/*
 * Copyright (c) 2015-2020, Pelion and affiliates.
 * SPDX-License-Identifier: Apache-2.0
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

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

#include "coap_security_handler.h"

#ifdef COAP_SECURITY_AVAILABLE

#include "mbedtls/version.h"
#include "mbedtls/sha256.h"
#include "mbedtls/error.h"
#include "mbedtls/platform.h"
#include "mbedtls/ssl_cookie.h"
#include "mbedtls/entropy.h"
#include "mbedtls/ctr_drbg.h"
#include "mbedtls/hmac_drbg.h"
#include "mbedtls/ssl_ciphersuites.h"

#include "ns_trace.h"
#include "nsdynmemLIB.h"
#include "coap_connection_handler.h"
#include "randLIB.h"

struct coap_security_s {
    mbedtls_ssl_config          _conf;
    mbedtls_ssl_context         _ssl;

#if defined(MBEDTLS_CTR_DRBG_C)
    mbedtls_ctr_drbg_context    _drbg;
#define DRBG_INIT mbedtls_ctr_drbg_init
#define DRBG_RANDOM mbedtls_ctr_drbg_random
#define DRBG_FREE mbedtls_ctr_drbg_free
#elif defined(MBEDTLS_HMAC_DRBG_C)
    mbedtls_hmac_drbg_context   _drbg;
#define DRBG_INIT mbedtls_hmac_drbg_init
#define DRBG_RANDOM mbedtls_hmac_drbg_random
#define DRBG_FREE mbedtls_hmac_drbg_free
#else
#error "CTR or HMAC must be defined for coap_security_handler!"
#endif

    mbedtls_entropy_context     _entropy;
    bool                        _is_started;
    simple_cookie_t             _cookie;
    key_block_t                 _keyblk;

    SecureConnectionMode        _conn_mode;
#if defined(MBEDTLS_X509_CRT_PARSE_C)
    mbedtls_x509_crt            _cacert;
    mbedtls_x509_crt            _owncert;
    mbedtls_pk_context          _pkey;
#endif

    uint8_t                     _pw[64];
    uint8_t                     _pw_len;

    bool                        _is_blocking;
    int8_t                      _socket_id;
    int8_t                      _timer_id;
    void                        *_handle;
    send_cb                     *_send_cb;
    receive_cb                  *_receive_cb;
    start_timer_cb              *_start_timer_cb;
    timer_status_cb             *_timer_status_cb;

};

#if !defined(MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE)
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
const int ECJPAKE_SUITES[] = {
    MBEDTLS_TLS_ECJPAKE_WITH_AES_128_CCM_8,
    0
};
#endif

#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
static const int PSK_SUITES[] = {
    MBEDTLS_TLS_PSK_WITH_AES_128_CBC_SHA256,
    MBEDTLS_TLS_PSK_WITH_AES_256_CCM_8,
    MBEDTLS_TLS_PSK_WITH_AES_128_CCM_8,
    0
};
#endif /* defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED) */
#endif /* !defined(MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE) */

#define TRACE_GROUP "CsSh"

static void set_timer(void *sec_obj, uint32_t int_ms, uint32_t fin_ms);
static int get_timer(void *sec_obj);

int entropy_poll(void *data, unsigned char *output, size_t len, size_t *olen);

//Point these back to M2MConnectionHandler!!!
int f_send(void *ctx, const unsigned char *buf, size_t len);
int f_recv(void *ctx, unsigned char *buf, size_t len);

static int coap_security_handler_init(coap_security_t *sec)
{
    const char *pers = "dtls_client";
#ifdef COAP_SERVICE_PROVIDE_STRONG_ENTROPY_SOURCE
    const int entropy_source_type = MBEDTLS_ENTROPY_SOURCE_STRONG;
#else
    const int entropy_source_type = MBEDTLS_ENTROPY_SOURCE_WEAK;
#endif

