gnunet-communicator-udp.c

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/*
     This file is part of GNUnet
     Copyright (C) 2010-2014, 2018, 2019 GNUnet e.V.
 
     GNUnet is free software: you can redistribute it and/or modify it
     under the terms of the GNU Affero General Public License as published
     by the Free Software Foundation, either version 3 of the License,
     or (at your option) any later version.
 
     GNUnet is distributed in the hope that it will be useful, but
     WITHOUT ANY WARRANTY; without even the implied warranty of
     MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
     Affero General Public License for more details.
 
     You should have received a copy of the GNU Affero General Public License
     along with this program.  If not, see <http://www.gnu.org/licenses/>.
 
     SPDX-License-Identifier: AGPL3.0-or-later
 */
 
#include "platform.h"
#include "gnunet_util_lib.h"
#include "gnunet_protocols.h"
#include "gnunet_signatures.h"
#include "gnunet_constants.h"
#include "gnunet_nt_lib.h"
#include "gnunet_nat_service.h"
#include "gnunet_statistics_service.h"
#include "gnunet_transport_application_service.h"
#include "gnunet_transport_communication_service.h"
 
#define DEFAULT_REKEY_TIME_INTERVAL GNUNET_TIME_UNIT_DAYS
 
#define PROTO_QUEUE_TIMEOUT GNUNET_TIME_UNIT_MINUTES
 
#define BROADCAST_FREQUENCY GNUNET_TIME_UNIT_MINUTES
 
#define INTERFACE_SCAN_FREQUENCY \
  GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MINUTES, 5)
 
#define ADDRESS_VALIDITY_PERIOD GNUNET_TIME_UNIT_HOURS
 
#define WORKING_QUEUE_INTERVALL \
  GNUNET_TIME_relative_multiply (GNUNET_TIME_UNIT_MICROSECONDS,1)
 
#define AES_KEY_SIZE (256 / 8)
 
#define AES_IV_SIZE (96 / 8)
 
#define GCM_TAG_SIZE (128 / 8)
 
#define GENERATE_AT_ONCE 2
 
#define KCN_THRESHOLD 92
 
#define KCN_TARGET 128
 
#define MAX_SQN_DELTA 160
 
#define MAX_SECRETS 128000
 
#define DEFAULT_REKEY_MAX_BYTES (1024LLU * 1024 * 1024 * 4LLU)
 
#define COMMUNICATOR_ADDRESS_PREFIX "udp"
 
#define COMMUNICATOR_CONFIG_SECTION "communicator-udp"
 
GNUNET_NETWORK_STRUCT_BEGIN
 
 
struct UdpHandshakeSignature
{
  struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
 
  struct GNUNET_PeerIdentity sender;
 
  struct GNUNET_PeerIdentity receiver;
 
  struct GNUNET_CRYPTO_EcdhePublicKey ephemeral;
 
  struct GNUNET_TIME_AbsoluteNBO monotonic_time;
};
 
 
struct InitialKX
{
  struct GNUNET_CRYPTO_EcdhePublicKey ephemeral;
 
  char gcm_tag[GCM_TAG_SIZE];
 
  int rekeying;
};
 
 
struct UDPConfirmation
{
  struct GNUNET_PeerIdentity sender;
 
  struct GNUNET_CRYPTO_EddsaSignature sender_sig;
 
  struct GNUNET_TIME_AbsoluteNBO monotonic_time;
 
  /* followed by messages */
 
  /* padding may follow actual messages */
};
 
 
struct UDPAck
{
  struct GNUNET_MessageHeader header;
 
  uint32_t sequence_max GNUNET_PACKED;
 
  uint32_t acks_available GNUNET_PACKED;
 
  struct GNUNET_HashCode cmac;
};
 
 
struct UdpBroadcastSignature
{
  struct GNUNET_CRYPTO_EccSignaturePurpose purpose;
 
  struct GNUNET_PeerIdentity sender;
 
  struct GNUNET_HashCode h_address;
};
 
 
struct UDPBroadcast
{
  struct GNUNET_PeerIdentity sender;
 
  struct GNUNET_CRYPTO_EddsaSignature sender_sig;
};
 
 
struct UDPBox
{
  struct GNUNET_ShortHashCode kid;
 
  char gcm_tag[GCM_TAG_SIZE];
 
  int rekeying;
};
 
struct UDPRekey
{
  struct GNUNET_ShortHashCode kid;
 
  char gcm_tag[GCM_TAG_SIZE];
 
  struct GNUNET_PeerIdentity sender;
};
 
GNUNET_NETWORK_STRUCT_END
 
struct SharedSecret;
 
 
struct KeyCacheEntry
{
  struct KeyCacheEntry *next;
 
  struct KeyCacheEntry *prev;
 
  struct GNUNET_ShortHashCode kid;
 
  struct SharedSecret *ss;
 
  uint32_t sequence_number;
};
 
 
struct SenderAddress;
 
struct ReceiverAddress;
 
struct SharedSecret
{
  struct SharedSecret *next;
 
  struct SharedSecret *prev;
 
  struct KeyCacheEntry *kce_head;
 
  struct KeyCacheEntry *kce_tail;
 
  struct SenderAddress *sender;
 
  struct ReceiverAddress *receiver;
 
  struct GNUNET_HashCode master;
 
  struct GNUNET_HashCode cmac;
 
  uint32_t sequence_used;
 
  uint32_t sequence_allowed;
 
  unsigned int active_kce_count;
};
 
 
struct SenderAddress
{
  struct SharedSecret *ss_rekey;
 
  int rekeying;
 
  struct GNUNET_PeerIdentity target;
 
  struct GNUNET_CONTAINER_HeapNode *hn;
 
  struct SharedSecret *ss_head;
 
  struct SharedSecret *ss_tail;
 
  struct sockaddr *address;
 
  socklen_t address_len;
 
  struct GNUNET_TIME_Absolute timeout;
 
  unsigned int num_secrets;
 
  unsigned int acks_available;
 
  enum GNUNET_NetworkType nt;
 
  int sender_destroy_called;
 
 
  struct GNUNET_SCHEDULER_Task *kce_task;
 
  struct GNUNET_SCHEDULER_Task *kce_task_rekey;
 
  int kce_task_finished;
};
 
 
struct ReceiverAddress
{
 
  struct SharedSecret *ss_rekey;
 
  unsigned int rekey_acks_available;
 
  uint64_t rekey_send_bytes;
 
  struct GNUNET_TIME_Absolute rekey_timeout;
 
  int rekeying;
 
  int number_rekeying_kce;
 
  struct GNUNET_PeerIdentity target;
 
  struct SharedSecret *ss_head;
 
  struct SharedSecret *ss_tail;
 
  char *foreign_addr;
 
  struct sockaddr *address;
 
  socklen_t address_len;
 
  struct GNUNET_CONTAINER_HeapNode *hn;
 
  struct GNUNET_MQ_Handle *kx_mq;
 
  struct GNUNET_MQ_Handle *d_mq;
 
  struct GNUNET_TRANSPORT_QueueHandle *kx_qh;
 
  struct GNUNET_TRANSPORT_QueueHandle *d_qh;
 
  struct GNUNET_TIME_Absolute timeout;
 
  size_t kx_mtu;
 
  size_t d_mtu;
 
  unsigned int num_secrets;
 
  unsigned int acks_available;
 
  enum GNUNET_NetworkType nt;
 
  int receiver_destroy_called;
};
 
struct BroadcastInterface
{
  struct BroadcastInterface *next;
 
  struct BroadcastInterface *prev;
 
  struct GNUNET_SCHEDULER_Task *broadcast_task;
 
  struct sockaddr *sa;
 
  struct sockaddr *ba;
 
  struct UDPBroadcast bcm;
 
  struct ipv6_mreq mcreq;
 
  socklen_t salen;
 
  int found;
};
 
static struct GNUNET_TIME_Relative rekey_interval;
 
static unsigned long long rekey_max_bytes;
struct SharedSecret *ss_finished;
 
static struct GNUNET_CONTAINER_MultiShortmap *key_cache;
 
static struct GNUNET_SCHEDULER_Task *read_task;
 
static struct GNUNET_SCHEDULER_Task *timeout_task;
 
static struct GNUNET_SCHEDULER_Task *broadcast_task;
 
static struct GNUNET_STATISTICS_Handle *stats;
 
static struct GNUNET_TRANSPORT_CommunicatorHandle *ch;
 
static struct GNUNET_CONTAINER_MultiPeerMap *receivers;
 
static struct GNUNET_CONTAINER_MultiPeerMap *senders;
 
static struct GNUNET_CONTAINER_Heap *senders_heap;
 
static struct GNUNET_CONTAINER_Heap *receivers_heap;
 
static struct BroadcastInterface *bi_head;
 
static struct BroadcastInterface *bi_tail;
 
static struct GNUNET_NETWORK_Handle *udp_sock;
 
static int have_v6_socket;
 
static struct GNUNET_PeerIdentity my_identity;
 
static struct GNUNET_CRYPTO_EddsaPrivateKey *my_private_key;
 
static const struct GNUNET_CONFIGURATION_Handle *cfg;
 
static struct GNUNET_TRANSPORT_ApplicationHandle *ah;
 
static struct GNUNET_NT_InterfaceScanner *is;
 
static struct GNUNET_NAT_Handle *nat;
 
static uint16_t my_port;
 
 
static void
bi_destroy (struct BroadcastInterface *bi)
{
  if (AF_INET6 == bi->sa->sa_family)
  {
    /* Leave the multicast group */
    if (GNUNET_OK != GNUNET_NETWORK_socket_setsockopt (udp_sock,
                                                       IPPROTO_IPV6,
                                                       IPV6_LEAVE_GROUP,
                                                       &bi->mcreq,
                                                       sizeof(bi->mcreq)))
    {
      GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "setsockopt");
    }
  }
  GNUNET_CONTAINER_DLL_remove (bi_head, bi_tail, bi);
  GNUNET_SCHEDULER_cancel (bi->broadcast_task);
  GNUNET_free (bi->sa);
  GNUNET_free (bi->ba);
  GNUNET_free (bi);
}
 
 
static void
receiver_destroy (struct ReceiverAddress *receiver)
{
 
  receiver->receiver_destroy_called = GNUNET_YES;
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Disconnecting receiver for peer `%s'\n",
              GNUNET_i2s (&receiver->target));
  /*if (NULL != (mq = receiver->kx_mq))
  {
    receiver->kx_mq = NULL;
    GNUNET_MQ_destroy (mq);
    }*/
  if (NULL != receiver->kx_qh)
  {
    GNUNET_TRANSPORT_communicator_mq_del (receiver->kx_qh);
    receiver->kx_qh = NULL;
    receiver->kx_mq = NULL;
  }
  /*if (NULL != (mq = receiver->d_mq))
  {
    receiver->d_mq = NULL;
    GNUNET_MQ_destroy (mq);
    }*/
  if (NULL != receiver->d_qh)
  {
    GNUNET_TRANSPORT_communicator_mq_del (receiver->d_qh);
    receiver->d_qh = NULL;
  }
  GNUNET_assert (GNUNET_YES ==
                 GNUNET_CONTAINER_multipeermap_remove (receivers,
                                                       &receiver->target,
                                                       receiver));
  GNUNET_assert (receiver == GNUNET_CONTAINER_heap_remove_node (receiver->hn));
  GNUNET_STATISTICS_set (stats,
                         "# receivers active",
                         GNUNET_CONTAINER_multipeermap_size (receivers),
                         GNUNET_NO);
  GNUNET_free (receiver->address);
  GNUNET_free (receiver->foreign_addr);
  GNUNET_free (receiver);
}
 
 
static void
kce_destroy (struct KeyCacheEntry *kce)
{
  struct SharedSecret *ss = kce->ss;
 
  ss->active_kce_count--;
  ss->sender->acks_available--;
  GNUNET_CONTAINER_DLL_remove (ss->kce_head, ss->kce_tail, kce);
  GNUNET_assert (GNUNET_YES == GNUNET_CONTAINER_multishortmap_remove (key_cache,
                                                                      &kce->kid,
                                                                      kce));
  GNUNET_free (kce);
}
 
 
static void
get_kid (const struct GNUNET_HashCode *msec,
         uint32_t serial,
         struct GNUNET_ShortHashCode *kid)
{
  uint32_t sid = htonl (serial);
 
