print-tcp.c - platform/external/tcpdump - Git at Google

 /*
  * Copyright (c) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
  *	The Regents of the University of California.  All rights reserved.
  *
  * Copyright (c) 1999-2004 The tcpdump.org project
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that: (1) source code distributions
  * retain the above copyright notice and this paragraph in its entirety, (2)
  * distributions including binary code include the above copyright notice and
  * this paragraph in its entirety in the documentation or other materials
  * provided with the distribution, and (3) all advertising materials mentioning
  * features or use of this software display the following acknowledgement:
  * ``This product includes software developed by the University of California,
  * Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
  * the University nor the names of its contributors may be used to endorse
  * or promote products derived from this software without specific prior
  * written permission.
  * THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
  * WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
  * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
  */

 #ifndef lint
 static const char rcsid[] _U_ =
     "@(#) $Header: /tcpdump/master/tcpdump/print-tcp.c,v 1.120.2.3 2005/10/16 06:05:46 guy Exp $ (LBL)";
 #endif

 #ifdef HAVE_CONFIG_H
 #include "config.h"
 #endif

 #include <tcpdump-stdinc.h>

 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>

 #include "interface.h"
 #include "addrtoname.h"
 #include "extract.h"

 #include "tcp.h"

 #include "ip.h"
 #ifdef INET6
 #include "ip6.h"
 #endif
 #include "ipproto.h"
 #include "rpc_auth.h"
 #include "rpc_msg.h"

 #include "nameser.h"

 #ifdef HAVE_LIBCRYPTO
 #include <openssl/md5.h>

 #define SIGNATURE_VALID		0
 #define SIGNATURE_INVALID	1
 #define CANT_CHECK_SIGNATURE	2

 static int tcp_verify_signature(const struct ip *ip, const struct tcphdr *tp,
     const u_char *data, int length, const u_char *rcvsig);
 #endif

 static void print_tcp_rst_data(register const u_char *sp, u_int length);

 #define MAX_RST_DATA_LEN	30


 struct tha {
 #ifndef INET6
 	struct in_addr src;
 	struct in_addr dst;
 #else
 	struct in6_addr src;
 	struct in6_addr dst;
 #endif /*INET6*/
 	u_int port;
 };

 struct tcp_seq_hash {
 	struct tcp_seq_hash *nxt;
 	struct tha addr;
 	tcp_seq seq;
 	tcp_seq ack;
 };

 #define TSEQ_HASHSIZE 919

 /* These tcp optinos do not have the size octet */
 #define ZEROLENOPT(o) ((o) == TCPOPT_EOL || (o) == TCPOPT_NOP)

 static struct tcp_seq_hash tcp_seq_hash[TSEQ_HASHSIZE];


 #ifndef TELNET_PORT
 #define TELNET_PORT	23
 #endif
 #ifndef BGP_PORT
 #define BGP_PORT	179
 #endif
 #define NETBIOS_SSN_PORT 139
 #ifndef PPTP_PORT
 #define PPTP_PORT	1723
 #endif
 #define BEEP_PORT        10288
 #ifndef NFS_PORT
 #define NFS_PORT	2049
 #endif
 #define MSDP_PORT	639
 #define LDP_PORT        646

 static int tcp_cksum(register const struct ip *ip,
 		     register const struct tcphdr *tp,
 		     register u_int len)
 {
 	union phu {
 		struct phdr {
 			u_int32_t src;
 			u_int32_t dst;
 			u_char mbz;
 			u_char proto;
 			u_int16_t len;
 		} ph;
 		u_int16_t pa[6];
 	} phu;
 	const u_int16_t *sp;

 	/* pseudo-header.. */
 	phu.ph.len = htons((u_int16_t)len);
 	phu.ph.mbz = 0;
 	phu.ph.proto = IPPROTO_TCP;
 	memcpy(&phu.ph.src, &ip->ip_src.s_addr, sizeof(u_int32_t));
 	if (IP_HL(ip) == 5)
 		memcpy(&phu.ph.dst, &ip->ip_dst.s_addr, sizeof(u_int32_t));
 	else
 		phu.ph.dst = ip_finddst(ip);

 	sp = &phu.pa[0];
 	return in_cksum((u_short *)tp, len,
 			sp[0]+sp[1]+sp[2]+sp[3]+sp[4]+sp[5]);
 }

 #ifdef INET6
 static int tcp6_cksum(const struct ip6_hdr *ip6, const struct tcphdr *tp,
 	u_int len)
 {
 	size_t i;
 	register const u_int16_t *sp;
 	u_int32_t sum;
 	union {
 		struct {
 			struct in6_addr ph_src;
 			struct in6_addr ph_dst;
 			u_int32_t	ph_len;
 			u_int8_t	ph_zero[3];
 			u_int8_t	ph_nxt;
 		} ph;
 		u_int16_t pa[20];
 	} phu;

 	/* pseudo-header */
 	memset(&phu, 0, sizeof(phu));
 	phu.ph.ph_src = ip6->ip6_src;
 	phu.ph.ph_dst = ip6->ip6_dst;
 	phu.ph.ph_len = htonl(len);
 	phu.ph.ph_nxt = IPPROTO_TCP;

 	sum = 0;
 	for (i = 0; i < sizeof(phu.pa) / sizeof(phu.pa[0]); i++)
 		sum += phu.pa[i];

 	sp = (const u_int16_t *)tp;

 	for (i = 0; i < (len & ~1); i += 2)
 		sum += *sp++;

 	if (len & 1)
 		sum += htons((*(const u_int8_t *)sp) << 8);

 	while (sum > 0xffff)
 		sum = (sum & 0xffff) + (sum >> 16);
 	sum = ~sum & 0xffff;

 	return (sum);
 }
 #endif

 void
 tcp_print(register const u_char *bp, register u_int length,
 	  register const u_char *bp2, int fragmented)
 {
 	register const struct tcphdr *tp;
 	register const struct ip *ip;
 	register u_char flags;
 	register u_int hlen;
 	register char ch;
 	u_int16_t sport, dport, win, urp;
 	u_int32_t seq, ack, thseq, thack;
 	int threv;
 #ifdef INET6
 	register const struct ip6_hdr *ip6;
 #endif

 	tp = (struct tcphdr *)bp;
 	ip = (struct ip *)bp2;
 #ifdef INET6
 	if (IP_V(ip) == 6)
 		ip6 = (struct ip6_hdr *)bp2;
 	else
 		ip6 = NULL;
 #endif /*INET6*/
 	ch = '\0';
 	if (!TTEST(tp->th_dport)) {
 		(void)printf("%s > %s: [|tcp]",
 			ipaddr_string(&ip->ip_src),
 			ipaddr_string(&ip->ip_dst));
 		return;
 	}

 	sport = EXTRACT_16BITS(&tp->th_sport);
 	dport = EXTRACT_16BITS(&tp->th_dport);

 	hlen = TH_OFF(tp) * 4;

