Merge pull request #492 from vel21ripn/nflog-print

[tcpdump] / print-esp.c

/*      $NetBSD: print-ah.c,v 1.4 1996/05/20 00:41:16 fvdl Exp $        */

/*
 * Copyright (c) 1988, 1989, 1990, 1991, 1992, 1993, 1994
 *      The Regents of the University of California.  All rights reserved.
 *
 * 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.
 */

/* \summary: IPSEC Encapsulating Security Payload (ESP) printer */

#ifdef HAVE_CONFIG_H
#include <config.h>
#endif

#include "netdissect-stdinc.h"

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

/* Any code in this file that depends on HAVE_LIBCRYPTO depends on
 * HAVE_OPENSSL_EVP_H too. Undefining the former when the latter isn't defined
 * is the simplest way of handling the dependency.
 */
#ifdef HAVE_LIBCRYPTO
#ifdef HAVE_OPENSSL_EVP_H
#include <openssl/evp.h>
#else
#undef HAVE_LIBCRYPTO
#endif
#endif

#include "netdissect.h"
#include "strtoaddr.h"
#include "extract.h"

#include "ascii_strcasecmp.h"

#include "ip.h"
#include "ip6.h"

/*
 * Copyright (C) 1995, 1996, 1997, and 1998 WIDE Project.
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the project 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 BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */

/*
 * RFC1827/2406 Encapsulated Security Payload.
 */

struct newesp {
        nd_uint32_t     esp_spi;        /* ESP */
        nd_uint32_t     esp_seq;        /* Sequence number */
        /*variable size*/               /* (IV and) Payload data */
        /*variable size*/               /* padding */
        /*8bit*/                        /* pad size */
        /*8bit*/                        /* next header */
        /*8bit*/                        /* next header */
        /*variable size, 32bit bound*/  /* Authentication data */
};

#ifdef HAVE_LIBCRYPTO
union inaddr_u {
        nd_ipv4 in4;
        nd_ipv6 in6;
};
struct sa_list {
        struct sa_list  *next;
        u_int           daddr_version;
        union inaddr_u  daddr;
        uint32_t        spi;          /* if == 0, then IKEv2 */
        int             initiator;
        u_char          spii[8];      /* for IKEv2 */
        u_char          spir[8];
        const EVP_CIPHER *evp;
        u_int           ivlen;
        int             authlen;
        u_char          authsecret[256];
        int             authsecret_len;
        u_char          secret[256];  /* is that big enough for all secrets? */
        int             secretlen;
};

#ifndef HAVE_EVP_CIPHER_CTX_NEW
/*
 * Allocate an EVP_CIPHER_CTX.
 * Used if we have an older version of OpenSSL that doesn't provide
 * routines to allocate and free them.
 */
static EVP_CIPHER_CTX *
EVP_CIPHER_CTX_new(void)
{
        EVP_CIPHER_CTX *ctx;

        ctx = malloc(sizeof(*ctx));
        if (ctx == NULL)
                return (NULL);
        memset(ctx, 0, sizeof(*ctx));
        return (ctx);
}

static void
EVP_CIPHER_CTX_free(EVP_CIPHER_CTX *ctx)
{
        EVP_CIPHER_CTX_cleanup(ctx);
        free(ctx);
}
#endif

#ifdef HAVE_EVP_DECRYPTINIT_EX
/*
 * Initialize the cipher by calling EVP_DecryptInit_ex(), because
 * calling EVP_DecryptInit() will reset the cipher context, clearing
 * the cipher, so calling it twice, with the second call having a
 * null cipher, will clear the already-set cipher.  EVP_DecryptInit_ex(),
 * however, won't reset the cipher context, so you can use it to specify
 * the IV in a second call after a first call to EVP_DecryptInit_ex()
 * to set the cipher and the key.
 *
 * XXX - is there some reason why we need to make two calls?
 */
static int
set_cipher_parameters(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *cipher,
                      const unsigned char *key,
                      const unsigned char *iv)
{
        return EVP_DecryptInit_ex(ctx, cipher, NULL, key, iv);
}
#else
/*
 * Initialize the cipher by calling EVP_DecryptInit(), because we don't
 * have EVP_DecryptInit_ex(); we rely on it not trashing the context.
 */
static int
set_cipher_parameters(EVP_CIPHER_CTX *ctx, const EVP_CIPHER *cipher,
                      const unsigned char *key,
                      const unsigned char *iv)
{
        return EVP_DecryptInit(ctx, cipher, key, iv);
}
#endif