  GNUNET_CRYPTO_hkdf (kid,
                      sizeof(*kid),
                      GCRY_MD_SHA512,
                      GCRY_MD_SHA256,
                      &sid,
                      sizeof(sid),
                      msec,
                      sizeof(*msec),
                      "UDP-KID",
                      strlen ("UDP-KID"),
                      NULL,
                      0);
}
 
 
static void
kce_generate (struct SharedSecret *ss, uint32_t seq)
{
  struct KeyCacheEntry *kce;
 
  GNUNET_assert (0 < seq);
  kce = GNUNET_new (struct KeyCacheEntry);
  kce->ss = ss;
  kce->sequence_number = seq;
  get_kid (&ss->master, seq, &kce->kid);
  GNUNET_CONTAINER_DLL_insert (ss->kce_head, ss->kce_tail, kce);
  ss->active_kce_count++;
  ss->sender->acks_available++;
  (void) GNUNET_CONTAINER_multishortmap_put (
    key_cache,
    &kce->kid,
    kce,
    GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);
  GNUNET_STATISTICS_set (stats,
                         "# KIDs active",
                         GNUNET_CONTAINER_multishortmap_size (key_cache),
                         GNUNET_NO);
}
 
 
static int
secret_destroy (struct SharedSecret *ss, int withoutKce)
{
  struct SenderAddress *sender;
  struct ReceiverAddress *receiver;
  struct KeyCacheEntry *kce;
 
  if (withoutKce && (ss->sequence_allowed > 0))
    return GNUNET_NO;
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "secret %s destroy %u %u\n",
              GNUNET_h2s (&ss->master),
              withoutKce,
              ss->sequence_allowed);
  if (NULL != (sender = ss->sender))
  {
    GNUNET_CONTAINER_DLL_remove (sender->ss_head, sender->ss_tail, ss);
    sender->num_secrets--;
  }
  if (NULL != (receiver = ss->receiver))
  {
    GNUNET_CONTAINER_DLL_remove (receiver->ss_head, receiver->ss_tail, ss);
    receiver->num_secrets--;
    // Uncomment this for alternativ 1 of backchannel functionality
    receiver->acks_available -= (ss->sequence_allowed - ss->sequence_used);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "%u receiver->acks_available 3\n",
                receiver->acks_available);
    // Until here for alternativ 1
  }
  while (NULL != (kce = ss->kce_head))
    kce_destroy (kce);
  GNUNET_STATISTICS_update (stats, "# Secrets active", -1, GNUNET_NO);
  GNUNET_STATISTICS_set (stats,
                         "# KIDs active",
                         GNUNET_CONTAINER_multishortmap_size (key_cache),
                         GNUNET_NO);
  GNUNET_free (ss);
  return GNUNET_YES;
}
 
 
static void
sender_destroy (struct SenderAddress *sender)
{
  sender->sender_destroy_called = GNUNET_YES;
  GNUNET_assert (
    GNUNET_YES ==
    GNUNET_CONTAINER_multipeermap_remove (senders, &sender->target, sender));
  GNUNET_assert (sender == GNUNET_CONTAINER_heap_remove_node (sender->hn));
  GNUNET_STATISTICS_set (stats,
                         "# senders active",
                         GNUNET_CONTAINER_multipeermap_size (senders),
                         GNUNET_NO);
  GNUNET_free (sender->address);
  GNUNET_free (sender);
}
 
 
static void
get_iv_key (const struct GNUNET_HashCode *msec,
            uint32_t serial,
            char key[AES_KEY_SIZE],
            char iv[AES_IV_SIZE])
{
  uint32_t sid = htonl (serial);
  char res[AES_KEY_SIZE + AES_IV_SIZE];
 
  GNUNET_CRYPTO_hkdf (res,
                      sizeof(res),
                      GCRY_MD_SHA512,
                      GCRY_MD_SHA256,
                      &sid,
                      sizeof(sid),
                      msec,
                      sizeof(*msec),
                      "UDP-IV-KEY",
                      strlen ("UDP-IV-KEY"),
                      NULL,
                      0);
  memcpy (key, res, AES_KEY_SIZE);
  memcpy (iv, &res[AES_KEY_SIZE], AES_IV_SIZE);
}
 
 
static void
reschedule_sender_timeout (struct SenderAddress *sender)
{
  sender->timeout =
    GNUNET_TIME_relative_to_absolute (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
  GNUNET_CONTAINER_heap_update_cost (sender->hn, sender->timeout.abs_value_us);
}
 
 
static void
reschedule_receiver_timeout (struct ReceiverAddress *receiver)
{
  receiver->timeout =
    GNUNET_TIME_relative_to_absolute (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
  GNUNET_CONTAINER_heap_update_cost (receiver->hn,
                                     receiver->timeout.abs_value_us);
}
 
 
static void
check_timeouts (void *cls)
{
  struct GNUNET_TIME_Relative st;
  struct GNUNET_TIME_Relative rt;
  struct GNUNET_TIME_Relative delay;
  struct ReceiverAddress *receiver;
  struct SenderAddress *sender;
 
  (void) cls;
  timeout_task = NULL;
  rt = GNUNET_TIME_UNIT_FOREVER_REL;
  while (NULL != (receiver = GNUNET_CONTAINER_heap_peek (receivers_heap)))
  {
    /* if (GNUNET_YES != receiver->receiver_destroy_called) */
    /* { */
    rt = GNUNET_TIME_absolute_get_remaining (receiver->timeout);
    if (0 != rt.rel_value_us)
      break;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Receiver timed out\n");
    receiver_destroy (receiver);
    // }
  }
  st = GNUNET_TIME_UNIT_FOREVER_REL;
  while (NULL != (sender = GNUNET_CONTAINER_heap_peek (senders_heap)))
  {
    if (GNUNET_YES != sender->sender_destroy_called)
    {
      st = GNUNET_TIME_absolute_get_remaining (sender->timeout);
      if (0 != st.rel_value_us)
        break;
      sender_destroy (sender);
    }
  }
  delay = GNUNET_TIME_relative_min (rt, st);
  if (delay.rel_value_us < GNUNET_TIME_UNIT_FOREVER_REL.rel_value_us)
    timeout_task = GNUNET_SCHEDULER_add_delayed (delay, &check_timeouts, NULL);
}
 
 
static void
calculate_cmac (struct SharedSecret *ss)
{
  GNUNET_CRYPTO_hkdf (&ss->cmac,
                      sizeof(ss->cmac),
                      GCRY_MD_SHA512,
                      GCRY_MD_SHA256,
                      "CMAC",
                      strlen ("CMAC"),
                      &ss->master,
                      sizeof(ss->master),
                      "UDP-CMAC",
                      strlen ("UDP-CMAC"),
                      NULL,
                      0);
}
 
 
static void
pass_plaintext_to_core (struct SenderAddress *sender,
                        const void *plaintext,
                        size_t plaintext_len)
{
  const struct GNUNET_MessageHeader *hdr = plaintext;
  const char *pos = plaintext;
 
  while (ntohs (hdr->size) <= plaintext_len)
  {
    GNUNET_STATISTICS_update (stats,
                              "# bytes given to core",
                              ntohs (hdr->size),
                              GNUNET_NO);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Giving %u bytes to TNG\n", ntohs (hdr->size));
    GNUNET_assert (GNUNET_SYSERR !=
                   GNUNET_TRANSPORT_communicator_receive (ch,
                                                          &sender->target,
                                                          hdr,
                                                          ADDRESS_VALIDITY_PERIOD,
                                                          NULL /* no flow control possible */
                                                          ,
                                                          NULL));
    /* move on to next message, if any */
    plaintext_len -= ntohs (hdr->size);
    if (plaintext_len < sizeof(*hdr))
      break;
    pos += ntohs (hdr->size);
    hdr = (const struct GNUNET_MessageHeader *) pos;
    // TODO for now..., we do not actually sen >1msg or have a way of telling
    // if we are done
    break;
  }
  GNUNET_STATISTICS_update (stats,
                            "# bytes padding discarded",
                            plaintext_len,
                            GNUNET_NO);
}
 
 
static void
setup_cipher (const struct GNUNET_HashCode *msec,
              uint32_t serial,
              gcry_cipher_hd_t *cipher)
{
  char key[AES_KEY_SIZE];
  char iv[AES_IV_SIZE];
  int rc;
 
  GNUNET_assert (0 ==
                 gcry_cipher_open (cipher,
                                   GCRY_CIPHER_AES256 /* low level: go for speed */,
                                   GCRY_CIPHER_MODE_GCM,
                                   0 /* flags */));
  get_iv_key (msec, serial, key, iv);
  rc = gcry_cipher_setkey (*cipher, key, sizeof(key));
  GNUNET_assert ((0 == rc) || ((char) rc == GPG_ERR_WEAK_KEY));
  rc = gcry_cipher_setiv (*cipher, iv, sizeof(iv));
  GNUNET_assert ((0 == rc) || ((char) rc == GPG_ERR_WEAK_KEY));
}
 
 
static int
try_decrypt (const struct SharedSecret *ss,
             const char tag[GCM_TAG_SIZE],
             uint32_t serial,
             const char *in_buf,
             size_t in_buf_size,
             char *out_buf)
{
  gcry_cipher_hd_t cipher;
 
  setup_cipher (&ss->master, serial, &cipher);
  GNUNET_assert (
    0 ==
    gcry_cipher_decrypt (cipher, out_buf, in_buf_size, in_buf, in_buf_size));
  if (0 != gcry_cipher_checktag (cipher, tag, GCM_TAG_SIZE))
  {
    gcry_cipher_close (cipher);
    GNUNET_STATISTICS_update (stats,
                              "# AEAD authentication failures",
                              1,
                              GNUNET_NO);
    return GNUNET_SYSERR;
  }
  gcry_cipher_close (cipher);
  return GNUNET_OK;
}
 
 
static struct SharedSecret *
setup_shared_secret_dec (const struct GNUNET_CRYPTO_EcdhePublicKey *ephemeral)
{
  struct SharedSecret *ss;
 
  ss = GNUNET_new (struct SharedSecret);
  GNUNET_CRYPTO_eddsa_ecdh (my_private_key, ephemeral, &ss->master);
  return ss;
}
 
 
static struct SharedSecret *
setup_shared_secret_enc (const struct GNUNET_CRYPTO_EcdhePrivateKey *ephemeral,
                         struct ReceiverAddress *receiver, int add_to_receiver)
{
  struct SharedSecret *ss;
 
  ss = GNUNET_new (struct SharedSecret);
  GNUNET_CRYPTO_ecdh_eddsa (ephemeral,
                            &receiver->target.public_key,
                            &ss->master);
  calculate_cmac (ss);
  ss->receiver = receiver;
  GNUNET_CONTAINER_DLL_insert (receiver->ss_head, receiver->ss_tail, ss);
  receiver->num_secrets++;
  GNUNET_STATISTICS_update (stats, "# Secrets active", 1, GNUNET_NO);
  return ss;
}
 
 
static void
setup_receiver_mq (struct ReceiverAddress *receiver);
 
static void
destroy_all_secrets (struct SharedSecret *ss, int withoutKce)
{
  struct SenderAddress *sender;
  struct ReceiverAddress *receiver;
  struct SharedSecret *ss_to_destroy;
  struct SharedSecret *ss_start;
  struct SharedSecret *pos;
  int at_least_one_destroyed = GNUNET_NO;
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Starting destroy all withoutKce: %u.\n",
              withoutKce);
 
  if (NULL != (sender = ss->sender))
  {
    ss_start = sender->ss_head;
  }
  else if (NULL != (receiver = ss->receiver))
  {
    ss_start = receiver->ss_head;
  }
  else
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Shared secret has no sender or receiver!\n");
    return;
  }
 
  pos = ss_start;
  while (NULL != pos)
  {
    ss_to_destroy = pos;
    pos = pos->next;
 
    if (ss != ss_to_destroy)
      at_least_one_destroyed = secret_destroy (ss_to_destroy, withoutKce);
  }
 
  if ((ss != ss_start) && ! at_least_one_destroyed)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Really destroying all.\n");
    destroy_all_secrets (ss_start, GNUNET_NO);
  }
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Finished destroy all.\n");
}
 
 
static void
add_acks (struct SharedSecret *ss, int acks_to_add)
{
 
  struct ReceiverAddress *receiver = ss->receiver;
 
