path: root/sys/netinet/ip_espdesmd5.c

/*	$OpenBSD: ip_espdesmd5.c,v 1.2 1997/02/24 14:06:40 niklas Exp $	*/

/*
 * The author of this code is John Ioannidis, ji@tla.org,
 * 	(except when noted otherwise).
 *
 * This code was written for BSD/OS in Athens, Greece, in November 1995.
 *
 * Ported to OpenBSD and NetBSD, with additional transforms, in December 1996,
 * by Angelos D. Keromytis, kermit@forthnet.gr.
 *
 * Copyright (C) 1995, 1996, 1997 by John Ioannidis and Angelos D. Keromytis.
 *	
 * Permission to use, copy, and modify this software without fee
 * is hereby granted, provided that this entire notice is included in
 * all copies of any software which is or includes a copy or
 * modification of this software.
 *
 * THIS SOFTWARE IS BEING PROVIDED "AS IS", WITHOUT ANY EXPRESS OR
 * IMPLIED WARRANTY. IN PARTICULAR, NEITHER AUTHOR MAKES ANY
 * REPRESENTATION OR WARRANTY OF ANY KIND CONCERNING THE
 * MERCHANTABILITY OF THIS SOFTWARE OR ITS FITNESS FOR ANY PARTICULAR
 * PURPOSE.
 */

/*
 * Based on draft-ietf-ipsec-esp-des-md5-03.txt.
 */

#include <sys/param.h>
#include <sys/systm.h>
#include <sys/malloc.h>
#include <sys/mbuf.h>
#include <sys/domain.h>
#include <sys/protosw.h>
#include <sys/socket.h>
#include <sys/errno.h>
#include <sys/time.h>
#include <sys/kernel.h>
#include <machine/cpu.h>

#include <net/if.h>
#include <net/route.h>
#include <net/netisr.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/in_pcb.h>
#include <netinet/in_var.h>
#include <netinet/ip_var.h>

#include <sys/socketvar.h>
#include <net/raw_cb.h>
#include <net/encap.h>

#include <netinet/ip_icmp.h>
#include <netinet/ip_ipsp.h>
#include <netinet/ip_esp.h>

extern struct ifnet loif;

extern void des_ecb_encrypt(caddr_t, caddr_t, caddr_t, int);
extern void des_set_key(caddr_t, caddr_t);

int
espdesmd5_attach()
{
	return 0;
}

/*
 * espdesmd5_init() is called when an SPI is being set up. It interprets the
 * encap_msghdr present in m, and sets up the transformation data, in
 * this case, the encryption and decryption key schedules
 */

int
espdesmd5_init(struct tdb *tdbp, struct xformsw *xsp, struct mbuf *m)
{
	struct espdesmd5_xdata *xd;
	struct encap_msghdr *em;
	struct espdesmd5_xencap txd;
	u_char buf[ESPDESMD5_KEYSZ];
	int len;
	MD5_CTX ctx;

	tdbp->tdb_xform = xsp;

	m = m_pullup(m, ESPDESMD5_ULENGTH);
	if (m == NULL)
	{
#ifdef ENCDEBUG
		if (encdebug)
		  printf("espdesmd5_init: can't pull up %d bytes\n", ESP_ULENGTH);
#endif ENCDEBUG
		return ENOBUFS;
	}

	MALLOC(tdbp->tdb_xdata, caddr_t, sizeof (struct espdesmd5_xdata),
	       M_XDATA, M_WAITOK);
	if (tdbp->tdb_xdata == NULL)
	  return ENOBUFS;
	bzero(tdbp->tdb_xdata, sizeof (struct espdesmd5_xdata));
	xd = (struct espdesmd5_xdata *)tdbp->tdb_xdata;

	em = mtod(m, struct encap_msghdr *);
	if (em->em_msglen - EMT_SETSPI_FLEN != ESPDESMD5_ULENGTH)
	{
		free((caddr_t)tdbp->tdb_xdata, M_XDATA);
		tdbp->tdb_xdata = NULL;
		return EINVAL;
	}

