massive rework of scalarproduct service, splitting into Alice and Bob

1 files changed, 1490 insertions, 0 deletions

diff --git a/src/scalarproduct/gnunet-service-scalarproduct_bob.c b/src/scalarproduct/gnunet-service-scalarproduct_bob.c
new file mode 100644
index 000000000..ee74b515a
--- /dev/null
+++ b/src/scalarproduct/gnunet-service-scalarproduct_bob.c
@@ -0,0 +1,1490 @@
+/*
+     This file is part of GNUnet.
+     (C) 2013, 2014 Christian Grothoff (and other contributing authors)
+
+     GNUnet is free software; you can redistribute it and/or modify
+     it under the terms of the GNU General Public License as published
+     by the Free Software Foundation; either version 3, 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
+     General Public License for more details.
+
+     You should have received a copy of the GNU General Public License
+     along with GNUnet; see the file COPYING.  If not, write to the
+     Free Software Foundation, Inc., 59 Temple Place - Suite 330,
+     Boston, MA 02111-1307, USA.
+ */
+/**
+ * @file scalarproduct/gnunet-service-scalarproduct_bob.c
+ * @brief scalarproduct service implementation
+ * @author Christian M. Fuchs
+ * @author Christian Grothoff
+ */
+#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-bob", __VA_ARGS__)
+
+
+/**
+ * An encrypted element key-value pair.
+ */
+struct MpiElement
+{
+  /**
+   * Key used to identify matching pairs of values to multiply.
+   * Points into an existing data structure, to avoid copying
+   * and doubling memory use.
+   */
+  const struct GNUNET_HashCode *key;
+
+  /**
+   * Value represented (a).
+   */
+  gcry_mpi_t value;
+};
+
+
+/**
+ * An incoming session from CADET.
+ */
+struct CadetIncomingSession;
+
+
+/**
+ * A scalarproduct session which tracks an offer for a
+ * multiplication service by a local client.
+ */
+struct BobServiceSession
+{
+
+  /**
+   * (hopefully) unique transaction ID
+   */
+  struct GNUNET_HashCode session_id;
+
+  /**
+   * The client this request is related to.
+   */
+  struct GNUNET_SERVER_Client *client;
+
+  /**
+   * Client message queue.
+   */
+  struct GNUNET_MQ_Handle *client_mq;
+
+  /**
+   * All non-0-value'd elements transmitted to us.
+   */
+  struct GNUNET_CONTAINER_MultiHashMap *intersected_elements;
+
+  /**
+   * Set of elements for which we will be conducting an intersection.
+   * The resulting elements are then used for computing the scalar product.
+   */
+  struct GNUNET_SET_Handle *intersection_set;
+
+  /**
+   * Set of elements for which will conduction an intersection.
+   * the resulting elements are then used for computing the scalar product.
+   */
+  struct GNUNET_SET_OperationHandle *intersection_op;
+
+  /**
+   * a(Alice)
+   */
+  struct MpiElement *sorted_elements;
+
+  /**
+   * E(ai)(Bob) after applying the mask
+   */
+  struct GNUNET_CRYPTO_PaillierCiphertext *e_a;
+
+  /**
+   * Bob's permutation p of R
+   */
+  struct GNUNET_CRYPTO_PaillierCiphertext *r;
+
+  /**
+   * Bob's permutation q of R
+   */
+  struct GNUNET_CRYPTO_PaillierCiphertext *r_prime;
+
+  /**
+   * Bob's "s"
+   */
+  struct GNUNET_CRYPTO_PaillierCiphertext s;
+
+  /**
+   * Bob's "s'"
+   */
+  struct GNUNET_CRYPTO_PaillierCiphertext s_prime;
+
+  /**
+   * Handle for our associated incoming CADET session, or NULL
+   * if we have not gotten one yet.
+   */
+  struct CadetIncomingSession *cadet;
+
+  /**
+   * The computed scalar
+   */
+  gcry_mpi_t product;
+
+  /**
+   * How many elements we were supplied with from the client
+   */
+  uint32_t total;
+
+  /**
+   * how many elements actually are used for the scalar product.
+   * Size of the arrays in @e r and @e r_prime.
+   */
+  uint32_t used_element_count;
+
+  /**
+   * already transferred elements (sent/received) for multipart messages, less or equal than @e used_element_count for
+   */
+  uint32_t transferred_element_count;
+
+  /**
+   * Is this session active (#GNUNET_YES), Concluded (#GNUNET_NO), or had an error (#GNUNET_SYSERR)
+   */
+  int32_t active;
+
+  /**
+   * Are we already in #destroy_service_session()?
+   */
+  int in_destroy;
+
+};
+
+
+/**
+ * An incoming session from CADET.
+ */
+struct CadetIncomingSession
+{
+
+  /**
+   * Associated client session, or NULL.
+   */
+  struct BobServiceSession *s;
+
+  /**
+   * The CADET channel.
+   */
+  struct GNUNET_CADET_Channel *channel;
+
+  /**
+   * Originator's peer identity. (Only for diagnostics.)
+   */
+  struct GNUNET_PeerIdentity peer;
+
+  /**
+   * (hopefully) unique transaction ID
+   */
+  struct GNUNET_HashCode session_id;
+
+  /**
+   * Public key of the remote service.
+   */
+  struct GNUNET_CRYPTO_PaillierPublicKey remote_pubkey;
+
+  /**
+   * The message queue for this channel.
