generated exception: " + ioe.getMessage(), ioe);
}
}
}
}
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