From b23f9b78a4220fda5ee8e1c4fc1bbae83dedeb39 Mon Sep 17 00:00:00 2001
From: Florian Dold <florian@dold.me>
Date: Sun, 17 Jan 2021 20:07:55 +0100
Subject: rename taler-helper-crypto-* to taler-exchange-secmod-*

---
 src/util/taler-exchange-secmod-rsa.c | 2077 ++++++++++++++++++++++++++++++++++
 1 file changed, 2077 insertions(+)
 create mode 100644 src/util/taler-exchange-secmod-rsa.c

(limited to 'src/util/taler-exchange-secmod-rsa.c')

diff --git a/src/util/taler-exchange-secmod-rsa.c b/src/util/taler-exchange-secmod-rsa.c
new file mode 100644
index 000000000..10a52af00
--- /dev/null
+++ b/src/util/taler-exchange-secmod-rsa.c
@@ -0,0 +1,2077 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2014-2020 Taler Systems SA
+
+  TALER 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.
+
+  TALER 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
+  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file util/taler-exchange-secmod-rsa.c
+ * @brief Standalone process to perform private key RSA operations
+ * @author Christian Grothoff
+ *
+ * Key design points:
+ * - EVERY thread of the exchange will have its own pair of connections to the
+ *   crypto helpers.  This way, every threat will also have its own /keys state
+ *   and avoid the need to synchronize on those.
+ * - auditor signatures and master signatures are to be kept in the exchange DB,
+ *   and merged with the public keys of the helper by the exchange HTTPD!
+ * - the main loop of the helper is SINGLE-THREADED, but there are
+ *   threads for crypto-workers which (only) do the signing in parallel,
+ *   working of a work-queue.
+ * - thread-safety: signing happens in parallel, thus when REMOVING private keys,
+ *   we must ensure that all signers are done before we fully free() the
+ *   private key. This is done by reference counting (as work is always
+ *   assigned and collected by the main thread).
+ */
+#include "platform.h"
+#include "taler_util.h"
+#include "taler-exchange-secmod-rsa.h"
+#include <gcrypt.h>
+#include <pthread.h>
+#include <sys/eventfd.h>
+#include "taler_error_codes.h"
+#include "taler_signatures.h"
+
+
+/**
+ * Information we keep per denomination.
+ */
+struct Denomination;
+
+
+/**
+ * One particular denomination key.
+ */
+struct DenominationKey
+{
+
+  /**
+   * Kept in a DLL of the respective denomination. Sorted by anchor time.
+   */
+  struct DenominationKey *next;
+
+  /**
+   * Kept in a DLL of the respective denomination. Sorted by anchor time.
+   */
+  struct DenominationKey *prev;
+
+  /**
+   * Denomination this key belongs to.
+   */
+  struct Denomination *denom;
+
+  /**
+   * Name of the file this key is stored under.
+   */
+  char *filename;
+
+  /**
+   * The private key of the denomination.
+   */
+  struct TALER_DenominationPrivateKey denom_priv;
+
+  /**
+   * The public key of the denomination.
+   */
+  struct TALER_DenominationPublicKey denom_pub;
+
+  /**
+   * Hash of this denomination's public key.
+   */
+  struct GNUNET_HashCode h_denom_pub;
+
+  /**
+   * Time at which this key is supposed to become valid.
+   */
+  struct GNUNET_TIME_Absolute anchor;
+
+  /**
+   * Reference counter. Counts the number of threads that are
+   * using this key at this time.
+   */
+  unsigned int rc;
+
+  /**
+   * Flag set to true if this key has been purged and the memory
+   * must be freed as soon as @e rc hits zero.
+   */
+  bool purge;
+
+};
+
+
+struct Denomination
+{
+
+  /**
+   * Kept in a DLL. Sorted by #denomination_action_time().
+   */
+  struct Denomination *next;
+
+  /**
+   * Kept in a DLL. Sorted by #denomination_action_time().
+   */
+  struct Denomination *prev;
+
+  /**
+   * Head of DLL of actual keys of this denomination.
+   */
+  struct DenominationKey *keys_head;
+
+  /**
+   * Tail of DLL of actual keys of this denomination.