  GNUNET_assert (NULL != ss);
  GNUNET_assert (NULL != receiver);
 
  if (NULL == receiver->d_qh)
  {
    receiver->d_qh =
      GNUNET_TRANSPORT_communicator_mq_add (ch,
                                            &receiver->target,
                                            receiver->foreign_addr,
                                            receiver->d_mtu,
                                            acks_to_add,
                                            1, /* Priority */
                                            receiver->nt,
                                            GNUNET_TRANSPORT_CS_OUTBOUND,
                                            receiver->d_mq);
  }
  else
  {
    GNUNET_TRANSPORT_communicator_mq_update (ch,
                                             receiver->d_qh,
                                             acks_to_add,
                                             1);
  }
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Tell transport we have %u more acks!\n",
              acks_to_add);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "%u kce for rekeying.\n",
              receiver->number_rekeying_kce);
 
  // Until here for alternativ 1
 
  /* move ss to head to avoid discarding it anytime soon! */
 
  GNUNET_CONTAINER_DLL_remove (receiver->ss_head, receiver->ss_tail, ss);
  GNUNET_CONTAINER_DLL_insert (receiver->ss_head, receiver->ss_tail, ss);
  destroy_all_secrets (ss, GNUNET_YES);
}
 
 
static uint32_t
reset_rekey_kces (struct ReceiverAddress *receiver,
                  uint32_t acks_to_add)
{
  int needed_for_rekeying;
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "%u kce for rekeying and %u acks_to_add\n",
              receiver->number_rekeying_kce,
              acks_to_add);
 
  needed_for_rekeying = (3 - receiver->number_rekeying_kce);
  if (acks_to_add <= needed_for_rekeying)
  {
    receiver->number_rekeying_kce += acks_to_add;
    acks_to_add = 0;
  }
  else
  {
    acks_to_add -= (3 - receiver->number_rekeying_kce);
    receiver->number_rekeying_kce = 3;
  }
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "%u kce for rekeying and %u acks_to_add\n",
              receiver->number_rekeying_kce,
              acks_to_add);
  return acks_to_add;
}
 
 
static void
add_acks_rekey (struct ReceiverAddress *receiver)
{
  uint32_t acks_to_add = receiver->ss_rekey->sequence_allowed;
 
  if (receiver->number_rekeying_kce < 3)
    acks_to_add = reset_rekey_kces (receiver, acks_to_add);
  receiver->acks_available = receiver->ss_rekey->sequence_allowed;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "%u receiver->acks_available 4\n",
              receiver->acks_available);
  /* add_acks (receiver->ss_rekey, acks_to_add - 3); */
  if (0 != acks_to_add)
  {
    add_acks (receiver->ss_rekey, acks_to_add);
  }
  receiver->ss_rekey = NULL;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "# rekeying successful\n");
  GNUNET_STATISTICS_update (stats,
                            "# rekeying successful",
                            1,
                            GNUNET_NO);
}
 
 
static int
handle_ack (void *cls, const struct GNUNET_PeerIdentity *pid, void *value)
{
  const struct UDPAck *ack = cls;
  struct ReceiverAddress *receiver = value;
  uint32_t acks_to_add;
  uint32_t allowed;
  // int needed_for_rekeying;
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "in handle ack with cmac %s\n",
              GNUNET_h2s (&ack->cmac));
 
  if (NULL != receiver->ss_rekey)
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "We have rekey secret with cmac %s \n",
                GNUNET_h2s (&receiver->ss_rekey->cmac));
 
  if ((NULL != receiver->ss_rekey) && (0 == memcmp (&ack->cmac,
                                                    &receiver->ss_rekey->cmac,
                                                    sizeof(struct
                                                           GNUNET_HashCode))) )
  {
    allowed = ntohl (ack->sequence_max);
 
    if (allowed > receiver->ss_rekey->sequence_allowed)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "%u > %u (%u %u) for rekey secrect %s\n", allowed,
                  receiver->ss_rekey->sequence_allowed,
                  receiver->acks_available,
                  ack->acks_available,
                  GNUNET_h2s (&receiver->ss_rekey->master));
 
      receiver->ss_rekey->sequence_allowed = allowed;
 
      if (GNUNET_NO == receiver->rekeying)
        add_acks_rekey (receiver);
 
      return GNUNET_NO;
    }
  }
 
  (void) pid;
  for (struct SharedSecret *ss = receiver->ss_head; NULL != ss; ss = ss->next)
  {
    if (0 == memcmp (&ack->cmac, &ss->cmac, sizeof(struct GNUNET_HashCode)))
    {
 
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Found matching mac\n");
 
      allowed = ntohl (ack->sequence_max);
 
      if (allowed > ss->sequence_allowed)
      {
        GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                    "%u > %u (%u %u) for secrect %s\n", allowed,
                    ss->sequence_allowed,
                    receiver->acks_available,
                    ack->acks_available,
                    GNUNET_h2s (&ss->master));
        // Uncomment this for alternativ 1 of backchannel functionality
        acks_to_add = (allowed - ss->sequence_allowed);
        if ((GNUNET_NO == receiver->rekeying) &&
            (receiver->number_rekeying_kce < 3) )
          acks_to_add = reset_rekey_kces (receiver, acks_to_add);
        /* if ((GNUNET_NO == receiver->rekeying) && */
        /*     (receiver->number_rekeying_kce < */
        /*      3) ) */
        /* { */
        /*   needed_for_rekeying = (3 - receiver->number_rekeying_kce); */
        /*   if (acks_to_add <= needed_for_rekeying) */
        /*   { */
        /*     receiver->number_rekeying_kce += acks_to_add; */
        /*     acks_to_add = 0; */
        /*   } */
        /*   else */
        /*   { */
        /*     acks_to_add -= (3 - receiver->number_rekeying_kce); */
        /*     receiver->number_rekeying_kce = 3; */
        /*   } */
        /* } */
        /* GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, */
        /*             "%u kce for rekeying\n", */
        /*             receiver->number_rekeying_kce); */
 
        if ((0 != acks_to_add) && (GNUNET_NO == receiver->rekeying))
        {
          receiver->acks_available += (allowed - ss->sequence_allowed);
          ss->sequence_allowed = allowed;
          GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                      "%u receiver->acks_available 5\n",
                      receiver->acks_available);
          add_acks (ss, acks_to_add);
        }
      }
      return GNUNET_NO;
    }
  }
  return GNUNET_YES;
}
 
 
static void
try_handle_plaintext (struct SenderAddress *sender,
                      const void *buf,
                      size_t buf_size)
{
  const struct GNUNET_MessageHeader *hdr =
    (const struct GNUNET_MessageHeader *) buf;
  const struct UDPAck *ack = (const struct UDPAck *) buf;
  uint16_t type;
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "try_handle_plaintext of size %u (%u %u) and type %u\n",
              buf_size,
              ntohs (hdr->size),
              sizeof(*hdr),
              ntohs (hdr->type));
  if (sizeof(*hdr) > buf_size)
    return; /* not even a header */
  if (ntohs (hdr->size) > buf_size)
    return; /* not even a header */
  type = ntohs (hdr->type);
  switch (type)
  {
  case GNUNET_MESSAGE_TYPE_COMMUNICATOR_UDP_ACK:
    /* lookup master secret by 'cmac', then update sequence_max */
    GNUNET_CONTAINER_multipeermap_get_multiple (receivers,
                                                &sender->target,
                                                &handle_ack,
                                                (void *) ack);
    /* There could be more messages after the ACK, handle those as well */
    buf += ntohs (hdr->size);
    buf_size -= ntohs (hdr->size);
    pass_plaintext_to_core (sender, buf, buf_size);
    break;
 
  case GNUNET_MESSAGE_TYPE_COMMUNICATOR_UDP_PAD:
    /* skip padding */
    break;
 
  default:
    pass_plaintext_to_core (sender, buf, buf_size);
  }
}
 
 
static void
kce_generate_cb (void *cls)
{
  struct SharedSecret *ss = cls;
 
  ss->sender->kce_task = NULL;
 
  if (((GNUNET_NO == ss->sender->rekeying) && (ss->sender->acks_available <
                                               KCN_TARGET) ) ||
      ((ss->sender->ss_rekey == ss) && (GNUNET_YES == ss->sender->rekeying) &&
       (ss->sender->acks_available < KCN_TARGET)))
  {
 
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Precomputing keys for master %s\n",
                GNUNET_h2s (&(ss->master)));
 
    for (int i = 0; i < GENERATE_AT_ONCE; i++)
      kce_generate (ss, ++ss->sequence_allowed);
 
    if (KCN_TARGET > ss->sender->acks_available)
    {
      ss->sender->kce_task = GNUNET_SCHEDULER_add_delayed (
        WORKING_QUEUE_INTERVALL,
        kce_generate_cb,
        ss);
    }
    else
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "We have enough keys.\n");
      ss_finished = ss;
      ss->sender->kce_task_finished = GNUNET_YES;
    }
  }
 
 
 
}
 
 
static void
kce_generate_rekey_cb (void *cls)
{
  struct SharedSecret *ss = cls;
 
  ss->sender->kce_task_rekey = NULL;
 
  if (NULL == ss->sender->kce_task)
  {
 
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Precomputing keys for rekey master %s\n",
                GNUNET_h2s (&(ss->master)));
 
    for (int i = 0; i < GENERATE_AT_ONCE; i++)
      kce_generate (ss, ++ss->sequence_allowed);
 
    ss->sender->kce_task = GNUNET_SCHEDULER_add_delayed (
      WORKING_QUEUE_INTERVALL,
      kce_generate_cb,
      ss);
    ss->sender->kce_task_rekey = NULL;
  }
  else
  {
    ss->sender->kce_task_rekey = GNUNET_SCHEDULER_add_delayed (
      WORKING_QUEUE_INTERVALL,
      kce_generate_rekey_cb,
      ss);
  }
}
 
 
static void
consider_ss_ack (struct SharedSecret *ss, int initial)
{
  struct GNUNET_SCHEDULER_Task *kce_task_rekey;
  struct GNUNET_SCHEDULER_Task *kce_task;
  int kce_task_finished;
 
  kce_task_rekey = ss->sender->kce_task_rekey;
  kce_task_finished = ss->sender->kce_task_finished;
  kce_task = ss->sender->kce_task;
 
  GNUNET_assert (NULL != ss->sender);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Considering SS UDPAck %s\n",
              GNUNET_i2s_full (&ss->sender->target));
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "We have %u acks available.\n",
              ss->sender->acks_available);
  /* drop ancient KeyCacheEntries */
  while ((NULL != ss->kce_head) &&
         (MAX_SQN_DELTA <
          ss->kce_head->sequence_number - ss->kce_tail->sequence_number))
    kce_destroy (ss->kce_tail);
 
 
  if (GNUNET_NO == initial)
    kce_generate (ss, ++ss->sequence_allowed);
 
  /*if (0 == ss->sender->acks_available)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Generating keys\n");
    while (ss->active_kce_count < KCN_TARGET)
      kce_generate (ss, ++ss->sequence_allowed);
      }*/
 
  if (NULL != kce_task)
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "kce_task is not NULL\n");
  if (kce_task_finished)
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "kce_task_finished: GNUNET_YES\n");
  if (initial)
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "initial: GNUNET_YES\n");
 
  if ( kce_task_finished || (GNUNET_NO == initial))
  {
    struct UDPAck ack;
    struct SharedSecret *ss_tell;
 
    if (GNUNET_NO != initial)
      ss_tell = ss_finished;
    else
      ss_tell = ss;
 
    ack.header.type = htons (GNUNET_MESSAGE_TYPE_COMMUNICATOR_UDP_ACK);
    ack.header.size = htons (sizeof(ack));
    ack.sequence_max = htonl (ss_tell->sequence_allowed);
    ack.acks_available = ss->sender->acks_available;
    ack.cmac = ss_tell->cmac;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Notifying transport of UDPAck %s with initial %u and master %s\n",
                GNUNET_i2s_full (&ss_tell->sender->target),
                initial,
                GNUNET_h2s (&(ss_tell->master)));
    GNUNET_TRANSPORT_communicator_notify (ch,
                                          &ss_tell->sender->target,
                                          COMMUNICATOR_ADDRESS_PREFIX,
                                          &ack.header);
    if (GNUNET_NO != initial)
    {
      destroy_all_secrets (ss, GNUNET_YES);
      ss->sender->kce_task_finished = GNUNET_NO;
    }
  }
  else if ((NULL == kce_task) && ((KCN_THRESHOLD >
                                   ss->sender->acks_available) ||
                                  (GNUNET_YES == ss->sender->rekeying) ||
                                  (ss->sender->num_secrets > MAX_SECRETS) ))
  {
 
