dos.c

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/****************************************************************************
*                                                                           *
*                         MSDOS Randomness-Gathering Code                   *
*                        Copyright Peter Gutmann 1996-2002                  *
*                                                                           *
****************************************************************************/

/* This module is part of the cryptlib continuously seeded pseudorandom
   number generator.  For usage conditions, see random.c.

   This code represents a template for randomness-gathering only and will
   need to be modified to provide OS-specific randomness.  In its current
   form it does not provide any usable entropy and should not be used as an
   entropy source */

/* General includes */

#include "crypt.h"

/* OS-specific includes */

#include <fcntl.h>
#include <io.h>
#include <time.h>

void fastPoll( void )
    {
    MESSAGE_DATA msgData;
    time_t timeStamp = time( NULL );

    /* There's not much we can do under DOS, we rely entirely on the
       /dev/random read for information */
    setMessageData( &msgData, &timeStamp, sizeof( time_t ) );
    krnlSendMessage( SYSTEM_OBJECT_HANDLE, IMESSAGE_SETATTRIBUTE_S,
                     &msgData, CRYPT_IATTRIBUTE_ENTROPY );
    }

void slowPoll( void )
    {
    MESSAGE_DATA msgData;
    BYTE buffer[ 128 ];
    int quality = 100, fd, count, total;

    /* Read 128 bytes from /dev/random and add it to the buffer.  Since DOS
       doesn't swap we don't need to be as careful about copying data to
       temporary buffers as we usually are.  We also have to use unbuffered
       I/O, since the high-level functions will read BUFSIZ bytes at once
       from the input, comletely draining the driver of any randomness */
    if( ( fd = open( "/dev/random$", O_RDONLY | O_BINARY) ) == -1 && \
        ( fd = open( "/dev/random", O_RDONLY | O_BINARY) ) == -1 )
        return;
    for( total = 0; total < sizeof( buffer ); )
        {
        count = read( fd, buffer + total, sizeof( buffer ) - total );
        if( count <= 0 )
            break;
        total += count;
        }
    close( fd );
    setMessageData( &msgData, buffer, total );
    krnlSendMessage( SYSTEM_OBJECT_HANDLE, IMESSAGE_SETATTRIBUTE_S,
                     &msgData, CRYPT_IATTRIBUTE_ENTROPY );
    zeroise( buffer, sizeof( buffer ) );
    krnlSendMessage( SYSTEM_OBJECT_HANDLE, IMESSAGE_SETATTRIBUTE,
                     &quality, CRYPT_IATTRIBUTE_ENTROPY_QUALITY );
    }