oscore_context.c

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/* -*- Mode: C; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
 
/*
 * Copyright (c) 2018, SICS, RISE AB
 * 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 Institute 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 INSTITUTE 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 INSTITUTE 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.
 *
 */
 
#include "coap3/coap_internal.h"
 
#include <stdio.h>
 
static void oscore_enter_context(coap_context_t *c_context,
                                 oscore_ctx_t *osc_ctx);
 
static size_t
compose_info(uint8_t *buffer,
             size_t buf_size,
             uint8_t alg,
             coap_bin_const_t *id,
             coap_bin_const_t *id_context,
             coap_str_const_t *type,
             size_t out_len) {
  size_t ret = 0;
  size_t rem_size = buf_size;
 
  ret += oscore_cbor_put_array(&buffer, &rem_size, 5);
  ret += oscore_cbor_put_bytes(&buffer,
                               &rem_size,
                               id ? id->s : NULL,
                               id ? id->length : 0);
  if (id_context != NULL && id_context->length > 0) {
    ret += oscore_cbor_put_bytes(&buffer,
                                 &rem_size,
                                 id_context->s,
                                 id_context->length);
  } else {
    ret += oscore_cbor_put_nil(&buffer, &rem_size);
  }
  ret += oscore_cbor_put_unsigned(&buffer, &rem_size, alg);
  ret += oscore_cbor_put_text(&buffer,
                              &rem_size,
                              (const char *)type->s,
                              type->length);
  ret += oscore_cbor_put_unsigned(&buffer, &rem_size, out_len);
  return ret;
}
 
uint8_t
oscore_bytes_equal(uint8_t *a_ptr,
                   uint8_t a_len,
                   uint8_t *b_ptr,
                   uint8_t b_len) {
  if (a_len != b_len) {
    return 0;
  }
 
  if (memcmp(a_ptr, b_ptr, a_len) == 0) {
    return 1;
  } else {
    return 0;
  }
}
 
static void
oscore_enter_context(coap_context_t *c_context, oscore_ctx_t *osc_ctx) {
  if (c_context->p_osc_ctx) {
    oscore_ctx_t *prev = c_context->p_osc_ctx;
    oscore_ctx_t *next = c_context->p_osc_ctx->next;
 
    while (next) {
      prev = next;
      next = next->next;
    }
    prev->next = osc_ctx;
  } else
    c_context->p_osc_ctx = osc_ctx;
}
 
static void
oscore_free_recipient(oscore_recipient_ctx_t *recipient) {
  coap_delete_bin_const(recipient->recipient_id);
  coap_delete_bin_const(recipient->recipient_key);
  coap_free_type(COAP_OSCORE_REC, recipient);
}
 
void
oscore_free_context(oscore_ctx_t *osc_ctx) {
  if (osc_ctx == NULL)
    return;
  if (osc_ctx->sender_context) {
    coap_delete_bin_const(osc_ctx->sender_context->sender_id);
    coap_delete_bin_const(osc_ctx->sender_context->sender_key);
    coap_free_type(COAP_OSCORE_SEN, osc_ctx->sender_context);
  }
 
  while (osc_ctx->recipient_chain) {
    oscore_recipient_ctx_t *next = osc_ctx->recipient_chain->next_recipient;
 
    oscore_free_recipient(osc_ctx->recipient_chain);
    osc_ctx->recipient_chain = next;
  }
 
  coap_delete_bin_const(osc_ctx->master_secret);
  coap_delete_bin_const(osc_ctx->master_salt);
  coap_delete_bin_const(osc_ctx->id_context);
  coap_delete_bin_const(osc_ctx->common_iv);
  coap_free_type(COAP_OSCORE_COM, osc_ctx);
}
 
void
oscore_free_contexts(coap_context_t *c_context) {
  while (c_context->p_osc_ctx) {
    oscore_ctx_t *osc_ctx = c_context->p_osc_ctx;
 
    c_context->p_osc_ctx = osc_ctx->next;
 
    oscore_free_context(osc_ctx);
  }
}
 
int
oscore_remove_context(coap_context_t *c_context, oscore_ctx_t *osc_ctx) {
  oscore_ctx_t *prev = NULL;
  oscore_ctx_t *next = c_context->p_osc_ctx;
  while (next) {
    if (next == osc_ctx) {
      if (prev != NULL)
        prev->next = next->next;
      else
        c_context->p_osc_ctx = next->next;
      oscore_free_context(next);
      return 1;
    }
    prev = next;
    next = next->next;
  }
  return 0;
}
 
