mirror of git://gcc.gnu.org/git/gcc.git
133 lines
4.5 KiB
Java
133 lines
4.5 KiB
Java
/* VMSecureRandom.java -- random seed generator.
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Copyright (C) 2006, 2010 Free Software Foundation, Inc.
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This file is a part of GNU Classpath.
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GNU Classpath is free software; you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation; either version 2 of the License, or (at
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your option) any later version.
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GNU Classpath is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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General Public License for more details.
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You should have received a copy of the GNU General Public License
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along with GNU Classpath; if not, write to the Free Software
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Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
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USA
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Linking this library statically or dynamically with other modules is
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making a combined work based on this library. Thus, the terms and
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conditions of the GNU General Public License cover the whole
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combination.
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As a special exception, the copyright holders of this library give you
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permission to link this library with independent modules to produce an
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executable, regardless of the license terms of these independent
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modules, and to copy and distribute the resulting executable under
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terms of your choice, provided that you also meet, for each linked
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independent module, the terms and conditions of the license of that
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module. An independent module is a module which is not derived from
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or based on this library. If you modify this library, you may extend
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this exception to your version of the library, but you are not
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obligated to do so. If you do not wish to do so, delete this
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exception statement from your version. */
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package java.security;
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/**
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* VM-specific methods for generating real (or almost real) random
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* seeds. VM implementors should write a version of this class that
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* reads random bytes from some system source.
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*
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* <p>The default implementation of this class runs eight threads that
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* increment counters in a tight loop, and XORs each counter to
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* produce one byte of seed data. This is not very efficient, and is
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* not guaranteed to be random (the thread scheduler is probably
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* deterministic, after all). If possible, VM implementors should
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* reimplement this class so it obtains a random seed from a system
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* facility, such as a system entropy gathering device or hardware
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* random number generator.
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*/
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final class VMSecureRandom
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{
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private VMSecureRandom() {} // Prohibits instantiation.
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/**
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* Generate a random seed. Implementations are free to generate
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* fewer random bytes than are requested, and leave the remaining
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* bytes of the destination buffer as zeros. Implementations SHOULD,
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* however, make a best-effort attempt to satisfy the request.
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*
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* @param buffer The destination buffer.
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* @param offset The offset in the buffer to start putting bytes.
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* @param length The number of random bytes to generate.
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*/
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static int generateSeed(byte[] buffer, int offset, int length)
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{
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if (length < 0)
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throw new IllegalArgumentException("length must be nonnegative");
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if (offset < 0 || offset + length > buffer.length)
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throw new IndexOutOfBoundsException();
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Spinner[] spinners = new Spinner[8];
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int n = 0x1;
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for (int i = 0; i < spinners.length; i++)
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{
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spinners[i] = new Spinner((byte) n);
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Thread t = new Thread(spinners[i]);
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t.start();
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n <<= 1;
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}
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// Wait until at least one spinner has started.
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while (!(spinners[0].running || spinners[1].running || spinners[2].running
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|| spinners[3].running || spinners[4].running || spinners[5].running
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|| spinners[6].running || spinners[7].running))
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{
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Thread.yield();
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}
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for (int i = offset; i < length; i++)
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{
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buffer[i] = (byte) (spinners[0].value ^ spinners[1].value ^ spinners[2].value
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^ spinners[3].value ^ spinners[4].value ^ spinners[5].value
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^ spinners[6].value ^ spinners[7].value);
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Thread.yield();
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}
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for (int i = 0; i < spinners.length; i++)
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spinners[i].stop();
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return length;
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}
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static class Spinner
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implements Runnable
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{
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volatile byte value;
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volatile boolean running;
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Spinner(final byte initial)
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{
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value = initial;
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}
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public void run()
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{
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running = true;
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while (running)
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value++;
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}
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void stop()
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{
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running = false;
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}
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}
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}
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