 	/*
 	 * If data present, header length valid, and NFS port used,
 	 * assume NFS.
 	 * Pass offset of data plus 4 bytes for RPC TCP msg length
 	 * to NFS print routines.
 	 */
 	if (!qflag && hlen >= sizeof(*tp) && hlen <= length) {
 		if ((u_char *)tp + 4 + sizeof(struct sunrpc_msg) <= snapend &&
 		    dport == NFS_PORT) {
 			nfsreq_print((u_char *)tp + hlen + 4, length - hlen,
 				     (u_char *)ip);
 			return;
 		} else if ((u_char *)tp + 4 + sizeof(struct sunrpc_msg)
 			   <= snapend &&
 			   sport == NFS_PORT) {
 			nfsreply_print((u_char *)tp + hlen + 4, length - hlen,
 				       (u_char *)ip);
 			return;
 		}
 	}
 #ifdef INET6
 	if (ip6) {
 		if (ip6->ip6_nxt == IPPROTO_TCP) {
 			(void)printf("%s.%s > %s.%s: ",
 				ip6addr_string(&ip6->ip6_src),
 				tcpport_string(sport),
 				ip6addr_string(&ip6->ip6_dst),
 				tcpport_string(dport));
 		} else {
 			(void)printf("%s > %s: ",
 				tcpport_string(sport), tcpport_string(dport));
 		}
 	} else
 #endif /*INET6*/
 	{
 		if (ip->ip_p == IPPROTO_TCP) {
 			(void)printf("%s.%s > %s.%s: ",
 				ipaddr_string(&ip->ip_src),
 				tcpport_string(sport),
 				ipaddr_string(&ip->ip_dst),
 				tcpport_string(dport));
 		} else {
 			(void)printf("%s > %s: ",
 				tcpport_string(sport), tcpport_string(dport));
 		}
 	}

 	if (hlen < sizeof(*tp)) {
 		(void)printf(" tcp %d [bad hdr length %u - too short, < %lu]",
 		    length - hlen, hlen, (unsigned long)sizeof(*tp));
 		return;
 	}

 	TCHECK(*tp);

 	seq = EXTRACT_32BITS(&tp->th_seq);
 	ack = EXTRACT_32BITS(&tp->th_ack);
 	win = EXTRACT_16BITS(&tp->th_win);
 	urp = EXTRACT_16BITS(&tp->th_urp);

 	if (qflag) {
 		(void)printf("tcp %d", length - hlen);
 		if (hlen > length) {
 			(void)printf(" [bad hdr length %u - too long, > %u]",
 			    hlen, length);
 		}
 		return;
 	}
 	if ((flags = tp->th_flags) & (TH_SYN|TH_FIN|TH_RST|TH_PUSH|
 				      TH_ECNECHO|TH_CWR)) {
 		if (flags & TH_SYN)
 			putchar('S');
 		if (flags & TH_FIN)
 			putchar('F');
 		if (flags & TH_RST)
 			putchar('R');
 		if (flags & TH_PUSH)
 			putchar('P');
 		if (flags & TH_CWR)
 			putchar('W');	/* congestion _W_indow reduced (ECN) */
 		if (flags & TH_ECNECHO)
 			putchar('E');	/* ecn _E_cho sent (ECN) */
 	} else
 		putchar('.');

 	if (!Sflag && (flags & TH_ACK)) {
 		register struct tcp_seq_hash *th;
 		const void *src, *dst;
 		register int rev;
 		struct tha tha;
 		/*
 		 * Find (or record) the initial sequence numbers for
 		 * this conversation.  (we pick an arbitrary
 		 * collating order so there's only one entry for
 		 * both directions).
 		 */
 #ifdef INET6
 		memset(&tha, 0, sizeof(tha));
 		rev = 0;
 		if (ip6) {
 			src = &ip6->ip6_src;
 			dst = &ip6->ip6_dst;
 			if (sport > dport)
 				rev = 1;
 			else if (sport == dport) {
 				if (memcmp(src, dst, sizeof ip6->ip6_dst) > 0)
 					rev = 1;
 			}
 			if (rev) {
 				memcpy(&tha.src, dst, sizeof ip6->ip6_dst);
 				memcpy(&tha.dst, src, sizeof ip6->ip6_src);
 				tha.port = dport << 16 | sport;
 			} else {
 				memcpy(&tha.dst, dst, sizeof ip6->ip6_dst);
 				memcpy(&tha.src, src, sizeof ip6->ip6_src);
 				tha.port = sport << 16 | dport;
 			}
 		} else {
 			src = &ip->ip_src;
 			dst = &ip->ip_dst;
 			if (sport > dport)
 				rev = 1;
 			else if (sport == dport) {
 				if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
 					rev = 1;
 			}
 			if (rev) {
 				memcpy(&tha.src, dst, sizeof ip->ip_dst);
 				memcpy(&tha.dst, src, sizeof ip->ip_src);
 				tha.port = dport << 16 | sport;
 			} else {
 				memcpy(&tha.dst, dst, sizeof ip->ip_dst);
 				memcpy(&tha.src, src, sizeof ip->ip_src);
 				tha.port = sport << 16 | dport;
 			}
 		}
 #else
 		rev = 0;
 		src = &ip->ip_src;
 		dst = &ip->ip_dst;
 		if (sport > dport)
 			rev = 1;
 		else if (sport == dport) {
 			if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
 				rev = 1;
 		}
 		if (rev) {
 			memcpy(&tha.src, dst, sizeof ip->ip_dst);
 			memcpy(&tha.dst, src, sizeof ip->ip_src);
 			tha.port = dport << 16 | sport;
 		} else {
 			memcpy(&tha.dst, dst, sizeof ip->ip_dst);
 			memcpy(&tha.src, src, sizeof ip->ip_src);
 			tha.port = sport << 16 | dport;
 		}
 #endif

 		threv = rev;
 		for (th = &tcp_seq_hash[tha.port % TSEQ_HASHSIZE];
 		     th->nxt; th = th->nxt)
 			if (memcmp((char *)&tha, (char *)&th->addr,
 				  sizeof(th->addr)) == 0)
 				break;

 		if (!th->nxt || (flags & TH_SYN)) {
 			/* didn't find it or new conversation */
 			if (th->nxt == NULL) {
 				th->nxt = (struct tcp_seq_hash *)
 					calloc(1, sizeof(*th));
 				if (th->nxt == NULL)
 					error("tcp_print: calloc");
 			}
 			th->addr = tha;
 			if (rev)
 				th->ack = seq, th->seq = ack - 1;
 			else
 				th->seq = seq, th->ack = ack - 1;
 		} else {
 			if (rev)
 				seq -= th->ack, ack -= th->seq;
 			else
 				seq -= th->seq, ack -= th->ack;
 		}

 		thseq = th->seq;
 		thack = th->ack;
 	} else {
 		/*fool gcc*/
 		thseq = thack = threv = 0;
 	}
 	if (hlen > length) {
 		(void)printf(" [bad hdr length %u - too long, > %u]",
 		    hlen, length);
 		return;
 	}

 	if (IP_V(ip) == 4 && vflag && !fragmented) {
 		u_int16_t sum, tcp_sum;
 		if (TTEST2(tp->th_sport, length)) {
 			sum = tcp_cksum(ip, tp, length);