#if defined(MBEDTLS_PLATFORM_C)
    if (mbedtls_platform_setup(NULL) != 0) {
        return -1;
    }
#endif /* MBEDTLS_PLATFORM_C */

    mbedtls_ssl_init(&sec->_ssl);
    mbedtls_ssl_config_init(&sec->_conf);
    DRBG_INIT(&sec->_drbg);
    mbedtls_entropy_init(&sec->_entropy);

#if defined(MBEDTLS_X509_CRT_PARSE_C)
    mbedtls_x509_crt_init(&sec->_cacert);
    mbedtls_x509_crt_init(&sec->_owncert);
    mbedtls_pk_init(&sec->_pkey);
#endif

    memset(&sec->_cookie, 0, sizeof(simple_cookie_t));
    memset(&sec->_keyblk, 0, sizeof(key_block_t));

    sec->_is_started = false;

    if (mbedtls_entropy_add_source(&sec->_entropy, entropy_poll, NULL,
                                   128, entropy_source_type) < 0) {
        return -1;
    }
#if defined(MBEDTLS_CTR_DRBG_C)
    if ((mbedtls_ctr_drbg_seed(&sec->_drbg, mbedtls_entropy_func, &sec->_entropy,
                               (const unsigned char *) pers,
                               strlen(pers))) != 0) {
        return -1;
    }
#elif defined(MBEDTLS_HMAC_DRBG_C)
    if ((mbedtls_hmac_drbg_seed(&sec->_drbg, mbedtls_md_info_from_type(MBEDTLS_MD_SHA256),
                                mbedtls_entropy_func, &sec->_entropy,
                                (const unsigned char *) pers,
                                strlen(pers))) != 0) {
        return -1;
    }
#else
#error "CTR or HMAC must be defined for coap_security_handler!"
#endif
    return 0;
}

bool coap_security_handler_is_started(const coap_security_t *sec)
{
    return sec->_is_started;
}

const void *coap_security_handler_keyblock(const coap_security_t *sec)
{
    return sec->_keyblk.value;
}

static void coap_security_handler_reset(coap_security_t *sec)
{
#if defined(MBEDTLS_X509_CRT_PARSE_C)
    mbedtls_x509_crt_free(&sec->_cacert);
    mbedtls_x509_crt_free(&sec->_owncert);
    mbedtls_pk_free(&sec->_pkey);
#endif

    mbedtls_entropy_free(&sec->_entropy);

    DRBG_FREE(&sec->_drbg);

    mbedtls_ssl_config_free(&sec->_conf);
    mbedtls_ssl_free(&sec->_ssl);
#if defined(MBEDTLS_PLATFORM_C)
    mbedtls_platform_teardown(NULL);
#endif /* MBEDTLS_PLATFORM_C */
}


coap_security_t *coap_security_create(int8_t socket_id, int8_t timer_id, void *handle, SecureConnectionMode mode,
                                      send_cb *socket_cb,
                                      receive_cb *receive_data_cb,
                                      start_timer_cb *timer_start_cb,
                                      timer_status_cb *timer_stat_cb)
{
    if (socket_cb == NULL || receive_data_cb == NULL || timer_start_cb == NULL || timer_stat_cb == NULL) {
        return NULL;
    }
    coap_security_t *this = ns_dyn_mem_alloc(sizeof(coap_security_t));
    if (!this) {
        return NULL;
    }
    memset(this, 0, sizeof(coap_security_t));
    if (-1 == coap_security_handler_init(this)) {
        ns_dyn_mem_free(this);
        return NULL;
    }
    this->_handle = handle;
    this->_conn_mode = mode;
    memset(this->_pw, 0, 64);
    this->_pw_len = 0;
    this->_socket_id = socket_id;
    this->_timer_id = timer_id;
    this->_send_cb = socket_cb;
    this->_receive_cb = receive_data_cb;
    this->_start_timer_cb = timer_start_cb;
    this->_timer_status_cb = timer_stat_cb;

    return this;
}

void coap_security_destroy(coap_security_t *sec)
{
    if (sec) {
        coap_security_handler_reset(sec);
        ns_dyn_mem_free(sec);
        sec = NULL;
    }
}

