gnunet-service-scalarproduct_alice.c

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/*
     This file is part of GNUnet.
     Copyright (C) 2013, 2014, 2017 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 <limits.h>
#include <gcrypt.h>
#include "gnunet_util_lib.h"
#include "gnunet_core_service.h"
#include "gnunet_cadet_service.h"
#include "gnunet_applications.h"
#include "gnunet_protocols.h"
#include "gnunet_scalarproduct_service.h"
#include "gnunet_set_service.h"
#include "scalarproduct.h"
#include "gnunet-service-scalarproduct.h"

#define LOG(kind, ...) \
  GNUNET_log_from (kind, "scalarproduct-alice", __VA_ARGS__)

struct MpiElement
{
  const struct GNUNET_HashCode *key;

  gcry_mpi_t value;
};


struct AliceServiceSession
{
  struct GNUNET_HashCode session_id;

  struct GNUNET_PeerIdentity peer;

  struct GNUNET_SERVICE_Client *client;

  struct GNUNET_MQ_Handle *client_mq;

  struct GNUNET_MQ_Handle *cadet_mq;

  struct GNUNET_CONTAINER_MultiHashMap *intersected_elements;

  struct GNUNET_SET_Handle *intersection_set;

  struct GNUNET_SET_OperationHandle *intersection_op;

  struct GNUNET_SET_ListenHandle *intersection_listen;

  struct GNUNET_CADET_Channel *channel;

  struct MpiElement *sorted_elements;

  struct GNUNET_CRYPTO_PaillierCiphertext *r;

  struct GNUNET_CRYPTO_PaillierCiphertext *r_prime;

  struct GNUNET_CRYPTO_PaillierCiphertext s;

  struct GNUNET_CRYPTO_PaillierCiphertext s_prime;

  gcry_mpi_t product;

  uint32_t total;

  uint32_t used_element_count;

  uint32_t client_received_element_count;

  uint32_t cadet_received_element_count;

  enum GNUNET_SCALARPRODUCT_ResponseStatus status;

  int in_destroy;
};


static const struct GNUNET_CONFIGURATION_Handle *cfg;

static struct GNUNET_CRYPTO_PaillierPublicKey my_pubkey;

static struct GNUNET_CRYPTO_PaillierPrivateKey my_privkey;

static gcry_mpi_t my_offset;

static struct GNUNET_CADET_Handle *my_cadet;


static int
free_element_cb (void *cls, const struct GNUNET_HashCode *key, void *value)
{
  struct GNUNET_SCALARPRODUCT_Element *e = value;

  GNUNET_free (e);
  return GNUNET_OK;
}


static void
destroy_service_session (struct AliceServiceSession *s)
{
  if (GNUNET_YES == s->in_destroy)
    return;
  s->in_destroy = GNUNET_YES;
  if (NULL != s->client)
  {
    struct GNUNET_SERVICE_Client *c = s->client;

    s->client = NULL;
    GNUNET_SERVICE_client_drop (c);
  }
  if (NULL != s->channel)
  {
    GNUNET_CADET_channel_destroy (s->channel);
    s->channel = NULL;
  }
  if (NULL != s->intersected_elements)
  {
    GNUNET_CONTAINER_multihashmap_iterate (s->intersected_elements,
                                           &free_element_cb,
                                           s);
    GNUNET_CONTAINER_multihashmap_destroy (s->intersected_elements);
    s->intersected_elements = NULL;
  }
  if (NULL != s->intersection_listen)
  {
    GNUNET_SET_listen_cancel (s->intersection_listen);
    s->intersection_listen = NULL;
  }
  if (NULL != s->intersection_op)
  {
    GNUNET_SET_operation_cancel (s->intersection_op);
    s->intersection_op = NULL;
  }
  if (NULL != s->intersection_set)
  {
    GNUNET_SET_destroy (s->intersection_set);
    s->intersection_set = NULL;
  }
  if (NULL != s->sorted_elements)
  {
    for (unsigned int i = 0; i < s->used_element_count; i++)
      gcry_mpi_release (s->sorted_elements[i].value);
    GNUNET_free (s->sorted_elements);
    s->sorted_elements = NULL;
  }
  if (NULL != s->r)
  {
    GNUNET_free (s->r);
    s->r = NULL;
  }
  if (NULL != s->r_prime)
  {
    GNUNET_free (s->r_prime);
    s->r_prime = NULL;
  }
  if (NULL != s->product)
  {
    gcry_mpi_release (s->product);
    s->product = NULL;
  }
  GNUNET_free (s);
}


