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authorupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
committerupstream source tree <ports@midipix.org>2015-03-15 20:14:05 -0400
commit554fd8c5195424bdbcabf5de30fdc183aba391bd (patch)
tree976dc5ab7fddf506dadce60ae936f43f58787092 /libjava/classpath/vm/reference/gnu/java/security/jce
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Diffstat (limited to 'libjava/classpath/vm/reference/gnu/java/security/jce')
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diff --git a/libjava/classpath/vm/reference/gnu/java/security/jce/prng/VMSecureRandom.java b/libjava/classpath/vm/reference/gnu/java/security/jce/prng/VMSecureRandom.java
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+++ b/libjava/classpath/vm/reference/gnu/java/security/jce/prng/VMSecureRandom.java
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+/* VMSecureRandom.java -- random seed generator.
+ Copyright (C) 2006 Free Software Foundation, Inc.
+
+This file is a part of GNU Classpath.
+
+GNU Classpath is free software; you can redistribute it and/or modify
+it under the terms of the GNU General Public License as published by
+the Free Software Foundation; either version 2 of the License, or (at
+your option) any later version.
+
+GNU Classpath 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 for more details.
+
+You should have received a copy of the GNU General Public License
+along with GNU Classpath; if not, write to the Free Software
+Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
+USA
+
+Linking this library statically or dynamically with other modules is
+making a combined work based on this library. Thus, the terms and
+conditions of the GNU General Public License cover the whole
+combination.
+
+As a special exception, the copyright holders of this library give you
+permission to link this library with independent modules to produce an
+executable, regardless of the license terms of these independent
+modules, and to copy and distribute the resulting executable under
+terms of your choice, provided that you also meet, for each linked
+independent module, the terms and conditions of the license of that
+module. An independent module is a module which is not derived from
+or based on this library. If you modify this library, you may extend
+this exception to your version of the library, but you are not
+obligated to do so. If you do not wish to do so, delete this
+exception statement from your version. */
+
+
+package gnu.java.security.jce.prng;
+
+/**
+ * VM-specific methods for generating real (or almost real) random
+ * seeds. VM implementors should write a version of this class that
+ * reads random bytes from some system source.
+ *
+ * <p>The default implementation of this class runs eight threads that
+ * increment counters in a tight loop, and XORs each counter to
+ * produce one byte of seed data. This is not very efficient, and is
+ * not guaranteed to be random (the thread scheduler is probably
+ * deterministic, after all). If possible, VM implementors should
+ * reimplement this class so it obtains a random seed from a system
+ * facility, such as a system entropy gathering device or hardware
+ * random number generator.
+ */
+final class VMSecureRandom
+{
+
+ /**
+ * Generate a random seed. Implementations are free to generate
+ * fewer random bytes than are requested, and leave the remaining
+ * bytes of the destination buffer as zeros. Implementations SHOULD,
+ * however, make a best-effort attempt to satisfy the request.
+ *
+ * @param buffer The destination buffer.
+ * @param offset The offset in the buffer to start putting bytes.
+ * @param length The number of random bytes to generate.
+ */
+ static int generateSeed(byte[] buffer, int offset, int length)
+ {
+ if (length < 0)
+ throw new IllegalArgumentException("length must be nonnegative");
+ if (offset < 0 || offset + length > buffer.length)
+ throw new IndexOutOfBoundsException();
+
+ Spinner[] spinners = new Spinner[8];
+ int n = 0x1;
+ for (int i = 0; i < spinners.length; i++)
+ {
+ spinners[i] = new Spinner((byte) n);
+ Thread t = new Thread(spinners[i]);
+ t.start();
+ n <<= 1;
+ }
+
+ // Wait until at least one spinner has started.
+ while (!(spinners[0].running || spinners[1].running || spinners[2].running
+ || spinners[3].running || spinners[4].running || spinners[5].running
+ || spinners[6].running || spinners[7].running))
+ {
+ Thread.yield();
+ }
+
+ for (int i = offset; i < length; i++)
+ {
+ buffer[i] = (byte) (spinners[0].value ^ spinners[1].value ^ spinners[2].value
+ ^ spinners[3].value ^ spinners[4].value ^ spinners[5].value
+ ^ spinners[6].value ^ spinners[7].value);
+ Thread.yield();
+ }
+
+ for (int i = 0; i < spinners.length; i++)
+ spinners[i].stop();
+
+ return length;
+ }
+
+ static class Spinner implements Runnable
+ {
+ volatile byte value;
+ volatile boolean running;
+
+ Spinner(final byte initial)
+ {
+ value = initial;
+ }
+
+ public void run()
+ {
+ running = true;
+ while (running)
+ value++;
+ }
+
+ private void stop()
+ {
+ running = false;
+ }
+ }
+}