+   */
+  struct GNUNET_MQ_Handle *cadet_mq;
+
+  /**
+   * Has this CADET session been added to the map yet?
+   * #GNUNET_YES if so, in which case @e session_id is
+   * the key.
+   */
+  int in_map;
+
+  /**
+   * Are we already in #destroy_cadet_session()?
+   */
+  int in_destroy;
+
+};
+
+
+/**
+ * GNUnet configuration handle
+ */
+static const struct GNUNET_CONFIGURATION_Handle *cfg;
+
+/**
+ * Service's own public key
+ */
+static struct GNUNET_CRYPTO_PaillierPublicKey my_pubkey;
+
+/**
+ * Service's own private key
+ */
+static struct GNUNET_CRYPTO_PaillierPrivateKey my_privkey;
+
+/**
+ * Service's offset for values that could possibly be negative but are plaintext for encryption.
+ */
+static gcry_mpi_t my_offset;
+
+/**
+ * Map of `struct BobServiceSession`, by session keys.
+ */
+static struct GNUNET_CONTAINER_MultiHashMap *client_sessions;
+
+/**
+ * Map of `struct CadetIncomingSession`, by session keys.
+ */
+static struct GNUNET_CONTAINER_MultiHashMap *cadet_sessions;
+
+/**
+ * Handle to the CADET service.
+ */
+static struct GNUNET_CADET_Handle *my_cadet;
+
+/**
+ * Certain events (callbacks for server & cadet operations) must not
+ * be queued after shutdown.
+ */
+static int do_shutdown;
+
+
+
+/**
+ * Finds a not terminated client session in the respective map based on
+ * session key.
+ *
+ * @param key the session key we want to search for
+ * @return the matching session, or NULL for none
+ */
+static struct BobServiceSession *
+find_matching_client_session (const struct GNUNET_HashCode *key)
+{
+  return GNUNET_CONTAINER_multihashmap_get (client_sessions,
+                                            key);
+}
+
+
+/**
+ * Finds a CADET session in the respective map based on session key.
+ *
+ * @param key the session key we want to search for
+ * @return the matching session, or NULL for none
+ */
+static struct CadetIncomingSession *
+find_matching_cadet_session (const struct GNUNET_HashCode *key)
+{
+  return GNUNET_CONTAINER_multihashmap_get (cadet_sessions,
+                                            key);
+}
+
+
+/**
+ * Destroy session state, we are done with it.
+ *
+ * @param session the session to free elements from
+ */
+static void
+destroy_cadet_session (struct CadetIncomingSession *s);
+
+
+/**
+ * Destroy session state, we are done with it.
+ *
+ * @param session the session to free elements from
+ */
+static void
+destroy_service_session (struct BobServiceSession *s)
+{
+  struct CadetIncomingSession *in;
+  unsigned int i;
+
+  if (GNUNET_YES == s->in_destroy)
+    return;
+  s->in_destroy = GNUNET_YES;
+  if (NULL != (in = s->cadet))
+  {
+    s->cadet = NULL;
+    destroy_cadet_session (in);
+  }
+  if (NULL != s->client_mq)
+  {
+    GNUNET_MQ_destroy (s->client_mq);
+    s->client_mq = NULL;
+  }
+  if (NULL != s->client)
+  {
+    GNUNET_SERVER_client_disconnect (s->client);
+    s->client = NULL;
+  }
+  GNUNET_assert (GNUNET_YES ==
+                 GNUNET_CONTAINER_multihashmap_remove (client_sessions,
+                                                       &s->session_id,
+                                                       s));
+  if (NULL != s->intersected_elements)
+  {
+    /* FIXME: free elements */
+    GNUNET_CONTAINER_multihashmap_destroy (s->intersected_elements);
+    s->intersected_elements = 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->e_a)
+  {
+    GNUNET_free (s->e_a);
+    s->e_a = NULL;
+  }
+  if (NULL != s->sorted_elements)
+  {
+    for (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);
+}
+
+
+/**
+ * Destroy incoming CADET session state, we are done with it.
+ *
+ * @param in the session to free elements from
+ */
+static void
+destroy_cadet_session (struct CadetIncomingSession *in)
+{
+  struct BobServiceSession *s;
+
+  if (GNUNET_YES == in->in_destroy)
+    return;
+  in->in_destroy = GNUNET_YES;
+  if (NULL != (s = in->s))
+  {
+    in->s = NULL;
+    destroy_service_session (s);
+  }
+  if (GNUNET_YES == in->in_map)
+  {
+    GNUNET_assert (GNUNET_YES ==
+                   GNUNET_CONTAINER_multihashmap_remove (cadet_sessions,
+                                                         &in->session_id,
+                                                         in));
+    in->in_map = GNUNET_NO;
+  }
+  if (NULL != in->cadet_mq)
+  {
+    GNUNET_MQ_destroy (in->cadet_mq);
+    in->cadet_mq = NULL;
+  }
+  if (NULL != in->channel)
+  {
+    GNUNET_CADET_channel_destroy (in->channel);
+    in->channel = NULL;
+  }
+  GNUNET_free (in);
+}
+
+
+/**
+ * Notify the client that the session has succeeded or failed.  This
+ * message gets sent to Bob's client if the operation completed or
+ * Alice disconnected.