	m_copydata(m, EMT_SETSPI_FLEN, em->em_msglen - EMT_SETSPI_FLEN, (caddr_t)&txd);

	if ((txd.edx_ivlen != 0) && (txd.edx_ivlen != 8))
	{
		free((caddr_t)tdbp->tdb_xdata, M_XDATA);
		tdbp->tdb_xdata = NULL;
		return EINVAL;
	}

	bzero(ipseczeroes, IPSEC_ZEROES_SIZE);	/* paranoid */

	xd->edx_ivlen = txd.edx_ivlen;
	xd->edx_bitmap = 0;
	xd->edx_wnd = txd.edx_wnd;

	/* Fix the IV */

#ifdef ENCDEBUG
	if (encdebug)
	{
		if (txd.edx_initiator)
		  printf("INITIATOR\n");
	  	printf("IV length: %d\n", txd.edx_ivlen);
	}
#endif
	if (txd.edx_ivlen)
	  bcopy(txd.edx_ivv, xd->edx_iv, ESPDESMD5_IVS);
	else
	{
		for (len = 0; len < ESPDESMD5_KEYSZ; len++)
		  buf[len] = txd.edx_initiator ? ESPDESMD5_IPADI :
						 ESPDESMD5_IPADR;

		realMD5Init(&ctx);
		MD5Update(&ctx, buf, ESPDESMD5_KEYSZ);
		MD5Update(&ctx, txd.edx_key, txd.edx_keylen);
	 	MD5Final(buf, &ctx);
		bcopy(buf, xd->edx_iv, ESPDESMD5_IVS);
#ifdef ENCDEBUG
		printf("IV ");
		if (encdebug)
		  for (len = 0; len < ESPDESMD5_IVS; len++)
		    printf(" %02x", xd->edx_iv[len]);
		printf("\n");
#endif
	}

	/* DES key */

	realMD5Init(&ctx);
	for (len = 0; len < ESPDESMD5_KEYSZ; len++)
	  buf[len] = txd.edx_initiator ? ESPDESMD5_DPADI : ESPDESMD5_DPADR;
	 
	MD5Update(&ctx, buf, ESPDESMD5_KEYSZ);
	MD5Update(&ctx, txd.edx_key, txd.edx_keylen);
	MD5Final(buf, &ctx);
	des_set_key((caddr_t)buf, (caddr_t)(xd->edx_eks));

	/* HMAC contexts */

	realMD5Init(&ctx);
	for (len = 0; len < ESPDESMD5_KEYSZ; len++)
	  buf[len] = txd.edx_initiator ? ESPDESMD5_HPADI : ESPDESMD5_HPADR;

	MD5Update(&ctx, buf, ESPDESMD5_KEYSZ);
	MD5Update(&ctx, txd.edx_key, txd.edx_keylen);
	MD5Final(buf, &ctx);

	bzero(buf + ESPDESMD5_ALEN, ESPDESMD5_KEYSZ - ESPDESMD5_ALEN);

	for (len = 0; len < ESPDESMD5_KEYSZ; len++)
	  buf[len] ^= ESPDESMD5_IPAD_VAL;

	realMD5Init(&ctx);
	MD5Update(&ctx, buf, ESPDESMD5_KEYSZ);
	xd->edx_ictx = ctx;

	for (len = 0; len < ESPDESMD5_KEYSZ; len++)
	  buf[len] ^= (ESPDESMD5_IPAD_VAL ^ ESPDESMD5_OPAD_VAL);

	realMD5Init(&ctx);
	MD5Update(&ctx, buf, ESPDESMD5_KEYSZ);
	xd->edx_octx = ctx;
	
	/* Replay counter */

	for (len = 0; len < ESPDESMD5_KEYSZ; len++)
	  buf[len] = txd.edx_initiator ? ESPDESMD5_RPADI : 
						 ESPDESMD5_RPADR;

	realMD5Init(&ctx);
	MD5Update(&ctx, buf, ESPDESMD5_KEYSZ);
	MD5Update(&ctx, txd.edx_key, txd.edx_keylen);
	MD5Final(buf, &ctx);
	bcopy(buf, (unsigned char *)&(xd->edx_rpl), ESPDESMD5_RPLENGTH);
	xd->edx_initial = xd->edx_rpl - 1;