+   */
+  struct DenominationKey *keys_tail;
+
+  /**
+   * How long can coins be withdrawn (generated)?  Should be small
+   * enough to limit how many coins will be signed into existence with
+   * the same key, but large enough to still provide a reasonable
+   * anonymity set.
+   */
+  struct GNUNET_TIME_Relative duration_withdraw;
+
+  /**
+   * What is the configuration section of this denomination type?  Also used
+   * for the directory name where the denomination keys are stored.
+   */
+  char *section;
+
+  /**
+   * Length of (new) RSA keys (in bits).
+   */
+  uint32_t rsa_keysize;
+};
+
+
+/**
+ * Actively worked on client request.
+ */
+struct WorkItem;
+
+
+/**
+ * Information we keep for a client connected to us.
+ */
+struct Client
+{
+
+  /**
+   * Kept in a DLL.
+   */
+  struct Client *next;
+
+  /**
+   * Kept in a DLL.
+   */
+  struct Client *prev;
+
+  /**
+   * Client address.
+   */
+  struct sockaddr_un addr;
+
+  /**
+   * Number of bytes used in @e addr.
+   */
+  socklen_t addr_size;
+
+};
+
+
+struct WorkItem
+{
+
+  /**
+   * Kept in a DLL.
+   */
+  struct WorkItem *next;
+
+  /**
+   * Kept in a DLL.
+   */
+  struct WorkItem *prev;
+
+  /**
+   * Key to be used for this operation.
+   */
+  struct DenominationKey *dk;
+
+  /**
+   * RSA signature over @e blinded_msg using @e dk. Result of doing the
+   * work. Initially NULL.
+   */
+  struct GNUNET_CRYPTO_RsaSignature *rsa_signature;
+
+  /**
+   * Coin_ev value to sign.
+   */
+  void *blinded_msg;
+
+  /**
+   * Number of bytes in #blinded_msg.
+   */
+  size_t blinded_msg_size;
+
+  /**
+   * Client address.
+   */
+  struct sockaddr_un addr;
+
+  /**
+   * Number of bytes used in @e addr.
+   */
+  socklen_t addr_size;
+
+};
+
+
+/**
+ * Return value from main().
+ */
+static int global_ret;
+
+/**
+ * Private key of this security module. Used to sign denomination key
+ * announcements.
+ */
+static struct TALER_SecurityModulePrivateKeyP smpriv;
+
+/**
+ * Public key of this security module.
+ */
+static struct TALER_SecurityModulePublicKeyP smpub;
+
+/**
+ * Number of worker threads to use. Default (0) is to use one per CPU core
+ * available.
+ * Length of the #workers array.
+ */
+static unsigned int num_workers;
+
+/**
+ * Time when the key update is executed.
+ * Either the actual current time, or a pretended time.
+ */
+static struct GNUNET_TIME_Absolute now;
+
+/**
+ * The time for the key update, as passed by the user
+ * on the command line.
+ */
+static struct GNUNET_TIME_Absolute now_tmp;
+
+/**
+ * Handle to the exchange's configuration
+ */
+static const struct GNUNET_CONFIGURATION_Handle *kcfg;
+
+/**
+ * Where do we store the keys?
+ */
+static char *keydir;
+
+/**
+ * How much should coin creation (@e duration_withdraw) duration overlap
+ * with the next denomination?  Basically, the starting time of two
+ * denominations is always @e duration_withdraw - #overlap_duration apart.
+ */
+static struct GNUNET_TIME_Relative overlap_duration;
+
+/**
+ * How long into the future do we pre-generate keys?
+ */
+static struct GNUNET_TIME_Relative lookahead_sign;
+
+/**
+ * All of our denominations, in a DLL. Sorted?
+ */
+static struct Denomination *denom_head;
+
+/**
+ * All of our denominations, in a DLL. Sorted?
+ */
+static struct Denomination *denom_tail;
+
+/**
+ * Map of hashes of public (RSA) keys to `struct DenominationKey *`
+ * with the respective private keys.
+ */
+static struct GNUNET_CONTAINER_MultiHashMap *keys;
+
+/**
+ * Our listen socket.