#ifdef MBEDTLS_SSL_SRV_C
/**** Random number functions ****/

/**
 * Get a random array of bytes.
 * Called back by mbedtls when it wants to fill a buffer with random data
 * Must return 0 on success.
 */
static int get_random(void *ctx, unsigned char *buf, size_t len)
{
    static int initialised = 0;
    uint32_t i;

    (void)ctx; /* No context */

    if (!initialised) {
        randLIB_seed_random();
        initialised = 1;
    }

    for (i = 0; i < len; i++) {
        buf[i] = (uint8_t)randLIB_get_8bit();
    }
    return 0; /* Success */
}

/**** Cookie functions ****/
static int simple_cookie_write(void *ctx,
                               unsigned char **p, unsigned char *end,
                               const unsigned char *info, size_t ilen)
{
    //TODO: As per RFC 6347 cookie must be stateless. This is not the case in here!
    //This should be fixed if we see that dos attack would be an issue.
    //this is proposed solution in RFC: Cookie = HMAC(Secret, Client-IP, Client-Parameters)
    //Secret is generated here and oftenly changed to prevent statistical attack
    simple_cookie_t *p_cookie = (simple_cookie_t *)ctx;

    /* Not using additional info */
    (void)info;
    (void)ilen;

    if ((size_t)(end - *p) < COOKIE_SIMPLE_LEN) {
        return MBEDTLS_ERR_SSL_BUFFER_TOO_SMALL;
    }

    /* Use a simple random number of length COOKIE_SIMPLE_LEN bytes */
    get_random(NULL, p_cookie->value, COOKIE_SIMPLE_LEN);
    memcpy(*p, p_cookie->value, COOKIE_SIMPLE_LEN);
    p_cookie->len = COOKIE_SIMPLE_LEN;
    *p += COOKIE_SIMPLE_LEN;
    return 0;
}

static int simple_cookie_check(void *ctx,
                               const unsigned char *cookie, size_t clen,
                               const unsigned char *info, size_t ilen)
{
    simple_cookie_t *p_cookie = (simple_cookie_t *)ctx;

    /* Not using additional info */
    (void)info;
    (void)ilen;

    if ((p_cookie->len == 0) ||
            (clen != p_cookie->len) ||
            (memcmp(cookie, p_cookie->value, p_cookie->len) != 0)) {
        return -1; /* This is what it is in mbedtls... */
    }
    return 0;
}
#endif // MBEDTLS_SSL_SRV_C

/**** Key export function ****/
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
#if (MBEDTLS_VERSION_MAJOR < 3)
static int export_key_block(void *ctx,
                            const unsigned char *mk, const unsigned char *kb,
                            size_t maclen, size_t keylen, size_t ivlen)
{
    key_block_t *p_key_block = (key_block_t *)ctx;

    /* Not using master key */
    (void)mk;

    /* Sanity check MAC and key lengths */
    if ((maclen != 0) || (((2 * keylen) + (2 * ivlen)) != KEY_BLOCK_LEN)) {
        return -1; /* Something seriously wrong! */
    }

    /* Copy the key block we are using */
    /* No need to skip over MAC keys, MAC len must be 0 if we are here */
    memcpy(p_key_block->value, kb /* + (2 * maclen)*/, (2 * keylen) + (2 * ivlen));
    return 0;
}
#endif
#endif

static int coap_security_handler_configure_keys(coap_security_t *sec, coap_security_keys_t keys, bool is_server)
{
    (void) is_server;

    int ret = -1;
    switch (sec->_conn_mode) {
        case CERTIFICATE: {
#if defined(MBEDTLS_X509_CRT_PARSE_C)
            if (keys._cert && mbedtls_x509_crt_parse(&sec->_owncert, keys._cert, keys._cert_len) < 0) {
                break;
            }