static void
prepare_client_end_notification (struct AliceServiceSession *session)
{
  struct ClientResponseMessage *msg;
  struct GNUNET_MQ_Envelope *e;

  if (NULL == session->client_mq)
    return; /* no client left to be notified */
  GNUNET_log (
    GNUNET_ERROR_TYPE_DEBUG,
    "Sending session-end notification with status %d to client for session %s\n",
    session->status,
    GNUNET_h2s (&session->session_id));
  e = GNUNET_MQ_msg (msg, GNUNET_MESSAGE_TYPE_SCALARPRODUCT_RESULT);
  msg->product_length = htonl (0);
  msg->status = htonl (session->status);
  GNUNET_MQ_send (session->client_mq, e);
}


static void
transmit_client_response (struct AliceServiceSession *s)
{
  struct ClientResponseMessage *msg;
  struct GNUNET_MQ_Envelope *e;
  unsigned char *product_exported = NULL;
  size_t product_length = 0;
  int32_t range;
  gcry_error_t rc;
  int sign;
  gcry_mpi_t value;

  if (NULL == s->product)
  {
    GNUNET_break (0);
    prepare_client_end_notification (s);
    return;
  }
  value = gcry_mpi_new (0);
  sign = gcry_mpi_cmp_ui (s->product, 0);
  if (0 > sign)
  {
    range = -1;
    gcry_mpi_sub (value, value, s->product);
  }
  else if (0 < sign)
  {
    range = 1;
    gcry_mpi_add (value, value, s->product);
  }
  else
  {
    /* result is exactly zero */
    range = 0;
  }
  gcry_mpi_release (s->product);
  s->product = NULL;

  if ((0 != range) && (0 != (rc = gcry_mpi_aprint (GCRYMPI_FMT_STD,
                                                   &product_exported,
                                                   &product_length,
                                                   value))))
  {
    LOG_GCRY (GNUNET_ERROR_TYPE_ERROR, "gcry_mpi_scan", rc);
    prepare_client_end_notification (s);
    return;
  }
  gcry_mpi_release (value);
  e = GNUNET_MQ_msg_extra (msg,
                           product_length,
                           GNUNET_MESSAGE_TYPE_SCALARPRODUCT_RESULT);
  msg->status = htonl (GNUNET_SCALARPRODUCT_STATUS_SUCCESS);
  msg->range = htonl (range);
  msg->product_length = htonl (product_length);
  if (NULL != product_exported)
  {
    GNUNET_memcpy (&msg[1], product_exported, product_length);
    GNUNET_free (product_exported);
  }
  GNUNET_MQ_send (s->client_mq, e);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Sent result to client, session %s has ended!\n",
              GNUNET_h2s (&s->session_id));
}


static void
cb_channel_destruction (void *cls, const struct GNUNET_CADET_Channel *channel)
{
  struct AliceServiceSession *s = cls;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Peer disconnected, terminating session %s with peer %s\n",
              GNUNET_h2s (&s->session_id),
              GNUNET_i2s (&s->peer));
  if (GNUNET_SCALARPRODUCT_STATUS_ACTIVE == s->status)
  {
    /* We didn't get an answer yet, fail with error */
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    prepare_client_end_notification (s);
  }
  s->channel = NULL;
}


static gcry_mpi_t
compute_square_sum_mpi_elements (const struct MpiElement *vector,
                                 uint32_t length)
{
  gcry_mpi_t elem;
  gcry_mpi_t sum;
  uint32_t i;

  GNUNET_assert (NULL != (sum = gcry_mpi_new (0)));
  GNUNET_assert (NULL != (elem = gcry_mpi_new (0)));
  for (i = 0; i < length; i++)
  {
    gcry_mpi_mul (elem, vector[i].value, vector[i].value);
    gcry_mpi_add (sum, sum, elem);
  }
  gcry_mpi_release (elem);
  return sum;
}


static gcry_mpi_t
compute_square_sum (const gcry_mpi_t *vector, uint32_t length)
{
  gcry_mpi_t elem;
  gcry_mpi_t sum;
  uint32_t i;