    // kce_generate (ss, ++ss->sequence_allowed);
    // kce_generate (ss, ++ss->sequence_allowed);
    // TODO This task must be per sender!
    kce_task = GNUNET_SCHEDULER_add_delayed (WORKING_QUEUE_INTERVALL,
                                             kce_generate_cb,
                                             ss);
    kce_task_finished = GNUNET_NO;
 
  }
  else if ((NULL == kce_task_rekey) && (GNUNET_YES ==
                                        ss->sender->rekeying) )
  {
    kce_task_rekey = GNUNET_SCHEDULER_add_delayed (WORKING_QUEUE_INTERVALL,
                                                   kce_generate_rekey_cb,
                                                   ss);
  }
}
 
 
static void
decrypt_box (const struct UDPBox *box,
             size_t box_len,
             struct KeyCacheEntry *kce)
{
  struct SharedSecret *ss = kce->ss;
  char out_buf[box_len - sizeof(*box)];
 
  GNUNET_assert (NULL != ss->sender);
  if (GNUNET_OK != try_decrypt (ss,
                                box->gcm_tag,
                                kce->sequence_number,
                                (const char *) &box[1],
                                sizeof(out_buf),
                                out_buf))
  {
    GNUNET_STATISTICS_update (stats,
                              "# Decryption failures with valid KCE",
                              1,
                              GNUNET_NO);
    kce_destroy (kce);
    return;
  }
  kce_destroy (kce);
  GNUNET_STATISTICS_update (stats,
                            "# bytes decrypted with BOX",
                            sizeof(out_buf),
                            GNUNET_NO);
  GNUNET_STATISTICS_update (stats,
                            "# messages decrypted with BOX",
                            1,
                            GNUNET_NO);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "decrypted UDPBox with kid %s\n",
              GNUNET_sh2s (&box->kid));
  try_handle_plaintext (ss->sender, out_buf, sizeof(out_buf));
  if ((GNUNET_NO == box->rekeying) && (GNUNET_YES == ss->sender->rekeying))
  {
    ss->sender->rekeying = GNUNET_NO;
    ss->sender->ss_rekey = NULL;
    // destroy_all_secrets (ss, GNUNET_NO);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Receiver stopped rekeying.\n");
  }
  else if (GNUNET_NO == box->rekeying)
    consider_ss_ack (ss, GNUNET_NO);
  else
  {
    ss->sender->rekeying = GNUNET_YES;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Got Box: Receiver doing rekeying.\n");
  }
}
 
 
static void
decrypt_rekey (const struct UDPRekey *rekey,
               size_t rekey_len,
               struct KeyCacheEntry *kce,
               struct SenderAddress *sender)
{
  struct SharedSecret *ss = kce->ss;
  struct SharedSecret *ss_rekey;
  char out_buf[rekey_len - sizeof(*rekey)];
  struct GNUNET_HashCode *master;
 
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "decrypt_rekey.\n");
 
  GNUNET_assert (NULL != ss->sender);
  if (GNUNET_OK != try_decrypt (ss,
                                rekey->gcm_tag,
                                kce->sequence_number,
                                (const char *) &rekey[1],
                                sizeof(out_buf),
                                out_buf))
  {
    GNUNET_STATISTICS_update (stats,
                              "# Decryption failures with valid KCE",
                              1,
                              GNUNET_NO);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Decryption with kid %s failed\n",
                GNUNET_sh2s (&rekey->kid));
    kce_destroy (kce);
    return;
  }
  kce_destroy (kce);
  GNUNET_STATISTICS_update (stats,
                            "# bytes decrypted with Rekey",
                            sizeof(out_buf),
                            GNUNET_NO);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "decrypted UDPRekey with kid %s\n",
              GNUNET_sh2s (&rekey->kid));
  /*cmac = (struct GNUNET_HashCode *) out_buf;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received secret with cmac %s \n",
              GNUNET_h2s (&cmac));*/
  // ss_rekey = (struct SharedSecret *) out_buf;
  master = (struct GNUNET_HashCode *) out_buf;
  ss_rekey = GNUNET_new (struct SharedSecret);
  ss_rekey->master = *master;
  calculate_cmac (ss_rekey);
  ss_rekey->sender = sender;
  // ss_rekey->sequence_used = 0;
  // ss_rekey->sequence_allowed = 0;
  /* ss_rekey->active_kce_count = 0; */
  /* ss_rekey->prev = NULL; */
  /* ss_rekey->next = NULL; */
  /* GNUNET_assert (ss_rekey->prev == NULL && sender->ss_head != ss_rekey); */
  /* GNUNET_assert (ss_rekey->next == NULL && sender->ss_tail != ss_rekey); */
  GNUNET_CONTAINER_DLL_insert (sender->ss_head, sender->ss_tail, ss_rekey);
  sender->ss_rekey = ss_rekey;
  sender->num_secrets++;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received secret with cmac %s\n",
              GNUNET_h2s (&(ss_rekey->cmac)));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received secret with master %s.\n",
              GNUNET_h2s (&(ss_rekey->master)));
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "We have %u sequence_allowed.\n",
              ss_rekey->sequence_allowed);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "We have a sender %p\n",
              ss_rekey->sender);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "We have %u acks available.\n",
              ss_rekey->sender->acks_available);
  consider_ss_ack (ss_rekey, GNUNET_YES);
 
}
 
 
struct SearchContext
{
  const struct sockaddr *address;
 
  socklen_t address_len;
 
  struct SenderAddress *sender;
};
 
 
static int
find_sender_by_address (void *cls,
                        const struct GNUNET_PeerIdentity *key,
                        void *value)
{
  struct SearchContext *sc = cls;
  struct SenderAddress *sender = value;
 
  if ((sender->address_len == sc->address_len) &&
      (0 == memcmp (sender->address, sc->address, sender->address_len)))
  {
    sc->sender = sender;
    return GNUNET_NO;   /* stop iterating! */
  }
  return GNUNET_YES;
}
 
 
static struct SenderAddress *
setup_sender (const struct GNUNET_PeerIdentity *target,
              const struct sockaddr *address,
              socklen_t address_len)
{
  struct SenderAddress *sender;
  struct SearchContext sc = { .address = address,
                              .address_len = address_len,
                              .sender = NULL };
 
  GNUNET_CONTAINER_multipeermap_get_multiple (senders,
                                              target,
                                              &find_sender_by_address,
                                              &sc);
  if (NULL != sc.sender)
  {
    reschedule_sender_timeout (sc.sender);
    return sc.sender;
  }
  sender = GNUNET_new (struct SenderAddress);
  sender->target = *target;
  sender->address = GNUNET_memdup (address, address_len);
  sender->address_len = address_len;
  (void) GNUNET_CONTAINER_multipeermap_put (
    senders,
    &sender->target,
    sender,
    GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);
  GNUNET_STATISTICS_set (stats,
                         "# senders active",
                         GNUNET_CONTAINER_multipeermap_size (receivers),
                         GNUNET_NO);
  sender->timeout =
    GNUNET_TIME_relative_to_absolute (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
  sender->hn = GNUNET_CONTAINER_heap_insert (senders_heap,
                                             sender,
                                             sender->timeout.abs_value_us);
  sender->nt = GNUNET_NT_scanner_get_type (is, address, address_len);
  if (NULL == timeout_task)
    timeout_task = GNUNET_SCHEDULER_add_now (&check_timeouts, NULL);
  return sender;
}
 
 
static int
verify_confirmation (const struct GNUNET_CRYPTO_EcdhePublicKey *ephemeral,
                     const struct UDPConfirmation *uc)
{
  struct UdpHandshakeSignature uhs;
 
  uhs.purpose.purpose = htonl (
    GNUNET_SIGNATURE_PURPOSE_COMMUNICATOR_UDP_HANDSHAKE);
  uhs.purpose.size = htonl (sizeof(uhs));
  uhs.sender = uc->sender;
  uhs.receiver = my_identity;
  uhs.ephemeral = *ephemeral;
  uhs.monotonic_time = uc->monotonic_time;
  return GNUNET_CRYPTO_eddsa_verify (
    GNUNET_SIGNATURE_PURPOSE_COMMUNICATOR_UDP_HANDSHAKE,
    &uhs,
    &uc->sender_sig,
    &uc->sender.public_key);
}
 
 
static char *
sockaddr_to_udpaddr_string (const struct sockaddr *address,
                            socklen_t address_len)
{
  char *ret;
 
  switch (address->sa_family)
  {
  case AF_INET:
    GNUNET_asprintf (&ret,
                     "%s-%s",
                     COMMUNICATOR_ADDRESS_PREFIX,
                     GNUNET_a2s (address, address_len));
    break;
 
  case AF_INET6:
    GNUNET_asprintf (&ret,
                     "%s-%s",
                     COMMUNICATOR_ADDRESS_PREFIX,
                     GNUNET_a2s (address, address_len));
    break;
 
  default:
    GNUNET_assert (0);
  }
  return ret;
}
 
 
static void
sock_read (void *cls)
{
  struct sockaddr_storage sa;
  struct sockaddr_in *addr_verify;
  socklen_t salen = sizeof(sa);
  char buf[UINT16_MAX];
  ssize_t rcvd;
 
  (void) cls;
  read_task = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
                                             udp_sock,
                                             &sock_read,
                                             NULL);
  rcvd = GNUNET_NETWORK_socket_recvfrom (udp_sock,
                                         buf,
                                         sizeof(buf),
                                         (struct sockaddr *) &sa,
                                         &salen);
  if (-1 == rcvd)
  {
    GNUNET_log_strerror (GNUNET_ERROR_TYPE_DEBUG, "recv");
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Read %lu bytes\n", rcvd);
 
  if (rcvd > sizeof(struct UDPRekey))
  {
    const struct UDPRekey *rekey;
    const struct UDPBox *box;
    struct KeyCacheEntry *kce;
    struct SenderAddress *sender;
    int do_decrypt = GNUNET_NO;
 
    rekey = (const struct UDPRekey *) buf;
    box = (const struct UDPBox *) buf;
    kce = GNUNET_CONTAINER_multishortmap_get (key_cache, &rekey->kid);
 
    if ((GNUNET_YES == box->rekeying) || (GNUNET_NO == box->rekeying))
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "UDPRekey has rekeying %u\n",
                  box->rekeying);
    else
      do_decrypt = GNUNET_YES;
 
    if ((GNUNET_YES == do_decrypt) && (NULL != kce) && (GNUNET_YES ==
                                                        kce->ss->sender->
                                                        rekeying))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "UDPRekey with kid %s\n",
                  GNUNET_sh2s (&rekey->kid));
      sender = setup_sender (&rekey->sender, (const struct sockaddr *) &sa,
                             salen);
 
      if (NULL != sender->ss_rekey)
        return;
 
      decrypt_rekey (rekey, (size_t) rcvd, kce, sender);
      return;
    }
  }
 
  /* first, see if it is a UDPBox */
  if (rcvd > sizeof(struct UDPBox))
  {
    const struct UDPBox *box;
    struct KeyCacheEntry *kce;
 
    box = (const struct UDPBox *) buf;
    kce = GNUNET_CONTAINER_multishortmap_get (key_cache, &box->kid);
    if (NULL != kce)
    {
      decrypt_box (box, (size_t) rcvd, kce);
      return;
    }
  }
 