+ */
+static struct GNUNET_NETWORK_Handle *unix_sock;
+
+/**
+ * Path where we are listening.
+ */
+static char *unixpath;
+
+/**
+ * Task run to accept new inbound connections.
+ */
+static struct GNUNET_SCHEDULER_Task *read_task;
+
+/**
+ * Task run to generate new keys.
+ */
+static struct GNUNET_SCHEDULER_Task *keygen_task;
+
+/**
+ * Head of DLL of clients connected to us.
+ */
+static struct Client *clients_head;
+
+/**
+ * Tail of DLL of clients connected to us.
+ */
+static struct Client *clients_tail;
+
+/**
+ * Head of DLL with pending signing operations.
+ */
+static struct WorkItem *work_head;
+
+/**
+ * Tail of DLL with pending signing operations.
+ */
+static struct WorkItem *work_tail;
+
+/**
+ * Lock for the work queue.
+ */
+static pthread_mutex_t work_lock;
+
+/**
+ * Condition variable for the semaphore of the work queue.
+ */
+static pthread_cond_t work_cond = PTHREAD_COND_INITIALIZER;
+
+/**
+ * Number of items in the work queue. Also used as the semaphore counter.
+ */
+static unsigned long long work_counter;
+
+/**
+ * Head of DLL with completed signing operations.
+ */
+static struct WorkItem *done_head;
+
+/**
+ * Tail of DLL with completed signing operations.
+ */
+static struct WorkItem *done_tail;
+
+/**
+ * Lock for the done queue.
+ */
+static pthread_mutex_t done_lock;
+
+/**
+ * Task waiting for work to be done.
+ */
+static struct GNUNET_SCHEDULER_Task *done_task;
+
+/**
+ * Signal used by threads to notify the #done_task that they
+ * completed work that is now in the done queue.
+ */
+static struct GNUNET_NETWORK_Handle *done_signal;
+
+/**
+ * Set once we are in shutdown and workers should terminate.
+ */
+static volatile bool in_shutdown;
+
+/**
+ * Array of #num_workers sign_worker() threads.
+ */
+static pthread_t *workers;
+
+
+/**
+ * Main function of a worker thread that signs.
+ *
+ * @param cls NULL
+ * @return NULL
+ */
+static void *
+sign_worker (void *cls)
+{
+  (void) cls;
+  GNUNET_assert (0 == pthread_mutex_lock (&work_lock));
+  while (! in_shutdown)
+  {
+    struct WorkItem *wi;
+
+    while (NULL != (wi = work_head))
+    {
+      /* take work from queue */
+      GNUNET_CONTAINER_DLL_remove (work_head,
+                                   work_tail,
+                                   wi);
+      work_counter--;
+      GNUNET_assert (0 == pthread_mutex_unlock (&work_lock));
+      wi->rsa_signature
+        = GNUNET_CRYPTO_rsa_sign_blinded (wi->dk->denom_priv.rsa_private_key,
+                                          wi->blinded_msg,
+                                          wi->blinded_msg_size);
+      /* put completed work into done queue */
+      GNUNET_assert (0 == pthread_mutex_lock (&done_lock));
+      GNUNET_CONTAINER_DLL_insert (done_head,
+                                   done_tail,
+                                   wi);
+      GNUNET_assert (0 == pthread_mutex_unlock (&done_lock));
+      {
+        uint64_t val = GNUNET_htonll (1);
+
+        /* raise #done_signal */
+        if (sizeof(val) !=
+            write (GNUNET_NETWORK_get_fd (done_signal),
+                   &val,
+                   sizeof (val)))
+          GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
+                               "write(eventfd)");
+      }
+      GNUNET_assert (0 == pthread_mutex_lock (&work_lock));
+    }
+    /* queue is empty, wait for work */
+    GNUNET_assert (0 ==
+                   pthread_cond_wait (&work_cond,
+                                      &work_lock));
+  }
+  GNUNET_assert (0 ==
+                 pthread_mutex_unlock (&work_lock));
+  return NULL;
+}
+
+
+/**
+ * Free @a client, releasing all (remaining) state.