static u_char *
do_decrypt(netdissect_options *ndo, const char *caller, struct sa_list *sa,
    const u_char *iv, const u_char *ct, unsigned int ctlen)
{
        EVP_CIPHER_CTX *ctx;
        unsigned int block_size;
        unsigned int ptlen;
        u_char *pt;
        int len;

        ctx = EVP_CIPHER_CTX_new();
        if (ctx == NULL) {
                /*
                 * Failed to initialize the cipher context.
                 * From a look at the OpenSSL code, this appears to
                 * mean "couldn't allocate memory for the cipher context";
                 * note that we're not passing any parameters, so there's
                 * not much else it can mean.
                 */
                (*ndo->ndo_error)(ndo, S_ERR_ND_MEM_ALLOC,
                    "%s: can't allocate memory for cipher context", caller);
                return NULL;
        }

        if (set_cipher_parameters(ctx, sa->evp, sa->secret, NULL) < 0) {
                EVP_CIPHER_CTX_free(ctx);
                (*ndo->ndo_warning)(ndo, "%s: espkey init failed", caller);
                return NULL;
        }
        if (set_cipher_parameters(ctx, NULL, NULL, iv) < 0) {
                EVP_CIPHER_CTX_free(ctx);
                (*ndo->ndo_warning)(ndo, "%s: IV init failed", caller);
                return NULL;
        }

        /*
         * At least as I read RFC 5996 section 3.14 and RFC 4303 section 2.4,
         * if the cipher has a block size of which the ciphertext's size must
         * be a multiple, the payload must be padded to make that happen, so
         * the ciphertext length must be a multiple of the block size.  Fail
         * if that's not the case.
         */
        block_size = (unsigned int)EVP_CIPHER_CTX_block_size(ctx);
        if ((ctlen % block_size) != 0) {
                EVP_CIPHER_CTX_free(ctx);
                (*ndo->ndo_warning)(ndo,
                    "%s: ciphertext size %u is not a multiple of the cipher block size %u",
                    caller, ctlen, block_size);
                return NULL;
        }

        /*
         * Attempt to allocate a buffer for the decrypted data, because
         * we can't decrypt on top of the input buffer.
         */
        ptlen = ctlen;
        pt = (u_char *)malloc(ptlen);
        if (pt == NULL) {
                EVP_CIPHER_CTX_free(ctx);
                (*ndo->ndo_error)(ndo, S_ERR_ND_MEM_ALLOC,
                    "%s: can't allocate memory for decryption buffer", caller);
                return NULL;
        }

        /*
         * The size of the ciphertext handed to us is a multiple of the
         * cipher block size, so we don't need to worry about padding.
         */
        if (!EVP_CIPHER_CTX_set_padding(ctx, 0)) {
                free(pt);
                EVP_CIPHER_CTX_free(ctx);
                (*ndo->ndo_warning)(ndo,
                    "%s: EVP_CIPHER_CTX_set_padding failed", caller);
                return NULL;
        }
        if (!EVP_DecryptUpdate(ctx, pt, &len, ct, ctlen)) {
                free(pt);
                EVP_CIPHER_CTX_free(ctx);
                (*ndo->ndo_warning)(ndo, "%s: EVP_DecryptUpdate failed",
                    caller);
                return NULL;
        }
        EVP_CIPHER_CTX_free(ctx);
        return pt;
}