  GNUNET_assert (NULL != (sum = gcry_mpi_new (0)));
  GNUNET_assert (NULL != (elem = gcry_mpi_new (0)));
  for (i = 0; i < length; i++)
  {
    gcry_mpi_mul (elem, vector[i], vector[i]);
    gcry_mpi_add (sum, sum, elem);
  }
  gcry_mpi_release (elem);
  return sum;
}


static gcry_mpi_t
compute_scalar_product (struct AliceServiceSession *session)
{
  uint32_t count;
  gcry_mpi_t t;
  gcry_mpi_t u;
  gcry_mpi_t u_prime;
  gcry_mpi_t p;
  gcry_mpi_t p_prime;
  gcry_mpi_t tmp;
  gcry_mpi_t r[session->used_element_count];
  gcry_mpi_t r_prime[session->used_element_count];
  gcry_mpi_t s;
  gcry_mpi_t s_prime;
  unsigned int i;

  count = session->used_element_count;
  // due to the introduced static offset S, we now also have to remove this
  // from the E(a_pi)(+)E(-b_pi-r_pi) and E(a_qi)(+)E(-r_qi) twice each,
  // the result is E((S + a_pi) + (S -b_pi-r_pi)) and E(S + a_qi + S - r_qi)
  for (i = 0; i < count; i++)
  {
    r[i] = gcry_mpi_new (0);
    GNUNET_CRYPTO_paillier_decrypt (&my_privkey,
                                    &my_pubkey,
                                    &session->r[i],
                                    r[i]);
    gcry_mpi_sub (r[i], r[i], my_offset);
    gcry_mpi_sub (r[i], r[i], my_offset);
    r_prime[i] = gcry_mpi_new (0);
    GNUNET_CRYPTO_paillier_decrypt (&my_privkey,
                                    &my_pubkey,
                                    &session->r_prime[i],
                                    r_prime[i]);
    gcry_mpi_sub (r_prime[i], r_prime[i], my_offset);
    gcry_mpi_sub (r_prime[i], r_prime[i], my_offset);
  }

  // calculate t = sum(ai)
  t = compute_square_sum_mpi_elements (session->sorted_elements, count);
  // calculate U
  u = gcry_mpi_new (0);
  tmp = compute_square_sum (r, count);
  gcry_mpi_sub (u, u, tmp);
  gcry_mpi_release (tmp);

  // calculate U'
  u_prime = gcry_mpi_new (0);
  tmp = compute_square_sum (r_prime, count);
  gcry_mpi_sub (u_prime, u_prime, tmp);

  GNUNET_assert (p = gcry_mpi_new (0));
  GNUNET_assert (p_prime = gcry_mpi_new (0));
  GNUNET_assert (s = gcry_mpi_new (0));
  GNUNET_assert (s_prime = gcry_mpi_new (0));

  // compute P
  GNUNET_CRYPTO_paillier_decrypt (&my_privkey, &my_pubkey, &session->s, s);
  GNUNET_CRYPTO_paillier_decrypt (&my_privkey,
                                  &my_pubkey,
                                  &session->s_prime,
                                  s_prime);

  // compute P
  gcry_mpi_add (p, s, t);
  gcry_mpi_add (p, p, u);

  // compute P'
  gcry_mpi_add (p_prime, s_prime, t);
  gcry_mpi_add (p_prime, p_prime, u_prime);

  gcry_mpi_release (t);
  gcry_mpi_release (u);
  gcry_mpi_release (u_prime);
  gcry_mpi_release (s);
  gcry_mpi_release (s_prime);