+ *
+ * @param session the associated client session to fail or succeed
+ */
+static void
+prepare_client_end_notification (struct BobServiceSession *session)
+{
+  struct ClientResponseMessage *msg;
+  struct GNUNET_MQ_Envelope *e;
+
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Sending session-end notification with status %d to client for session %s\n",
+              session->active,
+              GNUNET_h2s (&session->session_id));
+  e = GNUNET_MQ_msg (msg,
+                     GNUNET_MESSAGE_TYPE_SCALARPRODUCT_RESULT);
+  msg->range = 0;
+  msg->product_length = htonl (0);
+  msg->status = htonl (session->active);
+  GNUNET_MQ_send (session->client_mq,
+                  e);
+}
+
+
+/**
+ * Function called whenever a channel is destroyed.  Should clean up
+ * any associated state.
+ *
+ * It must NOT call #GNUNET_CADET_channel_destroy() on the channel.
+ *
+ * @param cls closure (set from #GNUNET_CADET_connect())
+ * @param channel connection to the other end (henceforth invalid)
+ * @param channel_ctx place where local state associated
+ *                   with the channel is stored
+ */
+static void
+cb_channel_destruction (void *cls,
+                        const struct GNUNET_CADET_Channel *channel,
+                        void *channel_ctx)
+{
+  struct CadetIncomingSession *in = channel_ctx;
+  struct BobServiceSession *s;
+
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Peer disconnected, terminating session %s with peer %s\n",
+              GNUNET_h2s (&in->session_id),
+              GNUNET_i2s (&in->peer));
+  in->channel = NULL;
+  if (NULL != (s = in->s))
+  {
+    if (GNUNET_YES == s->active)
+    {
+      s->active = GNUNET_SYSERR;
+      prepare_client_end_notification (s);
+    }
+  }
+  destroy_cadet_session (in);
+}
+
+
+/**
+ * MQ finished giving our last message to CADET, now notify
+ * the client that we are finished.
+ */
+static void
+bob_cadet_done_cb (void *cls)
+{
+  struct BobServiceSession *session = cls;
+
+  session->active = GNUNET_NO; /* that means, done */
+  prepare_client_end_notification (session);
+}
+
+
+/**
+ * Maximum count of elements we can put into a multipart message
+ */
+#define ELEMENT_CAPACITY ((GNUNET_SERVER_MAX_MESSAGE_SIZE - 1 - sizeof (struct MultipartMessage)) / sizeof (struct GNUNET_CRYPTO_PaillierCiphertext))
+
+
+/**
+ * Send a multipart chunk of a service response from Bob to Alice.
+ * This element only contains the two permutations of R, R'.
+ *
+ * @param s the associated service session
+ */
+static void
+transmit_bobs_cryptodata_message_multipart (struct BobServiceSession *s)
+{
+  struct GNUNET_CRYPTO_PaillierCiphertext *payload;
+  struct MultipartMessage *msg;
+  struct GNUNET_MQ_Envelope *e;
+  unsigned int i;
+  unsigned int j;
+  uint32_t todo_count;
+
+  while (s->transferred_element_count != s->used_element_count)
+  {
+    todo_count = s->used_element_count - s->transferred_element_count;
+    if (todo_count > ELEMENT_CAPACITY / 2)
+      todo_count = ELEMENT_CAPACITY / 2;
+
+    e = GNUNET_MQ_msg_extra (msg,
+                             todo_count * sizeof (struct GNUNET_CRYPTO_PaillierCiphertext) * 2,
+                             GNUNET_MESSAGE_TYPE_SCALARPRODUCT_BOB_CRYPTODATA_MULTIPART);
+    msg->contained_element_count = htonl (todo_count);
+    payload = (struct GNUNET_CRYPTO_PaillierCiphertext *) &msg[1];
+    for (i = s->transferred_element_count, j = 0; i < s->transferred_element_count + todo_count; i++)
+    {
+      //r[i][p] and r[i][q]
+      memcpy (&payload[j++],
+              &s->r[i],
+              sizeof (struct GNUNET_CRYPTO_PaillierCiphertext));
+      memcpy (&payload[j++],
+              &s->r_prime[i],
+              sizeof (struct GNUNET_CRYPTO_PaillierCiphertext));
+    }
+    s->transferred_element_count += todo_count;
+    if (s->transferred_element_count == s->used_element_count)
+      GNUNET_MQ_notify_sent (e,
+                             &bob_cadet_done_cb,
+                             s);
+    GNUNET_MQ_send (s->cadet->cadet_mq,
+                    e);
+  }
+}
+
+
+/**
+ * Bob generates the response message to be sent to Alice after
+ * computing the values (1), (2), S and S'.
