/*
 * $Source: /usr/src/kerberosIV/des/RCS/new_rnd_key.c,v $
 * $Author: bostic $
 *
 * Copyright 1988 by the Massachusetts Institute of Technology.
 *
 * For copying and distribution information, please see the file
 * <mit-copyright.h>.
 *
 * New pseudo-random key generator, using DES encryption to make the
 * pseudo-random cycle as hard to break as DES.
 *
 * Written by Mark Lillibridge, MIT Project Athena
 *
 * Under U.S. law, this software may not be exported outside the US
 * without license from the U.S. Commerce department.
 */

#ifndef	lint
static char rcsid_new_rnd_key_c[] =
"$Header: /usr/src/kerberosIV/des/RCS/new_rnd_key.c,v 4.2 91/02/25 15:14:22 bostic Exp $";
#endif	lint

#include <mit-copyright.h>

#include <des.h>
#include "des_internal.h"

extern void des_fixup_key_parity();
extern int des_is_weak_key();

void des_set_random_generator_seed(), des_set_sequence_number();
void des_generate_random_block();

/*
 * des_new_random_key: create a random des key
 *
 * Requires: des_set_random_number_generater_seed must be at called least
 *           once before this routine is called.
 *
 * Notes: the returned key has correct parity and is guarenteed not
 *        to be a weak des key.  Des_generate_random_block is used to
 *        provide the random bits.
 */
int
des_new_random_key(key)
     des_cblock key;
{
    do {
	des_generate_random_block(key);
	des_fixup_key_parity(key);
    } while (des_is_weak_key(key));

    return(0);
}

/*
 * des_init_random_number_generator:
 *
 *    This routine takes a secret key possibly shared by a number
 * of servers and uses it to generate a random number stream that is
 * not shared by any of the other servers.  It does this by using the current
 * process id, host id, and the current time to the nearest second.  The
 * resulting stream seed is not useful information for cracking the secret
 * key.   Moreover, this routine keeps no copy of the secret key.
 * This routine is used for example, by the kerberos server(s) with the
 * key in question being the kerberos master key.
 *
 * Note: this routine calls des_set_random_generator_seed.
 */
#ifndef BSDUNIX
  you lose...   (aka, you get to implement an analog of this for your
		 system...)
#else

#include <sys/time.h>

void des_init_random_number_generator(key)
     des_cblock key;
{
    struct { /* This must be 64 bits exactly */
	long process_id;
	long host_id;
    } seed;
    struct timeval time; /* this must also be 64 bits exactly */
    des_cblock new_key;
    long gethostid();

    /*
     * use a host id and process id in generating the seed to ensure
     * that different servers have different streams:
     */
    seed.host_id = gethostid();
    seed.process_id = getpid();

    /*
     * Generate a tempory value that depends on the key, host_id, and
     * process_id such that it gives no useful information about the key:
     */
    des_set_random_generator_seed(key);
    des_set_sequence_number((unsigned char *)&seed);
    des_new_random_key(new_key);

    /*
     * use it to select a random stream:
     */      
    des_set_random_generator_seed(new_key);

    /*
     * use a time stamp to ensure that a server started later does not reuse
     * an old stream:
     */
    gettimeofday(&time, (struct timezone *)0);
    des_set_sequence_number((unsigned char *)&time);

    /*
     * use the time stamp finally to select the final seed using the
     * current random number stream:
     */
    des_new_random_key(new_key);
    des_set_random_generator_seed(new_key);
}

#endif /* ifdef BSDUNIX */

/*
 * This module implements a random number generator faculty such that the next
 * number in any random number stream is very hard to predict without knowing
 * the seed for that stream even given the preceeding random numbers.
 */

/*
 * The secret des key schedule for the current stream of random numbers:
 */
static des_key_schedule random_sequence_key;

/*
 * The sequence # in the current stream of random numbers:
 */
static unsigned char sequence_number[8];

/*
 * des_set_random_generator_seed: this routine is used to select a random
 *                                number stream.  The stream that results is
 *                                totally determined by the passed in key.
 *                                (I.e., calling this routine again with the
 *                                same key allows repeating a sequence of
 *                                random numbers)
 *
 * Requires: key is a valid des key.  I.e., has correct parity and is not a
 *           weak des key.
 */
void
des_set_random_generator_seed(key)
     des_cblock key;
{
    register int i;

    /* select the new stream: (note errors are not possible here...) */
    des_key_sched(key, random_sequence_key);

    /* "seek" to the start of the stream: */
    for (i=0; i<8; i++)
      sequence_number[i] = 0;
}

/*
 * des_set_sequence_number: this routine is used to set the sequence number
 *                          of the current random number stream.  This routine
 *                          may be used to "seek" within the current random
 *                          number stream.
 *
 * Note that des_set_random_generator_seed resets the sequence number to 0.
 */
void
des_set_sequence_number(new_sequence_number)
     des_cblock new_sequence_number;
{
    bcopy((char *)new_sequence_number, (char *)sequence_number,
	  sizeof(sequence_number));
}

/*
 * des_generate_random_block: routine to return the next random number
 *                            from the current random number stream.
 *                            The returned number is 64 bits long.
 *
 * Requires: des_set_random_generator_seed must have been called at least once
 *           before this routine is called.
 */
void des_generate_random_block(block)
     des_cblock block;
{
    int i;

    /*
     * Encrypt the sequence number to get the new random block:
     */
    des_ecb_encrypt(sequence_number, block, random_sequence_key, 1);

    /*
     * Increment the sequence number as an 8 byte unsigned number with wrap:
     * (using LSB here)
     */
    for (i=0; i<8; i++) {
	sequence_number[i] = (sequence_number[i] + 1) & 0xff;
	if (sequence_number[i])
	  break;
    }
}