#ifdef ENCDEBUG
	if (encdebug)
	  printf("Initial replay counter: %x (%x)\n", xd->edx_rpl,
		 xd->edx_initial);
#endif
	
	bzero(&txd, sizeof(struct espdesmd5_xencap));
	bzero(buf, ESPDESMD5_KEYSZ);
	bzero(&ctx, sizeof(MD5_CTX));

	return 0;
}

int
espdesmd5_zeroize(struct tdb *tdbp)
{
	FREE(tdbp->tdb_xdata, M_XDATA);
	return 0;
}


struct mbuf *
espdesmd5_input(struct mbuf *m, struct tdb *tdb)
{
	struct espdesmd5_xdata *xd;
	struct ip *ip, ipo;
	u_char iv[8], niv[8], blk[8], auth[ESPDESMD5_ALEN];
	u_char iauth[ESPDESMD5_ALEN];
	u_char *idat, *odat;
	struct esp *esp;
	struct ifnet *rcvif;
	int plen, ilen, olen, i, authp, oplen, errc;
	u_int32_t rplc, tbitmap, trpl;
	u_char padsize, nextproto;
	struct mbuf *mi, *mo;
	MD5_CTX ctx;

	xd = (struct espdesmd5_xdata *)tdb->tdb_xdata;

	rcvif = m->m_pkthdr.rcvif;
	if (rcvif == NULL)
	{
#ifdef ENCDEBUG
		if (encdebug)
		  printf("espdesmd5_input: receive interface is NULL!!!\n");
#endif ENCDEBUG
		rcvif = &loif;
	}

	ip = mtod(m, struct ip *);
	ipo = *ip;
	esp = (struct esp *)(ip + 1);

	plen = m->m_pkthdr.len - sizeof (struct ip) - sizeof (u_long) - xd->edx_ivlen;
	if (plen & 07)
	{
#ifdef ENCDEBUG
		if (encdebug)
		  printf("espdesmd5_input: payload not a multiple of 8 octets\n");
#endif ENCDEBUG
		espstat.esps_badilen++;
		m_freem(m);
		return NULL;
	}

	oplen = plen;
	ilen = m->m_len - sizeof (struct ip) - ESPDESMD5_IVS - sizeof(u_long);
	idat = mtod(m, unsigned char *) + sizeof (struct ip) + sizeof(u_long) +
	       ESPDESMD5_IVS;

	if (xd->edx_ivlen == 0)		/* KeyIV in use */
	{
		bcopy(xd->edx_iv, iv, ESPDESMD5_IVS);
	  	ilen += ESPDESMD5_IVS;
		idat -= ESPDESMD5_IVS;
	}
	else
	  bcopy(idat - ESPDESMD5_IVS, iv, ESPDESMD5_IVS);

	olen = ilen;
	odat = idat;
	mi = mo = m;
	i = 0;
	authp = 0;

	ctx = xd->edx_ictx;

	MD5Update(&ctx, (unsigned char *)&(tdb->tdb_spi), sizeof(u_int32_t));
	MD5Update(&ctx, iv, ESPDESMD5_IVS);

#ifdef ENCDEBUG
	printf("IV ");
	for (i = 0; i < ESPDESMD5_IVS; i++)
	  printf(" %02x", iv[i]);
	printf("\n");
	i = 0;
#endif

