1 files changed, 129 insertions, 0 deletions
diff --git a/libjava/classpath/vm/reference/java/security/VMSecureRandom.java b/libjava/classpath/vm/reference/java/security/VMSecureRandom.java
new file mode 100644
index 000000000..bea154977
--- /dev/null
+++ b/libjava/classpath/vm/reference/java/security/VMSecureRandom.java
@@ -0,0 +1,129 @@
+/* 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 java.security;
+
+/**
+ * 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;
+    }
+  }
+}