/*
 *  oscore_find_context
 * Finds OSCORE context for rcpkey_id and optional ctxkey_id
 * rcpkey_id can be 0 length.
 * Updates recipient_ctx.
 */
oscore_ctx_t *
oscore_find_context(const coap_context_t *c_context,
                    const coap_bin_const_t rcpkey_id,
                    const coap_bin_const_t *ctxkey_id,
                    uint8_t *oscore_r2,
                    oscore_recipient_ctx_t **recipient_ctx) {
  oscore_ctx_t *pt = c_context->p_osc_ctx;
 
  *recipient_ctx = NULL;
  assert(rcpkey_id.length == 0 || rcpkey_id.s != NULL);
  while (pt != NULL) {
    int ok = 0;
    oscore_recipient_ctx_t *rpt = pt->recipient_chain;
 
    while (rpt) {
      ok = 0;
      if (rcpkey_id.length == rpt->recipient_id->length) {
        if (rcpkey_id.length != 0)
          ok = memcmp(rpt->recipient_id->s, rcpkey_id.s, rcpkey_id.length) != 0;
        if (oscore_r2) {
          if (pt->id_context != NULL && pt->id_context->length > 8) {
            ok = ok + (memcmp(pt->id_context->s, oscore_r2, 8) != 0);
          } else {
            ok += 1;
          }
        } else if (ctxkey_id) {
          if (pt->id_context != NULL) {
            if (ctxkey_id->length != pt->id_context->length)
              ok += 1;
            else
              ok = ok + (memcmp(pt->id_context->s,
                                ctxkey_id->s,
                                ctxkey_id->length) != 0);
          } else if (ctxkey_id->length > 0)
            ok += 1;
        }
        if (ok == 0) {
          /* optional id context and recipient id are the same  */
          *recipient_ctx = rpt;
          return pt; /* OSCORE context found */
        }
      }
      rpt = rpt->next_recipient;
    } /* while rpt */
    pt = pt->next;
  } /* end while */
  return NULL;
}
 
#define OSCORE_LOG_SIZE 16
void
oscore_log_hex_value(coap_log_t level,
                     const char *name,
                     coap_bin_const_t *value) {
  size_t i;
 
  if (value == NULL) {
    coap_log(level, "    %-16s\n", name);
    return;
  }
  if (value->length == 0) {
    coap_log(level, "    %-16s <>\n", name);
    return;
  }
  if (coap_get_log_level() >= level) {
    for (i = 0; i < value->length; i += OSCORE_LOG_SIZE) {
      char number[3 * OSCORE_LOG_SIZE + 4];
 
      oscore_convert_to_hex(&value->s[i],
                            value->length - i > OSCORE_LOG_SIZE ?
                            OSCORE_LOG_SIZE : value->length - i,
                            number,
                            sizeof(number));
      coap_log(level, "    %-16s %s\n", i == 0 ? name : "", number);
    }
  }
}
 
void
oscore_log_int_value(coap_log_t level, const char *name, int value) {
  coap_log(level, "    %-16s %2d\n", name, value);
}
 
void
oscore_log_char_value(coap_log_t level, const char *name, const char *value) {
  coap_log(level, "    %-16s %s\n", name, value);
}
 
void
oscore_convert_to_hex(const uint8_t *src,
                      size_t src_len,
                      char *dest,
                      size_t dst_len) {
  /*
   * Last output character will be '\000'
   * (If output undersized, add trailing ... to indicate this.
   */
  size_t space = (dst_len - 4) / 3;
  uint32_t qq;
 