/*
 * This will allocate a new buffer containing the decrypted data.
 * It returns 1 on success and 0 on failure.
 *
 * It will push the new buffer and the values of ndo->ndo_packetp and
 * ndo->ndo_snapend onto the buffer stack, and change ndo->ndo_packetp
 * and ndo->ndo_snapend to refer to the new buffer.
 *
 * Our caller must pop the buffer off the stack when it's finished
 * dissecting anything in it and before it does any dissection of
 * anything in the old buffer.  That will free the new buffer.
 */
USES_APPLE_DEPRECATED_API
int esp_print_decrypt_buffer_by_ikev2(netdissect_options *ndo,
                                      int initiator,
                                      const u_char spii[8],
                                      const u_char spir[8],
                                      const u_char *buf, const u_char *end)
{
        struct sa_list *sa;
        const u_char *iv;
        const u_char *ct;
        unsigned int ctlen;
        u_char *pt;

        /* initiator arg is any non-zero value */
        if(initiator) initiator=1;

        /* see if we can find the SA, and if so, decode it */
        for (sa = ndo->ndo_sa_list_head; sa != NULL; sa = sa->next) {
                if (sa->spi == 0
                    && initiator == sa->initiator
                    && memcmp(spii, sa->spii, 8) == 0
                    && memcmp(spir, sa->spir, 8) == 0)
                        break;
        }

        if(sa == NULL) return 0;
        if(sa->evp == NULL) return 0;

        /*
         * remove authenticator, and see if we still have something to
         * work with
         */
        end = end - sa->authlen;
        iv  = buf;
        ct = iv + sa->ivlen;
        ctlen = end-ct;

        if(end <= ct) return 0;

        pt = do_decrypt(ndo, "esp_print_decrypt_buffer_by_ikev2", sa, iv,
            ct, ctlen);
        if (pt == NULL)
                return 0;

        /*
         * Switch to the output buffer for dissection, and save it
         * on the buffer stack so it can be freed; our caller must
         * pop it when done.
         */
        if (!nd_push_buffer(ndo, pt, pt, pt + ctlen)) {
                free(pt);
                return 0;
        }

        return 1;
}
USES_APPLE_RST

static void esp_print_addsa(netdissect_options *ndo,
                            struct sa_list *sa, int sa_def)
{
        /* copy the "sa" */

        struct sa_list *nsa;

        /* malloc() return used in a 'struct sa_list': do not free() */
        nsa = (struct sa_list *)malloc(sizeof(struct sa_list));
        if (nsa == NULL)
                (*ndo->ndo_error)(ndo, S_ERR_ND_MEM_ALLOC,
                                  "esp_print_addsa: malloc");

        *nsa = *sa;

        if (sa_def)
                ndo->ndo_sa_default = nsa;

        nsa->next = ndo->ndo_sa_list_head;
        ndo->ndo_sa_list_head = nsa;
}


static u_int hexdigit(netdissect_options *ndo, char hex)
{
        if (hex >= '0' && hex <= '9')
                return (hex - '0');
        else if (hex >= 'A' && hex <= 'F')
                return (hex - 'A' + 10);
        else if (hex >= 'a' && hex <= 'f')
                return (hex - 'a' + 10);
        else {
                (*ndo->ndo_error)(ndo, S_ERR_ND_ESP_SECRET,
                                  "invalid hex digit %c in espsecret\n", hex);
        }
}

static u_int hex2byte(netdissect_options *ndo, char *hexstring)
{
        u_int byte;

        byte = (hexdigit(ndo, hexstring[0]) << 4) + hexdigit(ndo, hexstring[1]);
        return byte;
}