  // compute product
  gcry_mpi_sub (p, p, p_prime);
  gcry_mpi_release (p_prime);
  tmp = gcry_mpi_set_ui (tmp, 2);
  gcry_mpi_div (p, NULL, p, tmp, 0);

  gcry_mpi_release (tmp);
  for (i = 0; i < count; i++)
  {
    gcry_mpi_release (session->sorted_elements[i].value);
    gcry_mpi_release (r[i]);
    gcry_mpi_release (r_prime[i]);
  }
  GNUNET_free (session->sorted_elements);
  session->sorted_elements = NULL;
  GNUNET_free (session->r);
  session->r = NULL;
  GNUNET_free (session->r_prime);
  session->r_prime = NULL;

  return p;
}


static int
check_bobs_cryptodata_multipart (
  void *cls,
  const struct BobCryptodataMultipartMessage *msg)
{
  struct AliceServiceSession *s = cls;
  uint32_t contained;
  size_t msg_size;
  size_t required_size;

  msg_size = ntohs (msg->header.size);
  contained = ntohl (msg->contained_element_count);
  required_size =
    sizeof(struct BobCryptodataMultipartMessage)
    + 2 * contained * sizeof(struct GNUNET_CRYPTO_PaillierCiphertext);
  if ((required_size != msg_size) ||
      (s->cadet_received_element_count + contained > s->used_element_count))
  {
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
handle_bobs_cryptodata_multipart (
  void *cls,
  const struct BobCryptodataMultipartMessage *msg)
{
  struct AliceServiceSession *s = cls;
  const struct GNUNET_CRYPTO_PaillierCiphertext *payload;
  size_t i;
  uint32_t contained;

  contained = ntohl (msg->contained_element_count);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received %u additional crypto values from Bob\n",
              (unsigned int) contained);

  payload = (const struct GNUNET_CRYPTO_PaillierCiphertext *) &msg[1];
  /* Convert each k[][perm] to its MPI_value */
  for (i = 0; i < contained; i++)
  {
    GNUNET_memcpy (&s->r[s->cadet_received_element_count + i],
                   &payload[2 * i],
                   sizeof(struct GNUNET_CRYPTO_PaillierCiphertext));
    GNUNET_memcpy (&s->r_prime[s->cadet_received_element_count + i],
                   &payload[2 * i],
                   sizeof(struct GNUNET_CRYPTO_PaillierCiphertext));
  }
  s->cadet_received_element_count += contained;
  GNUNET_CADET_receive_done (s->channel);
  if (s->cadet_received_element_count != s->used_element_count)
    return; /* more to come */

  s->product = compute_scalar_product (s);
  transmit_client_response (s);
}


static int
check_bobs_cryptodata_message (void *cls,
                               const struct BobCryptodataMessage *msg)
{
  struct AliceServiceSession *s = cls;
  uint32_t contained;
  uint16_t msg_size;
  size_t required_size;

  msg_size = ntohs (msg->header.size);
  contained = ntohl (msg->contained_element_count);
  required_size =
    sizeof(struct BobCryptodataMessage)
    + 2 * contained * sizeof(struct GNUNET_CRYPTO_PaillierCiphertext)
    + 2 * sizeof(struct GNUNET_CRYPTO_PaillierCiphertext);
  if ((msg_size != required_size) || (contained > UINT16_MAX) ||
      (s->used_element_count < contained))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (NULL == s->sorted_elements)
  {
    /* we're not ready yet, how can Bob be? */
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (s->total != s->client_received_element_count)
  {
    /* we're not ready yet, how can Bob be? */
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
handle_bobs_cryptodata_message (void *cls,
                                const struct BobCryptodataMessage *msg)
{
  struct AliceServiceSession *s = cls;
  const struct GNUNET_CRYPTO_PaillierCiphertext *payload;
  uint32_t i;
  uint32_t contained;

  contained = ntohl (msg->contained_element_count);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Received %u crypto values from Bob\n",
              (unsigned int) contained);
  payload = (const struct GNUNET_CRYPTO_PaillierCiphertext *) &msg[1];
  GNUNET_memcpy (&s->s,
                 &payload[0],
                 sizeof(struct GNUNET_CRYPTO_PaillierCiphertext));
  GNUNET_memcpy (&s->s_prime,
                 &payload[1],
                 sizeof(struct GNUNET_CRYPTO_PaillierCiphertext));
  payload = &payload[2];

  s->r = GNUNET_new_array (s->used_element_count,
                           struct GNUNET_CRYPTO_PaillierCiphertext);
  s->r_prime = GNUNET_new_array (s->used_element_count,
                                 struct GNUNET_CRYPTO_PaillierCiphertext);
  for (i = 0; i < contained; i++)
  {
    GNUNET_memcpy (&s->r[i],
                   &payload[2 * i],
                   sizeof(struct GNUNET_CRYPTO_PaillierCiphertext));
    GNUNET_memcpy (&s->r_prime[i],
                   &payload[2 * i + 1],
                   sizeof(struct GNUNET_CRYPTO_PaillierCiphertext));
  }
  s->cadet_received_element_count = contained;
  GNUNET_CADET_receive_done (s->channel);