  for (qq = 0; qq < src_len && qq < space; qq++) {
    char tmp = src[qq] >> 4;
    if (tmp > 9)
      tmp = tmp + 0x61 - 10;
    else
      tmp = tmp + 0x30;
    dest[qq * 3] = tmp;
    tmp = src[qq] & 0xf;
    if (tmp > 9)
      tmp = tmp + 0x61 - 10;
    else
      tmp = tmp + 0x30;
    dest[qq * 3 + 1] = tmp;
    dest[qq * 3 + 2] = 0x20;
  }
  if (qq != src_len) {
    dest[qq * 3] = '.';
    dest[qq * 3 + 1] = '.';
    dest[qq * 3 + 2] = '.';
    qq++;
  }
  dest[qq * 3] = 0;
}
 
static coap_bin_const_t *
oscore_build_key(oscore_ctx_t *osc_ctx,
                 coap_bin_const_t *id,
                 coap_str_const_t *type,
                 size_t out_len) {
  uint8_t info_buffer[80];
  size_t info_len;
  uint8_t hkdf_tmp[CONTEXT_KEY_LEN > CONTEXT_INIT_VECT_LEN ?
                                   CONTEXT_KEY_LEN :
                                   CONTEXT_INIT_VECT_LEN];
 
  info_len = compose_info(info_buffer,
                          sizeof(info_buffer),
                          osc_ctx->aead_alg,
                          id,
                          osc_ctx->id_context,
                          type,
                          out_len);
  if (info_len == 0 || info_len > sizeof(info_buffer))
    return NULL;
 
  if (!oscore_hkdf(osc_ctx->hkdf_alg,
                   osc_ctx->master_salt,
                   osc_ctx->master_secret,
                   info_buffer,
                   info_len,
                   hkdf_tmp,
                   out_len))
    return NULL;
  return coap_new_bin_const(hkdf_tmp, out_len);
}
 
static void
oscore_log_context(oscore_ctx_t *osc_ctx, const char *heading) {
#if COAP_MAX_LOGGING_LEVEL < _COAP_LOG_OSCORE
  (void)osc_ctx;
  (void)heading;
#else /* COAP_MAX_LOGGING_LEVEL >= _COAP_LOG_OSCORE */
  if (coap_get_log_level() >= COAP_LOG_OSCORE) {
    char buffer[30];
    oscore_recipient_ctx_t *next = osc_ctx->recipient_chain;
    size_t count = 0;
 
    coap_log_oscore("%s\n", heading);
    oscore_log_char_value(COAP_LOG_OSCORE, "AEAD alg",
                          cose_get_alg_name(osc_ctx->aead_alg, buffer,
                                            sizeof(buffer)));
    oscore_log_char_value(COAP_LOG_OSCORE, "HKDF alg",
                          cose_get_hkdf_alg_name(osc_ctx->hkdf_alg, buffer,
                                                 sizeof(buffer)));
    oscore_log_hex_value(COAP_LOG_OSCORE, "ID Context", osc_ctx->id_context);
    oscore_log_hex_value(COAP_LOG_OSCORE,
                         "Master Secret",
                         osc_ctx->master_secret);
    oscore_log_hex_value(COAP_LOG_OSCORE, "Master Salt", osc_ctx->master_salt);
    oscore_log_hex_value(COAP_LOG_OSCORE, "Common IV", osc_ctx->common_iv);
    oscore_log_hex_value(COAP_LOG_OSCORE,
                         "Sender ID",
                         osc_ctx->sender_context->sender_id);
    oscore_log_hex_value(COAP_LOG_OSCORE,
                         "Sender Key",
                         osc_ctx->sender_context->sender_key);
    while (next) {
      snprintf(buffer, sizeof(buffer), "Recipient ID[%zu]", count);
      oscore_log_hex_value(COAP_LOG_OSCORE,
                           buffer,
                           next->recipient_id);
      snprintf(buffer, sizeof(buffer), "Recipient Key[%zu]", count);
      oscore_log_hex_value(COAP_LOG_OSCORE,
                           buffer,
                           next->recipient_key);
      count++;
      next = next->next_recipient;
    }
  }
#endif /* COAP_MAX_LOGGING_LEVEL >= _COAP_LOG_OSCORE */
}
 
void
oscore_update_ctx(oscore_ctx_t *osc_ctx, coap_bin_const_t *id_context) {
  coap_bin_const_t *temp;
 