	/*
	 * At this point:
	 *   plen is # of encapsulated payload octets
	 *   ilen is # of octets left in this mbuf
	 *   idat is first encapsulated payload octed in this mbuf
	 *   same for olen and odat
	 *   iv contains the IV.
	 *   mi and mo point to the first mbuf
	 *
	 * From now on until the end of the mbuf chain:
	 *   . move the next eight octets of the chain into blk[]
	 *     (ilen, idat, and mi are adjusted accordingly)
	 *     and save it back into iv[]
	 *   . decrypt blk[], xor with iv[], put back into chain
	 *     (olen, odat, amd mo are adjusted accordingly)
	 *   . repeat
	 */

	while (plen > 0)		/* while not done */
	{
		while (ilen == 0)	/* we exhausted previous mbuf */
		{
			mi = mi->m_next;
			if (mi == NULL)
			  panic("espdesmd5_input: bad chain (i)\n");
			ilen = mi->m_len;
			idat = (u_char *)mi->m_data;
		}

		blk[i] = niv[i] = *idat++;
		i++;
		ilen--;

		if (i == 8)
		{
			des_ecb_encrypt(blk, blk, (caddr_t)(xd->edx_eks), 0);
			for (i=0; i<8; i++)
			{
				while (olen == 0)
				{
					mo = mo->m_next;
					if (mo == NULL)
					  panic("espdesmd5_input: bad chain (o)\n");
					olen = mo->m_len;
					odat = (u_char *)mo->m_data;
				}
				*odat = blk[i] ^ iv[i];
				iv[i] = niv[i];
				blk[i] = *odat++; /* needed elsewhere */
				olen--;
			}
			i = 0;

			if (plen < ESPDESMD5_ALEN)
			{
				bcopy(blk, auth + authp, ESPDESMD5_DESBLK);
				authp += ESPDESMD5_DESBLK;
#ifdef ENCDEBUG
				if (encdebug)
				  printf("Copying authenticator from %d\n",
					 plen);
#endif
			}
			else
			{
			  	if (plen == ESPDESMD5_ALEN + 1)
			  	{
					nextproto = blk[7];
					padsize = blk[6];
#ifdef ENCDEBUG
					if (encdebug)
					  printf("Next protocol: %d\nPadsize: %d\n", nextproto, padsize);
#endif
			  	}
				else
				  if (plen + 7 == oplen)
				  {
#ifdef ENCDEBUG
					if (encdebug)
					  printf("SEQ %02x %02x %02x %02x\n",
						 blk[0], blk[1], blk[2], 
						 blk[3]);
#endif
					tbitmap = xd->edx_bitmap; /* Save it */
					trpl = xd->edx_rpl;
				     	rplc = ntohl(*((u_int32_t *)blk));
					if ((errc = checkreplaywindow32(rplc, xd->edx_initial, &(xd->edx_rpl), xd->edx_wnd, &(xd->edx_bitmap))) != 0)
					{
						switch (errc)
						{
							case 1:
#ifdef ENCDEBUG
							  printf("espdesmd5_input: replay counter wrapped\n");
#endif
							  espstat.esps_wrap++;
							  break;
							case 2:
#ifdef ENCDEBUG
						 	  printf("espdesmd5_input: received old packet, seq = %08x\n", rplc);
#endif
							  espstat.esps_replay++;
							  break;
							case 3:
#ifdef ENCDEBUG
						 	  printf("espdesmd5_input: packet already received\n");
#endif
							  espstat.esps_replay++;
							  break;
						}
						m_freem(m);
						return NULL;
					}
				  }

				MD5Update(&ctx, blk, ESPDESMD5_DESBLK);
			}
		}

		plen--;
	}

	/*
	 * Now, the entire chain has been decrypted.
	 */

	MD5Final(iauth, &ctx);
	ctx = xd->edx_octx;
	MD5Update(&ctx, iauth, ESPDESMD5_ALEN);
	MD5Final(iauth, &ctx);