  if (s->cadet_received_element_count != s->used_element_count)
  {
    /* More to come */
    return;
  }
  s->product = compute_scalar_product (s);
  transmit_client_response (s);
}


static int
copy_element_cb (void *cls, const struct GNUNET_HashCode *key, void *value)
{
  struct AliceServiceSession *s = cls;
  struct GNUNET_SCALARPRODUCT_Element *e = value;
  gcry_mpi_t mval;
  int64_t val;

  mval = gcry_mpi_new (0);
  val = (int64_t) GNUNET_ntohll (e->value);
  if (0 > val)
    gcry_mpi_sub_ui (mval, mval, -val);
  else
    gcry_mpi_add_ui (mval, mval, val);
  s->sorted_elements[s->used_element_count].value = mval;
  s->sorted_elements[s->used_element_count].key = &e->key;
  s->used_element_count++;
  return GNUNET_OK;
}


static int
element_cmp (const void *a, const void *b)
{
  const struct MpiElement *ma = a;
  const struct MpiElement *mb = b;

  return GNUNET_CRYPTO_hash_cmp (ma->key, mb->key);
}


#define ELEMENT_CAPACITY                          \
  ((GNUNET_CONSTANTS_MAX_CADET_MESSAGE_SIZE - 1   \
    - sizeof(struct AliceCryptodataMessage))       \
   / sizeof(struct GNUNET_CRYPTO_PaillierCiphertext))


static void
send_alices_cryptodata_message (struct AliceServiceSession *s)
{
  struct AliceCryptodataMessage *msg;
  struct GNUNET_MQ_Envelope *e;
  struct GNUNET_CRYPTO_PaillierCiphertext *payload;
  unsigned int i;
  uint32_t todo_count;
  gcry_mpi_t a;
  uint32_t off;

  s->sorted_elements = GNUNET_malloc (
    GNUNET_CONTAINER_multihashmap_size (s->intersected_elements)
    * sizeof(struct MpiElement));
  s->used_element_count = 0;
  GNUNET_CONTAINER_multihashmap_iterate (s->intersected_elements,
                                         &copy_element_cb,
                                         s);
  LOG (GNUNET_ERROR_TYPE_DEBUG,
       "Finished intersection, %d items remain\n",
       s->used_element_count);
  qsort (s->sorted_elements,
         s->used_element_count,
         sizeof(struct MpiElement),
         &element_cmp);
  off = 0;
  while (off < s->used_element_count)
  {
    todo_count = s->used_element_count - off;
    if (todo_count > ELEMENT_CAPACITY)
      todo_count = ELEMENT_CAPACITY;
    GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
                "Sending %u/%u crypto values to Bob\n",
                (unsigned int) todo_count,
                (unsigned int) s->used_element_count);

    e =
      GNUNET_MQ_msg_extra (msg,
                           todo_count
                           * sizeof(struct GNUNET_CRYPTO_PaillierCiphertext),
                           GNUNET_MESSAGE_TYPE_SCALARPRODUCT_ALICE_CRYPTODATA);
    msg->contained_element_count = htonl (todo_count);
    payload = (struct GNUNET_CRYPTO_PaillierCiphertext *) &msg[1];
    a = gcry_mpi_new (0);
    for (i = off; i < off + todo_count; i++)
    {
      gcry_mpi_add (a, s->sorted_elements[i].value, my_offset);
      GNUNET_assert (
        3 ==
        GNUNET_CRYPTO_paillier_encrypt (&my_pubkey, a, 3, &payload[i - off]));
    }
    gcry_mpi_release (a);
    off += todo_count;
    GNUNET_MQ_send (s->cadet_mq, e);
  }
}


static void
cb_intersection_element_removed (void *cls,
                                 const struct GNUNET_SET_Element *element,
                                 uint64_t current_size,
                                 enum GNUNET_SET_Status status)
{
  struct AliceServiceSession *s = cls;
  struct GNUNET_SCALARPRODUCT_Element *se;