+ *
+ *  (1)[]: $E_A(a_{pi(i)}) times E_A(- r_{pi(i)} - b_{pi(i)}) &= E_A(a_{pi(i)} - r_{pi(i)} - b_{pi(i)})$
+ *  (2)[]: $E_A(a_{pi'(i)}) times E_A(- r_{pi'(i)}) &= E_A(a_{pi'(i)} - r_{pi'(i)})$
+ *      S: $S := E_A(sum (r_i + b_i)^2)$
+ *     S': $S' := E_A(sum r_i^2)$
+ *
+ * @param s the associated requesting session with Alice
+ */
+static void
+transmit_bobs_cryptodata_message (struct BobServiceSession *s)
+{
+  struct ServiceResponseMessage *msg;
+  struct GNUNET_MQ_Envelope *e;
+  struct GNUNET_CRYPTO_PaillierCiphertext *payload;
+  unsigned int i;
+
+  s->transferred_element_count = (GNUNET_SERVER_MAX_MESSAGE_SIZE - 1 - sizeof (struct ServiceResponseMessage)) /
+    (sizeof (struct GNUNET_CRYPTO_PaillierCiphertext) * 2) - 2;
+  if (s->transferred_element_count > s->used_element_count)
+    s->transferred_element_count = s->used_element_count;
+
+  e = GNUNET_MQ_msg_extra (msg,
+                           (2 + s->transferred_element_count * 2)
+                           * sizeof (struct GNUNET_CRYPTO_PaillierCiphertext),
+                           GNUNET_MESSAGE_TYPE_SCALARPRODUCT_BOB_CRYPTODATA);
+  msg->total_element_count = htonl (s->total);
+  msg->used_element_count = htonl (s->used_element_count);
+  msg->contained_element_count = htonl (s->transferred_element_count);
+  msg->key = s->session_id;
+
+  payload = (struct GNUNET_CRYPTO_PaillierCiphertext *) &msg[1];
+  memcpy (&payload[0],
+          &s->s,
+          sizeof (struct GNUNET_CRYPTO_PaillierCiphertext));
+  memcpy (&payload[1],
+          &s->s_prime,
+          sizeof (struct GNUNET_CRYPTO_PaillierCiphertext));
+
+  payload = &payload[2];
+  // convert k[][]
+  for (i = 0; i < s->transferred_element_count; i++)
+  {
+    //k[i][p] and k[i][q]
+    memcpy (&payload[i * 2],
+            &s->r[i],
+            sizeof (struct GNUNET_CRYPTO_PaillierCiphertext));
+    memcpy (&payload[i * 2 + 1],
+            &s->r_prime[i],
+            sizeof (struct GNUNET_CRYPTO_PaillierCiphertext));
+  }
+  if (s->transferred_element_count == s->used_element_count)
+    GNUNET_MQ_notify_sent (e,
+                           &bob_cadet_done_cb,
+                           s);
+  GNUNET_MQ_send (s->cadet->cadet_mq,
+                  e);
+  transmit_bobs_cryptodata_message_multipart (s);
+}
+
+
+/**
+ * Computes the square sum over a vector of a given length.
+ *
+ * @param vector the vector to compute over
+ * @param length the length of the vector
+ * @return an MPI value containing the calculated sum, never NULL
+ */
+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;
+}
+
+
+/**
+ * Compute the values
+ *  (1)[]: $E_A(a_{pi(i)}) otimes E_A(- r_{pi(i)} - b_{pi(i)}) &= E_A(a_{pi(i)} - r_{pi(i)} - b_{pi(i)})$
+ *  (2)[]: $E_A(a_{pi'(i)}) otimes E_A(- r_{pi'(i)}) &= E_A(a_{pi'(i)} - r_{pi'(i)})$
+ *      S: $S := E_A(sum (r_i + b_i)^2)$
+ *     S': $S' := E_A(sum r_i^2)$
+ *
+ * @param request the requesting session + bob's requesting peer
+ */
+static void
+compute_service_response (struct BobServiceSession *session)
+{
+  uint32_t i;
+  unsigned int *p;
+  unsigned int *q;
+  uint32_t count;
+  gcry_mpi_t *rand;
+  gcry_mpi_t tmp;
+  const struct MpiElement *b;
+  struct GNUNET_CRYPTO_PaillierCiphertext *a;
+  struct GNUNET_CRYPTO_PaillierCiphertext *r;
+  struct GNUNET_CRYPTO_PaillierCiphertext *r_prime;
+
+  count = session->used_element_count;
+  a = session->e_a;
+  b = session->sorted_elements;
+  q = GNUNET_CRYPTO_random_permute (GNUNET_CRYPTO_QUALITY_WEAK,
+                                    count);
+  p = GNUNET_CRYPTO_random_permute (GNUNET_CRYPTO_QUALITY_WEAK,
+                                    count);
+  rand = GNUNET_malloc (sizeof (gcry_mpi_t) * count);
+  for (i = 0; i < count; i++)
+    GNUNET_assert (NULL != (rand[i] = gcry_mpi_new (0)));
+  r = GNUNET_malloc (sizeof (struct GNUNET_CRYPTO_PaillierCiphertext) * count);
+  r_prime = GNUNET_malloc (sizeof (struct GNUNET_CRYPTO_PaillierCiphertext) * count);
+
+  for (i = 0; i < count; i++)
+  {
+    int32_t svalue;
+
+    svalue = (int32_t) GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK,
+                                                 UINT32_MAX);
+    // long to gcry_mpi_t
+    if (svalue < 0)
+      gcry_mpi_sub_ui (rand[i],
+                       rand[i],
+                       - svalue);
+    else
+      rand[i] = gcry_mpi_set_ui (rand[i], svalue);
+  }
+
+  tmp = gcry_mpi_new (0);
+  // encrypt the element
+  // for the sake of readability I decided to have dedicated permutation
+  // vectors, which get rid of all the lookups in p/q.