+ *
+ * @param[in] client data to free
+ */
+static void
+free_client (struct Client *client)
+{
+  GNUNET_CONTAINER_DLL_remove (clients_head,
+                               clients_tail,
+                               client);
+  GNUNET_free (client);
+}
+
+
+/**
+ * Function run to read incoming requests from a client.
+ *
+ * @param cls the `struct Client`
+ */
+static void
+read_job (void *cls);
+
+
+/**
+ * Free @a dk. It must already have been removed from #keys and the
+ * denomination's DLL.
+ *
+ * @param[in] dk key to free
+ */
+static void
+free_dk (struct DenominationKey *dk)
+{
+  GNUNET_free (dk->filename);
+  GNUNET_CRYPTO_rsa_private_key_free (dk->denom_priv.rsa_private_key);
+  GNUNET_CRYPTO_rsa_public_key_free (dk->denom_pub.rsa_public_key);
+  GNUNET_free (dk);
+}
+
+
+/**
+ * Send a message starting with @a hdr to @a client.  We expect that
+ * the client is mostly able to handle everything at whatever speed
+ * we have (after all, the crypto should be the slow part). However,
+ * especially on startup when we send all of our keys, it is possible
+ * that the client cannot keep up. In that case, we throttle when
+ * sending fails. This does not work with poll() as we cannot specify
+ * the sendto() target address with poll(). So we nanosleep() instead.
+ *
+ * @param addr address where to send the message
+ * @param addr_size number of bytes in @a addr
+ * @param hdr beginning of the message, length indicated in size field
+ * @return #GNUNET_OK on success
+ */
+static int
+transmit (const struct sockaddr_un *addr,
+          socklen_t addr_size,
+          const struct GNUNET_MessageHeader *hdr)
+{
+  for (unsigned int i = 0; i<100; i++)
+  {
+    ssize_t ret = sendto (GNUNET_NETWORK_get_fd (unix_sock),
+                          hdr,
+                          ntohs (hdr->size),
+                          0 /* no flags => blocking! */,
+                          (const struct sockaddr *) addr,
+                          addr_size);
+    if ( (-1 == ret) &&
+         (EAGAIN == errno) )
+    {
+      /* _Maybe_ with blocking sendto(), this should no
+         longer be needed; still keeping it just in case. */
+      /* Wait a bit, in case client is just too slow */
+      struct timespec req = {
+        .tv_sec = 0,
+        .tv_nsec = 1000
+      };
+      nanosleep (&req, NULL);
+      continue;
+    }
+    if (ret == ntohs (hdr->size))
+      return GNUNET_OK;
+    if (ret != ntohs (hdr->size))
+      break;
+  }
+  GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
+                       "sendto");
+  return GNUNET_SYSERR;
+}
+
+
+/**
+ * Process completed tasks that are in the #done_head queue, sending
+ * the result back to the client (and resuming the client).
+ *
+ * @param cls NULL
+ */
+static void
+handle_done (void *cls)
+{
+  uint64_t data;
+  (void) cls;
+
+  /* consume #done_signal */
+  if (sizeof (data) !=
+      read (GNUNET_NETWORK_get_fd (done_signal),
+            &data,
+            sizeof (data)))
+    GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
+                         "read(eventfd)");
+  done_task = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                             done_signal,
+                                             &handle_done,
+                                             NULL);
+  GNUNET_assert (0 == pthread_mutex_lock (&done_lock));
+  while (NULL != done_head)
+  {
+    struct WorkItem *wi = done_head;
+
+    GNUNET_CONTAINER_DLL_remove (done_head,
+                                 done_tail,
+                                 wi);
+    GNUNET_assert (0 == pthread_mutex_unlock (&done_lock));
+    if (NULL == wi->rsa_signature)
+    {
+      struct TALER_CRYPTO_SignFailure sf = {
+        .header.size = htons (sizeof (sf)),
+        .header.type = htons (TALER_HELPER_RSA_MT_RES_SIGN_FAILURE),
+        .ec = htonl (TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE)
+      };
+
+      GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                  "Signing request failed, worker failed to produce signature\n");