#ifdef ENCDEBUG
	printf("RECEIVED ");
	for (rplc = 0; rplc < ESPDESMD5_ALEN; rplc++)
	  printf(" %02x", auth[rplc]);
	printf("\nSHOULD HAVE ");
	for (rplc = 0; rplc < ESPDESMD5_ALEN; rplc++)
	  printf(" %02x", iauth[rplc]);
	printf("\n");
#endif

	if (bcmp(auth, iauth, ESPDESMD5_ALEN))
	{
#ifdef ENCDEBUG
		if (encdebug)
		  printf("espdesmd5_input: bad auth\n");
#endif
		xd->edx_rpl = trpl;
		xd->edx_bitmap = tbitmap;  /* Restore */
		espstat.esps_badauth++;
		m_freem(m);
		return NULL;
	}

	m_adj(m, - padsize - 2 - ESPDESMD5_ALEN);
	m_adj(m, 4 + xd->edx_ivlen + ESPDESMD5_RPLENGTH);

	if (m->m_len < sizeof (struct ip))
	{
		m = m_pullup(m, sizeof (struct ip));
		if (m == NULL)
		{
			xd->edx_rpl = trpl;
			xd->edx_bitmap = tbitmap;
			return NULL;
		}
	}

	ip = mtod(m, struct ip *);
	ipo.ip_p = nextproto;
	ipo.ip_id = htons(ipo.ip_id);
	ipo.ip_off = 0;
	ipo.ip_len += sizeof (struct ip) - ESPDESMD5_RPLENGTH - 4 - xd->edx_ivlen - padsize - 2 - ESPDESMD5_ALEN;
#ifdef ENCDEBUG
	if (encdebug)
	  printf("IP packet size %d\n", ipo.ip_len);
#endif
	ipo.ip_len = htons(ipo.ip_len);
	ipo.ip_sum = 0;
	*ip = ipo;
	ip->ip_sum = in_cksum(m, sizeof (struct ip));

	return m;
}

int
espdesmd5_output(struct mbuf *m, struct sockaddr_encap *gw, struct tdb *tdb, struct mbuf **mp)
{
	struct espdesmd5_xdata *xd;
	struct ip *ip, ipo;
	int i, ilen, olen, ohlen, nh, rlen, plen, padding;
	u_int32_t rplc;
	u_long spi;
	struct mbuf *mi, *mo, *ms;
	u_char *pad, *idat, *odat;
	u_char iv[ESPDESMD5_IVS], blk[8], auth[ESPDESMD5_ALEN];
	MD5_CTX ctx;

	m = m_pullup(m, sizeof (struct ip));   /* Get IP header in one mbuf */
	if (m == NULL)
	  return ENOBUFS;

	ip = mtod(m, struct ip *);
	spi = tdb->tdb_spi;
	
	xd = (struct espdesmd5_xdata *)tdb->tdb_xdata;
	ilen = ntohs(ip->ip_len);    /* Size of the packet */
	ohlen = sizeof (u_int32_t) + xd->edx_ivlen; /* size of plaintext ESP */

	if (xd->edx_rpl == xd->edx_initial)
	{
#ifdef ENCDEBUG
	    if (encdebug)
	      printf("espdesmd5_output: replay counter wrapped\n");
#endif
	    espstat.esps_wrap++;
	    return EHOSTDOWN;   /* XXX */
	}
	
	ipo = *ip;
	nh = ipo.ip_p;

#ifdef ENCDEBUG
	if (encdebug)
	  printf("espdesmd5_output: next protocol is %d\n", nh);
#endif

	/* Raw payload length */
	rlen = ESPDESMD5_RPLENGTH + ilen - sizeof (struct ip); 

        padding = ((8 - ((rlen + 2) % 8)) % 8) + 2;

	pad = (u_char *)m_pad(m, padding);
	if (pad == NULL)
	  return ENOBUFS;

	pad[padding-2] = padding - 2;
	pad[padding-1] = nh;

#ifdef ENCDEBUG
	if (encdebug)
	  printf("espdesmd5_output: padding %d bytes\n", padding);
#endif

	plen = rlen + padding + ESPDESMD5_ALEN;

	ctx = xd->edx_ictx;  /* Get inner padding cached */

	bcopy(xd->edx_iv, iv, ESPDESMD5_IVS);

	MD5Update(&ctx, (u_char *)&spi, sizeof(u_long));
	MD5Update(&ctx, iv, ESPDESMD5_IVS);
	rplc = htonl(xd->edx_rpl);
	MD5Update(&ctx, (unsigned char *)&rplc, ESPDESMD5_RPLENGTH);
	xd->edx_rpl++;