                         (void)printf(", cksum 0x%04x",EXTRACT_16BITS(&tp->th_sum));
 			if (sum != 0) {
 				tcp_sum = EXTRACT_16BITS(&tp->th_sum);
 				(void)printf(" (incorrect (-> 0x%04x),",in_cksum_shouldbe(tcp_sum, sum));
 			} else
 				(void)printf(" (correct),");
 		}
 	}
 #ifdef INET6
 	if (IP_V(ip) == 6 && ip6->ip6_plen && vflag && !fragmented) {
 		u_int16_t sum,tcp_sum;
 		if (TTEST2(tp->th_sport, length)) {
 			sum = tcp6_cksum(ip6, tp, length);
                         (void)printf(", cksum 0x%04x",EXTRACT_16BITS(&tp->th_sum));
 			if (sum != 0) {
 				tcp_sum = EXTRACT_16BITS(&tp->th_sum);
 				(void)printf(" (incorrect (-> 0x%04x),",in_cksum_shouldbe(tcp_sum, sum));
 			} else
 				(void)printf(" (correct),");

 		}
 	}
 #endif

 	length -= hlen;
 	if (vflag > 1 || length > 0 || flags & (TH_SYN | TH_FIN | TH_RST))
 		(void)printf(" %u:%u(%u)", seq, seq + length, length);
 	if (flags & TH_ACK)
 		(void)printf(" ack %u", ack);

 	(void)printf(" win %d", win);

 	if (flags & TH_URG)
 		(void)printf(" urg %d", urp);
 	/*
 	 * Handle any options.
 	 */
 	if (hlen > sizeof(*tp)) {
 		register const u_char *cp;
 		register u_int i, opt, datalen;
 		register u_int len;

 		hlen -= sizeof(*tp);
 		cp = (const u_char *)tp + sizeof(*tp);
 		putchar(' ');
 		ch = '<';
 		while (hlen > 0) {
 			putchar(ch);
 			TCHECK(*cp);
 			opt = *cp++;
 			if (ZEROLENOPT(opt))
 				len = 1;
 			else {
 				TCHECK(*cp);
 				len = *cp++;	/* total including type, len */
 				if (len < 2 || len > hlen)
 					goto bad;
 				--hlen;		/* account for length byte */
 			}
 			--hlen;			/* account for type byte */
 			datalen = 0;

 /* Bail if "l" bytes of data are not left or were not captured  */
 #define LENCHECK(l) { if ((l) > hlen) goto bad; TCHECK2(*cp, l); }

 			switch (opt) {

 			case TCPOPT_MAXSEG:
 				(void)printf("mss");
 				datalen = 2;
 				LENCHECK(datalen);
 				(void)printf(" %u", EXTRACT_16BITS(cp));

 				break;

 			case TCPOPT_EOL:
 				(void)printf("eol");
 				break;

 			case TCPOPT_NOP:
 				(void)printf("nop");
 				break;

 			case TCPOPT_WSCALE:
 				(void)printf("wscale");
 				datalen = 1;
 				LENCHECK(datalen);
 				(void)printf(" %u", *cp);
 				break;

 			case TCPOPT_SACKOK:
 				(void)printf("sackOK");
 				break;

 			case TCPOPT_SACK:
 				datalen = len - 2;
 				if (datalen % 8 != 0) {
 					(void)printf("malformed sack");
 				} else {
 					u_int32_t s, e;

 					(void)printf("sack %d ", datalen / 8);
 					for (i = 0; i < datalen; i += 8) {
 						LENCHECK(i + 4);
 						s = EXTRACT_32BITS(cp + i);
 						LENCHECK(i + 8);
 						e = EXTRACT_32BITS(cp + i + 4);
 						if (threv) {
 							s -= thseq;
 							e -= thseq;
 						} else {
 							s -= thack;
 							e -= thack;
 						}
 						(void)printf("{%u:%u}", s, e);
 					}
 				}
 				break;

 			case TCPOPT_ECHO:
 				(void)printf("echo");
 				datalen = 4;
 				LENCHECK(datalen);
 				(void)printf(" %u", EXTRACT_32BITS(cp));
 				break;

 			case TCPOPT_ECHOREPLY:
 				(void)printf("echoreply");
 				datalen = 4;
 				LENCHECK(datalen);
 				(void)printf(" %u", EXTRACT_32BITS(cp));
 				break;

 			case TCPOPT_TIMESTAMP:
 				(void)printf("timestamp");
 				datalen = 8;
 				LENCHECK(4);
 				(void)printf(" %u", EXTRACT_32BITS(cp));
 				LENCHECK(datalen);
 				(void)printf(" %u", EXTRACT_32BITS(cp + 4));
 				break;

 			case TCPOPT_CC:
 				(void)printf("cc");
 				datalen = 4;
 				LENCHECK(datalen);
 				(void)printf(" %u", EXTRACT_32BITS(cp));
 				break;

 			case TCPOPT_CCNEW:
 				(void)printf("ccnew");
 				datalen = 4;
 				LENCHECK(datalen);
 				(void)printf(" %u", EXTRACT_32BITS(cp));
 				break;

 			case TCPOPT_CCECHO:
 				(void)printf("ccecho");
 				datalen = 4;
 				LENCHECK(datalen);
 				(void)printf(" %u", EXTRACT_32BITS(cp));
 				break;

 			case TCPOPT_SIGNATURE:
 				(void)printf("md5:");
 				datalen = TCP_SIGLEN;
 				LENCHECK(datalen);
 #ifdef HAVE_LIBCRYPTO
 				switch (tcp_verify_signature(ip, tp,
 				    bp + TH_OFF(tp) * 4, length, cp)) {

 				case SIGNATURE_VALID:
 					(void)printf("valid");
 					break;

 				case SIGNATURE_INVALID:
 					(void)printf("invalid");
 					break;

 				case CANT_CHECK_SIGNATURE:
 					(void)printf("can't check - ");
 					for (i = 0; i < TCP_SIGLEN; ++i)
 						(void)printf("%02x", cp[i]);
 					break;
 				}
 #else
 				for (i = 0; i < TCP_SIGLEN; ++i)
 					(void)printf("%02x", cp[i]);
 #endif
 				break;

 			default:
 				(void)printf("opt-%u:", opt);
 				datalen = len - 2;
 				for (i = 0; i < datalen; ++i) {
 					LENCHECK(i);
 					(void)printf("%02x", cp[i]);
 				}
 				break;
 			}