  /* Update with new ID Context */
  coap_delete_bin_const(osc_ctx->id_context);
  osc_ctx->id_context = id_context;
 
  /* Update sender_key, recipient_key and common_iv */
  temp = osc_ctx->sender_context->sender_key;
  osc_ctx->sender_context->sender_key =
      oscore_build_key(osc_ctx,
                       osc_ctx->sender_context->sender_id,
                       coap_make_str_const("Key"),
                       CONTEXT_KEY_LEN);
  if (!osc_ctx->sender_context->sender_key)
    osc_ctx->sender_context->sender_key = temp;
  else
    coap_delete_bin_const(temp);
  temp = osc_ctx->recipient_chain->recipient_key;
  osc_ctx->recipient_chain->recipient_key =
      oscore_build_key(osc_ctx,
                       osc_ctx->recipient_chain->recipient_id,
                       coap_make_str_const("Key"),
                       CONTEXT_KEY_LEN);
  if (!osc_ctx->recipient_chain->recipient_key)
    osc_ctx->recipient_chain->recipient_key = temp;
  else
    coap_delete_bin_const(temp);
  temp = osc_ctx->common_iv;
  osc_ctx->common_iv = oscore_build_key(osc_ctx,
                                        NULL,
                                        coap_make_str_const("IV"),
                                        CONTEXT_INIT_VECT_LEN);
  if (!osc_ctx->common_iv)
    osc_ctx->common_iv = temp;
  else
    coap_delete_bin_const(temp);
 
  oscore_log_context(osc_ctx, "Updated Common context");
}
 
oscore_ctx_t *
oscore_duplicate_ctx(coap_context_t *c_context,
                     oscore_ctx_t *o_osc_ctx,
                     coap_bin_const_t *sender_id,
                     coap_bin_const_t *recipient_id,
                     coap_bin_const_t *id_context) {
  oscore_ctx_t *osc_ctx = NULL;
  oscore_sender_ctx_t *sender_ctx = NULL;
  coap_bin_const_t *copy_rid = NULL;
 
  osc_ctx = coap_malloc_type(COAP_OSCORE_COM, sizeof(oscore_ctx_t));
  if (osc_ctx == NULL)
    goto error;
  memset(osc_ctx, 0, sizeof(oscore_ctx_t));
 
  sender_ctx = coap_malloc_type(COAP_OSCORE_SEN, sizeof(oscore_sender_ctx_t));
  if (sender_ctx == NULL)
    goto error;
  memset(sender_ctx, 0, sizeof(oscore_sender_ctx_t));
 
  osc_ctx->sender_context = sender_ctx;
  if (o_osc_ctx->master_secret)
    osc_ctx->master_secret =
        coap_new_bin_const(o_osc_ctx->master_secret->s,
                           o_osc_ctx->master_secret->length);
  if (o_osc_ctx->master_salt)
    osc_ctx->master_salt = coap_new_bin_const(o_osc_ctx->master_salt->s,
                                              o_osc_ctx->master_salt->length);
  osc_ctx->aead_alg = o_osc_ctx->aead_alg;
  osc_ctx->hkdf_alg = o_osc_ctx->hkdf_alg;
  if (id_context)
    osc_ctx->id_context = coap_new_bin_const(id_context->s, id_context->length);
  osc_ctx->ssn_freq = o_osc_ctx->ssn_freq;
  osc_ctx->replay_window_size = o_osc_ctx->replay_window_size;
  osc_ctx->rfc8613_b_1_2 = o_osc_ctx->rfc8613_b_1_2;
  osc_ctx->rfc8613_b_2 = o_osc_ctx->rfc8613_b_2;
  osc_ctx->save_seq_num_func = o_osc_ctx->save_seq_num_func;
  osc_ctx->save_seq_num_func_param = o_osc_ctx->save_seq_num_func_param;
 