/*
 * returns size of binary, 0 on failure.
 */
static
int espprint_decode_hex(netdissect_options *ndo,
                        u_char *binbuf, unsigned int binbuf_len,
                        char *hex)
{
        unsigned int len;
        int i;

        len = strlen(hex) / 2;

        if (len > binbuf_len) {
                (*ndo->ndo_warning)(ndo, "secret is too big: %u\n", len);
                return 0;
        }

        i = 0;
        while (hex[0] != '\0' && hex[1]!='\0') {
                binbuf[i] = hex2byte(ndo, hex);
                hex += 2;
                i++;
        }

        return i;
}

/*
 * decode the form:    SPINUM@IP <tab> ALGONAME:0xsecret
 */

USES_APPLE_DEPRECATED_API
static int
espprint_decode_encalgo(netdissect_options *ndo,
                        char *decode, struct sa_list *sa)
{
        size_t i;
        const EVP_CIPHER *evp;
        int authlen = 0;
        char *colon, *p;

        colon = strchr(decode, ':');
        if (colon == NULL) {
                (*ndo->ndo_warning)(ndo, "failed to decode espsecret: %s\n", decode);
                return 0;
        }
        *colon = '\0';

        if (strlen(decode) > strlen("-hmac96") &&
            !strcmp(decode + strlen(decode) - strlen("-hmac96"),
                    "-hmac96")) {
                p = strstr(decode, "-hmac96");
                *p = '\0';
                authlen = 12;
        }
        if (strlen(decode) > strlen("-cbc") &&
            !strcmp(decode + strlen(decode) - strlen("-cbc"), "-cbc")) {
                p = strstr(decode, "-cbc");
                *p = '\0';
        }
        evp = EVP_get_cipherbyname(decode);

        if (!evp) {
                (*ndo->ndo_warning)(ndo, "failed to find cipher algo %s\n", decode);
                sa->evp = NULL;
                sa->authlen = 0;
                sa->ivlen = 0;
                return 0;
        }

        sa->evp = evp;
        sa->authlen = authlen;
        /* This returns an int, but it should never be negative */
        sa->ivlen = EVP_CIPHER_iv_length(evp);

        colon++;
        if (colon[0] == '0' && colon[1] == 'x') {
                /* decode some hex! */

                colon += 2;
                sa->secretlen = espprint_decode_hex(ndo, sa->secret, sizeof(sa->secret), colon);
                if(sa->secretlen == 0) return 0;
        } else {
                i = strlen(colon);

                if (i < sizeof(sa->secret)) {
                        memcpy(sa->secret, colon, i);
                        sa->secretlen = i;
                } else {
                        memcpy(sa->secret, colon, sizeof(sa->secret));
                        sa->secretlen = sizeof(sa->secret);
                }
        }

        return 1;
}
USES_APPLE_RST

/*
 * for the moment, ignore the auth algorithm, just hard code the authenticator
 * length. Need to research how openssl looks up HMAC stuff.
 */
static int
espprint_decode_authalgo(netdissect_options *ndo,
                         char *decode, struct sa_list *sa)
{
        char *colon;

        colon = strchr(decode, ':');
        if (colon == NULL) {
                (*ndo->ndo_warning)(ndo, "failed to decode espsecret: %s\n", decode);
                return 0;
        }
        *colon = '\0';

        if(ascii_strcasecmp(decode,"sha1") == 0 ||
           ascii_strcasecmp(decode,"md5") == 0) {
                sa->authlen = 12;
        }
        return 1;
}

static void esp_print_decode_ikeline(netdissect_options *ndo, char *line,
                                     const char *file, int lineno)
{
        /* it's an IKEv2 secret, store it instead */
        struct sa_list sa1;

        char *init;
        char *icookie, *rcookie;
        int   ilen, rlen;
        char *authkey;
        char *enckey;

        init = strsep(&line, " \t");
        icookie = strsep(&line, " \t");
        rcookie = strsep(&line, " \t");
        authkey = strsep(&line, " \t");
        enckey  = strsep(&line, " \t");

        /* if any fields are missing */
        if(!init || !icookie || !rcookie || !authkey || !enckey) {
                (*ndo->ndo_warning)(ndo, "print_esp: failed to find all fields for ikev2 at %s:%u",
                                    file, lineno);

                return;
        }

        ilen = strlen(icookie);
        rlen = strlen(rcookie);

        if((init[0]!='I' && init[0]!='R')
           || icookie[0]!='0' || icookie[1]!='x'
           || rcookie[0]!='0' || rcookie[1]!='x'
           || ilen!=18
           || rlen!=18) {
                (*ndo->ndo_warning)(ndo, "print_esp: line %s:%u improperly formatted.",
                                    file, lineno);