  switch (status)
  {
  case GNUNET_SET_STATUS_OK:
    /* this element has been removed from the set */
    se = GNUNET_CONTAINER_multihashmap_get (s->intersected_elements,
                                            element->data);
    GNUNET_assert (NULL != se);
    LOG (GNUNET_ERROR_TYPE_DEBUG,
         "Intersection removed element with key %s and value %lld\n",
         GNUNET_h2s (&se->key),
         (long long) GNUNET_ntohll (se->value));
    GNUNET_assert (
      GNUNET_YES ==
      GNUNET_CONTAINER_multihashmap_remove (s->intersected_elements,
                                            element->data,
                                            se));
    GNUNET_free (se);
    return;

  case GNUNET_SET_STATUS_DONE:
    s->intersection_op = NULL;
    if (NULL != s->intersection_set)
    {
      GNUNET_SET_destroy (s->intersection_set);
      s->intersection_set = NULL;
    }
    send_alices_cryptodata_message (s);
    return;

  case GNUNET_SET_STATUS_HALF_DONE:
    /* unexpected for intersection */
    GNUNET_break (0);
    return;

  case GNUNET_SET_STATUS_FAILURE:
    /* unhandled status code */
    LOG (GNUNET_ERROR_TYPE_DEBUG, "Set intersection failed!\n");
    if (NULL != s->intersection_listen)
    {
      GNUNET_SET_listen_cancel (s->intersection_listen);
      s->intersection_listen = NULL;
    }
    s->intersection_op = NULL;
    if (NULL != s->intersection_set)
    {
      GNUNET_SET_destroy (s->intersection_set);
      s->intersection_set = NULL;
    }
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    prepare_client_end_notification (s);
    return;

  default:
    GNUNET_break (0);
    return;
  }
}


static void
cb_intersection_request_alice (void *cls,
                               const struct GNUNET_PeerIdentity *other_peer,
                               const struct GNUNET_MessageHeader *context_msg,
                               struct GNUNET_SET_Request *request)
{
  struct AliceServiceSession *s = cls;

  if (0 != GNUNET_memcmp (other_peer, &s->peer))
  {
    GNUNET_break_op (0);
    return;
  }
  s->intersection_op = GNUNET_SET_accept (request,
                                          GNUNET_SET_RESULT_REMOVED,
                                          (struct GNUNET_SET_Option[]){ { 0 } },
                                          &cb_intersection_element_removed,
                                          s);
  if (NULL == s->intersection_op)
  {
    GNUNET_break (0);
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    prepare_client_end_notification (s);
    return;
  }
  if (GNUNET_OK != GNUNET_SET_commit (s->intersection_op, s->intersection_set))
  {
    GNUNET_break (0);
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    prepare_client_end_notification (s);
    return;
  }
}


static void
client_request_complete_alice (struct AliceServiceSession *s)
{
  struct GNUNET_MQ_MessageHandler cadet_handlers[] =
  { GNUNET_MQ_hd_var_size (bobs_cryptodata_message,
                           GNUNET_MESSAGE_TYPE_SCALARPRODUCT_BOB_CRYPTODATA,
                           struct BobCryptodataMessage,
                           s),
    GNUNET_MQ_hd_var_size (
      bobs_cryptodata_multipart,
      GNUNET_MESSAGE_TYPE_SCALARPRODUCT_BOB_CRYPTODATA_MULTIPART,
      struct BobCryptodataMultipartMessage,
      s),
    GNUNET_MQ_handler_end () };
  struct ServiceRequestMessage *msg;
  struct GNUNET_MQ_Envelope *e;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Creating new channel for session with key %s.\n",
              GNUNET_h2s (&s->session_id));
  s->channel = GNUNET_CADET_channel_create (my_cadet,
                                            s,
                                            &s->peer,
                                            &s->session_id,
                                            NULL,
                                            &cb_channel_destruction,
                                            cadet_handlers);
  if (NULL == s->channel)
  {
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    prepare_client_end_notification (s);
    return;
  }
  s->cadet_mq = GNUNET_CADET_get_mq (s->channel);
  s->intersection_listen = GNUNET_SET_listen (cfg,
                                              GNUNET_SET_OPERATION_INTERSECTION,
                                              &s->session_id,
                                              &cb_intersection_request_alice,
                                              s);
  if (NULL == s->intersection_listen)
  {
    s->status = GNUNET_SCALARPRODUCT_STATUS_FAILURE;
    GNUNET_CADET_channel_destroy (s->channel);
    s->channel = NULL;
    prepare_client_end_notification (s);
    return;
  }

