src/crypto/crandom.c

   1 /*
   2  * Copyright (c) 2009 Joshua Oreman <oremanj@rwcr.net>.
   3  *
   4  * This program is free software; you can redistribute it and/or
   5  * modify it under the terms of the GNU General Public License as
   6  * published by the Free Software Foundation; either version 2 of the
   7  * License, or any later version.
   8  *
   9  * This program is distributed in the hope that it will be useful, but
  10  * WITHOUT ANY WARRANTY; without even the implied warranty of
  11  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  12  * General Public License for more details.
  13  *
  14  * You should have received a copy of the GNU General Public License
  15  * along with this program; if not, write to the Free Software
  16  * Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.
  17  */
  18
  19 FILE_LICENCE ( GPL2_OR_LATER );
  20
  21 /** @file
  22  *
  23  * Cryptographically strong random number generator
  24  *
  25  * Currently the cryptographic part is not implemented, and this just
  26  * uses random().
  27  */
  28
  29 #include <gpxe/crypto.h>
  30 #include <stdlib.h>
  31
  32 /**
  33  * Get cryptographically strong random bytes
  34  *
  35  * @v buf       Buffer in which to store random bytes
  36  * @v len       Number of random bytes to generate
  37  *
  38  * @b WARNING: This function is currently underimplemented, and does
  39  * not give numbers any stronger than random()!
  40  */
  41 void get_random_bytes ( void *buf, size_t len )
  42 {
  43         u8 *bufp = buf;
  44
  45         /*
  46          * Somewhat arbitrarily, choose the 0x00FF0000-masked byte
  47          * returned by random() as having good entropy. PRNGs often
  48          * don't provide good entropy in lower bits, and the top byte
  49          * might show a pattern because of sign issues.
  50          */
  51
  52         while ( len-- ) {
  53                 *bufp++ = ( random() >> 16 ) & 0xFF;
  54         }
  55 }