+  // however, ap/aq are not absolutely necessary but are just abstraction
+  // Calculate Kp = E(S + a_pi) (+) E(S - r_pi - b_pi)
+  for (i = 0; i < count; i++)
+  {
+    // E(S - r_pi - b_pi)
+    gcry_mpi_sub (tmp, my_offset, rand[p[i]]);
+    gcry_mpi_sub (tmp, tmp, b[p[i]].value);
+    GNUNET_CRYPTO_paillier_encrypt (&session->cadet->remote_pubkey,
+                                    tmp,
+                                    2,
+                                    &r[i]);
+
+    // E(S - r_pi - b_pi) * E(S + a_pi) ==  E(2*S + a - r - b)
+    GNUNET_CRYPTO_paillier_hom_add (&session->cadet->remote_pubkey,
+                                    &r[i],
+                                    &a[p[i]],
+                                    &r[i]);
+  }
+
+  // Calculate Kq = E(S + a_qi) (+) E(S - r_qi)
+  for (i = 0; i < count; i++)
+  {
+    // E(S - r_qi)
+    gcry_mpi_sub (tmp, my_offset, rand[q[i]]);
+    GNUNET_assert (2 == GNUNET_CRYPTO_paillier_encrypt (&session->cadet->remote_pubkey,
+                                                        tmp,
+                                                        2,
+                                                        &r_prime[i]));
+
+    // E(S - r_qi) * E(S + a_qi) == E(2*S + a_qi - r_qi)
+    GNUNET_assert (1 == GNUNET_CRYPTO_paillier_hom_add (&session->cadet->remote_pubkey,
+                                                        &r_prime[i],
+                                                        &a[q[i]],
+                                                        &r_prime[i]));
+  }
+
+  // Calculate S' =  E(SUM( r_i^2 ))
+  tmp = compute_square_sum (rand, count);
+  GNUNET_CRYPTO_paillier_encrypt (&session->cadet->remote_pubkey,
+                                  tmp,
+                                  1,
+                                  &session->s_prime);
+
+  // Calculate S = E(SUM( (r_i + b_i)^2 ))
+  for (i = 0; i < count; i++)
+    gcry_mpi_add (rand[i], rand[i], b[i].value);
+  tmp = compute_square_sum (rand, count);
+  GNUNET_CRYPTO_paillier_encrypt (&session->cadet->remote_pubkey,
+                                  tmp,
+                                  1,
+                                  &session->s);
+
+  session->r = r;
+  session->r_prime = r_prime;
+
+  // release rand, b and a
+  for (i = 0; i < count; i++)
+    gcry_mpi_release (rand[i]);
+  gcry_mpi_release (tmp);
+  GNUNET_free (session->e_a);
+  session->e_a = NULL;
+  GNUNET_free (p);
+  GNUNET_free (q);
+  GNUNET_free (rand);
+
+  // copy the r[], r_prime[], S and Stick into a new message, prepare_service_response frees these
+}
+
+
+
+
+
+/**
+ * Iterator to copy over messages from the hash map
+ * into an array for sorting.
+ *
+ * @param cls the `struct AliceServiceSession *`
+ * @param key the key (unused)
+ * @param value the `struct GNUNET_SCALARPRODUCT_Element *`
+ */
+static int
+copy_element_cb (void *cls,
+                 const struct GNUNET_HashCode *key,
+                 void *value)
+{
+  struct BobServiceSession *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;
+}
+
+
+/**
+ * Compare two `struct MpiValue`s by key for sorting.
+ *
+ * @param a pointer to first `struct MpiValue *`
+ * @param b pointer to first `struct MpiValue *`
+ * @return -1 for a < b, 0 for a=b, 1 for a > b.
+ */
+static int
+element_cmp (const void *a,
+             const void *b)
+{
+  const struct MpiElement *ma = *(const struct MpiElement **) a;
+  const struct MpiElement *mb = *(const struct MpiElement **) b;
+
+  return GNUNET_CRYPTO_hash_cmp (ma->key,
+                                 mb->key);
+}
+
+
+/**
+ * Intersection operation and receiving data via CADET from
+ * Alice are both done, compute and transmit our reply via
+ * CADET.
+ *
+ * @param s session to transmit reply for.
+ */
+static void
+transmit_cryptographic_reply (struct BobServiceSession *s)
+{
+  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->intersected_elements,
+         s->used_element_count,
+         sizeof (struct MpiElement),
+         &element_cmp);
+  compute_service_response (s);
+  transmit_bobs_cryptodata_message (s);
+}
+
+
+/**
+ * Handle a multipart-chunk of a request from another service to
+ * calculate a scalarproduct with us.