 			/* Account for data printed */
 			cp += datalen;
 			hlen -= datalen;

 			/* Check specification against observed length */
 			++datalen;			/* option octet */
 			if (!ZEROLENOPT(opt))
 				++datalen;		/* size octet */
 			if (datalen != len)
 				(void)printf("[len %d]", len);
 			ch = ',';
 			if (opt == TCPOPT_EOL)
 				break;
 		}
 		putchar('>');
 	}

 	if (length <= 0)
 		return;

 	/*
 	 * Decode payload if necessary.
 	 */
 	bp += TH_OFF(tp) * 4;
 	if (flags & TH_RST) {
 		if (vflag)
 			print_tcp_rst_data(bp, length);
 	} else {
 		if (sport == TELNET_PORT || dport == TELNET_PORT) {
 			if (!qflag && vflag)
 				telnet_print(bp, length);
 		} else if (sport == BGP_PORT || dport == BGP_PORT)
 			bgp_print(bp, length);
 		else if (sport == PPTP_PORT || dport == PPTP_PORT)
 			pptp_print(bp);
 #ifdef TCPDUMP_DO_SMB
 		else if (sport == NETBIOS_SSN_PORT || dport == NETBIOS_SSN_PORT)
 			nbt_tcp_print(bp, length);
 #endif
 		else if (sport == BEEP_PORT || dport == BEEP_PORT)
 			beep_print(bp, length);
 		else if (length > 2 &&
 		    (sport == NAMESERVER_PORT || dport == NAMESERVER_PORT ||
 		     sport == MULTICASTDNS_PORT || dport == MULTICASTDNS_PORT)) {
 			/*
 			 * TCP DNS query has 2byte length at the head.
 			 * XXX packet could be unaligned, it can go strange
 			 */
 			ns_print(bp + 2, length - 2, 0);
 		} else if (sport == MSDP_PORT || dport == MSDP_PORT) {
 			msdp_print(bp, length);
 		}
                 else if (length > 0 && (sport == LDP_PORT || dport == LDP_PORT)) {
                         ldp_print(bp, length);
 		}
 	}
 	return;
 bad:
 	fputs("[bad opt]", stdout);
 	if (ch != '\0')
 		putchar('>');
 	return;
 trunc:
 	fputs("[|tcp]", stdout);
 	if (ch != '\0')
 		putchar('>');
 }

 /*
  * RFC1122 says the following on data in RST segments:
  *
  *         4.2.2.12  RST Segment: RFC-793 Section 3.4
  *
  *            A TCP SHOULD allow a received RST segment to include data.
  *
  *            DISCUSSION
  *                 It has been suggested that a RST segment could contain
  *                 ASCII text that encoded and explained the cause of the
  *                 RST.  No standard has yet been established for such
  *                 data.
  *
  */

 static void
 print_tcp_rst_data(register const u_char *sp, u_int length)
 {
 	int c;

 	if (TTEST2(*sp, length))
 		printf(" [RST");
 	else
 		printf(" [!RST");
 	if (length > MAX_RST_DATA_LEN) {
 		length = MAX_RST_DATA_LEN;	/* can use -X for longer */
 		putchar('+');			/* indicate we truncate */
 	}
 	putchar(' ');
 	while (length-- && sp <= snapend) {
 		c = *sp++;
 		safeputchar(c);
 	}
 	putchar(']');
 }

 #ifdef HAVE_LIBCRYPTO
 static int
 tcp_verify_signature(const struct ip *ip, const struct tcphdr *tp,
     const u_char *data, int length, const u_char *rcvsig)
 {
         struct tcphdr tp1;
 	u_char sig[TCP_SIGLEN];
 	char zero_proto = 0;
 	MD5_CTX ctx;
 	u_int16_t savecsum, tlen;
 #ifdef INET6
 	struct ip6_hdr *ip6;
 #endif
 	u_int32_t len32;
 	u_int8_t nxt;

 	tp1 = *tp;

 	if (tcpmd5secret == NULL)
 		return (CANT_CHECK_SIGNATURE);

 	MD5_Init(&ctx);
 	/*
 	 * Step 1: Update MD5 hash with IP pseudo-header.
 	 */
 	if (IP_V(ip) == 4) {
 		MD5_Update(&ctx, (char *)&ip->ip_src, sizeof(ip->ip_src));
 		MD5_Update(&ctx, (char *)&ip->ip_dst, sizeof(ip->ip_dst));
 		MD5_Update(&ctx, (char *)&zero_proto, sizeof(zero_proto));
 		MD5_Update(&ctx, (char *)&ip->ip_p, sizeof(ip->ip_p));
 		tlen = EXTRACT_16BITS(&ip->ip_len) - IP_HL(ip) * 4;
 		tlen = htons(tlen);
 		MD5_Update(&ctx, (char *)&tlen, sizeof(tlen));
 #ifdef INET6
 	} else if (IP_V(ip) == 6) {
 		ip6 = (struct ip6_hdr *)ip;
 		MD5_Update(&ctx, (char *)&ip6->ip6_src, sizeof(ip6->ip6_src));
 		MD5_Update(&ctx, (char *)&ip6->ip6_dst, sizeof(ip6->ip6_dst));
 		len32 = htonl(ntohs(ip6->ip6_plen));
 		MD5_Update(&ctx, (char *)&len32, sizeof(len32));
 		nxt = 0;
 		MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
 		MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
 		MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
 		nxt = IPPROTO_TCP;
 		MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
 #endif
 	} else
 		return (CANT_CHECK_SIGNATURE);