  e = GNUNET_MQ_msg (msg,
                     GNUNET_MESSAGE_TYPE_SCALARPRODUCT_SESSION_INITIALIZATION);
  msg->session_id = s->session_id;
  msg->public_key = my_pubkey;
  GNUNET_MQ_send (s->cadet_mq, e);
}


static int
check_alice_client_message_multipart (
  void *cls,
  const struct ComputationBobCryptodataMultipartMessage *msg)
{
  struct AliceServiceSession *s = cls;
  uint32_t contained_count;
  uint16_t msize;

  msize = ntohs (msg->header.size);
  contained_count = ntohl (msg->element_count_contained);
  if ((msize !=
       (sizeof(struct ComputationBobCryptodataMultipartMessage)
        + contained_count * sizeof(struct GNUNET_SCALARPRODUCT_Element))) ||
      (0 == contained_count) ||
      (s->total == s->client_received_element_count) ||
      (s->total < s->client_received_element_count + contained_count))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
handle_alice_client_message_multipart (
  void *cls,
  const struct ComputationBobCryptodataMultipartMessage *msg)
{
  struct AliceServiceSession *s = cls;
  uint32_t contained_count;
  const struct GNUNET_SCALARPRODUCT_Element *elements;
  struct GNUNET_SET_Element set_elem;
  struct GNUNET_SCALARPRODUCT_Element *elem;

  contained_count = ntohl (msg->element_count_contained);
  s->client_received_element_count += contained_count;
  elements = (const struct GNUNET_SCALARPRODUCT_Element *) &msg[1];
  for (uint32_t i = 0; i < contained_count; i++)
  {
    elem = GNUNET_new (struct GNUNET_SCALARPRODUCT_Element);
    GNUNET_memcpy (elem,
                   &elements[i],
                   sizeof(struct GNUNET_SCALARPRODUCT_Element));
    if (GNUNET_SYSERR == GNUNET_CONTAINER_multihashmap_put (
          s->intersected_elements,
          &elem->key,
          elem,
          GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY))
    {
      GNUNET_break (0);
      GNUNET_free (elem);
      continue;
    }
    set_elem.data = &elem->key;
    set_elem.size = sizeof(elem->key);
    set_elem.element_type = 0;
    GNUNET_SET_add_element (s->intersection_set, &set_elem, NULL, NULL);
    s->used_element_count++;
  }
  GNUNET_SERVICE_client_continue (s->client);
  if (s->total != s->client_received_element_count)
  {
    /* more to come */
    return;
  }
  client_request_complete_alice (s);
}


static int
check_alice_client_message (void *cls,
                            const struct AliceComputationMessage *msg)
{
  struct AliceServiceSession *s = cls;
  uint16_t msize;
  uint32_t total_count;
  uint32_t contained_count;

  if (NULL != s->intersected_elements)
  {
    /* only one concurrent session per client connection allowed,
       simplifies logic a lot... */
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  msize = ntohs (msg->header.size);
  total_count = ntohl (msg->element_count_total);
  contained_count = ntohl (msg->element_count_contained);
  if ((0 == total_count) || (0 == contained_count) ||
      (msize !=
       (sizeof(struct AliceComputationMessage)
        + contained_count * sizeof(struct GNUNET_SCALARPRODUCT_Element))))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


static void
handle_alice_client_message (void *cls,
                             const struct AliceComputationMessage *msg)
{
  struct AliceServiceSession *s = cls;
  uint32_t contained_count;
  uint32_t total_count;
  const struct GNUNET_SCALARPRODUCT_Element *elements;
  struct GNUNET_SET_Element set_elem;
  struct GNUNET_SCALARPRODUCT_Element *elem;