                (*ndo->ndo_warning)(ndo, "init=%s icookie=%s(%u) rcookie=%s(%u)",
                                    init, icookie, ilen, rcookie, rlen);

                return;
        }

        sa1.spi = 0;
        sa1.initiator = (init[0] == 'I');
        if(espprint_decode_hex(ndo, sa1.spii, sizeof(sa1.spii), icookie+2)!=8)
                return;

        if(espprint_decode_hex(ndo, sa1.spir, sizeof(sa1.spir), rcookie+2)!=8)
                return;

        if(!espprint_decode_encalgo(ndo, enckey, &sa1)) return;

        if(!espprint_decode_authalgo(ndo, authkey, &sa1)) return;

        esp_print_addsa(ndo, &sa1, FALSE);
}

/*
 *
 * special form: file /name
 * causes us to go read from this file instead.
 *
 */
static void esp_print_decode_onesecret(netdissect_options *ndo, char *line,
                                       const char *file, int lineno)
{
        struct sa_list sa1;
        int sa_def;

        char *spikey;
        char *decode;

        spikey = strsep(&line, " \t");
        sa_def = 0;
        memset(&sa1, 0, sizeof(struct sa_list));

        /* if there is only one token, then it is an algo:key token */
        if (line == NULL) {
                decode = spikey;
                spikey = NULL;
                /* sa1.daddr.version = 0; */
                /* memset(&sa1.daddr, 0, sizeof(sa1.daddr)); */
                /* sa1.spi = 0; */
                sa_def    = 1;
        } else
                decode = line;

        if (spikey && ascii_strcasecmp(spikey, "file") == 0) {
                /* open file and read it */
                FILE *secretfile;
                char  fileline[1024];
                int   subfile_lineno=0;
                char  *nl;
                char *filename = line;

                secretfile = fopen(filename, FOPEN_READ_TXT);
                if (secretfile == NULL) {
                        (*ndo->ndo_error)(ndo, S_ERR_ND_OPEN_FILE,
                                          "print_esp: can't open %s: %s\n",
                                          filename, strerror(errno));
                }

                while (fgets(fileline, sizeof(fileline)-1, secretfile) != NULL) {
                        subfile_lineno++;
                        /* remove newline from the line */
                        nl = strchr(fileline, '\n');
                        if (nl)
                                *nl = '\0';
                        if (fileline[0] == '#') continue;
                        if (fileline[0] == '\0') continue;

                        esp_print_decode_onesecret(ndo, fileline, filename, subfile_lineno);
                }
                fclose(secretfile);

                return;
        }

        if (spikey && ascii_strcasecmp(spikey, "ikev2") == 0) {
                esp_print_decode_ikeline(ndo, line, file, lineno);
                return;
        }

        if (spikey) {

                char *spistr, *foo;
                uint32_t spino;

                spistr = strsep(&spikey, "@");
                if (spistr == NULL) {
                        (*ndo->ndo_warning)(ndo, "print_esp: failed to find the @ token");
                        return;
                }

                spino = strtoul(spistr, &foo, 0);
                if (spistr == foo || !spikey) {
                        (*ndo->ndo_warning)(ndo, "print_esp: failed to decode spi# %s\n", foo);
                        return;
                }

                sa1.spi = spino;

                if (strtoaddr6(spikey, &sa1.daddr.in6) == 1) {
                        sa1.daddr_version = 6;
                } else if (strtoaddr(spikey, &sa1.daddr.in4) == 1) {
                        sa1.daddr_version = 4;
                } else {
                        (*ndo->ndo_warning)(ndo, "print_esp: can not decode IP# %s\n", spikey);
                        return;
                }
        }