#ifdef ENCDEBUG
	if (encdebug)
	  printf("espdesmd5_output: using replay counter %x\n",
		 xd->edx_rpl - 1);
#endif
	mi = m;

	/* MD5 the data */
	while (mi != NULL)
	{
#ifdef ENCDEBUG
		if (encdebug)
		  printf("espdesmd5_output: MD5'ing %d bytes\n", mi->m_len);
#endif
		if (mi == m)
		  MD5Update(&ctx, (u_char *)mi->m_data + sizeof(struct ip),
			    mi->m_len - sizeof(struct ip));
		else
	    	  MD5Update(&ctx, (u_char *)mi->m_data, mi->m_len);
	    	mi = mi->m_next;
	}

	MD5Final(auth, &ctx);
	ctx = xd->edx_octx;
	MD5Update(&ctx, auth, ESPDESMD5_ALEN);
	MD5Final(auth, &ctx);   /* That's the authenticator */

	/* 
	 * This routine is different from espdes_output() in that
	 * here we construct the whole packet before starting encrypting.
	 */

	m = m_pullup(m, sizeof(struct ip) + ESPDESMD5_RPLENGTH + 
		     sizeof(u_int32_t) + xd->edx_ivlen);
	if (m == NULL)
	  return ENOBUFS;

	/* Copy data if necessary */
	if (m->m_len - sizeof(struct ip))
	{
#ifdef ENCDEBUG
		if (encdebug)
		  printf("espdesmd5_output: pushing data\n");
#endif
	    	ms = m_copym(m, sizeof(struct ip), m->m_len - sizeof(struct ip),
			     M_DONTWAIT);
	    	if (ms == NULL)
	      	  return ENOBUFS;
	
	    	ms->m_next = m->m_next;
	    	m->m_next = ms;
		m->m_len = sizeof(struct ip);
	}
	
	/* Copy SPI, IV (or not) and replay counter */
	bcopy((caddr_t)&spi, mtod(m, caddr_t) + sizeof (struct ip), 
	      sizeof (u_int32_t));
	bcopy((caddr_t)iv,  mtod(m, caddr_t) + sizeof (struct ip) + 
	      sizeof (u_int32_t), xd->edx_ivlen);
	bcopy((caddr_t)&rplc, mtod(m, caddr_t) + sizeof(struct ip) + 
	      sizeof(u_int32_t) + xd->edx_ivlen, ESPDESMD5_RPLENGTH);

#ifdef ENCDEBUG
	if (encdebug)
	  printf("espdesmd5_output: replay counter (wire value) %x\n", rplc);
#endif

	/* Adjust the length accordingly */
	m->m_len += sizeof(u_int32_t) + ESPDESMD5_RPLENGTH + xd->edx_ivlen;
	m->m_pkthdr.len += sizeof(u_int32_t) + ESPDESMD5_RPLENGTH + 
			   xd->edx_ivlen;

#ifdef ENCDEBUG
	if (encdebug)
	  printf("espdesmd5_output: mbuf chain length %d\n", m->m_pkthdr.len);
#endif

	/* Let's append the authenticator too */
	MGET(ms, M_DONTWAIT, MT_DATA);
	if (ms == NULL)
	  return ENOBUFS;

	bcopy(auth, mtod(ms, u_char *), ESPDESMD5_ALEN);
	ms->m_len = ESPDESMD5_ALEN;

	m_cat(m, ms);
	m->m_pkthdr.len += ESPDESMD5_ALEN;  /* Adjust length */
	
#ifdef ENCDEBUG
	if (encdebug)
	  printf("espdesmd5_output: final mbuf chain length %d\n",
		 m->m_pkthdr.len);
#endif

	ilen = olen = m->m_len - sizeof (struct ip) - sizeof(u_int32_t) - 
	       xd->edx_ivlen;
	idat = odat = mtod(m, u_char *) + sizeof (struct ip) +
	       sizeof(u_int32_t) + xd->edx_ivlen;
	i = 0;
	mi = mo = m;