  if (o_osc_ctx->master_secret) {
    /* sender_ key */
    sender_ctx->sender_key = oscore_build_key(osc_ctx,
                                              sender_id,
                                              coap_make_str_const("Key"),
                                              CONTEXT_KEY_LEN);
    if (!sender_ctx->sender_key)
      goto error;
 
    /* common IV */
    osc_ctx->common_iv = oscore_build_key(osc_ctx,
                                          NULL,
                                          coap_make_str_const("IV"),
                                          CONTEXT_INIT_VECT_LEN);
    if (!osc_ctx->common_iv)
      goto error;
  }
 
  /*
   * Need to set the last Sender Seq Num based on ssn_freq
   * The value should only change if there is a change to ssn_freq
   * and (potentially) be lower than seq, then save_seq_num_func() is
   * immediately called on next SSN update.
   */
  sender_ctx->next_seq = 0;
  sender_ctx->seq = 0;
 
  sender_ctx->sender_id = coap_new_bin_const(sender_id->s, sender_id->length);
 
  copy_rid = coap_new_bin_const(recipient_id->s, recipient_id->length);
  if (copy_rid == NULL)
    goto error;
  if (oscore_add_recipient(osc_ctx, copy_rid, 0) == NULL)
    goto error;
 
  oscore_log_context(osc_ctx, "New Common context");
  oscore_enter_context(c_context, osc_ctx);
 
  return osc_ctx;
 
error:
  oscore_free_context(osc_ctx);
  return NULL;
}
 
oscore_ctx_t *
oscore_derive_ctx(coap_context_t *c_context, coap_oscore_conf_t *oscore_conf) {
  oscore_ctx_t *osc_ctx = NULL;
  oscore_sender_ctx_t *sender_ctx = NULL;
  size_t i;
 
  osc_ctx = coap_malloc_type(COAP_OSCORE_COM, sizeof(oscore_ctx_t));
  if (osc_ctx == NULL)
    goto error;
  memset(osc_ctx, 0, sizeof(oscore_ctx_t));
 
  sender_ctx = coap_malloc_type(COAP_OSCORE_SEN, sizeof(oscore_sender_ctx_t));
  if (sender_ctx == NULL)
    goto error;
  memset(sender_ctx, 0, sizeof(oscore_sender_ctx_t));
 
  osc_ctx->sender_context = sender_ctx;
  osc_ctx->master_secret = oscore_conf->master_secret;
  osc_ctx->master_salt = oscore_conf->master_salt;
  osc_ctx->aead_alg = oscore_conf->aead_alg;
  osc_ctx->hkdf_alg = oscore_conf->hkdf_alg;
  osc_ctx->id_context = oscore_conf->id_context;
  osc_ctx->ssn_freq = oscore_conf->ssn_freq ? oscore_conf->ssn_freq : 1;
  osc_ctx->replay_window_size = oscore_conf->replay_window ?
                                oscore_conf->replay_window :
                                COAP_OSCORE_DEFAULT_REPLAY_WINDOW;
  osc_ctx->rfc8613_b_1_2 = oscore_conf->rfc8613_b_1_2;
  osc_ctx->rfc8613_b_2 = oscore_conf->rfc8613_b_2;
  osc_ctx->save_seq_num_func = oscore_conf->save_seq_num_func;
  osc_ctx->save_seq_num_func_param = oscore_conf->save_seq_num_func_param;
 
  if (oscore_conf->master_secret) {
    /* sender_ key */
    if (oscore_conf->break_sender_key)
      /* Interop testing */
      sender_ctx->sender_key = oscore_build_key(osc_ctx,
                                                oscore_conf->sender_id,
                                                coap_make_str_const("BAD"),
                                                CONTEXT_KEY_LEN);
    else
      sender_ctx->sender_key = oscore_build_key(osc_ctx,
                                                oscore_conf->sender_id,
                                                coap_make_str_const("Key"),
                                                CONTEXT_KEY_LEN);
    if (!sender_ctx->sender_key)
      goto error;
 