        if (decode) {
                /* skip any blank spaces */
                while (*decode == ' ' || *decode == '\t' || *decode == '\r' || *decode == '\n')
                        decode++;

                if(!espprint_decode_encalgo(ndo, decode, &sa1)) {
                        return;
                }
        }

        esp_print_addsa(ndo, &sa1, sa_def);
}

USES_APPLE_DEPRECATED_API
static void esp_init(netdissect_options *ndo _U_)
{
        /*
         * 0.9.6 doesn't appear to define OPENSSL_API_COMPAT, so
         * we check whether it's undefined or it's less than the
         * value for 1.1.0.
         */
#if !defined(OPENSSL_API_COMPAT) || OPENSSL_API_COMPAT < 0x10100000L
        OpenSSL_add_all_algorithms();
#endif
        EVP_add_cipher_alias(SN_des_ede3_cbc, "3des");
}
USES_APPLE_RST

void esp_print_decodesecret(netdissect_options *ndo)
{
        char *line;
        char *p;
        static int initialized = 0;

        if (!initialized) {
                esp_init(ndo);
                initialized = 1;
        }

        p = ndo->ndo_espsecret;

        while (p && p[0] != '\0') {
                /* pick out the first line or first thing until a comma */
                if ((line = strsep(&p, "\n,")) == NULL) {
                        line = p;
                        p = NULL;
                }

                esp_print_decode_onesecret(ndo, line, "cmdline", 0);
        }

        ndo->ndo_espsecret = NULL;
}

#endif

#ifdef HAVE_LIBCRYPTO
#define USED_IF_LIBCRYPTO
#else
#define USED_IF_LIBCRYPTO _U_
#endif

#ifdef HAVE_LIBCRYPTO
USES_APPLE_DEPRECATED_API
#endif
void
esp_print(netdissect_options *ndo,
          const u_char *bp, u_int length,
          const u_char *bp2 USED_IF_LIBCRYPTO,
          u_int ver USED_IF_LIBCRYPTO,
          int fragmented USED_IF_LIBCRYPTO,
          u_int ttl_hl USED_IF_LIBCRYPTO)
{
        const struct newesp *esp;
        const u_char *ep;
#ifdef HAVE_LIBCRYPTO
        const struct ip *ip;
        struct sa_list *sa = NULL;
        const struct ip6_hdr *ip6 = NULL;
        const u_char *iv;
        u_int ivlen;
        u_int payloadlen;
        const u_char *ct;
        u_char *pt;
        u_int padlen;
        u_int nh;
#endif

        ndo->ndo_protocol = "esp";
        esp = (const struct newesp *)bp;

        /* 'ep' points to the end of available data. */
        ep = ndo->ndo_snapend;

        if ((const u_char *)(esp + 1) >= ep) {
                nd_print_trunc(ndo);
                return;
        }
        ND_PRINT("ESP(spi=0x%08x", GET_BE_U_4(esp->esp_spi));
        ND_PRINT(",seq=0x%x)", GET_BE_U_4(esp->esp_seq));
        ND_PRINT(", length %u", length);

#ifdef HAVE_LIBCRYPTO
        /* initiailize SAs */
        if (ndo->ndo_sa_list_head == NULL) {
                if (!ndo->ndo_espsecret)
                        return;

                esp_print_decodesecret(ndo);
        }

        if (ndo->ndo_sa_list_head == NULL)
                return;

        ip = (const struct ip *)bp2;
        switch (ver) {
        case 6:
                ip6 = (const struct ip6_hdr *)bp2;
                /* we do not attempt to decrypt jumbograms */
                if (!GET_BE_U_2(ip6->ip6_plen))
                        return;
                /* XXX - check whether it's fragmented? */
                /* if we can't get nexthdr, we do not need to decrypt it */