+ *
+ * @param cls closure (set from #GNUNET_CADET_connect)
+ * @param channel connection to the other end
+ * @param channel_ctx place to store local state associated with the @a channel
+ * @param message the actual message
+ * @return #GNUNET_OK to keep the connection open,
+ *         #GNUNET_SYSERR to close it (signal serious error)
+ */
+static int
+handle_alices_cryptodata_message (void *cls,
+                                  struct GNUNET_CADET_Channel *channel,
+                                  void **channel_ctx,
+                                  const struct GNUNET_MessageHeader *message)
+{
+  struct CadetIncomingSession *in = *channel_ctx;
+  struct BobServiceSession *s;
+  const struct AliceCryptodataMessage *msg;
+  const struct GNUNET_CRYPTO_PaillierCiphertext *payload;
+  uint32_t contained_elements;
+  size_t msg_length;
+  uint16_t msize;
+  unsigned int max;
+
+  if (NULL == in)
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  s = in->s;
+  if (NULL == s)
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  msize = ntohs (message->size);
+  if (msize <= sizeof (struct AliceCryptodataMessage))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  msg = (const struct AliceCryptodataMessage *) message;
+  contained_elements = ntohl (msg->contained_element_count);
+  /* Our intersection may still be ongoing, but this is nevertheless
+     an upper bound on the required array size */
+  max = GNUNET_CONTAINER_multihashmap_size (s->intersected_elements);
+  msg_length = sizeof (struct AliceCryptodataMessage)
+    + contained_elements * sizeof (struct GNUNET_CRYPTO_PaillierCiphertext);
+  if ( (msize != msg_length) ||
+       (0 == contained_elements) ||
+       (contained_elements > UINT16_MAX) ||
+       (max < contained_elements + s->transferred_element_count) )
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
+  payload = (const struct GNUNET_CRYPTO_PaillierCiphertext *) &msg[1];
+  if (NULL == s->e_a)
+    s->e_a = GNUNET_malloc (sizeof (struct GNUNET_CRYPTO_PaillierCiphertext) *
+                            max);
+  memcpy (&s->e_a[s->transferred_element_count],
+          payload,
+          sizeof (struct GNUNET_CRYPTO_PaillierCiphertext) * contained_elements);
+  s->transferred_element_count += contained_elements;
+
+  if ( (s->transferred_element_count == max) &&
+       (NULL == s->intersection_op) )
+  {
+    /* intersection has finished also on our side, and
+       we got the full set, so we can proceed with the
+       CADET response(s) */
+    transmit_cryptographic_reply (s);
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Callback for set operation results. Called for each element
+ * that needs to be removed from the result set.
+ *
+ * @param cls closure with the `struct BobServiceSession`
+ * @param element a result element, only valid if status is #GNUNET_SET_STATUS_OK
+ * @param status what has happened with the set intersection?
+ */
+static void
+cb_intersection_element_removed (void *cls,
+                                 const struct GNUNET_SET_Element *element,
+                                 enum GNUNET_SET_Status status)
+{
+  struct BobServiceSession *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);
+    LOG (GNUNET_ERROR_TYPE_DEBUG,
+         "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;
+    s->intersection_set = NULL;
+    if (s->transferred_element_count ==
+        GNUNET_CONTAINER_multihashmap_size (s->intersected_elements))
+    {
+      /* CADET transmission from Alice is also already done,
+         start with our own reply */
+      transmit_cryptographic_reply (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");
+    s->intersection_op = NULL;
+    s->intersection_set = NULL;
+    s->active = GNUNET_SYSERR;
+    prepare_client_end_notification (s);
+    return;
+  default:
+    GNUNET_break (0);
+    return;
+  }
+}
+
+
+/**
+ * We've paired up a client session with an incoming CADET request.
+ * Initiate set intersection work.
+ *
+ * @param s client session to start intersection for
+ */
+static void
+start_intersection (struct BobServiceSession *s)
+{
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Got session with key %s and a matching element set, processing.\n",
+              GNUNET_h2s (&s->session_id));
+
+  s->intersection_op
+    = GNUNET_SET_prepare (&s->cadet->peer,
+                          &s->session_id,
+                          NULL,
+                          GNUNET_SET_RESULT_REMOVED,
+                          &cb_intersection_element_removed,
+                          s);
+  GNUNET_SET_commit (s->intersection_op,
+                     s->intersection_set);
+}
+
+
+/**
+ * Handle a request from Alice to calculate a scalarproduct with us (Bob).
+ *
+ * @param cls closure (set from #GNUNET_CADET_connect)
+ * @param channel connection to the other end
+ * @param channel_ctx place to store the `struct CadetIncomingSession *`
+ * @param message the actual message
+ * @return #GNUNET_OK to keep the connection open,
+ *         #GNUNET_SYSERR to close it (signal serious error)
+ */
+static int
+handle_alices_computation_request (void *cls,
+                                   struct GNUNET_CADET_Channel *channel,
+                                   void **channel_ctx,
+                                   const struct GNUNET_MessageHeader *message)
+{
+  struct CadetIncomingSession *in = *channel_ctx;
+  struct BobServiceSession *s;
+  const struct ServiceRequestMessage *msg;
+
+  if (ntohs (message->size) != sizeof (struct ServiceRequestMessage))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  msg = (const struct ServiceRequestMessage *) message;
+  if (GNUNET_YES == in->in_map)
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (NULL != find_matching_cadet_session (&msg->session_id))
+  {
+    /* not unique, got one like this already */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  in->session_id = msg->session_id;
+  in->remote_pubkey = msg->public_key;
+  GNUNET_assert (GNUNET_YES ==
+                 GNUNET_CONTAINER_multihashmap_put (cadet_sessions,
+                                                    &in->session_id,
+                                                    in,
+                                                    GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));
+  s = find_matching_client_session (&in->session_id);
+  if (NULL == s)
+  {
+    /* no client waiting for this request, wait for client */
+    return GNUNET_OK;
+  }
+  GNUNET_assert (NULL == s->cadet);
+  /* pair them up */
+  in->s = s;
+  s->cadet = in;
+  if (s->transferred_element_count == s->total)
+    start_intersection (s);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Function called for inbound channels on Bob's end.  Does some
+ * preliminary initialization, more happens after we get Alice's first
+ * message.