 	/*
 	 * Step 2: Update MD5 hash with TCP header, excluding options.
 	 * The TCP checksum must be set to zero.
 	 */
 	savecsum = tp1.th_sum;
 	tp1.th_sum = 0;
 	MD5_Update(&ctx, (char *)&tp1, sizeof(struct tcphdr));
 	tp1.th_sum = savecsum;
 	/*
 	 * Step 3: Update MD5 hash with TCP segment data, if present.
 	 */
 	if (length > 0)
 		MD5_Update(&ctx, data, length);
 	/*
 	 * Step 4: Update MD5 hash with shared secret.
 	 */
 	MD5_Update(&ctx, tcpmd5secret, strlen(tcpmd5secret));
 	MD5_Final(sig, &ctx);

 	if (memcmp(rcvsig, sig, TCP_SIGLEN) == 0)
 		return (SIGNATURE_VALID);
 	else
 		return (SIGNATURE_INVALID);
 }
 #endif /* HAVE_LIBCRYPTO */
	/*
	* Copyright (c) 1988, 1989, 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1997
	* The Regents of the University of California. All rights reserved.
	*
	* Copyright (c) 1999-2004 The tcpdump.org project
	*
	* Redistribution and use in source and binary forms, with or without
	* modification, are permitted provided that: (1) source code distributions
	* retain the above copyright notice and this paragraph in its entirety, (2)
	* distributions including binary code include the above copyright notice and
	* this paragraph in its entirety in the documentation or other materials
	* provided with the distribution, and (3) all advertising materials mentioning
	* features or use of this software display the following acknowledgement:
	* ``This product includes software developed by the University of California,
	* Lawrence Berkeley Laboratory and its contributors.'' Neither the name of
	* the University nor the names of its contributors may be used to endorse
	* or promote products derived from this software without specific prior
	* written permission.
	* THIS SOFTWARE IS PROVIDED ``AS IS'' AND WITHOUT ANY EXPRESS OR IMPLIED
	* WARRANTIES, INCLUDING, WITHOUT LIMITATION, THE IMPLIED WARRANTIES OF
	* MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE.
	*/

	#ifndef lint
	static const char rcsid[] _U_ =
	"@(#) $Header: /tcpdump/master/tcpdump/print-tcp.c,v 1.120.2.3 2005/10/16 06:05:46 guy Exp $ (LBL)";
	#endif

	#ifdef HAVE_CONFIG_H
	#include "config.h"
	#endif

	#include <tcpdump-stdinc.h>

	#include <stdio.h>
	#include <stdlib.h>
	#include <string.h>

	#include "interface.h"
	#include "addrtoname.h"
	#include "extract.h"

	#include "tcp.h"

	#include "ip.h"
	#ifdef INET6
	#include "ip6.h"
	#endif
	#include "ipproto.h"
	#include "rpc_auth.h"
	#include "rpc_msg.h"

	#include "nameser.h"

	#ifdef HAVE_LIBCRYPTO
	#include <openssl/md5.h>

	#define SIGNATURE_VALID 0
	#define SIGNATURE_INVALID 1
	#define CANT_CHECK_SIGNATURE 2

	static int tcp_verify_signature(const struct ip ip, const struct tcphdr tp,
	const u_char data, int length, const u_char rcvsig);
	#endif

	static void print_tcp_rst_data(register const u_char *sp, u_int length);

	#define MAX_RST_DATA_LEN 30


	struct tha {
	#ifndef INET6
	struct in_addr src;
	struct in_addr dst;
	#else
	struct in6_addr src;
	struct in6_addr dst;
	#endif /INET6/
	u_int port;
	};

	struct tcp_seq_hash {
	struct tcp_seq_hash *nxt;
	struct tha addr;
	tcp_seq seq;
	tcp_seq ack;
	};

	#define TSEQ_HASHSIZE 919

	/* These tcp optinos do not have the size octet */
	#define ZEROLENOPT(o) ((o) == TCPOPT_EOL \|\| (o) == TCPOPT_NOP)

	static struct tcp_seq_hash tcp_seq_hash[TSEQ_HASHSIZE];


	#ifndef TELNET_PORT
	#define TELNET_PORT 23
	#endif
	#ifndef BGP_PORT
	#define BGP_PORT 179
	#endif
	#define NETBIOS_SSN_PORT 139
	#ifndef PPTP_PORT
	#define PPTP_PORT 1723
	#endif
	#define BEEP_PORT 10288
	#ifndef NFS_PORT
	#define NFS_PORT 2049
	#endif
	#define MSDP_PORT 639
	#define LDP_PORT 646

	static int tcp_cksum(register const struct ip *ip,
	register const struct tcphdr *tp,
	register u_int len)
	{
	union phu {
	struct phdr {
	u_int32_t src;
	u_int32_t dst;
	u_char mbz;
	u_char proto;
	u_int16_t len;
	} ph;
	u_int16_t pa[6];
	} phu;
	const u_int16_t *sp;

	/* pseudo-header.. */
	phu.ph.len = htons((u_int16_t)len);
	phu.ph.mbz = 0;
	phu.ph.proto = IPPROTO_TCP;
	memcpy(&phu.ph.src, &ip->ip_src.s_addr, sizeof(u_int32_t));
	if (IP_HL(ip) == 5)
	memcpy(&phu.ph.dst, &ip->ip_dst.s_addr, sizeof(u_int32_t));
	else
	phu.ph.dst = ip_finddst(ip);

	sp = &phu.pa[0];
	return in_cksum((u_short *)tp, len,
	sp[0]+sp[1]+sp[2]+sp[3]+sp[4]+sp[5]);
	}

	#ifdef INET6
	static int tcp6_cksum(const struct ip6_hdr ip6, const struct tcphdr tp,
	u_int len)
	{
	size_t i;
	register const u_int16_t *sp;
	u_int32_t sum;
	union {
	struct {
	struct in6_addr ph_src;
	struct in6_addr ph_dst;
	u_int32_t ph_len;
	u_int8_t ph_zero[3];
	u_int8_t ph_nxt;
	} ph;
	u_int16_t pa[20];
	} phu;

	/* pseudo-header */
	memset(&phu, 0, sizeof(phu));
	phu.ph.ph_src = ip6->ip6_src;
	phu.ph.ph_dst = ip6->ip6_dst;
	phu.ph.ph_len = htonl(len);
	phu.ph.ph_nxt = IPPROTO_TCP;

	sum = 0;
	for (i = 0; i < sizeof(phu.pa) / sizeof(phu.pa[0]); i++)
	sum += phu.pa[i];

	sp = (const u_int16_t *)tp;

	for (i = 0; i < (len & ~1); i += 2)
	sum += *sp++;

	if (len & 1)
	sum += htons(((const u_int8_t )sp) << 8);

	while (sum > 0xffff)
	sum = (sum & 0xffff) + (sum >> 16);
	sum = ~sum & 0xffff;

	return (sum);
	}
	#endif

	void
	tcp_print(register const u_char *bp, register u_int length,
	register const u_char *bp2, int fragmented)
	{
	register const struct tcphdr *tp;
	register const struct ip *ip;
	register u_char flags;
	register u_int hlen;
	register char ch;
	u_int16_t sport, dport, win, urp;
	u_int32_t seq, ack, thseq, thack;
	int threv;
	#ifdef INET6
	register const struct ip6_hdr *ip6;
	#endif

	tp = (struct tcphdr *)bp;
	ip = (struct ip *)bp2;
	#ifdef INET6
	if (IP_V(ip) == 6)
	ip6 = (struct ip6_hdr *)bp2;
	else
	ip6 = NULL;
	#endif /INET6/
	ch = '\0';
	if (!TTEST(tp->th_dport)) {
	(void)printf("%s > %s: [\|tcp]",
	ipaddr_string(&ip->ip_src),
	ipaddr_string(&ip->ip_dst));
	return;
	}

	sport = EXTRACT_16BITS(&tp->th_sport);
	dport = EXTRACT_16BITS(&tp->th_dport);

	hlen = TH_OFF(tp) * 4;