#if (MBEDTLS_VERSION_MAJOR >= 3)
            if (mbedtls_pk_parse_key(&sec->_pkey, keys._priv_key, keys._priv_key_len, NULL, 0, DRBG_RANDOM, &sec->_drbg) < 0) {
                break;
            }
#else
            if (mbedtls_pk_parse_key(&sec->_pkey, keys._priv_key, keys._priv_key_len, NULL, 0) < 0) {
                break;
            }
#endif

            if (0 != mbedtls_ssl_conf_own_cert(&sec->_conf, &sec->_owncert, &sec->_pkey)) {
                break;
            }

            mbedtls_ssl_conf_authmode(&sec->_conf, MBEDTLS_SSL_VERIFY_NONE);
            mbedtls_ssl_conf_ca_chain(&sec->_conf, &sec->_owncert, NULL);
            ret = 0;
#endif
            break;
        }
        case PSK: {
#if defined(MBEDTLS_KEY_EXCHANGE__SOME__PSK_ENABLED)
            if (0 != mbedtls_ssl_conf_psk(&sec->_conf, keys._priv_key, keys._priv_key_len, keys._cert, keys._cert_len)) {
                break;
            }
#if !defined(MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE)
            mbedtls_ssl_conf_ciphersuites(&sec->_conf, PSK_SUITES);
#endif /* !defined(MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE) */
            ret = 0;
#endif
            break;
        }
        case ECJPAKE: {
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
            if (mbedtls_ssl_set_hs_ecjpake_password(&sec->_ssl, keys._key, keys._key_len) != 0) {
                return -1;
            }
#if !defined(MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE)
            mbedtls_ssl_conf_ciphersuites(&sec->_conf, ECJPAKE_SUITES);
#endif /* !defined(MBEDTLS_SSL_CONF_SINGLE_CIPHERSUITE) */

#if (MBEDTLS_VERSION_MAJOR >= 3)
            tr_error("FATAL ERROR: support for mbedtls_ssl_set_export_keys_cb() not implemented");
#else
            //NOTE: If thread starts supporting PSK in other modes, then this will be needed!
            mbedtls_ssl_conf_export_keys_cb(&sec->_conf,
                                            export_key_block,
                                            &sec->_keyblk);
#endif

            ret = 0;
#endif
            break;
        }

        default:
            break;
    }
    return ret;
}

int coap_security_handler_connect_non_blocking(coap_security_t *sec, bool is_server, SecureSocketMode sock_mode, coap_security_keys_t keys, uint32_t timeout_min, uint32_t timeout_max)
{
    if (!sec) {
        return -1;
    }
    sec->_is_blocking = false;

    int endpoint = MBEDTLS_SSL_IS_CLIENT;
    if (is_server) {
        endpoint = MBEDTLS_SSL_IS_SERVER;
    }

    int mode = MBEDTLS_SSL_TRANSPORT_DATAGRAM;
    if (sock_mode == TLS) {
        mode = MBEDTLS_SSL_TRANSPORT_STREAM;
    }

    if ((mbedtls_ssl_config_defaults(&sec->_conf,
                                     endpoint,
                                     mode, 0)) != 0) {
        return -1;
    }

    if (!timeout_max && !timeout_min) {
        mbedtls_ssl_conf_handshake_timeout(&sec->_conf, DTLS_HANDSHAKE_TIMEOUT_MIN, DTLS_HANDSHAKE_TIMEOUT_MAX);
    } else {
        mbedtls_ssl_conf_handshake_timeout(&sec->_conf, timeout_min, timeout_max);
    }

#if !defined(MBEDTLS_SSL_CONF_RNG)
    mbedtls_ssl_conf_rng(&sec->_conf, DRBG_RANDOM, &sec->_drbg);
#endif

    if ((mbedtls_ssl_setup(&sec->_ssl, &sec->_conf)) != 0) {
        return -1;
    }

    // Defines MBEDTLS_SSL_CONF_RECV/SEND/RECV_TIMEOUT define global functions which should be the same for all
    // callers of mbedtls_ssl_set_bio_ctx and there should be only one ssl context. If these rules don't apply,
    // these defines can't be used.
#if !defined(MBEDTLS_SSL_CONF_RECV) && !defined(MBEDTLS_SSL_CONF_SEND) && !defined(MBEDTLS_SSL_CONF_RECV_TIMEOUT)
    mbedtls_ssl_set_bio(&sec->_ssl, sec,
                        f_send, f_recv, NULL);
#else
    mbedtls_ssl_set_bio_ctx(&sec->_ssl, sec);
#endif /* !defined(MBEDTLS_SSL_CONF_RECV) && !defined(MBEDTLS_SSL_CONF_SEND) && !defined(MBEDTLS_SSL_CONF_RECV_TIMEOUT) */