+      (void) transmit (&wi->addr,
+                       wi->addr_size,
+                       &sf.header);
+    }
+    else
+    {
+      struct TALER_CRYPTO_SignResponse *sr;
+      void *buf;
+      size_t buf_size;
+      size_t tsize;
+
+      buf_size = GNUNET_CRYPTO_rsa_signature_encode (wi->rsa_signature,
+                                                     &buf);
+      tsize = sizeof (*sr) + buf_size;
+      GNUNET_assert (tsize < UINT16_MAX);
+      sr = GNUNET_malloc (tsize);
+      sr->header.size = htons (tsize);
+      sr->header.type = htons (TALER_HELPER_RSA_MT_RES_SIGNATURE);
+      memcpy (&sr[1],
+              buf,
+              buf_size);
+      GNUNET_free (buf);
+      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                  "Sending RSA signature\n");
+      (void) transmit (&wi->addr,
+                       wi->addr_size,
+                       &sr->header);
+      GNUNET_free (sr);
+    }
+    {
+      struct DenominationKey *dk = wi->dk;
+
+      dk->rc--;
+      if ( (0 == dk->rc) &&
+           (dk->purge) )
+        free_dk (dk);
+    }
+    GNUNET_free (wi);
+    GNUNET_assert (0 == pthread_mutex_lock (&done_lock));
+  }
+  GNUNET_assert (0 == pthread_mutex_unlock (&done_lock));
+
+}
+
+
+/**
+ * Handle @a client request @a sr to create signature. Create the
+ * signature using the respective key and return the result to
+ * the client.
+ *
+ * @param addr address of the client making the request
+ * @param addr_size number of bytes in @a addr
+ * @param sr the request details
+ */
+static void
+handle_sign_request (const struct sockaddr_un *addr,
+                     socklen_t addr_size,
+                     const struct TALER_CRYPTO_SignRequest *sr)
+{
+  struct DenominationKey *dk;
+  struct WorkItem *wi;
+  const void *blinded_msg = &sr[1];
+  size_t blinded_msg_size = ntohs (sr->header.size) - sizeof (*sr);
+
+  dk = GNUNET_CONTAINER_multihashmap_get (keys,
+                                          &sr->h_denom_pub);
+  if (NULL == dk)
+  {
+    struct TALER_CRYPTO_SignFailure sf = {
+      .header.size = htons (sizeof (sr)),
+      .header.type = htons (TALER_HELPER_RSA_MT_RES_SIGN_FAILURE),
+      .ec = htonl (TALER_EC_EXCHANGE_GENERIC_DENOMINATION_KEY_UNKNOWN)
+    };
+
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Signing request failed, denomination key %s unknown\n",
+                GNUNET_h2s (&sr->h_denom_pub));
+    (void) transmit (addr,
+                     addr_size,
+                     &sf.header);
+    return;
+  }
+  if (0 !=
+      GNUNET_TIME_absolute_get_remaining (dk->anchor).rel_value_us)
+  {
+    /* it is too early */
+    struct TALER_CRYPTO_SignFailure sf = {
+      .header.size = htons (sizeof (sr)),
+      .header.type = htons (TALER_HELPER_RSA_MT_RES_SIGN_FAILURE),
+      .ec = htonl (TALER_EC_EXCHANGE_DENOMINATION_HELPER_TOO_EARLY)
+    };
+
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Signing request failed, denomination key %s is not yet valid\n",
+                GNUNET_h2s (&sr->h_denom_pub));
+    (void) transmit (addr,
+                     addr_size,
+                     &sf.header);
+    return;
+  }
+
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Received request to sign over %u bytes with key %s\n",
+              (unsigned int) blinded_msg_size,
+              GNUNET_h2s (&sr->h_denom_pub));
+  wi = GNUNET_new (struct WorkItem);
+  wi->addr = *addr;
+  wi->addr_size = addr_size;
+  wi->dk = dk;
+  dk->rc++;
+  wi->blinded_msg = GNUNET_memdup (blinded_msg,
+                                   blinded_msg_size);
+  wi->blinded_msg_size = blinded_msg_size;
+  GNUNET_assert (0 == pthread_mutex_lock (&work_lock));
+  work_counter++;
+  GNUNET_CONTAINER_DLL_insert (work_head,
+                               work_tail,
+                               wi);
+  GNUNET_assert (0 == pthread_mutex_unlock (&work_lock));
+  GNUNET_assert (0 == pthread_cond_signal (&work_cond));
+}
+
+
+/**
+ * Notify @a client about @a dk becoming available.