	/*
	* If data present, header length valid, and NFS port used,
	* assume NFS.
	* Pass offset of data plus 4 bytes for RPC TCP msg length
	* to NFS print routines.
	*/
	if (!qflag && hlen >= sizeof(*tp) && hlen <= length) {
	if ((u_char *)tp + 4 + sizeof(struct sunrpc_msg) <= snapend &&
	dport == NFS_PORT) {
	nfsreq_print((u_char *)tp + hlen + 4, length - hlen,
	(u_char *)ip);
	return;
	} else if ((u_char *)tp + 4 + sizeof(struct sunrpc_msg)
	<= snapend &&
	sport == NFS_PORT) {
	nfsreply_print((u_char *)tp + hlen + 4, length - hlen,
	(u_char *)ip);
	return;
	}
	}
	#ifdef INET6
	if (ip6) {
	if (ip6->ip6_nxt == IPPROTO_TCP) {
	(void)printf("%s.%s > %s.%s: ",
	ip6addr_string(&ip6->ip6_src),
	tcpport_string(sport),
	ip6addr_string(&ip6->ip6_dst),
	tcpport_string(dport));
	} else {
	(void)printf("%s > %s: ",
	tcpport_string(sport), tcpport_string(dport));
	}
	} else
	#endif /INET6/
	{
	if (ip->ip_p == IPPROTO_TCP) {
	(void)printf("%s.%s > %s.%s: ",
	ipaddr_string(&ip->ip_src),
	tcpport_string(sport),
	ipaddr_string(&ip->ip_dst),
	tcpport_string(dport));
	} else {
	(void)printf("%s > %s: ",
	tcpport_string(sport), tcpport_string(dport));
	}
	}

	if (hlen < sizeof(*tp)) {
	(void)printf(" tcp %d [bad hdr length %u - too short, < %lu]",
	length - hlen, hlen, (unsigned long)sizeof(*tp));
	return;
	}

	TCHECK(*tp);

	seq = EXTRACT_32BITS(&tp->th_seq);
	ack = EXTRACT_32BITS(&tp->th_ack);
	win = EXTRACT_16BITS(&tp->th_win);
	urp = EXTRACT_16BITS(&tp->th_urp);

	if (qflag) {
	(void)printf("tcp %d", length - hlen);
	if (hlen > length) {
	(void)printf(" [bad hdr length %u - too long, > %u]",
	hlen, length);
	}
	return;
	}
	if ((flags = tp->th_flags) & (TH_SYN\|TH_FIN\|TH_RST\|TH_PUSH\|
	TH_ECNECHO\|TH_CWR)) {
	if (flags & TH_SYN)
	putchar('S');
	if (flags & TH_FIN)
	putchar('F');
	if (flags & TH_RST)
	putchar('R');
	if (flags & TH_PUSH)
	putchar('P');
	if (flags & TH_CWR)
	putchar('W'); /* congestion _W_indow reduced (ECN) */
	if (flags & TH_ECNECHO)
	putchar('E'); /* ecn _E_cho sent (ECN) */
	} else
	putchar('.');

	if (!Sflag && (flags & TH_ACK)) {
	register struct tcp_seq_hash *th;
	const void src, dst;
	register int rev;
	struct tha tha;
	/*
	* Find (or record) the initial sequence numbers for
	* this conversation. (we pick an arbitrary
	* collating order so there's only one entry for
	* both directions).
	*/
	#ifdef INET6
	memset(&tha, 0, sizeof(tha));
	rev = 0;
	if (ip6) {
	src = &ip6->ip6_src;
	dst = &ip6->ip6_dst;
	if (sport > dport)
	rev = 1;
	else if (sport == dport) {
	if (memcmp(src, dst, sizeof ip6->ip6_dst) > 0)
	rev = 1;
	}
	if (rev) {
	memcpy(&tha.src, dst, sizeof ip6->ip6_dst);
	memcpy(&tha.dst, src, sizeof ip6->ip6_src);
	tha.port = dport << 16 \| sport;
	} else {
	memcpy(&tha.dst, dst, sizeof ip6->ip6_dst);
	memcpy(&tha.src, src, sizeof ip6->ip6_src);
	tha.port = sport << 16 \| dport;
	}
	} else {
	src = &ip->ip_src;
	dst = &ip->ip_dst;
	if (sport > dport)
	rev = 1;
	else if (sport == dport) {
	if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
	rev = 1;
	}
	if (rev) {
	memcpy(&tha.src, dst, sizeof ip->ip_dst);
	memcpy(&tha.dst, src, sizeof ip->ip_src);
	tha.port = dport << 16 \| sport;
	} else {
	memcpy(&tha.dst, dst, sizeof ip->ip_dst);
	memcpy(&tha.src, src, sizeof ip->ip_src);
	tha.port = sport << 16 \| dport;
	}
	}
	#else
	rev = 0;
	src = &ip->ip_src;
	dst = &ip->ip_dst;
	if (sport > dport)
	rev = 1;
	else if (sport == dport) {
	if (memcmp(src, dst, sizeof ip->ip_dst) > 0)
	rev = 1;
	}
	if (rev) {
	memcpy(&tha.src, dst, sizeof ip->ip_dst);
	memcpy(&tha.dst, src, sizeof ip->ip_src);
	tha.port = dport << 16 \| sport;
	} else {
	memcpy(&tha.dst, dst, sizeof ip->ip_dst);
	memcpy(&tha.src, src, sizeof ip->ip_src);
	tha.port = sport << 16 \| dport;
	}
	#endif

	threv = rev;
	for (th = &tcp_seq_hash[tha.port % TSEQ_HASHSIZE];
	th->nxt; th = th->nxt)
	if (memcmp((char )&tha, (char )&th->addr,
	sizeof(th->addr)) == 0)
	break;

