des_setkey.cpp

DES密码体制的安全性应该不依赖于算法的保密

/* crypto/des/set_key.c */
/* Copyright (C) 1995-1996 Eric Young ([e-mail])
 * All rights reserved.
 */
#include "stdafx.h"
 
#include "des_locl.h"
#include "sk.h"

static int check_parity(des_cblock (*));

int des_check_key=0;

void des_set_odd_parity(des_cblock *key)
{
	int i;

	for (i=0; i<DES_KEY_SZ; i++)
		(*key)[i]=odd_parity[(*key)[i]];
}

static int check_parity(des_cblock *key)
{
	int i;

	for (i=0; i<DES_KEY_SZ; i++)
	{
		if ((*key)[i] != odd_parity[(*key)[i]])
			return(0);
	}
	return(1);
}

/* Weak and semi week keys as take from
 * %A D.W. Davies
 * %A W.L. Price
 * %T Security for Computer Networks
 * %I John Wiley & Sons
 * %D 1984
 * Many thanks to [e-mail] (Steven Bellovin) for the reference
 * (and actual cblock values).
 */
#define NUM_WEAK_KEY	16
static des_cblock weak_keys[NUM_WEAK_KEY]=
{
	/* weak keys */
	{0x01,0x01,0x01,0x01,0x01,0x01,0x01,0x01},
	{0xFE,0xFE,0xFE,0xFE,0xFE,0xFE,0xFE,0xFE},
	{0x1F,0x1F,0x1F,0x1F,0x1F,0x1F,0x1F,0x1F},
	{0xE0,0xE0,0xE0,0xE0,0xE0,0xE0,0xE0,0xE0},
	/* semi-weak keys */
	{0x01,0xFE,0x01,0xFE,0x01,0xFE,0x01,0xFE},
	{0xFE,0x01,0xFE,0x01,0xFE,0x01,0xFE,0x01},
	{0x1F,0xE0,0x1F,0xE0,0x0E,0xF1,0x0E,0xF1},
	{0xE0,0x1F,0xE0,0x1F,0xF1,0x0E,0xF1,0x0E},
	{0x01,0xE0,0x01,0xE0,0x01,0xF1,0x01,0xF1},
	{0xE0,0x01,0xE0,0x01,0xF1,0x01,0xF1,0x01},
	{0x1F,0xFE,0x1F,0xFE,0x0E,0xFE,0x0E,0xFE},
	{0xFE,0x1F,0xFE,0x1F,0xFE,0x0E,0xFE,0x0E},
	{0x01,0x1F,0x01,0x1F,0x01,0x0E,0x01,0x0E},
	{0x1F,0x01,0x1F,0x01,0x0E,0x01,0x0E,0x01},
	{0xE0,0xFE,0xE0,0xFE,0xF1,0xFE,0xF1,0xFE},
	{0xFE,0xE0,0xFE,0xE0,0xFE,0xF1,0xFE,0xF1}
};

int des_is_weak_key(des_cblock *key)
{
	int i;

	for (i=0; i<NUM_WEAK_KEY; i++)
		/* Added == 0 to comparision, I obviously don't run
		 * this section very often :-(, thanks to
		 * [e-mail] for the fix
		 * eay 93/06/29 */
	if (memcmp((const void *)weak_keys[i], (const void *)key, sizeof(*key)) == 0) return(1);
	return(0);
}

/* NOW DEFINED IN des_local.h
 * See ecb_encrypt.c for a pseudo description of these macros.
 * #define PERM_OP(a,b,t,n,m) ((t)=((((a)>>(n))^(b))&(m)),\
 * 	(b)^=(t),\
 * 	(a)=((a)^((t)<<(n))))
 */

#define HPERM_OP(a,t,n,m) ((t)=((((a)<<(16-(n)))^(a))&(m)),\
	(a)=(a)^(t)^(t>>(16-(n))))

/* return 0 if key parity is odd (correct),
 * return -1 if key parity error,
 * return -2 if illegal weak key.
 */
int des_set_key(des_cblock *key, des_key_schedule schedule)
{
	static int shifts2[16]={0,0,1,1,1,1,1,1,0,1,1,1,1,1,1,0};
	register DES_LONG c,d,t,s;
	register unsigned char *in;
	register DES_LONG *k;
	register int i;

	if (des_check_key)
	{
		if (!check_parity(key))
			return(-1);

		if (des_is_weak_key(key))
			return(-2);
	}

	k=(DES_LONG *)schedule;
	in=(unsigned char *)key;

	c2l(in,c);
	c2l(in,d);

	/* I now do it in 47 simple operations :-)
	 * Thanks to John Fletcher ([e-mail])
	 * for the inspiration. :-) */
	PERM_OP (d,c,t,4,0x0f0f0f0fL);
	HPERM_OP(c,t,-2,0xcccc0000L);
	HPERM_OP(d,t,-2,0xcccc0000L);
	PERM_OP (d,c,t,1,0x55555555L);
	PERM_OP (c,d,t,8,0x00ff00ffL);
	PERM_OP (d,c,t,1,0x55555555L);
	d=	(((d&0x000000ffL)<<16L)| (d&0x0000ff00L)     |
		 ((d&0x00ff0000L)>>16L)|((c&0xf0000000L)>>4L));
	c&=0x0fffffffL;

	for (i=0; i<ITERATIONS; i++)
	{
		if (shifts2[i])
			{ c=((c>>2L)|(c<<26L)); d=((d>>2L)|(d<<26L)); }
		else
			{ c=((c>>1L)|(c<<27L)); d=((d>>1L)|(d<<27L)); }
		c&=0x0fffffffL;
		d&=0x0fffffffL;
		/* could be a few less shifts but I am to lazy at this
		 * point in time to investigate */
		s=	des_skb[0][ (c    )&0x3f                ]|
			des_skb[1][((c>> 6)&0x03)|((c>> 7L)&0x3c)]|
			des_skb[2][((c>>13)&0x0f)|((c>>14L)&0x30)]|
			des_skb[3][((c>>20)&0x01)|((c>>21L)&0x06) |
						  ((c>>22L)&0x38)];
		t=	des_skb[4][ (d    )&0x3f                ]|
			des_skb[5][((d>> 7L)&0x03)|((d>> 8L)&0x3c)]|
			des_skb[6][ (d>>15L)&0x3f                ]|
			des_skb[7][((d>>21L)&0x0f)|((d>>22L)&0x30)];

		/* table contained 0213 4657 */
		*(k++)=((t<<16L)|(s&0x0000ffffL))&0xffffffffL;
		s=     ((s>>16L)|(t&0xffff0000L));
		
		s=(s<<4L)|(s>>28L);
		*(k++)=s&0xffffffffL;
	}
	return(0);
}

int des_key_sched(des_cblock *key, des_key_schedule schedule)
{
	return(des_set_key(key,schedule));
}