Add more nd_print_trunc() calls

[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 {
        struct in_addr in4;
        struct in6_addr 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;
        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_CIPHERINIT_EX
/*
 * Initialize the cipher by calling EVP_CipherInit_ex(), because
 * calling EVP_CipherInit() 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_CipherInit_ex(),
 * however, won't reset the cipher context, so you can use it to specify
 * the IV oin a second call after a first call to EVP_CipherInit_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, int enc)
{
        return EVP_CipherInit_ex(ctx, cipher, NULL, key, iv, enc);
}
#else
/*
 * Initialize the cipher by calling EVP_CipherInit(), because we don't
 * have EVP_CipherInit_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, int enc)
{
        return EVP_CipherInit(ctx, cipher, key, iv, enc);
}
#endif

/*
 * this will adjust ndo_packetp and ndo_snapend to 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;
        unsigned int len;
        EVP_CIPHER_CTX *ctx;
        unsigned int block_size, output_buffer_size;
        u_char *output_buffer;

        /* 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;
        buf = buf + sa->ivlen;
        len = end-buf;

        if(end <= buf) return 0;

        ctx = EVP_CIPHER_CTX_new();
        if (ctx == NULL)
                return 0;
        if (set_cipher_parameters(ctx, sa->evp, sa->secret, NULL, 0) < 0)
                (*ndo->ndo_warning)(ndo, "espkey init failed");
        set_cipher_parameters(ctx, NULL, NULL, iv, 0);
        /*
         * Allocate a buffer for the decrypted data.
         * The output buffer must be separate from the input buffer, and
         * its size must be a multiple of the cipher block size.
         */
        block_size = (unsigned int)EVP_CIPHER_CTX_block_size(ctx);
        output_buffer_size = len + (block_size - len % block_size);
        output_buffer = (u_char *)malloc(output_buffer_size);
        if (output_buffer == NULL) {
                (*ndo->ndo_error)(ndo, S_ERR_ND_MEM_ALLOC,
                        "can't allocate memory for decryption buffer");
                EVP_CIPHER_CTX_free(ctx);
                return 0;
        }
        EVP_Cipher(ctx, output_buffer, buf, len);
        EVP_CIPHER_CTX_free(ctx);

        /*
         * XXX - of course this is wrong, because buf is a const buffer,
         * but changing this would require a more complicated fix.
         */
        memcpy(buf, output_buffer, len);
        free(output_buffer);

        ndo->ndo_packetp = buf;
        ndo->ndo_snapend = end;

        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);
                return 0;
        }
}

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;
        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 algorith, 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(colon,"sha1") == 0 ||
           ascii_strcasecmp(colon,"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));
                        return;
                }

                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, "@");

                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 (isspace((unsigned char)*decode))
                        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
USES_APPLE_DEPRECATED_API
#endif
int
esp_print(netdissect_options *ndo,
          const u_char *bp, const int length, const u_char *bp2
#ifndef HAVE_LIBCRYPTO
        _U_
#endif
        ,
        u_int *nhdr
#ifndef HAVE_LIBCRYPTO
        _U_
#endif
        ,
        u_int *padlen
#ifndef HAVE_LIBCRYPTO
        _U_
#endif
        )
{
        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;
        int advance;
        int len;
        u_char *secret;
        int ivlen = 0;
        const u_char *ivoff;
        const u_char *p;
        EVP_CIPHER_CTX *ctx;
        unsigned int block_size, output_buffer_size;
        u_char *output_buffer;
#endif

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

#ifdef HAVE_LIBCRYPTO
        secret = NULL;
        advance = 0;
#endif

#if 0
        /* keep secret out of a register */
        p = (u_char *)&secret;
#endif

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

        if ((const u_char *)(esp + 1) >= ep) {
                nd_print_trunc(ndo);
                goto fail;
        }
        ND_PRINT("ESP(spi=0x%08x", EXTRACT_BE_U_4(esp->esp_spi));
        ND_PRINT(",seq=0x%x)", EXTRACT_BE_U_4(esp->esp_seq));
        ND_PRINT(", length %u", length);

#ifndef HAVE_LIBCRYPTO
        goto fail;
#else
        /* initiailize SAs */
        if (ndo->ndo_sa_list_head == NULL) {
                if (!ndo->ndo_espsecret)
                        goto fail;

                esp_print_decodesecret(ndo);
        }

        if (ndo->ndo_sa_list_head == NULL)
                goto fail;

        ip = (const struct ip *)bp2;
        switch (IP_V(ip)) {
        case 6:
                ip6 = (const struct ip6_hdr *)bp2;
                /* we do not attempt to decrypt jumbograms */
                if (!EXTRACT_BE_U_2(ip6->ip6_plen))
                        goto fail;
                /* if we can't get nexthdr, we do not need to decrypt it */
                len = sizeof(struct ip6_hdr) + EXTRACT_BE_U_2(ip6->ip6_plen);

                /* 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 == EXTRACT_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 (EXTRACT_BE_U_2(ip->ip_off) & IP_MF)
                        goto fail;
                len = EXTRACT_BE_U_2(ip->ip_len);

                /* 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 == EXTRACT_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:
                goto fail;
        }

        /* 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)
                goto fail;

        /* if we can't get nexthdr, we do not need to decrypt it */
        if (ep - bp2 < len)
                goto fail;
        if (ep - bp2 > len) {
                /* FCS included at end of frame (NetBSD 1.6 or later) */
                ep = bp2 + len;
        }

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

        if (sa->evp) {
                ctx = EVP_CIPHER_CTX_new();
                if (ctx != NULL) {
                        if (set_cipher_parameters(ctx, sa->evp, secret, NULL, 0) < 0)
                                (*ndo->ndo_warning)(ndo, "espkey init failed");

                        p = ivoff;
                        set_cipher_parameters(ctx, NULL, NULL, p, 0);
                        len = ep - (p + ivlen);

                        /*
                         * Allocate a buffer for the decrypted data.
                         * The output buffer must be separate from the
                         * input buffer, and its size must be a multiple
                         * of the cipher block size.
                         */
                        block_size = (unsigned int)EVP_CIPHER_CTX_block_size(ctx);
                        output_buffer_size = len + (block_size - len % block_size);
                        output_buffer = (u_char *)malloc(output_buffer_size);
                        if (output_buffer == NULL) {
                                (*ndo->ndo_error)(ndo, S_ERR_ND_MEM_ALLOC,
                                        "esp_print: malloc decryption buffer");
                                EVP_CIPHER_CTX_free(ctx);
                                return -1;
                        }

                        EVP_Cipher(ctx, output_buffer, p + ivlen, len);
                        EVP_CIPHER_CTX_free(ctx);
                        /*
                         * XXX - of course this is wrong, because buf is a
                         * const buffer, but changing this would require a
                         * more complicated fix.
                         */
                        memcpy(p + ivlen, output_buffer, len);
                        free(output_buffer);
                        advance = ivoff - (const u_char *)esp + ivlen;
                } else
                        advance = sizeof(struct newesp);
        } else
                advance = sizeof(struct newesp);

        /* sanity check for pad length */
        if (ep - bp < EXTRACT_U_1(ep - 2))
                goto fail;

        if (padlen)
                *padlen = EXTRACT_U_1(ep - 2) + 2;

        if (nhdr)
                *nhdr = EXTRACT_U_1(ep - 1);

        ND_PRINT(": ");
        return advance;
#endif

fail:
        return -1;
}
#ifdef HAVE_LIBCRYPTO
USES_APPLE_RST
#endif