+ *
+ * @param[in,out] client the client to notify; possible freed if transmission fails
+ * @param dk the key to notify @a client about
+ * @return #GNUNET_OK on success
+ */
+static int
+notify_client_dk_add (struct Client *client,
+                      const struct DenominationKey *dk)
+{
+  struct Denomination *denom = dk->denom;
+  size_t nlen = strlen (denom->section) + 1;
+  struct TALER_CRYPTO_RsaKeyAvailableNotification *an;
+  size_t buf_len;
+  void *buf;
+  void *p;
+  size_t tlen;
+
+  buf_len = GNUNET_CRYPTO_rsa_public_key_encode (dk->denom_pub.rsa_public_key,
+                                                 &buf);
+  GNUNET_assert (buf_len < UINT16_MAX);
+  GNUNET_assert (nlen < UINT16_MAX);
+  tlen = buf_len + nlen + sizeof (*an);
+  GNUNET_assert (tlen < UINT16_MAX);
+  an = GNUNET_malloc (tlen);
+  an->header.size = htons ((uint16_t) tlen);
+  an->header.type = htons (TALER_HELPER_RSA_MT_AVAIL);
+  an->pub_size = htons ((uint16_t) buf_len);
+  an->section_name_len = htons ((uint16_t) nlen);
+  an->anchor_time = GNUNET_TIME_absolute_hton (dk->anchor);
+  an->duration_withdraw = GNUNET_TIME_relative_hton (denom->duration_withdraw);
+  TALER_exchange_secmod_rsa_sign (&dk->h_denom_pub,
+                                  denom->section,
+                                  dk->anchor,
+                                  denom->duration_withdraw,
+                                  &smpriv,
+                                  &an->secm_sig);
+  an->secm_pub = smpub;
+  p = (void *) &an[1];
+  memcpy (p,
+          buf,
+          buf_len);
+  GNUNET_free (buf);
+  memcpy (p + buf_len,
+          denom->section,
+          nlen);
+  {
+    int ret = GNUNET_OK;
+
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Sending RSA denomination key %s (%s)\n",
+                GNUNET_h2s (&dk->h_denom_pub),
+                denom->section);
+    if (GNUNET_OK !=
+        transmit (&client->addr,
+                  client->addr_size,
+                  &an->header))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                  "Client %s must have disconnected\n",
+                  client->addr.sun_path);
+      free_client (client);
+      ret = GNUNET_SYSERR;
+    }
+    GNUNET_free (an);
+    return ret;
+  }
+}
+
+
+/**
+ * Notify @a client about @a dk being purged.
+ *
+ * @param[in,out] client the client to notify; possible freed if transmission fails
+ * @param dk the key to notify @a client about
+ * @return #GNUNET_OK on success
+ */
+static int
+notify_client_dk_del (struct Client *client,
+                      const struct DenominationKey *dk)
+{
+  struct TALER_CRYPTO_RsaKeyPurgeNotification pn = {
+    .header.type = htons (TALER_HELPER_RSA_MT_PURGE),
+    .header.size = htons (sizeof (pn)),
+    .h_denom_pub = dk->h_denom_pub
+  };
+
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Sending RSA denomination expiration %s\n",
+              GNUNET_h2s (&dk->h_denom_pub));
+  if (GNUNET_OK !=
+      transmit (&client->addr,
+                client->addr_size,
+                &pn.header))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Client %s must have disconnected\n",
+                client->addr.sun_path);
+    free_client (client);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Initialize key material for denomination key @a dk (also on disk).