  total_count = ntohl (msg->element_count_total);
  contained_count = ntohl (msg->element_count_contained);
  s->peer = msg->peer;
  s->status = GNUNET_SCALARPRODUCT_STATUS_ACTIVE;
  s->total = total_count;
  s->client_received_element_count = contained_count;
  s->session_id = msg->session_key;
  elements = (const struct GNUNET_SCALARPRODUCT_Element *) &msg[1];
  s->intersected_elements =
    GNUNET_CONTAINER_multihashmap_create (s->total, GNUNET_YES);
  s->intersection_set =
    GNUNET_SET_create (cfg, GNUNET_SET_OPERATION_INTERSECTION);

  for (uint32_t i = 0; i < contained_count; i++)
  {
    if (0 == GNUNET_ntohll (elements[i].value))
      continue;
    elem = GNUNET_new (struct GNUNET_SCALARPRODUCT_Element);
    GNUNET_memcpy (elem,
                   &elements[i],
                   sizeof(struct GNUNET_SCALARPRODUCT_Element));
    if (GNUNET_SYSERR == GNUNET_CONTAINER_multihashmap_put (
          s->intersected_elements,
          &elem->key,
          elem,
          GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY))
    {
      /* element with same key encountered twice! */
      GNUNET_break (0);
      GNUNET_free (elem);
      continue;
    }
    set_elem.data = &elem->key;
    set_elem.size = sizeof(elem->key);
    set_elem.element_type = 0;
    GNUNET_SET_add_element (s->intersection_set, &set_elem, NULL, NULL);
    s->used_element_count++;
  }
  GNUNET_SERVICE_client_continue (s->client);
  if (s->total != s->client_received_element_count)
  {
    /* wait for multipart msg */
    return;
  }
  client_request_complete_alice (s);
}


static void
shutdown_task (void *cls)
{
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG, "Shutting down, initiating cleanup.\n");
  // FIXME: we have to cut our connections to CADET first!
  if (NULL != my_cadet)
  {
    GNUNET_CADET_disconnect (my_cadet);
    my_cadet = NULL;
  }
}


static void *
client_connect_cb (void *cls,
                   struct GNUNET_SERVICE_Client *client,
                   struct GNUNET_MQ_Handle *mq)
{
  struct AliceServiceSession *s;

  s = GNUNET_new (struct AliceServiceSession);
  s->client = client;
  s->client_mq = mq;
  return s;
}


static void
client_disconnect_cb (void *cls,
                      struct GNUNET_SERVICE_Client *client,
                      void *app_cls)
{
  struct AliceServiceSession *s = app_cls;

  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "Client %p disconnected from us.\n",
              client);
  s->client = NULL;
  s->client_mq = NULL;
  destroy_service_session (s);
}


static void
run (void *cls,
     const struct GNUNET_CONFIGURATION_Handle *c,
     struct GNUNET_SERVICE_Handle *service)
{
  cfg = c;
  /*
     offset has to be sufficiently small to allow computation of:
     m1+m2 mod n == (S + a) + (S + b) mod n,
     if we have more complex operations, this factor needs to be lowered */
  my_offset = gcry_mpi_new (GNUNET_CRYPTO_PAILLIER_BITS / 3);
  gcry_mpi_set_bit (my_offset, GNUNET_CRYPTO_PAILLIER_BITS / 3);
  GNUNET_CRYPTO_paillier_create (&my_pubkey, &my_privkey);
  my_cadet = GNUNET_CADET_connect (cfg);
  GNUNET_SCHEDULER_add_shutdown (&shutdown_task, NULL);
  if (NULL == my_cadet)
  {
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR, _ ("Connect to CADET failed\n"));
    GNUNET_SCHEDULER_shutdown ();
    return;
  }
}


GNUNET_SERVICE_MAIN (
  "scalarproduct-alice",
  GNUNET_SERVICE_OPTION_NONE,
  &run,
  &client_connect_cb,
  &client_disconnect_cb,
  NULL,
  GNUNET_MQ_hd_var_size (alice_client_message,
                         GNUNET_MESSAGE_TYPE_SCALARPRODUCT_CLIENT_TO_ALICE,
                         struct AliceComputationMessage,
                         NULL),
  GNUNET_MQ_hd_var_size (
    alice_client_message_multipart,
    GNUNET_MESSAGE_TYPE_SCALARPRODUCT_CLIENT_MULTIPART_ALICE,
    struct ComputationBobCryptodataMultipartMessage,
    NULL),
  GNUNET_MQ_handler_end ());


/* end of gnunet-service-scalarproduct_alice.c */