  /* next, check if it is a broadcast */
  if (sizeof(struct UDPBroadcast) == rcvd)
  {
    const struct UDPBroadcast *ub;
    struct UdpBroadcastSignature uhs;
    struct GNUNET_PeerIdentity sender;
 
    addr_verify = GNUNET_memdup (&sa, salen);
    addr_verify->sin_port = 0;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "received UDPBroadcast from %s\n",
                GNUNET_a2s ((const struct sockaddr *) addr_verify, salen));
    ub = (const struct UDPBroadcast *) buf;
    uhs.purpose.purpose = htonl (
      GNUNET_SIGNATURE_PURPOSE_COMMUNICATOR_UDP_BROADCAST);
    uhs.purpose.size = htonl (sizeof(uhs));
    uhs.sender = ub->sender;
    sender = ub->sender;
    if (0 == memcmp (&sender, &my_identity, sizeof (struct
                                                    GNUNET_PeerIdentity)))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Received our own broadcast\n");
      return;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "checking UDPBroadcastSignature for %s\n",
                GNUNET_i2s (&sender));
    GNUNET_CRYPTO_hash ((struct sockaddr *) addr_verify, salen, &uhs.h_address);
    if (GNUNET_OK ==
        GNUNET_CRYPTO_eddsa_verify (
          GNUNET_SIGNATURE_PURPOSE_COMMUNICATOR_UDP_BROADCAST,
          &uhs,
          &ub->sender_sig,
          &ub->sender.public_key))
    {
      char *addr_s;
      enum GNUNET_NetworkType nt;
 
      addr_s =
        sockaddr_to_udpaddr_string ((const struct sockaddr *) &sa, salen);
      GNUNET_STATISTICS_update (stats, "# broadcasts received", 1, GNUNET_NO);
      /* use our own mechanism to determine network type */
      nt =
        GNUNET_NT_scanner_get_type (is, (const struct sockaddr *) &sa, salen);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "validating address %s received from UDPBroadcast\n",
                  GNUNET_i2s (&sender));
      GNUNET_TRANSPORT_application_validate (ah, &sender, nt, addr_s);
      GNUNET_free (addr_s);
      return;
    }
    else
    {
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  "VerifyingPeer %s is verifying UDPBroadcast\n",
                  GNUNET_i2s (&my_identity));
      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
                  "Verifying UDPBroadcast from %s failed\n",
                  GNUNET_i2s (&ub->sender));
    }
    GNUNET_free (addr_verify);
    /* continue with KX, mostly for statistics... */
  }
 
 
  /* finally, test if it is a KX */
  if (rcvd < sizeof(struct UDPConfirmation) + sizeof(struct InitialKX))
  {
    GNUNET_STATISTICS_update (stats,
                              "# messages dropped (no kid, too small for KX)",
                              1,
                              GNUNET_NO);
    return;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Got KX\n");
  {
    const struct InitialKX *kx;
    struct SharedSecret *ss;
    char pbuf[rcvd - sizeof(struct InitialKX)];
    const struct UDPConfirmation *uc;
    struct SenderAddress *sender;
 
    kx = (const struct InitialKX *) buf;
    ss = setup_shared_secret_dec (&kx->ephemeral);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Before DEC\n");
 
    if (GNUNET_OK != try_decrypt (ss,
                                  kx->gcm_tag,
                                  0,
                                  &buf[sizeof(*kx)],
                                  sizeof(pbuf),
                                  pbuf))
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Unable to decrypt tag, dropping...\n");
      GNUNET_free (ss);
      GNUNET_STATISTICS_update (
        stats,
        "# messages dropped (no kid, AEAD decryption failed)",
        1,
        GNUNET_NO);
      return;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Before VERIFY\n");
 
    uc = (const struct UDPConfirmation *) pbuf;
    if (GNUNET_OK != verify_confirmation (&kx->ephemeral, uc))
    {
      GNUNET_break_op (0);
      GNUNET_free (ss);
      GNUNET_STATISTICS_update (stats,
                                "# messages dropped (sender signature invalid)",
                                1,
                                GNUNET_NO);
      return;
    }
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Before SETUP_SENDER\n");
 
    calculate_cmac (ss);
    sender = setup_sender (&uc->sender, (const struct sockaddr *) &sa, salen);
    ss->sender = sender;
    GNUNET_CONTAINER_DLL_insert (sender->ss_head, sender->ss_tail, ss);
    sender->num_secrets++;
    GNUNET_STATISTICS_update (stats, "# Secrets active", 1, GNUNET_NO);
    GNUNET_STATISTICS_update (stats,
                              "# messages decrypted without BOX",
                              1,
                              GNUNET_NO);
    try_handle_plaintext (sender, &uc[1], sizeof(pbuf) - sizeof(*uc));
    if ((GNUNET_NO == kx->rekeying) && (GNUNET_YES == ss->sender->rekeying))
    {
      ss->sender->rekeying = GNUNET_NO;
      sender->ss_rekey = NULL;
      // destroy_all_secrets (ss, GNUNET_NO);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Receiver stopped rekeying.\n");
    }
    else if (GNUNET_NO == kx->rekeying)
      consider_ss_ack (ss, GNUNET_YES);
    else
    {
      ss->sender->rekeying = GNUNET_YES;
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Got KX: Receiver doing rekeying.\n");
    }
    /*if (sender->num_secrets > MAX_SECRETS)
      secret_destroy (sender->ss_tail);*/
  }
}
 
 
static struct sockaddr *
udp_address_to_sockaddr (const char *bindto, socklen_t *sock_len)
{
  struct sockaddr *in;
  unsigned int port;
  char dummy[2];
  char *colon;
  char *cp;
 
  if (1 == sscanf (bindto, "%u%1s", &port, dummy))
  {
    /* interpreting value as just a PORT number */
    if (port > UINT16_MAX)
    {
      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                  "BINDTO specification `%s' invalid: value too large for port\n",
                  bindto);
      return NULL;
    }
    if ((GNUNET_NO == GNUNET_NETWORK_test_pf (PF_INET6)) ||
        (GNUNET_YES ==
         GNUNET_CONFIGURATION_get_value_yesno (cfg,
                                               COMMUNICATOR_CONFIG_SECTION,
                                               "DISABLE_V6")))
    {
      struct sockaddr_in *i4;
 
      i4 = GNUNET_malloc (sizeof(struct sockaddr_in));
      i4->sin_family = AF_INET;
      i4->sin_port = htons ((uint16_t) port);
      *sock_len = sizeof(struct sockaddr_in);
      in = (struct sockaddr *) i4;
    }
    else
    {
      struct sockaddr_in6 *i6;
 
      i6 = GNUNET_malloc (sizeof(struct sockaddr_in6));
      i6->sin6_family = AF_INET6;
      i6->sin6_port = htons ((uint16_t) port);
      *sock_len = sizeof(struct sockaddr_in6);
      in = (struct sockaddr *) i6;
    }
    return in;
  }
  cp = GNUNET_strdup (bindto);
  colon = strrchr (cp, ':');
  if (NULL != colon)
  {
    /* interpret value after colon as port */
    *colon = '\0';
    colon++;
    if (1 == sscanf (colon, "%u%1s", &port, dummy))
    {
      /* interpreting value as just a PORT number */
      if (port > UINT16_MAX)
      {
        GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                    "BINDTO specification `%s' invalid: value too large for port\n",
                    bindto);
        GNUNET_free (cp);
        return NULL;
      }
    }
    else
    {
      GNUNET_log (
        GNUNET_ERROR_TYPE_ERROR,
        "BINDTO specification `%s' invalid: last ':' not followed by number\n",
        bindto);
      GNUNET_free (cp);
      return NULL;
    }
  }
  else
  {
    /* interpret missing port as 0, aka pick any free one */
    port = 0;
  }
  {
    /* try IPv4 */
    struct sockaddr_in v4;
    if (1 == inet_pton (AF_INET, cp, &v4.sin_addr))
    {
      v4.sin_family = AF_INET;
      v4.sin_port = htons ((uint16_t) port);
#if HAVE_SOCKADDR_IN_SIN_LEN
      v4.sin_len = sizeof(struct sockaddr_in);
#endif
      in = GNUNET_memdup (&v4, sizeof(struct sockaddr_in));
      *sock_len = sizeof(struct sockaddr_in);
      GNUNET_free (cp);
      return in;
    }
  }
  {
    /* try IPv6 */
    struct sockaddr_in6 v6;
    const char *start;
 
    start = cp;
    if (('[' == *cp) && (']' == cp[strlen (cp) - 1]))
    {
      start++;   /* skip over '[' */
      cp[strlen (cp) - 1] = '\0';  /* eat ']' */
    }
    if (1 == inet_pton (AF_INET6, start, &v6.sin6_addr))
    {
      v6.sin6_family = AF_INET6;
      v6.sin6_port = htons ((uint16_t) port);
#if HAVE_SOCKADDR_IN_SIN_LEN
      v6.sin6_len = sizeof(sizeof(struct sockaddr_in6));
#endif
      in = GNUNET_memdup (&v6, sizeof(v6));
      *sock_len = sizeof(v6);
      GNUNET_free (cp);
      return in;
    }
  }
  /* #5528 FIXME (feature!): maybe also try getnameinfo()? */
  GNUNET_free (cp);
  return NULL;
}
 
 
static void
do_pad (gcry_cipher_hd_t out_cipher, char *dgram, size_t pad_size)
{
  char pad[pad_size];
 
  GNUNET_CRYPTO_random_block (GNUNET_CRYPTO_QUALITY_WEAK, pad, sizeof(pad));
  if (sizeof(pad) > sizeof(struct GNUNET_MessageHeader))
  {
    struct GNUNET_MessageHeader hdr =
    { .size = htons (sizeof(pad)),
      .type = htons (GNUNET_MESSAGE_TYPE_COMMUNICATOR_UDP_PAD) };
 
    memcpy (pad, &hdr, sizeof(hdr));
  }
  GNUNET_assert (
    0 ==
    gcry_cipher_encrypt (out_cipher, dgram, sizeof(pad), pad, sizeof(pad)));
}
 
 
static void
mq_send_kx (struct GNUNET_MQ_Handle *mq,
            const struct GNUNET_MessageHeader *msg,
            void *impl_state)
{
  struct ReceiverAddress *receiver = impl_state;
  uint16_t msize = ntohs (msg->size);
  struct UdpHandshakeSignature uhs;
  struct UDPConfirmation uc;
  struct InitialKX kx;
  struct GNUNET_CRYPTO_EcdhePrivateKey epriv;
  char dgram[receiver->kx_mtu + sizeof(uc) + sizeof(kx)];
  size_t dpos;
  gcry_cipher_hd_t out_cipher;
  struct SharedSecret *ss;
 
  GNUNET_assert (mq == receiver->kx_mq);
  if (msize > receiver->kx_mtu)
  {
    GNUNET_break (0);
    if (GNUNET_YES != receiver->receiver_destroy_called)
      receiver_destroy (receiver);
    return;
  }
  reschedule_receiver_timeout (receiver);
 