+ *
+ * @param cls closure
+ * @param channel new handle to the channel
+ * @param initiator peer that started the channel
+ * @param port unused
+ * @param options unused
+ * @return session associated with the channel
+ */
+static void *
+cb_channel_incoming (void *cls,
+                     struct GNUNET_CADET_Channel *channel,
+                     const struct GNUNET_PeerIdentity *initiator,
+                     uint32_t port,
+                     enum GNUNET_CADET_ChannelOption options)
+{
+  struct CadetIncomingSession *in;
+
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "New incoming channel from peer %s.\n",
+              GNUNET_i2s (initiator));
+  in = GNUNET_new (struct CadetIncomingSession);
+  in->peer = *initiator;
+  in->channel = channel;
+  return in;
+}
+
+
+/**
+ * We're receiving additional set data. Add it to our
+ * set and if we are done, initiate the transaction.
+ *
+ * @param cls closure
+ * @param client identification of the client
+ * @param message the actual message
+ */
+static void
+GSS_handle_bob_client_message_multipart (void *cls,
+                                         struct GNUNET_SERVER_Client *client,
+                                         const struct GNUNET_MessageHeader *message)
+{
+  const struct ComputationMultipartMessage * msg;
+  struct BobServiceSession *s;
+  uint32_t contained_count;
+  const struct GNUNET_SCALARPRODUCT_Element *elements;
+  uint32_t i;
+  uint16_t msize;
+  struct GNUNET_SET_Element set_elem;
+  struct GNUNET_SCALARPRODUCT_Element *elem;
+
+  s = GNUNET_SERVER_client_get_user_context (client,
+                                             struct BobServiceSession);
+  if (NULL == s)
+  {
+    /* session needs to already exist */
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  msize = ntohs (message->size);
+  if (msize < sizeof (struct ComputationMultipartMessage))
+  {
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  msg = (const struct ComputationMultipartMessage *) message;
+  contained_count = ntohl (msg->element_count_contained);
+
+  if ( (msize != (sizeof (struct ComputationMultipartMessage) +
+                  contained_count * sizeof (struct GNUNET_SCALARPRODUCT_Element))) ||
+       (0 == contained_count) ||
+       (UINT16_MAX < contained_count) ||
+       (s->total == s->transferred_element_count) ||
+       (s->total < s->transferred_element_count + contained_count) )
+  {
+    GNUNET_break_op (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  elements = (const struct GNUNET_SCALARPRODUCT_Element *) &msg[1];
+  for (i = 0; i < contained_count; i++)
+  {
+    if (0 == GNUNET_ntohll (elements[i].value))
+      continue;
+    elem = GNUNET_new (struct GNUNET_SCALARPRODUCT_Element);
+    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->transferred_element_count += contained_count;
+  GNUNET_SERVER_receive_done (client,
+                              GNUNET_OK);
+  if (s->total != s->transferred_element_count)
+  {
+    /* more to come */
+    return;
+  }
+  if (NULL == s->cadet)
+  {
+    /* no Alice waiting for this request, wait for Alice */
+    return;
+  }
+  start_intersection (s);
+}
+
+
+/**
+ * Handler for Bob's a client request message.  Bob is in the response
+ * role, keep the values + session and waiting for a matching session
+ * or process a waiting request from Alice.
+ *
+ * @param cls closure
+ * @param client identification of the client
+ * @param message the actual message
+ */
+static void
+GSS_handle_bob_client_message (void *cls,
+                               struct GNUNET_SERVER_Client *client,
+                               const struct GNUNET_MessageHeader *message)
+{
+  const struct BobComputationMessage *msg;
+  struct BobServiceSession *s;
+  struct CadetIncomingSession *in;
+  uint32_t contained_count;
+  uint32_t total_count;
+  const struct GNUNET_SCALARPRODUCT_Element *elements;
+  uint32_t i;
+  struct GNUNET_SET_Element set_elem;
+  struct GNUNET_SCALARPRODUCT_Element *elem;
+  uint16_t msize;
+
+  s = GNUNET_SERVER_client_get_user_context (client,
+                                             struct BobServiceSession);
+  if (NULL != s)
+  {
+    /* only one concurrent session per client connection allowed,
+       simplifies logic a lot... */
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  msize = ntohs (message->size);
+  if (msize < sizeof (struct BobComputationMessage))
+  {
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  msg = (const struct BobComputationMessage *) message;
+  total_count = ntohl (msg->element_count_total);
+  contained_count = ntohl (msg->element_count_contained);
+  if ( (0 == total_count) ||
+       (0 == contained_count) ||
+       (UINT16_MAX < contained_count) ||
+       (msize != (sizeof (struct BobComputationMessage) +
+                  contained_count * sizeof (struct GNUNET_SCALARPRODUCT_Element))) )
+  {
+    GNUNET_break_op (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+  if (NULL != find_matching_client_session (&msg->session_key))
+  {
+    GNUNET_break (0);
+    GNUNET_SERVER_receive_done (client,
+                                GNUNET_SYSERR);
+    return;
+  }
+
+  s = GNUNET_new (struct BobServiceSession);
+  s->active = GNUNET_YES;
+  s->client = client;
+  s->client_mq = GNUNET_MQ_queue_for_server_client (client);
+  s->total = total_count;
+  s->transferred_element_count = contained_count;
+  s->session_id = msg->session_key;
+  GNUNET_break (GNUNET_YES ==
+                GNUNET_CONTAINER_multihashmap_put (client_sessions,
+                                                   &s->session_id,
+                                                   s,
+                                                   GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY));
+  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 (i = 0; i < contained_count; i++)
+  {
+    if (0 == GNUNET_ntohll (elements[i].value))
+      continue;
+    elem = GNUNET_new (struct GNUNET_SCALARPRODUCT_Element);
+    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_SERVER_client_set_user_context (client,
+                                         s);
+  GNUNET_SERVER_receive_done (client,
+                              GNUNET_YES);
+  if (s->total != s->transferred_element_count)
+  {
+    /* multipart msg */
+    return;
+  }
+  in = find_matching_cadet_session (&s->session_id);
+  if (NULL == in)
+  {
+    /* nothing yet, wait for Alice */
+    return;
+  }
+  GNUNET_assert (NULL == in->s);
+  /* pair them up */
+  in->s = s;
+  s->cadet = in;
+  start_intersection (s);
+}
+
+
+/**
+ * Task run during shutdown.