    /* common IV */
    osc_ctx->common_iv = oscore_build_key(osc_ctx,
                                          NULL,
                                          coap_make_str_const("IV"),
                                          CONTEXT_INIT_VECT_LEN);
    if (!osc_ctx->common_iv)
      goto error;
  }
 
  /*
   * Need to set the last Sender Seq Num based on ssn_freq
   * The value should only change if there is a change to ssn_freq
   * and (potentially) be lower than seq, then save_seq_num_func() is
   * immediately called on next SSN update.
   */
  sender_ctx->next_seq = oscore_conf->start_seq_num -
                         (oscore_conf->start_seq_num % (oscore_conf->ssn_freq > 0 ? oscore_conf->ssn_freq : 1));
 
  sender_ctx->sender_id = oscore_conf->sender_id;
  sender_ctx->seq = oscore_conf->start_seq_num;
 
  for (i = 0; i < oscore_conf->recipient_id_count; i++) {
    if (oscore_add_recipient(osc_ctx, oscore_conf->recipient_id[i],
                             oscore_conf->break_recipient_key) == NULL) {
      coap_log_warn("OSCORE: Failed to add Client ID\n");
      goto error;
    }
  }
  oscore_log_context(osc_ctx, "Common context");
 
  oscore_enter_context(c_context, osc_ctx);
 
  return osc_ctx;
 
error:
  coap_free_type(COAP_OSCORE_COM, osc_ctx);
  coap_free_type(COAP_OSCORE_SEN, sender_ctx);
  return NULL;
}
 
oscore_recipient_ctx_t *
oscore_add_recipient(oscore_ctx_t *osc_ctx, coap_bin_const_t *rid,
                     uint32_t break_key) {
  oscore_recipient_ctx_t *rcp_ctx = osc_ctx->recipient_chain;
  oscore_recipient_ctx_t *recipient_ctx = NULL;
 
  if (rid->length > 7) {
    coap_log_warn("oscore_add_recipient: Maximum size of recipient_id is 7 bytes\n");
    return NULL;
  }
  /* Check this is not a duplicate recipient id */
  while (rcp_ctx) {
    if (rcp_ctx->recipient_id->length == rid->length &&
        memcmp(rcp_ctx->recipient_id->s, rid->s, rid->length) == 0) {
      coap_delete_bin_const(rid);
      return NULL;
    }
    rcp_ctx = rcp_ctx->next_recipient;
  }
  recipient_ctx = (oscore_recipient_ctx_t *)coap_malloc_type(
                      COAP_OSCORE_REC,
                      sizeof(oscore_recipient_ctx_t));
  if (recipient_ctx == NULL)
    return NULL;
  memset(recipient_ctx, 0, sizeof(oscore_recipient_ctx_t));
 
  if (osc_ctx->master_secret) {
    if (break_key)
      /* Interop testing */
      recipient_ctx->recipient_key = oscore_build_key(osc_ctx,
                                                      rid,
                                                      coap_make_str_const("BAD"),
                                                      CONTEXT_KEY_LEN);
    else
      recipient_ctx->recipient_key = oscore_build_key(osc_ctx,
                                                      rid,
                                                      coap_make_str_const("Key"),
                                                      CONTEXT_KEY_LEN);
    if (!recipient_ctx->recipient_key) {
      coap_free_type(COAP_OSCORE_REC, recipient_ctx);
      return NULL;
    }
  }
 
  recipient_ctx->recipient_id = rid;
  recipient_ctx->initial_state = 1;
  recipient_ctx->osc_ctx = osc_ctx;
 