	if (!th->nxt \|\| (flags & TH_SYN)) {
	/* didn't find it or new conversation */
	if (th->nxt == NULL) {
	th->nxt = (struct tcp_seq_hash *)
	calloc(1, sizeof(*th));
	if (th->nxt == NULL)
	error("tcp_print: calloc");
	}
	th->addr = tha;
	if (rev)
	th->ack = seq, th->seq = ack - 1;
	else
	th->seq = seq, th->ack = ack - 1;
	} else {
	if (rev)
	seq -= th->ack, ack -= th->seq;
	else
	seq -= th->seq, ack -= th->ack;
	}

	thseq = th->seq;
	thack = th->ack;
	} else {
	/fool gcc/
	thseq = thack = threv = 0;
	}
	if (hlen > length) {
	(void)printf(" [bad hdr length %u - too long, > %u]",
	hlen, length);
	return;
	}

	if (IP_V(ip) == 4 && vflag && !fragmented) {
	u_int16_t sum, tcp_sum;
	if (TTEST2(tp->th_sport, length)) {
	sum = tcp_cksum(ip, tp, length);

	(void)printf(", cksum 0x%04x",EXTRACT_16BITS(&tp->th_sum));
	if (sum != 0) {
	tcp_sum = EXTRACT_16BITS(&tp->th_sum);
	(void)printf(" (incorrect (-> 0x%04x),",in_cksum_shouldbe(tcp_sum, sum));
	} else
	(void)printf(" (correct),");
	}
	}
	#ifdef INET6
	if (IP_V(ip) == 6 && ip6->ip6_plen && vflag && !fragmented) {
	u_int16_t sum,tcp_sum;
	if (TTEST2(tp->th_sport, length)) {
	sum = tcp6_cksum(ip6, tp, length);
	(void)printf(", cksum 0x%04x",EXTRACT_16BITS(&tp->th_sum));
	if (sum != 0) {
	tcp_sum = EXTRACT_16BITS(&tp->th_sum);
	(void)printf(" (incorrect (-> 0x%04x),",in_cksum_shouldbe(tcp_sum, sum));
	} else
	(void)printf(" (correct),");

	}
	}
	#endif

	length -= hlen;
	if (vflag > 1 \|\| length > 0 \|\| flags & (TH_SYN \| TH_FIN \| TH_RST))
	(void)printf(" %u:%u(%u)", seq, seq + length, length);
	if (flags & TH_ACK)
	(void)printf(" ack %u", ack);

	(void)printf(" win %d", win);

	if (flags & TH_URG)
	(void)printf(" urg %d", urp);
	/*
	* Handle any options.
	*/
	if (hlen > sizeof(*tp)) {
	register const u_char *cp;
	register u_int i, opt, datalen;
	register u_int len;

	hlen -= sizeof(*tp);
	cp = (const u_char )tp + sizeof(tp);
	putchar(' ');
	ch = '<';
	while (hlen > 0) {
	putchar(ch);
	TCHECK(*cp);
	opt = *cp++;
	if (ZEROLENOPT(opt))
	len = 1;
	else {
	TCHECK(*cp);
	len = cp++; / total including type, len */
	if (len < 2 \|\| len > hlen)
	goto bad;
	--hlen; /* account for length byte */
	}
	--hlen; /* account for type byte */
	datalen = 0;

	/* Bail if "l" bytes of data are not left or were not captured */
	#define LENCHECK(l) { if ((l) > hlen) goto bad; TCHECK2(*cp, l); }

	switch (opt) {

	case TCPOPT_MAXSEG:
	(void)printf("mss");
	datalen = 2;
	LENCHECK(datalen);
	(void)printf(" %u", EXTRACT_16BITS(cp));

	break;

	case TCPOPT_EOL:
	(void)printf("eol");
	break;

	case TCPOPT_NOP:
	(void)printf("nop");
	break;

	case TCPOPT_WSCALE:
	(void)printf("wscale");
	datalen = 1;
	LENCHECK(datalen);
	(void)printf(" %u", *cp);
	break;

	case TCPOPT_SACKOK:
	(void)printf("sackOK");
	break;

	case TCPOPT_SACK:
	datalen = len - 2;
	if (datalen % 8 != 0) {
	(void)printf("malformed sack");
	} else {
	u_int32_t s, e;

	(void)printf("sack %d ", datalen / 8);
	for (i = 0; i < datalen; i += 8) {
	LENCHECK(i + 4);
	s = EXTRACT_32BITS(cp + i);
	LENCHECK(i + 8);
	e = EXTRACT_32BITS(cp + i + 4);
	if (threv) {
	s -= thseq;
	e -= thseq;
	} else {
	s -= thack;
	e -= thack;
	}
	(void)printf("{%u:%u}", s, e);
	}
	}
	break;

	case TCPOPT_ECHO:
	(void)printf("echo");
	datalen = 4;
	LENCHECK(datalen);
	(void)printf(" %u", EXTRACT_32BITS(cp));
	break;

	case TCPOPT_ECHOREPLY:
	(void)printf("echoreply");
	datalen = 4;
	LENCHECK(datalen);
	(void)printf(" %u", EXTRACT_32BITS(cp));
	break;

	case TCPOPT_TIMESTAMP:
	(void)printf("timestamp");
	datalen = 8;
	LENCHECK(4);
	(void)printf(" %u", EXTRACT_32BITS(cp));
	LENCHECK(datalen);
	(void)printf(" %u", EXTRACT_32BITS(cp + 4));
	break;

	case TCPOPT_CC:
	(void)printf("cc");
	datalen = 4;
	LENCHECK(datalen);
	(void)printf(" %u", EXTRACT_32BITS(cp));
	break;

	case TCPOPT_CCNEW:
	(void)printf("ccnew");
	datalen = 4;
	LENCHECK(datalen);
	(void)printf(" %u", EXTRACT_32BITS(cp));
	break;

	case TCPOPT_CCECHO:
	(void)printf("ccecho");
	datalen = 4;
	LENCHECK(datalen);
	(void)printf(" %u", EXTRACT_32BITS(cp));
	break;

	case TCPOPT_SIGNATURE:
	(void)printf("md5:");
	datalen = TCP_SIGLEN;
	LENCHECK(datalen);
	#ifdef HAVE_LIBCRYPTO
	switch (tcp_verify_signature(ip, tp,
	bp + TH_OFF(tp) * 4, length, cp)) {

	case SIGNATURE_VALID:
	(void)printf("valid");
	break;

	case SIGNATURE_INVALID:
	(void)printf("invalid");
	break;

	case CANT_CHECK_SIGNATURE:
	(void)printf("can't check - ");
	for (i = 0; i < TCP_SIGLEN; ++i)
	(void)printf("%02x", cp[i]);
	break;
	}
	#else
	for (i = 0; i < TCP_SIGLEN; ++i)
	(void)printf("%02x", cp[i]);
	#endif
	break;

	default:
	(void)printf("opt-%u:", opt);
	datalen = len - 2;
	for (i = 0; i < datalen; ++i) {
	LENCHECK(i);
	(void)printf("%02x", cp[i]);
	}
	break;
	}

