libjava/gnu/java/security/jce/prng/VMSecureRandom.java

   1 /* VMSecureRandom.java -- random seed generator.
   2    Copyright (C) 2006, 2009  Free Software Foundation, Inc.
   3
   4 This file is a part of GNU Classpath.
   5
   6 GNU Classpath is free software; you can redistribute it and/or modify
   7 it under the terms of the GNU General Public License as published by
   8 the Free Software Foundation; either version 2 of the License, or (at
   9 your option) any later version.
  10
  11 GNU Classpath is distributed in the hope that it will be useful, but
  12 WITHOUT ANY WARRANTY; without even the implied warranty of
  13 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  14 General Public License for more details.
  15
  16 You should have received a copy of the GNU General Public License
  17 along with GNU Classpath; if not, write to the Free Software
  18 Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301
  19 USA
  20
  21 Linking this library statically or dynamically with other modules is
  22 making a combined work based on this library.  Thus, the terms and
  23 conditions of the GNU General Public License cover the whole
  24 combination.
  25
  26 As a special exception, the copyright holders of this library give you
  27 permission to link this library with independent modules to produce an
  28 executable, regardless of the license terms of these independent
  29 modules, and to copy and distribute the resulting executable under
  30 terms of your choice, provided that you also meet, for each linked
  31 independent module, the terms and conditions of the license of that
  32 module.  An independent module is a module which is not derived from
  33 or based on this library.  If you modify this library, you may extend
  34 this exception to your version of the library, but you are not
  35 obligated to do so.  If you do not wish to do so, delete this
  36 exception statement from your version.  */
  37
  38
  39 package gnu.java.security.jce.prng;
  40
  41 /**
  42  * VM-specific methods for generating real (or almost real) random
  43  * seeds. VM implementors should write a version of this class that
  44  * reads random bytes from some system source.
  45  */
  46 final class VMSecureRandom
  47 {
  48
  49   /**
  50    * <p>
  51    * Generate a random seed. Implementations are free to generate
  52    * fewer random bytes than are requested, and leave the remaining
  53    * bytes of the destination buffer as zeros. Implementations SHOULD,
  54    * however, make a best-effort attempt to satisfy the request.
  55    * </p>
  56    * <p>
  57    * The GCJ implementation uses a native method to read bytes from
  58    * a system random source (e.g. /dev/random).
  59    * </p>
  60    *
  61    * @param buffer The destination buffer.
  62    * @param offset The offset in the buffer to start putting bytes.
  63    * @param length The number of random bytes to generate.
  64    * @return the number of bytes generated.
  65    */
  66   static int generateSeed(byte[] buffer, int offset, int length)
  67   {
  68     if (length < 0)
  69       throw new IllegalArgumentException("length must be nonnegative");
  70     if (offset < 0 || offset + length > buffer.length)
  71       throw new IndexOutOfBoundsException();
  72
  73     return natGenerateSeed(buffer, offset, length);
  74   }
  75
  76   static native int natGenerateSeed(byte[] buffer, int offset, int length);
  77
  78 }