    // Defines MBEDTLS_SSL_CONF_SET_TIMER/GET_TIMER define global functions which should be the same for all
    // callers of mbedtls_ssl_set_timer_cb and there should be only one ssl context. If these rules don't apply,
    // these defines can't be used.
#if !defined(MBEDTLS_SSL_CONF_SET_TIMER) && !defined(MBEDTLS_SSL_CONF_GET_TIMER)
    mbedtls_ssl_set_timer_cb(&sec->_ssl, sec, set_timer,
                             get_timer);
#endif /* !defined(MBEDTLS_SSL_CONF_SET_TIMER) && !defined(MBEDTLS_SSL_CONF_GET_TIMER) */

#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
    //TODO: Figure out better way!!!
    //Password should never be stored in multiple places!!!
    if ((sec->_conn_mode == ECJPAKE) && is_server && keys._key_len > 0) {
        memcpy(sec->_pw, keys._key, keys._key_len);
        sec->_pw_len = keys._key_len;
    }
#endif

    if (coap_security_handler_configure_keys(sec, keys, is_server) != 0) {
        tr_debug("security credential configure failed");
        return -1;
    }

#ifdef MBEDTLS_SSL_SRV_C
    mbedtls_ssl_conf_dtls_cookies(&sec->_conf, simple_cookie_write,
                                  simple_cookie_check,
                                  &sec->_cookie);
#endif

#if !defined(MBEDTLS_SSL_CONF_MIN_MINOR_VER) || !defined(MBEDTLS_SSL_CONF_MIN_MAJOR_VER)
    mbedtls_ssl_conf_min_version(&sec->_conf, MBEDTLS_SSL_MAJOR_VERSION_3, MBEDTLS_SSL_MAJOR_VERSION_3);
#endif /* !defined(MBEDTLS_SSL_CONF_MIN_MINOR_VER) || !defined(MBEDTLS_SSL_CONF_MIN_MAJOR_VER) */

#if !defined(MBEDTLS_SSL_CONF_MAX_MINOR_VER) || !defined(MBEDTLS_SSL_CONF_MAX_MAJOR_VER)
    mbedtls_ssl_conf_max_version(&sec->_conf, MBEDTLS_SSL_MAJOR_VERSION_3, MBEDTLS_SSL_MAJOR_VERSION_3);
#endif /* !defined(MBEDTLS_SSL_CONF_MAX_MINOR_VER) || !defined(MBEDTLS_SSL_CONF_MAX_MAJOR_VER) */

    sec->_is_started = true;

    int ret = mbedtls_ssl_handshake_step(&sec->_ssl);
    if (ret == 0) {
        ret = mbedtls_ssl_handshake_step(&sec->_ssl);
        if (is_server && 0 == ret) {
            ret = coap_security_handler_continue_connecting(sec);
        }
    }

    if (ret >= 0) {
        ret = 1;
    } else {
        ret = -1;
    }
    return ret;
}

int coap_security_handler_continue_connecting(coap_security_t *sec)
{
    int ret = -1;

    while (ret != MBEDTLS_ERR_SSL_WANT_READ) {
        ret = mbedtls_ssl_handshake_step(&sec->_ssl);
        if (MBEDTLS_ERR_SSL_HELLO_VERIFY_REQUIRED == ret) {
            mbedtls_ssl_session_reset(&sec->_ssl);
#if defined(MBEDTLS_KEY_EXCHANGE_ECJPAKE_ENABLED)
            if (mbedtls_ssl_set_hs_ecjpake_password(&sec->_ssl, sec->_pw, sec->_pw_len) != 0) {
                return -1;
            }
#endif
            return 1;
        } else if (ret && (ret != MBEDTLS_ERR_SSL_WANT_READ && ret != MBEDTLS_ERR_SSL_WANT_WRITE)) {
            return ret;
        }