	/* Account for data printed */
	cp += datalen;
	hlen -= datalen;

	/* Check specification against observed length */
	++datalen; /* option octet */
	if (!ZEROLENOPT(opt))
	++datalen; /* size octet */
	if (datalen != len)
	(void)printf("[len %d]", len);
	ch = ',';
	if (opt == TCPOPT_EOL)
	break;
	}
	putchar('>');
	}

	if (length <= 0)
	return;

	/*
	* Decode payload if necessary.
	*/
	bp += TH_OFF(tp) * 4;
	if (flags & TH_RST) {
	if (vflag)
	print_tcp_rst_data(bp, length);
	} else {
	if (sport == TELNET_PORT \|\| dport == TELNET_PORT) {
	if (!qflag && vflag)
	telnet_print(bp, length);
	} else if (sport == BGP_PORT \|\| dport == BGP_PORT)
	bgp_print(bp, length);
	else if (sport == PPTP_PORT \|\| dport == PPTP_PORT)
	pptp_print(bp);
	#ifdef TCPDUMP_DO_SMB
	else if (sport == NETBIOS_SSN_PORT \|\| dport == NETBIOS_SSN_PORT)
	nbt_tcp_print(bp, length);
	#endif
	else if (sport == BEEP_PORT \|\| dport == BEEP_PORT)
	beep_print(bp, length);
	else if (length > 2 &&
	(sport == NAMESERVER_PORT \|\| dport == NAMESERVER_PORT \|\|
	sport == MULTICASTDNS_PORT \|\| dport == MULTICASTDNS_PORT)) {
	/*
	* TCP DNS query has 2byte length at the head.
	* XXX packet could be unaligned, it can go strange
	*/
	ns_print(bp + 2, length - 2, 0);
	} else if (sport == MSDP_PORT \|\| dport == MSDP_PORT) {
	msdp_print(bp, length);
	}
	else if (length > 0 && (sport == LDP_PORT \|\| dport == LDP_PORT)) {
	ldp_print(bp, length);
	}
	}
	return;
	bad:
	fputs("[bad opt]", stdout);
	if (ch != '\0')
	putchar('>');
	return;
	trunc:
	fputs("[\|tcp]", stdout);
	if (ch != '\0')
	putchar('>');
	}

	/*
	* RFC1122 says the following on data in RST segments:
	*
	* 4.2.2.12 RST Segment: RFC-793 Section 3.4
	*
	* A TCP SHOULD allow a received RST segment to include data.
	*
	* DISCUSSION
	* It has been suggested that a RST segment could contain
	* ASCII text that encoded and explained the cause of the
	* RST. No standard has yet been established for such
	* data.
	*
	*/

	static void
	print_tcp_rst_data(register const u_char *sp, u_int length)
	{
	int c;

	if (TTEST2(*sp, length))
	printf(" [RST");
	else
	printf(" [!RST");
	if (length > MAX_RST_DATA_LEN) {
	length = MAX_RST_DATA_LEN; /* can use -X for longer */
	putchar('+'); /* indicate we truncate */
	}
	putchar(' ');
	while (length-- && sp <= snapend) {
	c = *sp++;
	safeputchar(c);
	}
	putchar(']');
	}

	#ifdef HAVE_LIBCRYPTO
	static int
	tcp_verify_signature(const struct ip ip, const struct tcphdr tp,
	const u_char data, int length, const u_char rcvsig)
	{
	struct tcphdr tp1;
	u_char sig[TCP_SIGLEN];
	char zero_proto = 0;
	MD5_CTX ctx;
	u_int16_t savecsum, tlen;
	#ifdef INET6
	struct ip6_hdr *ip6;
	#endif
	u_int32_t len32;
	u_int8_t nxt;

	tp1 = *tp;

	if (tcpmd5secret == NULL)
	return (CANT_CHECK_SIGNATURE);

	MD5_Init(&ctx);
	/*
	* Step 1: Update MD5 hash with IP pseudo-header.
	*/
	if (IP_V(ip) == 4) {
	MD5_Update(&ctx, (char *)&ip->ip_src, sizeof(ip->ip_src));
	MD5_Update(&ctx, (char *)&ip->ip_dst, sizeof(ip->ip_dst));
	MD5_Update(&ctx, (char *)&zero_proto, sizeof(zero_proto));
	MD5_Update(&ctx, (char *)&ip->ip_p, sizeof(ip->ip_p));
	tlen = EXTRACT_16BITS(&ip->ip_len) - IP_HL(ip) * 4;
	tlen = htons(tlen);
	MD5_Update(&ctx, (char *)&tlen, sizeof(tlen));
	#ifdef INET6
	} else if (IP_V(ip) == 6) {
	ip6 = (struct ip6_hdr *)ip;
	MD5_Update(&ctx, (char *)&ip6->ip6_src, sizeof(ip6->ip6_src));
	MD5_Update(&ctx, (char *)&ip6->ip6_dst, sizeof(ip6->ip6_dst));
	len32 = htonl(ntohs(ip6->ip6_plen));
	MD5_Update(&ctx, (char *)&len32, sizeof(len32));
	nxt = 0;
	MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
	MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
	MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
	nxt = IPPROTO_TCP;
	MD5_Update(&ctx, (char *)&nxt, sizeof(nxt));
	#endif
	} else
	return (CANT_CHECK_SIGNATURE);

	/*
	* Step 2: Update MD5 hash with TCP header, excluding options.
	* The TCP checksum must be set to zero.
	*/
	savecsum = tp1.th_sum;
	tp1.th_sum = 0;
	MD5_Update(&ctx, (char *)&tp1, sizeof(struct tcphdr));
	tp1.th_sum = savecsum;
	/*
	* Step 3: Update MD5 hash with TCP segment data, if present.
	*/
	if (length > 0)
	MD5_Update(&ctx, data, length);
	/*
	* Step 4: Update MD5 hash with shared secret.
	*/
	MD5_Update(&ctx, tcpmd5secret, strlen(tcpmd5secret));
	MD5_Final(sig, &ctx);

	if (memcmp(rcvsig, sig, TCP_SIGLEN) == 0)
	return (SIGNATURE_VALID);
	else
	return (SIGNATURE_INVALID);
	}
	#endif /* HAVE_LIBCRYPTO */