#ifdef ENCDEBUG
	if (encdebug)
	  printf("espdesmd5_output: starting encryption with ilen=%d, plen=%d\n", ilen, plen);
#endif

	while (plen > 0)		/* while not done */
	{
		while (ilen == 0)	/* we exhausted previous mbuf */
		{
			mi = mi->m_next;
			if (mi == NULL)
			  panic("espdesmd5_output: bad chain (i)\n");
			ilen = mi->m_len;
			idat = (u_char *)mi->m_data;
		}

		blk[i] = *idat++ ^ iv[i];
		
		i++;
		ilen--;

		if (i == 8)   /* We have full block */
		{
			des_ecb_encrypt(blk, blk, (caddr_t)(xd->edx_eks), 1);
			for (i=0; i<8; i++)
			{
				while (olen == 0)
				{
					mo = mo->m_next;
					if (mo == NULL)
					  panic("espdesmd5_output: bad chain (o)\n");
					olen = mo->m_len;
					odat = (u_char *)mo->m_data;
				}
				*odat++ = blk[i];
				iv[i] = blk[i];
				olen--;
			}
			i = 0;
		}

		plen--;
	}

#ifdef ENCDEBUG
	if (encdebug)
	  printf("espdesmd5_output: almost done now\n");
#endif

	bcopy(iv, xd->edx_iv, ESPDESMD5_IVS); /* New IV */

	/* Fix the length and the next protocol, copy back and off we go */
	ipo.ip_len = htons(sizeof (struct ip) + ohlen + rlen + padding +
	    ESPDESMD5_ALEN);
	ipo.ip_p = IPPROTO_ESP;
	bcopy((caddr_t)&ipo, mtod(m, caddr_t), sizeof(struct ip));
	
	*mp = m;
	return 0;
}	


/*
 * both versions of the checkreplaywindow for 32 and 64 bit counters
 * return 0 on success
 * return 1 for counter == 0
 * return 2 for very old packet
 * return 3 for packet within current window but already received
 */

int
checkreplaywindow64(u_int64_t seq, u_int64_t *lastseq, u_int64_t window, u_int64_t *bitmap)
{
	u_int64_t diff;

	if (seq == 0)
	  return 1;

	if (seq > *lastseq)
	{
		diff = seq - *lastseq;
		if (diff < window)
	  	  *bitmap = ((*bitmap) << diff) | 1;
	 	else
	  	  *bitmap = 1;
		*lastseq = seq;
		return 0;
	}
	diff = *lastseq - seq;
	if (diff >= window)
	{
		espstat.esps_wrap++;
	  	return 2;
	}
	if ((*bitmap) & (((u_int64_t) 1) << diff))
	{
		espstat.esps_replay++;
	  	return 3;
	}
	*bitmap |= (((u_int64_t) 1) << diff);
	return 0;
}

int
checkreplaywindow32(u_int32_t seq, u_int32_t initial, u_int32_t *lastseq, u_int32_t window, u_int32_t *bitmap)
{
	u_int32_t diff;

#ifdef ENCDEBUG
	if (encdebug)
	  printf("checkreplaywindow32: seq=%x lastseq=%x\n", seq, *lastseq);
#endif

	seq -= initial;

	if (seq == 0)
	  return 1;

	if (seq > *lastseq - initial)
	{
		diff = seq - (*lastseq - initial);
		if (diff < window)
	  	  *bitmap = ((*bitmap) << diff) | 1;
	 	else
	  	  *bitmap = 1;
		*lastseq = seq + initial;
		return 0;
	}
	diff = *lastseq - initial - seq;
	if (diff >= window)
	{
		espstat.esps_wrap++;
	  	return 2;
	}
	if ((*bitmap) & (((u_int32_t) 1) << diff))
	{
		espstat.esps_replay++;
	  	return 3;
	}
	*bitmap |= (((u_int32_t) 1) << diff);
	return 0;
}