+ *
+ * @param cls unused
+ * @param tc unused
+ */
+static void
+shutdown_task (void *cls,
+               const struct GNUNET_SCHEDULER_TaskContext *tc)
+{
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Shutting down, initiating cleanup.\n");
+  do_shutdown = GNUNET_YES;
+  // FIXME: is there a need to shutdown active sessions?
+  if (NULL != my_cadet)
+  {
+    GNUNET_CADET_disconnect (my_cadet);
+    my_cadet = NULL;
+  }
+  GNUNET_CONTAINER_multihashmap_destroy (client_sessions);
+  client_sessions = NULL;
+  GNUNET_CONTAINER_multihashmap_destroy (cadet_sessions);
+  cadet_sessions = NULL;
+}
+
+
+/**
+ * A client disconnected.
+ *
+ * Remove the associated session(s), release data structures
+ * and cancel pending outgoing transmissions to the client.
+ *
+ * @param cls closure, NULL
+ * @param client identification of the client
+ */
+static void
+handle_client_disconnect (void *cls,
+                          struct GNUNET_SERVER_Client *client)
+{
+  struct BobServiceSession *s;
+
+  if (NULL == client)
+    return;
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Client disconnected from us.\n",
+              client);
+  s = GNUNET_SERVER_client_get_user_context (client,
+                                             struct BobServiceSession);
+  if (NULL == s)
+    return;
+  s->client = NULL;
+  destroy_service_session (s);
+}
+
+
+/**
+ * Initialization of the program and message handlers
+ *
+ * @param cls closure
+ * @param server the initialized server
+ * @param c configuration to use
+ */
+static void
+run (void *cls,
+     struct GNUNET_SERVER_Handle *server,
+     const struct GNUNET_CONFIGURATION_Handle *c)
+{
+  static const struct GNUNET_SERVER_MessageHandler server_handlers[] = {
+    { &GSS_handle_bob_client_message, NULL,
+      GNUNET_MESSAGE_TYPE_SCALARPRODUCT_CLIENT_TO_BOB,
+      0},
+    { &GSS_handle_bob_client_message_multipart, NULL,
+      GNUNET_MESSAGE_TYPE_SCALARPRODUCT_CLIENT_MUTLIPART_BOB,
+      0},
+    { NULL, NULL, 0, 0}
+  };
+  static const struct GNUNET_CADET_MessageHandler cadet_handlers[] = {
+    { &handle_alices_computation_request,
+      GNUNET_MESSAGE_TYPE_SCALARPRODUCT_SESSION_INITIALIZATION,
+      sizeof (struct ServiceRequestMessage) },
+    { &handle_alices_cryptodata_message,
+      GNUNET_MESSAGE_TYPE_SCALARPRODUCT_ALICE_CRYPTODATA,
+      0},
+    { NULL, 0, 0}
+  };
+  static const uint32_t ports[] = {
+    GNUNET_APPLICATION_TYPE_SCALARPRODUCT,
+    0
+  };
+
+  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);
+  GNUNET_SERVER_add_handlers (server,
+                              server_handlers);
+  GNUNET_SERVER_disconnect_notify (server,
+                                   &handle_client_disconnect,
+                                   NULL);
+  client_sessions = GNUNET_CONTAINER_multihashmap_create (128,
+                                                          GNUNET_YES);
+  cadet_sessions = GNUNET_CONTAINER_multihashmap_create (128,
+                                                         GNUNET_YES);
+  my_cadet = GNUNET_CADET_connect (cfg, NULL,
+                                   &cb_channel_incoming,
+                                   &cb_channel_destruction,
+                                   cadet_handlers,
+                                   ports);
+  if (NULL == my_cadet)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                _("Connect to CADET failed\n"));
+    GNUNET_SCHEDULER_shutdown ();
+    return;
+  }
+  GNUNET_SCHEDULER_add_delayed (GNUNET_TIME_UNIT_FOREVER_REL,
+                                &shutdown_task,
+                                NULL);
+}
+
+
+/**
+ * The main function for the scalarproduct service.
+ *
+ * @param argc number of arguments from the command line
+ * @param argv command line arguments
+ * @return 0 ok, 1 on error
+ */
+int
+main (int argc,
+      char *const *argv)
+{
+  return (GNUNET_OK ==
+          GNUNET_SERVICE_run (argc, argv,
+                              "scalarproduct-bob",
+                              GNUNET_SERVICE_OPTION_NONE,
+                              &run, NULL)) ? 0 : 1;
+}
+
+/* end of gnunet-service-scalarproduct_bob.c */