private static byte[] generateAlternativeSeed() {
try {
ByteArrayOutputStream bout = new ByteArrayOutputStream();
DataOutputStream out = new DataOutputStream(bout);
// milliseconds
out.writeLong(System.currentTimeMillis());
// nanoseconds if available
try {
Method m = System.class.getMethod("nanoTime");
if (m != null) {
Object o = m.invoke(null);
out.writeUTF(o.toString());
}
} catch (Exception e) {
// nanoTime not found, this is ok (only exists for JDK 1.5 and higher)
out.writeUTF(e.toString());
}
// memory
out.writeInt(new Object().hashCode());
Runtime runtime = Runtime.getRuntime();
out.writeLong(runtime.freeMemory());
out.writeLong(runtime.maxMemory());
out.writeLong(runtime.totalMemory());
// environment
try {
String s = System.getProperties().toString();
// can't use writeUTF, as the string
// might be larger than 64 KB
out.writeInt(s.length());
out.write(s.getBytes("UTF-8"));
} catch (Exception e) {
warn("generateAlternativeSeed", e);
}
// host name and ip addresses (if any)
try {
// workaround for the Google App Engine: don't use InetAddress
Class<?> inetAddressClass = Class.forName("java.net.InetAddress");
Object localHost = inetAddressClass.getMethod("getLocalHost").invoke(null);
String hostName = inetAddressClass.getMethod("getHostName").invoke(localHost).toString();
out.writeUTF(hostName);
Object[] list =
(Object[])
inetAddressClass.getMethod("getAllByName", String.class).invoke(null, hostName);
Method getAddress = inetAddressClass.getMethod("getAddress");
for (Object o : list) {
out.write((byte[]) getAddress.invoke(o));
}
} catch (Throwable e) {
// on some system, InetAddress is not supported
// on some system, InetAddress.getLocalHost() doesn't work
// for some reason (incorrect configuration)
}
// timing (a second thread is already running usually)
for (int j = 0; j < 16; j++) {
int i = 0;
long end = System.currentTimeMillis();
while (end == System.currentTimeMillis()) {
i++;
}
out.writeInt(i);
}
out.close();
return bout.toByteArray();
} catch (IOException e) {
warn("generateAlternativeSeed", e);
return new byte[1];
}
}
private static synchronized SecureRandom getSecureRandom() {
if (cachedSecureRandom != null) {
return cachedSecureRandom;
}
// Workaround for SecureRandom problem as described in
// http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=6202721
// Can not do that in a static initializer block, because
// threads are not started until after the initializer block exits
try {
cachedSecureRandom = SecureRandom.getInstance("SHA1PRNG");
// On some systems, secureRandom.generateSeed() is very slow.
// In this case it is initialized using our own seed implementation
// and afterwards (in the thread) using the regular algorithm.
Runnable runnable =
new Runnable() {
public void run() {
try {
SecureRandom sr = SecureRandom.getInstance("SHA1PRNG");
byte[] seed = sr.generateSeed(20);
synchronized (cachedSecureRandom) {
cachedSecureRandom.setSeed(seed);
seeded = true;
}
} catch (Exception e) {
// NoSuchAlgorithmException
warn("SecureRandom", e);
}
}
};
try {
Thread t = new Thread(runnable, "Generate Seed");
// let the process terminate even if generating the seed is really slow
t.setDaemon(true);
t.start();
Thread.yield();
try {
// normally, generateSeed takes less than 200 ms
t.join(400);
} catch (InterruptedException e) {
warn("InterruptedException", e);
}
if (!seeded) {
byte[] seed = generateAlternativeSeed();
// this never reduces randomness
synchronized (cachedSecureRandom) {
cachedSecureRandom.setSeed(seed);
}
}
} catch (SecurityException e) {
// workaround for the Google App Engine: don't use a thread
runnable.run();
generateAlternativeSeed();
}
} catch (Exception e) {
// NoSuchAlgorithmException
warn("SecureRandom", e);
cachedSecureRandom = new SecureRandom();
}
return cachedSecureRandom;
}