  rcp_ctx = osc_ctx->recipient_chain;
  recipient_ctx->next_recipient = rcp_ctx;
  osc_ctx->recipient_chain = recipient_ctx;
  return recipient_ctx;
}
 
int
oscore_delete_recipient(oscore_ctx_t *osc_ctx, coap_bin_const_t *rid) {
  oscore_recipient_ctx_t *prev = NULL;
  oscore_recipient_ctx_t *next = osc_ctx->recipient_chain;
  while (next) {
    if (next->recipient_id->length == rid->length &&
        memcmp(next->recipient_id->s, rid->s, rid->length) == 0) {
      if (prev != NULL)
        prev->next_recipient = next->next_recipient;
      else
        osc_ctx->recipient_chain = next->next_recipient;
      oscore_free_recipient(next);
      return 1;
    }
    prev = next;
    next = next->next_recipient;
  }
  return 0;
}
 
void
oscore_free_association(oscore_association_t *association) {
  if (association) {
    coap_delete_pdu(association->sent_pdu);
    coap_delete_bin_const(association->token);
    coap_delete_bin_const(association->aad);
    coap_delete_bin_const(association->nonce);
    coap_delete_bin_const(association->partial_iv);
    coap_free_type(COAP_STRING, association);
  }
}
 
int
oscore_new_association(coap_session_t *session,
                       coap_pdu_t *sent_pdu,
                       coap_bin_const_t *token,
                       oscore_recipient_ctx_t *recipient_ctx,
                       coap_bin_const_t *aad,
                       coap_bin_const_t *nonce,
                       coap_bin_const_t *partial_iv,
                       int is_observe) {
  oscore_association_t *association;
 
  association = coap_malloc_type(COAP_STRING, sizeof(oscore_association_t));
  if (association == NULL)
    return 0;
 
  memset(association, 0, sizeof(oscore_association_t));
  association->recipient_ctx = recipient_ctx;
  association->is_observe = is_observe;
 
  if (sent_pdu) {
    size_t size;
    const uint8_t *data;
 
    association->sent_pdu = coap_pdu_duplicate(sent_pdu, session,
                                               token->length, token->s, NULL);
    if (association->sent_pdu == NULL)
      goto error;
    if (coap_get_data(sent_pdu, &size, &data)) {
      coap_add_data(association->sent_pdu, size, data);
    }
  }
  association->token = coap_new_bin_const(token->s, token->length);
  if (association->token == NULL)
    goto error;
 
  if (aad) {
    association->aad = coap_new_bin_const(aad->s, aad->length);
    if (association->aad == NULL)
      goto error;
  }
 
  if (nonce) {
    association->nonce = coap_new_bin_const(nonce->s, nonce->length);
    if (association->nonce == NULL)
      goto error;
  }
 
  if (partial_iv) {
    association->partial_iv =
        coap_new_bin_const(partial_iv->s, partial_iv->length);
    if (association->partial_iv == NULL)
      goto error;
  }
 
  OSCORE_ASSOCIATIONS_ADD(session->associations, association);
  return 1;
 
error:
  oscore_free_association(association);
  return 0;
}
 
oscore_association_t *
oscore_find_association(coap_session_t *session, coap_bin_const_t *token) {
  oscore_association_t *association;
 
  OSCORE_ASSOCIATIONS_FIND(session->associations, token, association);
  return association;
}
 
int
oscore_delete_association(coap_session_t *session,
                          oscore_association_t *association) {
  if (association) {
    OSCORE_ASSOCIATIONS_DELETE(session->associations, association);
    oscore_free_association(association);
    return 1;
  }
  return 0;
}
 
void
oscore_delete_server_associations(coap_session_t *session) {
  if (session) {
    oscore_association_t *association;
    oscore_association_t *tmp;
 
    OSCORE_ASSOCIATIONS_ITER_SAFE(session->associations, association, tmp) {
      OSCORE_ASSOCIATIONS_DELETE(session->associations, association);
      oscore_free_association(association);
    }
    session->associations = NULL;
  }
}