                /* see if we can find the SA, and if so, decode it */
                for (sa = ndo->ndo_sa_list_head; sa != NULL; sa = sa->next) {
                        if (sa->spi == GET_BE_U_4(esp->esp_spi) &&
                            sa->daddr_version == 6 &&
                            UNALIGNED_MEMCMP(&sa->daddr.in6, &ip6->ip6_dst,
                                   sizeof(nd_ipv6)) == 0) {
                                break;
                        }
                }
                break;
        case 4:
                /* nexthdr & padding are in the last fragment */
                if (fragmented)
                        return;

                /* see if we can find the SA, and if so, decode it */
                for (sa = ndo->ndo_sa_list_head; sa != NULL; sa = sa->next) {
                        if (sa->spi == GET_BE_U_4(esp->esp_spi) &&
                            sa->daddr_version == 4 &&
                            UNALIGNED_MEMCMP(&sa->daddr.in4, &ip->ip_dst,
                                   sizeof(nd_ipv4)) == 0) {
                                break;
                        }
                }
                break;
        default:
                return;
        }

        /* if we didn't find the specific one, then look for
         * an unspecified one.
         */
        if (sa == NULL)
                sa = ndo->ndo_sa_default;

        /* if not found fail */
        if (sa == NULL)
                return;

        /* pointer to the IV, if there is one */
        iv = (const u_char *)(esp + 1) + 0;
        /* length of the IV, if there is one; 0, if there isn't */
        ivlen = sa->ivlen;

        /*
         * Get a pointer to the ciphertext.
         *
         * p points to the beginning of the payload, i.e. to the
         * initialization vector, so if we skip past the initialization
         * vector, it points to the beginning of the ciphertext.
         */
        ct = iv + ivlen;

        /*
         * Make sure the authentication data/integrity check value length
         * isn't bigger than the total amount of data available after
         * the ESP header and initialization vector is removed and,
         * if not, slice the authentication data/ICV off.
         */
        if (ep - ct < sa->authlen) {
                nd_print_trunc(ndo);
                return;
        }
        ep = ep - sa->authlen;

        /*
         * Calculate the length of the ciphertext.  ep points to
         * the beginning of the authentication data/integrity check
         * value, i.e. right past the end of the ciphertext;
         */
        payloadlen = ep - ct;

        if (sa->evp == NULL)
                return;

        /*
         * If the next header value is past the end of the available
         * data, we won't be able to fetch it once we've decrypted
         * the ciphertext, so there's no point in decrypting the data.
         *
         * Report it as truncation.
         */
        if (!ND_TTEST_1(ep - 1)) {
                nd_print_trunc(ndo);
                return;
        }

        pt = do_decrypt(ndo, "esp_print", sa, iv, ct, payloadlen);
        if (pt == NULL)
                return;

        /*
         * Switch to the output buffer for dissection, and
         * save it on the buffer stack so it can be freed.
         */
        ep = pt + payloadlen;
        if (!nd_push_buffer(ndo, pt, pt, ep)) {
                free(pt);
                (*ndo->ndo_error)(ndo, S_ERR_ND_MEM_ALLOC,
                        "esp_print: can't push buffer on buffer stack");
        }

        /*
         * Sanity check for pad length; if it, plus 2 for the pad
         * length and next header fields, is bigger than the ciphertext
         * length (which is also the plaintext length), it's too big.
         *
         * XXX - the check can fail if the packet is corrupt *or* if
         * it was not decrypted with the correct key, so that the
         * "plaintext" is not what was being sent.
         */
        padlen = GET_U_1(ep - 2);
        if (padlen + 2 > payloadlen) {
                nd_print_trunc(ndo);
                return;
        }

        /* Get the next header */
        nh = GET_U_1(ep - 1);

        ND_PRINT(": ");

        /* Now dissect the plaintext. */
        ip_print_demux(ndo, pt, payloadlen - (padlen + 2), ver, fragmented,
            ttl_hl, nh, bp2);

        /* Pop the buffer, freeing it. */
        nd_pop_packet_info(ndo);
#endif
}
#ifdef HAVE_LIBCRYPTO
USES_APPLE_RST
#endif