  /* setup key material */
  GNUNET_CRYPTO_ecdhe_key_create (&epriv);
 
  ss = setup_shared_secret_enc (&epriv, receiver, GNUNET_YES);
 
  if (receiver->num_secrets > MAX_SECRETS)
  {
    destroy_all_secrets (ss, GNUNET_YES);
  }
 
  setup_cipher (&ss->master, 0, &out_cipher);
  /* compute 'uc' */
  uc.sender = my_identity;
  uc.monotonic_time =
    GNUNET_TIME_absolute_hton (GNUNET_TIME_absolute_get_monotonic (cfg));
  uhs.purpose.purpose = htonl (
    GNUNET_SIGNATURE_PURPOSE_COMMUNICATOR_UDP_HANDSHAKE);
  uhs.purpose.size = htonl (sizeof(uhs));
  uhs.sender = my_identity;
  uhs.receiver = receiver->target;
  GNUNET_CRYPTO_ecdhe_key_get_public (&epriv, &uhs.ephemeral);
  uhs.monotonic_time = uc.monotonic_time;
  GNUNET_CRYPTO_eddsa_sign (my_private_key,
                            &uhs,
                            &uc.sender_sig);
  /* Leave space for kx */
  dpos = sizeof(kx);
  /* Append encrypted uc to dgram */
  GNUNET_assert (0 == gcry_cipher_encrypt (out_cipher,
                                           &dgram[dpos],
                                           sizeof(uc),
                                           &uc,
                                           sizeof(uc)));
  dpos += sizeof(uc);
  /* Append encrypted payload to dgram */
  GNUNET_assert (
    0 == gcry_cipher_encrypt (out_cipher, &dgram[dpos], msize, msg, msize));
  dpos += msize;
  do_pad (out_cipher, &dgram[dpos], sizeof(dgram) - dpos);
  /* Datagram starts with kx */
  kx.ephemeral = uhs.ephemeral;
  GNUNET_assert (
    0 == gcry_cipher_gettag (out_cipher, kx.gcm_tag, sizeof(kx.gcm_tag)));
  gcry_cipher_close (out_cipher);
  if (GNUNET_NO == receiver->rekeying)
    kx.rekeying = GNUNET_NO;
  else
    kx.rekeying = GNUNET_YES;
  memcpy (dgram, &kx, sizeof(kx));
  if (-1 == GNUNET_NETWORK_socket_sendto (udp_sock,
                                          dgram,
                                          sizeof(dgram),
                                          receiver->address,
                                          receiver->address_len))
    GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "send");
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sending KX with payload size %u to %s\n",
              msize,
              GNUNET_a2s (receiver->address,
                          receiver->address_len));
  GNUNET_MQ_impl_send_continue (mq);
}
 
 
static void
check_for_rekeying (struct ReceiverAddress *receiver, struct UDPBox *box)
{
 
  struct GNUNET_TIME_Relative rt;
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Timeout is %llu\n.",
              (unsigned long long) receiver->rekey_timeout.abs_value_us);
 
  if (0 == receiver->rekey_timeout.abs_value_us)
  {
    receiver->rekey_timeout = GNUNET_TIME_relative_to_absolute (
      rekey_interval);
  }
  else
  {
    rt = GNUNET_TIME_absolute_get_remaining (receiver->rekey_timeout);
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Relative time is %llu and timeout is %llu\n.",
                (unsigned long long) rt.rel_value_us,
                (unsigned long long) receiver->rekey_timeout.abs_value_us);
 
    if ((0 == rt.rel_value_us) || (receiver->rekey_send_bytes >
                                   rekey_max_bytes) )
    {
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Bytes send %llu greater than %llu max bytes\n.",
                  (unsigned long long) receiver->rekey_send_bytes,
                  rekey_max_bytes);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Relative time is %llu and timeout is %llu\n.",
                  (unsigned long long) rt.rel_value_us,
                  (unsigned long long) receiver->rekey_timeout.abs_value_us);
 
      receiver->rekey_timeout.abs_value_us = 0;
      receiver->rekey_send_bytes = 0;
      receiver->ss_rekey = NULL;
      // destroy_all_secrets (ss, GNUNET_NO);
      receiver->rekeying = GNUNET_YES;
      receiver->rekey_acks_available = receiver->acks_available;
      box->rekeying = GNUNET_YES;
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sender started rekeying.\n");
      if (GNUNET_YES == box->rekeying)
        GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                    "Sending rekeying with kid %s\n",
                    GNUNET_sh2s (&box->kid));
    }
  }
}
 
 
static void
send_UDPRekey (struct ReceiverAddress *receiver, struct SharedSecret *ss)
{
  uint8_t is_ss_rekey_sequence_allowed_zero = GNUNET_NO;
  uint8_t is_acks_available_below = GNUNET_NO;
  uint8_t send_rekey = GNUNET_NO;
  uint16_t not_below;
  struct GNUNET_CRYPTO_EcdhePrivateKey epriv;
  struct UDPRekey *rekey;
  size_t dpos;
 
  char rekey_dgram[sizeof(struct UDPRekey) + receiver->d_mtu];
 
  if (NULL != receiver->ss_rekey)
  {
    not_below = (receiver->rekey_acks_available
                 - (receiver->rekey_acks_available % 3)) / 3;
    is_ss_rekey_sequence_allowed_zero = (0 ==
                                         receiver->ss_rekey->sequence_allowed);
    is_acks_available_below = (receiver->acks_available >= not_below);
    send_rekey = (0 == (receiver->acks_available - not_below) % not_below) &&
                 is_acks_available_below && is_ss_rekey_sequence_allowed_zero;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "send_rekey: %u, %u, %u\n",
                send_rekey,
                receiver->rekey_acks_available,
                receiver->acks_available);
  }
  else if (NULL == receiver->ss_rekey)
  {
    /* setup key material */
    GNUNET_CRYPTO_ecdhe_key_create (&epriv);
    receiver->ss_rekey = setup_shared_secret_enc (&epriv, receiver,
                                                  GNUNET_NO);
    receiver->ss_rekey->sequence_allowed = 0;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Setup secret with cmac %s\n",
                GNUNET_h2s (&(receiver->ss_rekey->cmac)));
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Setup secret with master %s.\n",
                GNUNET_h2s (&(receiver->ss_rekey->master)));
  }
 
  if (send_rekey)
  {
    GNUNET_assert (0 != receiver->number_rekeying_kce);
    gcry_cipher_hd_t rekey_out_cipher;
 
    while (NULL != ss && ss->sequence_used >= ss->sequence_allowed)
    {
      ss = ss->prev;
    }
 
    if (NULL != ss)
    {
      rekey = (struct UDPRekey *) rekey_dgram;
      rekey->sender = my_identity;
      ss->sequence_used++;
      get_kid (&ss->master, ss->sequence_used, &rekey->kid);
      receiver->number_rekeying_kce--;
      setup_cipher (&ss->master, ss->sequence_used, &rekey_out_cipher);
      /* Append encrypted payload to dgram */
      dpos = sizeof(struct UDPRekey);
 
      GNUNET_assert (
        0 == gcry_cipher_encrypt (rekey_out_cipher, &rekey_dgram[dpos],
                                  sizeof(receiver->ss_rekey->master),
                                  &(receiver->ss_rekey->master),
                                  sizeof(receiver->ss_rekey->master)));
      dpos += sizeof(receiver->ss_rekey->master);
      /* GNUNET_assert ( */
      /*   0 == gcry_cipher_encrypt (rekey_out_cipher, &rekey_dgram[dpos], */
      /*                             /\*sizeof(receiver->ss_rekey->cmac), */
      /*                             &(receiver->ss_rekey->cmac), */
      /*                             sizeof(receiver->ss_rekey->cmac))); */
      /*                             dpos += sizeof(receiver->ss_rekey->cmac);*\/ */
      /*                             sizeof(receiver->ss_rekey), */
      /*                             receiver->ss_rekey, */
      /*                             sizeof(receiver->ss_rekey))); */
      /* dpos += sizeof(receiver->ss_rekey); */
      do_pad (rekey_out_cipher, &rekey_dgram[dpos], sizeof(rekey_dgram)
              - dpos);
      GNUNET_assert (0 == gcry_cipher_gettag (rekey_out_cipher,
                                              rekey->gcm_tag,
                                              sizeof(rekey->gcm_tag)));
      gcry_cipher_close (rekey_out_cipher);
 
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sending rekey with kid %s and master %s\n",
                  GNUNET_sh2s (&rekey->kid),
                  GNUNET_h2s (&(receiver->ss_rekey->master)));
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sending rekey with cmac %s\n",
                  GNUNET_h2s (&(receiver->ss_rekey->cmac)));
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "%u rekey kces left.\n",
                  receiver->number_rekeying_kce);
 
      if (-1 == GNUNET_NETWORK_socket_sendto (udp_sock,
                                              rekey_dgram,
                                              sizeof(rekey_dgram),
                                              receiver->address,
                                              receiver->address_len))
        GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "send");
 
      receiver->acks_available--;
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "%u receiver->acks_available 1\n",
                  receiver->acks_available);
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Sending UDPRekey to %s\n", GNUNET_a2s (receiver->address,
                                                          receiver->
                                                          address_len));
    }
  }
}
 
 
static void
mq_send_d (struct GNUNET_MQ_Handle *mq,
           const struct GNUNET_MessageHeader *msg,
           void *impl_state)
{
  struct ReceiverAddress *receiver = impl_state;
  uint16_t msize = ntohs (msg->size);
 
  GNUNET_assert (mq == receiver->d_mq);
  if ((msize > receiver->d_mtu) ||
      (0 == receiver->acks_available))
  {
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "msize: %u, mtu: %lu, acks: %u\n",
                msize,
                receiver->d_mtu,
                receiver->acks_available);
 
    GNUNET_break (0);
    if (GNUNET_YES != receiver->receiver_destroy_called)
      receiver_destroy (receiver);
    return;
  }
  reschedule_receiver_timeout (receiver);
 
  /* begin "BOX" encryption method, scan for ACKs from tail! */
  for (struct SharedSecret *ss = receiver->ss_tail; NULL != ss; ss = ss->prev)
  {
    if (0 < ss->sequence_used)
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "Trying to send UDPBox with shared secrect %s sequence_used %u and ss->sequence_allowed %u\n",
                  GNUNET_h2s (&ss->master),
                  ss->sequence_used,
                  ss->sequence_allowed);
    // Uncomment this for alternativ 1 of backchannel functionality
    if (ss->sequence_used >= ss->sequence_allowed)
    // Until here for alternativ 1
    // Uncomment this for alternativ 2 of backchannel functionality
    // if (0 == ss->sequence_allowed)
    // Until here for alternativ 2
    {
      continue;
    }
    char dgram[sizeof(struct UDPBox) + receiver->d_mtu];
    struct UDPBox *box;
    gcry_cipher_hd_t out_cipher;
    size_t dpos;
 
    box = (struct UDPBox *) dgram;
    ss->sequence_used++;
    get_kid (&ss->master, ss->sequence_used, &box->kid);
    setup_cipher (&ss->master, ss->sequence_used, &out_cipher);
    /* Append encrypted payload to dgram */
    dpos = sizeof(struct UDPBox);
    GNUNET_assert (
      0 == gcry_cipher_encrypt (out_cipher, &dgram[dpos], msize, msg, msize));
    dpos += msize;
    do_pad (out_cipher, &dgram[dpos], sizeof(dgram) - dpos);
    GNUNET_assert (0 == gcry_cipher_gettag (out_cipher,
                                            box->gcm_tag,
                                            sizeof(box->gcm_tag)));
    gcry_cipher_close (out_cipher);
 
    receiver->rekey_send_bytes += sizeof(struct UDPBox) + receiver->d_mtu;
 
    if (GNUNET_NO == receiver->rekeying)
      box->rekeying = GNUNET_NO;
    else
      box->rekeying = GNUNET_YES;
 
    if (-1 == GNUNET_NETWORK_socket_sendto (udp_sock,
                                            dgram,
                                            sizeof(dgram),
                                            receiver->address,
                                            receiver->address_len))
      GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "send");
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Sending UDPBox with payload size %u, %u acks left\n",
                msize,
                receiver->acks_available);
    GNUNET_MQ_impl_send_continue (mq);
    receiver->acks_available--;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "%u receiver->acks_available 2\n",
                receiver->acks_available);
    check_for_rekeying (receiver, box);
    if (0 == receiver->acks_available - receiver->number_rekeying_kce)
    {
      /* We have no more ACKs */
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "No more acks\n");
      if (GNUNET_YES == receiver->rekeying)
      {
        receiver->rekeying = GNUNET_NO;
        GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                    "Sender stopped rekeying\n");
 
        if ((NULL != receiver->ss_rekey) && (0 <
                                             receiver->ss_rekey->
                                             sequence_allowed) )
          add_acks_rekey (receiver);
      }
    }
    else if ((GNUNET_YES == receiver->rekeying)  )
    {
      send_UDPRekey (receiver, ss);
    }
 
    return;
  }
}
 
 
static void
mq_destroy_d (struct GNUNET_MQ_Handle *mq, void *impl_state)
{
  struct ReceiverAddress *receiver = impl_state;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Default MQ destroyed\n");
  if (mq == receiver->d_mq)
  {
    receiver->d_mq = NULL;
    if (GNUNET_YES != receiver->receiver_destroy_called)
      receiver_destroy (receiver);
  }
}
 
 
static void
mq_destroy_kx (struct GNUNET_MQ_Handle *mq, void *impl_state)
{
  struct ReceiverAddress *receiver = impl_state;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "KX MQ destroyed\n");
  if (mq == receiver->kx_mq)
  {
    receiver->kx_mq = NULL;
    if (GNUNET_YES != receiver->receiver_destroy_called)
      receiver_destroy (receiver);
  }
}
 
 
static void
mq_cancel (struct GNUNET_MQ_Handle *mq, void *impl_state)
{
  /* Cancellation is impossible with UDP; bail */
  GNUNET_assert (0);
}
 
 
static void
mq_error (void *cls, enum GNUNET_MQ_Error error)
{
  struct ReceiverAddress *receiver = cls;
 
  GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
              "MQ error in queue to %s: %d\n",
              GNUNET_i2s (&receiver->target),
              (int) error);
  receiver_destroy (receiver);
}
 
 
static void
setup_receiver_mq (struct ReceiverAddress *receiver)
{
  size_t base_mtu;
 
  /*if (NULL != receiver->kx_qh)
    {
    GNUNET_TRANSPORT_communicator_mq_del (receiver->kx_qh);
    receiver->kx_qh = NULL;
    }
    if (NULL != receiver->d_qh)
    {
    GNUNET_TRANSPORT_communicator_mq_del (receiver->d_qh);
    receiver->d_qh = NULL;
    }*/
  // GNUNET_assert (NULL == receiver->mq);
  switch (receiver->address->sa_family)
  {
  case AF_INET:
    base_mtu = 1480     /* Ethernet MTU, 1500 - Ethernet header - VLAN tag */
               - sizeof(struct GNUNET_TUN_IPv4Header) /* 20 */
               - sizeof(struct GNUNET_TUN_UdpHeader) /* 8 */;
    break;
 
  case AF_INET6:
    base_mtu = 1280     /* Minimum MTU required by IPv6 */
               - sizeof(struct GNUNET_TUN_IPv6Header) /* 40 */
               - sizeof(struct GNUNET_TUN_UdpHeader) /* 8 */;
    break;
 
  default:
    GNUNET_assert (0);
    break;
  }
  /* MTU based on full KX messages */
  receiver->kx_mtu = base_mtu - sizeof(struct InitialKX)   /* 48 */
                     - sizeof(struct UDPConfirmation); /* 104 */
  /* MTU based on BOXed messages */
  receiver->d_mtu = base_mtu - sizeof(struct UDPBox);
 
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Setting up MQs and QHs\n");
  /* => Effective MTU for CORE will range from 1080 (IPv6 + KX) to
     1404 (IPv4 + Box) bytes, depending on circumstances... */
  if (NULL == receiver->kx_mq)
    receiver->kx_mq = GNUNET_MQ_queue_for_callbacks (&mq_send_kx,
                                                     &mq_destroy_kx,
                                                     &mq_cancel,
                                                     receiver,
                                                     NULL,
                                                     &mq_error,
                                                     receiver);
  if (NULL == receiver->d_mq)
    receiver->d_mq = GNUNET_MQ_queue_for_callbacks (&mq_send_d,
                                                    &mq_destroy_d,
                                                    &mq_cancel,
                                                    receiver,
                                                    NULL,
                                                    &mq_error,
                                                    receiver);
 
  receiver->kx_qh =
    GNUNET_TRANSPORT_communicator_mq_add (ch,
                                          &receiver->target,
                                          receiver->foreign_addr,
                                          receiver->kx_mtu,
                                          GNUNET_TRANSPORT_QUEUE_LENGTH_UNLIMITED,
                                          0, /* Priority */
                                          receiver->nt,
                                          GNUNET_TRANSPORT_CS_OUTBOUND,
                                          receiver->kx_mq);
}
 
 
static int
mq_init (void *cls, const struct GNUNET_PeerIdentity *peer, const char *address)
{
  struct ReceiverAddress *receiver;
  const char *path;
  struct sockaddr *in;
  socklen_t in_len;
 
  if (0 != strncmp (address,
                    COMMUNICATOR_ADDRESS_PREFIX "-",
                    strlen (COMMUNICATOR_ADDRESS_PREFIX "-")))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  path = &address[strlen (COMMUNICATOR_ADDRESS_PREFIX "-")];
  in = udp_address_to_sockaddr (path, &in_len);
 
  receiver = GNUNET_new (struct ReceiverAddress);
  receiver->address = in;
  receiver->address_len = in_len;
  receiver->target = *peer;
  receiver->nt = GNUNET_NT_scanner_get_type (is, in, in_len);
  (void) GNUNET_CONTAINER_multipeermap_put (
    receivers,
    &receiver->target,
    receiver,
    GNUNET_CONTAINER_MULTIHASHMAPOPTION_MULTIPLE);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Added %s to receivers\n",
              GNUNET_i2s_full (&receiver->target));
  receiver->timeout =
    GNUNET_TIME_relative_to_absolute (GNUNET_CONSTANTS_IDLE_CONNECTION_TIMEOUT);
  receiver->hn = GNUNET_CONTAINER_heap_insert (receivers_heap,
                                               receiver,
                                               receiver->timeout.abs_value_us);
  GNUNET_STATISTICS_set (stats,
                         "# receivers active",
                         GNUNET_CONTAINER_multipeermap_size (receivers),
                         GNUNET_NO);
  receiver->foreign_addr =
    sockaddr_to_udpaddr_string (receiver->address, receiver->address_len);
  setup_receiver_mq (receiver);
  if (NULL == timeout_task)
    timeout_task = GNUNET_SCHEDULER_add_now (&check_timeouts, NULL);
  return GNUNET_OK;
}
 
 
static int
get_receiver_delete_it (void *cls,
                        const struct GNUNET_PeerIdentity *target,
                        void *value)
{
  struct ReceiverAddress *receiver = value;
 
  (void) cls;
  (void) target;
  receiver_destroy (receiver);
  return GNUNET_OK;
}
 
 
static int
get_sender_delete_it (void *cls,
                      const struct GNUNET_PeerIdentity *target,
                      void *value)
{
  struct SenderAddress *sender = value;
 
  (void) cls;
  (void) target;
 
  if (NULL != sender->kce_task_rekey)
  {
    GNUNET_SCHEDULER_cancel (sender->kce_task_rekey);
    sender->kce_task_rekey = NULL;
  }
  if (NULL != sender->kce_task)
  {
    GNUNET_SCHEDULER_cancel (sender->kce_task);
    sender->kce_task = NULL;
  }
 
  sender_destroy (sender);
  return GNUNET_OK;
}
 
 
static void
do_shutdown (void *cls)
{
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "do_shutdown\n");
  if (NULL != nat)
  {
    GNUNET_NAT_unregister (nat);
    nat = NULL;
  }
  while (NULL != bi_head)
    bi_destroy (bi_head);
  if (NULL != broadcast_task)
  {
    GNUNET_SCHEDULER_cancel (broadcast_task);
    broadcast_task = NULL;
  }
  if (NULL != timeout_task)
  {
    GNUNET_SCHEDULER_cancel (timeout_task);
    timeout_task = NULL;
  }
  if (NULL != read_task)
  {
    GNUNET_SCHEDULER_cancel (read_task);
    read_task = NULL;
  }
  if (NULL != udp_sock)
  {
    GNUNET_break (GNUNET_OK ==
                  GNUNET_NETWORK_socket_close (udp_sock));
    udp_sock = NULL;
  }
  GNUNET_CONTAINER_multipeermap_iterate (receivers,
                                         &get_receiver_delete_it,
                                         NULL);
  GNUNET_CONTAINER_multipeermap_destroy (receivers);
  GNUNET_CONTAINER_multipeermap_iterate (senders,
                                         &get_sender_delete_it,
                                         NULL);
  GNUNET_CONTAINER_multipeermap_destroy (senders);
  GNUNET_CONTAINER_multishortmap_destroy (key_cache);
  GNUNET_CONTAINER_heap_destroy (senders_heap);
  GNUNET_CONTAINER_heap_destroy (receivers_heap);
  if (NULL != timeout_task)
  {
    GNUNET_SCHEDULER_cancel (timeout_task);
    timeout_task = NULL;
  }
  if (NULL != ch)
  {
    GNUNET_TRANSPORT_communicator_disconnect (ch);
    ch = NULL;
  }
  if (NULL != ah)
  {
    GNUNET_TRANSPORT_application_done (ah);
    ah = NULL;
  }
  if (NULL != stats)
  {
    GNUNET_STATISTICS_destroy (stats, GNUNET_NO);
    stats = NULL;
  }
  if (NULL != my_private_key)
  {
    GNUNET_free (my_private_key);
    my_private_key = NULL;
  }
  if (NULL != is)
  {
    GNUNET_NT_scanner_done (is);
    is = NULL;
  }
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "do_shutdown finished\n");
}
 
 
static void
enc_notify_cb (void *cls,
               const struct GNUNET_PeerIdentity *sender,
               const struct GNUNET_MessageHeader *msg)
{
  const struct UDPAck *ack;
 
  (void) cls;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Storing UDPAck received from backchannel from %s\n",
              GNUNET_i2s_full (sender));
  if ((ntohs (msg->type) != GNUNET_MESSAGE_TYPE_COMMUNICATOR_UDP_ACK) ||
      (ntohs (msg->size) != sizeof(struct UDPAck)))
  {
    GNUNET_break_op (0);
    return;
  }
  ack = (const struct UDPAck *) msg;
  GNUNET_CONTAINER_multipeermap_get_multiple (receivers,
                                              sender,
                                              &handle_ack,
                                              (void *) ack);
}
 
 
static void
nat_address_cb (void *cls,
                void **app_ctx,
                int add_remove,
                enum GNUNET_NAT_AddressClass ac,
                const struct sockaddr *addr,
                socklen_t addrlen)
{
  char *my_addr;
  struct GNUNET_TRANSPORT_AddressIdentifier *ai;
 
  if (GNUNET_YES == add_remove)
  {
    enum GNUNET_NetworkType nt;
 
    GNUNET_asprintf (&my_addr,
                     "%s-%s",
                     COMMUNICATOR_ADDRESS_PREFIX,
                     GNUNET_a2s (addr, addrlen));
    nt = GNUNET_NT_scanner_get_type (is, addr, addrlen);
    ai =
      GNUNET_TRANSPORT_communicator_address_add (ch,
                                                 my_addr,
                                                 nt,
                                                 GNUNET_TIME_UNIT_FOREVER_REL);
    GNUNET_free (my_addr);
    *app_ctx = ai;
  }
  else
  {
    ai = *app_ctx;
    GNUNET_TRANSPORT_communicator_address_remove (ai);
    *app_ctx = NULL;
  }
}
 
 
static void
ifc_broadcast (void *cls)
{
  struct BroadcastInterface *bi = cls;
  struct GNUNET_TIME_Relative delay;
 
  delay = BROADCAST_FREQUENCY;
  delay.rel_value_us =
    GNUNET_CRYPTO_random_u64 (GNUNET_CRYPTO_QUALITY_WEAK, delay.rel_value_us);
  bi->broadcast_task =
    GNUNET_SCHEDULER_add_delayed (delay, &ifc_broadcast, bi);
 
  switch (bi->sa->sa_family)
  {
  case AF_INET: {
      static int yes = 1;
      static int no = 0;
      ssize_t sent;
 
      if (GNUNET_OK !=
          GNUNET_NETWORK_socket_setsockopt (udp_sock,
                                            SOL_SOCKET,
                                            SO_BROADCAST,
                                            &yes,
                                            sizeof(int)))
        GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
                             "setsockopt");
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "creating UDPBroadcast from %s\n",
                  GNUNET_i2s (&(bi->bcm.sender)));
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "sending UDPBroadcast to add %s\n",
                  GNUNET_a2s (bi->ba, bi->salen));
      sent = GNUNET_NETWORK_socket_sendto (udp_sock,
                                           &bi->bcm,
                                           sizeof(bi->bcm),
                                           bi->ba,
                                           bi->salen);
      if (-1 == sent)
        GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
                             "sendto");
      if (GNUNET_OK != GNUNET_NETWORK_socket_setsockopt (udp_sock,
                                                         SOL_SOCKET,
                                                         SO_BROADCAST,
                                                         &no,
                                                         sizeof(int)))
        GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
                             "setsockopt");
      break;
    }
 
  case AF_INET6: {
      ssize_t sent;
      struct sockaddr_in6 dst;
 
      dst.sin6_family = AF_INET6;
      dst.sin6_port = htons (my_port);
      dst.sin6_addr = bi->mcreq.ipv6mr_multiaddr;
      dst.sin6_scope_id = ((struct sockaddr_in6 *) bi->ba)->sin6_scope_id;
 
      GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                  "sending UDPBroadcast\n");
      sent = GNUNET_NETWORK_socket_sendto (udp_sock,
                                           &bi->bcm,
                                           sizeof(bi->bcm),
                                           (const struct sockaddr *) &dst,
                                           sizeof(dst));
      if (-1 == sent)
        GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "sendto");
      break;
    }
 
  default:
    GNUNET_break (0);
    break;
  }
}
 
 
static int
iface_proc (void *cls,
            const char *name,
            int isDefault,
            const struct sockaddr *addr,
            const struct sockaddr *broadcast_addr,
            const struct sockaddr *netmask,
            socklen_t addrlen)
{
  struct BroadcastInterface *bi;
  enum GNUNET_NetworkType network;
  struct UdpBroadcastSignature ubs;
 
  (void) cls;
  (void) netmask;
  if (NULL == addr)
    return GNUNET_YES; /* need to know our address! */
  network = GNUNET_NT_scanner_get_type (is, addr, addrlen);
  if (GNUNET_NT_LOOPBACK == network)
  {
    /* Broadcasting on loopback does not make sense */
    return GNUNET_YES;
  }
  for (bi = bi_head; NULL != bi; bi = bi->next)
  {
    if ((bi->salen == addrlen) && (0 == memcmp (addr, bi->sa, addrlen)))
    {
      bi->found = GNUNET_YES;
      return GNUNET_OK;
    }
  }
 
  if ((AF_INET6 == addr->sa_family) && (NULL == broadcast_addr))
    return GNUNET_OK; /* broadcast_addr is required for IPv6! */
  if ((AF_INET6 == addr->sa_family) && (GNUNET_YES != have_v6_socket))
    return GNUNET_OK; /* not using IPv6 */
 
  bi = GNUNET_new (struct BroadcastInterface);
  bi->sa = GNUNET_memdup (addr,
                          addrlen);
  if ( (NULL != broadcast_addr) &&
       (addrlen == sizeof (struct sockaddr_in)) )
  {
    struct sockaddr_in *ba;
 
    ba = GNUNET_memdup (broadcast_addr,
                        addrlen);
    ba->sin_port = htons (2086); /* always GNUnet port, ignore configuration! */
    bi->ba = (struct sockaddr *) ba;
  }
  bi->salen = addrlen;
  bi->found = GNUNET_YES;
  bi->bcm.sender = my_identity;
  ubs.purpose.purpose = htonl (
    GNUNET_SIGNATURE_PURPOSE_COMMUNICATOR_UDP_BROADCAST);
  ubs.purpose.size = htonl (sizeof(ubs));
  ubs.sender = my_identity;
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "creating UDPBroadcastSignature for %s\n",
              GNUNET_a2s (addr, addrlen));
  GNUNET_CRYPTO_hash (addr, addrlen, &ubs.h_address);
  GNUNET_CRYPTO_eddsa_sign (my_private_key,
                            &ubs,
                            &bi->bcm.sender_sig);
  if (NULL != bi->ba)
  {
    bi->broadcast_task = GNUNET_SCHEDULER_add_now (&ifc_broadcast, bi);
    GNUNET_CONTAINER_DLL_insert (bi_head, bi_tail, bi);
  }
  if ((AF_INET6 == addr->sa_family) && (NULL != broadcast_addr))
  {
    /* Create IPv6 multicast request */
    const struct sockaddr_in6 *s6 =
      (const struct sockaddr_in6 *) broadcast_addr;
 
    GNUNET_assert (
      1 == inet_pton (AF_INET6, "FF05::13B", &bi->mcreq.ipv6mr_multiaddr));
 
    /* http://tools.ietf.org/html/rfc2553#section-5.2:
     *
     * IPV6_JOIN_GROUP
     *
     * Join a multicast group on a specified local interface.  If the
     * interface index is specified as 0, the kernel chooses the local
     * interface.  For example, some kernels look up the multicast
     * group in the normal IPv6 routing table and using the resulting
     * interface; we do this for each interface, so no need to use
     * zero (anymore...).
     */bi->mcreq.ipv6mr_interface = s6->sin6_scope_id;
 
    /* Join the multicast group */
    if (GNUNET_OK != GNUNET_NETWORK_socket_setsockopt (udp_sock,
                                                       IPPROTO_IPV6,
                                                       IPV6_JOIN_GROUP,
                                                       &bi->mcreq,
                                                       sizeof(bi->mcreq)))
    {
      GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING, "setsockopt");
    }
  }
  return GNUNET_OK;
}
 
 
static void
do_broadcast (void *cls)
{
  struct BroadcastInterface *bin;
 
  (void) cls;
  for (struct BroadcastInterface *bi = bi_head; NULL != bi; bi = bi->next)
    bi->found = GNUNET_NO;
  GNUNET_OS_network_interfaces_list (&iface_proc, NULL);
  for (struct BroadcastInterface *bi = bi_head; NULL != bi; bi = bin)
  {
    bin = bi->next;
    if (GNUNET_NO == bi->found)
      bi_destroy (bi);
  }
  broadcast_task = GNUNET_SCHEDULER_add_delayed (INTERFACE_SCAN_FREQUENCY,
                                                 &do_broadcast,
                                                 NULL);
}
 
 
static void
run (void *cls,
     char *const *args,
     const char *cfgfile,
     const struct GNUNET_CONFIGURATION_Handle *c)
{
  char *bindto;
  struct sockaddr *in;
  socklen_t in_len;
  struct sockaddr_storage in_sto;
  socklen_t sto_len;
 
  (void) cls;
  cfg = c;
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_string (cfg,
                                             COMMUNICATOR_CONFIG_SECTION,
                                             "BINDTO",
                                             &bindto))
  {
    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
                               COMMUNICATOR_CONFIG_SECTION,
                               "BINDTO");
    return;
  }
 
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_time (cfg,
                                           COMMUNICATOR_CONFIG_SECTION,
                                           "REKEY_INTERVAL",
                                           &rekey_interval))
    rekey_interval = DEFAULT_REKEY_TIME_INTERVAL;
 
  if (GNUNET_OK !=
      GNUNET_CONFIGURATION_get_value_size (cfg,
                                           COMMUNICATOR_CONFIG_SECTION,
                                           "REKEY_MAX_BYTES",
                                           &rekey_max_bytes))
    rekey_max_bytes = DEFAULT_REKEY_MAX_BYTES;
 
  in = udp_address_to_sockaddr (bindto, &in_len);
  if (NULL == in)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Failed to setup UDP socket address with path `%s'\n",
                bindto);
    GNUNET_free (bindto);
    return;
  }
  udp_sock =
    GNUNET_NETWORK_socket_create (in->sa_family,
                                  SOCK_DGRAM,
                                  IPPROTO_UDP);
  if (NULL == udp_sock)
  {
    GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR, "socket");
    GNUNET_free (in);
    GNUNET_free (bindto);
    return;
  }
  if (AF_INET6 == in->sa_family)
    have_v6_socket = GNUNET_YES;
  if (GNUNET_OK !=
      GNUNET_NETWORK_socket_bind (udp_sock,
                                  in,
                                  in_len))
  {
    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
                              "bind",
                              bindto);
    GNUNET_NETWORK_socket_close (udp_sock);
    udp_sock = NULL;
    GNUNET_free (in);
    GNUNET_free (bindto);
    return;
  }
 
  /* We might have bound to port 0, allowing the OS to figure it out;
     thus, get the real IN-address from the socket */
  sto_len = sizeof(in_sto);
  if (0 != getsockname (GNUNET_NETWORK_get_fd (udp_sock),
                        (struct sockaddr *) &in_sto,
                        &sto_len))
  {
    memcpy (&in_sto, in, in_len);
    sto_len = in_len;
  }
  GNUNET_free (in);
  GNUNET_free (bindto);
  in = (struct sockaddr *) &in_sto;
  in_len = sto_len;
  GNUNET_log_from_nocheck (GNUNET_ERROR_TYPE_DEBUG,
                           "transport",
                           "Bound to `%s'\n",
                           GNUNET_a2s ((const struct sockaddr *) &in_sto,
                                       sto_len));
  switch (in->sa_family)
  {
  case AF_INET:
    my_port = ntohs (((struct sockaddr_in *) in)->sin_port);
    break;
 
  case AF_INET6:
    my_port = ntohs (((struct sockaddr_in6 *) in)->sin6_port);
    break;
 
  default:
    GNUNET_break (0);
    my_port = 0;
  }
  stats = GNUNET_STATISTICS_create ("C-UDP", cfg);
  senders = GNUNET_CONTAINER_multipeermap_create (32, GNUNET_YES);
  receivers = GNUNET_CONTAINER_multipeermap_create (32, GNUNET_YES);
  senders_heap = GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);
  receivers_heap =
    GNUNET_CONTAINER_heap_create (GNUNET_CONTAINER_HEAP_ORDER_MIN);
  key_cache = GNUNET_CONTAINER_multishortmap_create (1024, GNUNET_YES);
  GNUNET_SCHEDULER_add_shutdown (&do_shutdown, NULL);
  is = GNUNET_NT_scanner_init ();
  my_private_key = GNUNET_CRYPTO_eddsa_key_create_from_configuration (cfg);
  if (NULL == my_private_key)
  {
    GNUNET_log (
      GNUNET_ERROR_TYPE_ERROR,
      _ (
        "Transport service is lacking key configuration settings. Exiting.\n"));
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  GNUNET_CRYPTO_eddsa_key_get_public (my_private_key, &my_identity.public_key);
  /* start reading */
  read_task = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
                                             udp_sock,
                                             &sock_read,
                                             NULL);
  ch = GNUNET_TRANSPORT_communicator_connect (cfg,
                                              COMMUNICATOR_CONFIG_SECTION,
                                              COMMUNICATOR_ADDRESS_PREFIX,
                                              GNUNET_TRANSPORT_CC_UNRELIABLE,
                                              &mq_init,
                                              NULL,
                                              &enc_notify_cb,
                                              NULL);
  if (NULL == ch)
  {
    GNUNET_break (0);
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  ah = GNUNET_TRANSPORT_application_init (cfg);
  if (NULL == ah)
  {
    GNUNET_break (0);
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
  /* start broadcasting */
  if (GNUNET_YES !=
      GNUNET_CONFIGURATION_get_value_yesno (cfg,
                                            COMMUNICATOR_CONFIG_SECTION,
                                            "DISABLE_BROADCAST"))
  {
    broadcast_task = GNUNET_SCHEDULER_add_now (&do_broadcast, NULL);
  }
  nat = GNUNET_NAT_register (cfg,
                             COMMUNICATOR_CONFIG_SECTION,
                             IPPROTO_UDP,
                             1 /* one address */,
                             (const struct sockaddr **) &in,
                             &in_len,
                             &nat_address_cb,
                             NULL /* FIXME: support reversal: #5529 */,
                             NULL /* closure */);
}
 
 
int
main (int argc, char *const *argv)
{
  static const struct GNUNET_GETOPT_CommandLineOption options[] = {
    GNUNET_GETOPT_OPTION_END
  };
  int ret;
 
  GNUNET_log_from_nocheck (GNUNET_ERROR_TYPE_DEBUG,
                           "transport",
                           "Starting udp communicator\n");
  if (GNUNET_OK != GNUNET_STRINGS_get_utf8_args (argc, argv, &argc, &argv))
    return 2;
 
  ret = (GNUNET_OK == GNUNET_PROGRAM_run (argc,
                                          argv,
                                          "gnunet-communicator-udp",
                                          _ ("GNUnet UDP communicator"),
                                          options,
                                          &run,
                                          NULL))
        ? 0
        : 1;
  GNUNET_free_nz ((void *) argv);
  return ret;
}
 
 
/* end of gnunet-communicator-udp.c */