#if (MBEDTLS_VERSION_MAJOR >= 3)
        if (sec->_ssl.private_state == MBEDTLS_SSL_HANDSHAKE_OVER) {
            return 0;
        }
#else
        if (sec->_ssl.state == MBEDTLS_SSL_HANDSHAKE_OVER) {
            return 0;
        }
#endif
    }

    if (ret == MBEDTLS_ERR_SSL_WANT_READ || ret == MBEDTLS_ERR_SSL_WANT_WRITE) {
        return 1;
    }

    return -1;
}


int coap_security_handler_send_message(coap_security_t *sec, unsigned char *message, size_t len)
{
    int ret = -1;

    if (sec) {
        do {
            ret = mbedtls_ssl_write(&sec->_ssl, (unsigned char *) message, len);
        } while (ret == MBEDTLS_ERR_SSL_WANT_READ ||
                 ret == MBEDTLS_ERR_SSL_WANT_WRITE);
    }

    return ret; //bytes written
}

int coap_security_send_close_alert(coap_security_t *sec)
{
    if (!sec) {
        return -1;
    }

    if (!mbedtls_ssl_close_notify(&sec->_ssl)) {
        return 0;
    }
    return -1;
}

int coap_security_handler_read(coap_security_t *sec, unsigned char *buffer, size_t len)
{
    int ret = -1;
    int max_loops = 100;

    if (sec && buffer) {
        memset(buffer, 0, len);
        do {
            ret = mbedtls_ssl_read(&sec->_ssl, buffer, len);
        } while ((ret == MBEDTLS_ERR_SSL_WANT_READ ||
                  ret == MBEDTLS_ERR_SSL_WANT_WRITE)
                 && --max_loops);
    }
    return ret; //bytes read
}

/**** Timer functions ****/

/**
 * Set timer function.
 * Called back by mbedtls when it wants to set a timer.
 * Accepts an intermediate and a final delay in milliseconds
 * If the final delay is 0, cancels the running timer.
 * TODO - might be better to use an event timer in conjunction with
 * CoAP tasklet
 */
static void set_timer(void *sec_obj, uint32_t int_ms, uint32_t fin_ms)
{
    coap_security_t *sec = (coap_security_t *)sec_obj;
    if (sec->_start_timer_cb) {
        sec->_start_timer_cb(sec->_timer_id, int_ms, fin_ms);
    }
}

/**
 * Get timer function.
 * Called back by mbedtls when it wants to get a timer state.
 * Returns the state of the current timer
 * TODO - might be better to use an event timer in conjunction with
 * CoAP tasklet
 */
static int get_timer(void *sec_obj)
{
    coap_security_t *sec = (coap_security_t *)sec_obj;
    if (sec->_timer_status_cb) {
        return sec->_timer_status_cb(sec->_timer_id);
    }
    return -1;
}

int f_send(void *ctx, const unsigned char *buf, size_t len)
{
    coap_security_t *sec = (coap_security_t *)ctx;
    return sec->_send_cb(sec->_socket_id, sec->_handle, buf, len);
}

int f_recv(void *ctx, unsigned char *buf, size_t len)
{
    coap_security_t *sec = (coap_security_t *)ctx;
    return sec->_receive_cb(sec->_socket_id, buf, len);
}

int entropy_poll(void *ctx, unsigned char *output, size_t len,
                 size_t *olen)
{
    (void)ctx;
    //TODO: change to more secure random
    randLIB_seed_random();
    char *c = (char *)ns_dyn_mem_temporary_alloc(len);
    if (!c) {
        return MBEDTLS_ERR_ENTROPY_SOURCE_FAILED;
    }
    memset(c, 0, len);
    for (uint16_t i = 0; i < len; i++) {
        *(c + i) = (char)randLIB_get_8bit();
    }
    memmove(output, c, len);
    *olen = len;

    ns_dyn_mem_free(c);
    return (0);
}

#endif // COAP_SECURITY_AVAILABLE