+ *
+ * @param[in,out] dk denomination key to compute key material for
+ * @param position where in the DLL will the @a dk go
+ * @return #GNUNET_OK on success
+ */
+static int
+setup_key (struct DenominationKey *dk,
+           struct DenominationKey *position)
+{
+  struct Denomination *denom = dk->denom;
+  struct GNUNET_CRYPTO_RsaPrivateKey *priv;
+  struct GNUNET_CRYPTO_RsaPublicKey *pub;
+  size_t buf_size;
+  void *buf;
+
+  priv = GNUNET_CRYPTO_rsa_private_key_create (denom->rsa_keysize);
+  if (NULL == priv)
+  {
+    GNUNET_break (0);
+    GNUNET_SCHEDULER_shutdown ();
+    global_ret = 40;
+    return GNUNET_SYSERR;
+  }
+  pub = GNUNET_CRYPTO_rsa_private_key_get_public (priv);
+  if (NULL == pub)
+  {
+    GNUNET_break (0);
+    GNUNET_CRYPTO_rsa_private_key_free (priv);
+    return GNUNET_SYSERR;
+  }
+  buf_size = GNUNET_CRYPTO_rsa_private_key_encode (priv,
+                                                   &buf);
+  GNUNET_CRYPTO_rsa_public_key_hash (pub,
+                                     &dk->h_denom_pub);
+  GNUNET_asprintf (&dk->filename,
+                   "%s/%s/%llu",
+                   keydir,
+                   denom->section,
+                   (unsigned long long) (dk->anchor.abs_value_us
+                                         / GNUNET_TIME_UNIT_SECONDS.rel_value_us));
+  if (GNUNET_OK !=
+      GNUNET_DISK_fn_write (dk->filename,
+                            buf,
+                            buf_size,
+                            GNUNET_DISK_PERM_USER_READ))
+  {
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
+                              "write",
+                              dk->filename);
+    GNUNET_free (buf);
+    GNUNET_CRYPTO_rsa_private_key_free (priv);
+    GNUNET_CRYPTO_rsa_public_key_free (pub);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_free (buf);
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Setup fresh private key %s in `%s'\n",
+              GNUNET_h2s (&dk->h_denom_pub),
+              dk->filename);
+  dk->denom_priv.rsa_private_key = priv;
+  dk->denom_pub.rsa_public_key = pub;
+
+  if (GNUNET_OK !=
+      GNUNET_CONTAINER_multihashmap_put (
+        keys,
+        &dk->h_denom_pub,
+        dk,
+        GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Duplicate private key created! Terminating.\n");
+    GNUNET_CRYPTO_rsa_private_key_free (dk->denom_priv.rsa_private_key);
+    GNUNET_CRYPTO_rsa_public_key_free (dk->denom_pub.rsa_public_key);
+    GNUNET_free (dk->filename);
+    GNUNET_free (dk);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_CONTAINER_DLL_insert_after (denom->keys_head,
+                                     denom->keys_tail,
+                                     position,
+                                     dk);
+
+  /* tell clients about new key */
+  {
+    struct Client *nxt;
+
+    for (struct Client *client = clients_head;
+         NULL != client;
+         client = nxt)
+    {
+      nxt = client->next;
+      if (GNUNET_OK !=
+          notify_client_dk_add (client,
+                                dk))
+      {
+        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                    "Failed to notify client about new key, client dropped\n");
+      }
+    }
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * A client informs us that a key has been revoked.
+ * Check if the key is still in use, and if so replace (!)
+ * it with a fresh key.
+ *
+ * @param addr address of the client making the request
+ * @param addr_size number of bytes in @a addr
+ * @param rr the revocation request
+ */
+static void
+handle_revoke_request (const struct sockaddr_un *addr,
+                       socklen_t addr_size,
+                       const struct TALER_CRYPTO_RevokeRequest *rr)
+{
+  struct DenominationKey *dk;
+  struct DenominationKey *ndk;
+  struct Denomination *denom;
+
+  dk = GNUNET_CONTAINER_multihashmap_get (keys,
+                                          &rr->h_denom_pub);
+  if (NULL == dk)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "Revocation request ignored, denomination key %s unknown\n",
+                GNUNET_h2s (&rr->h_denom_pub));
+    return;
+  }
+
+  /* kill existing key, done first to ensure this always happens */
+  if (0 != unlink (dk->filename))
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
+                              "unlink",
+                              dk->filename);
+  /* Setup replacement key */
+  denom = dk->denom;
+  ndk = GNUNET_new (struct DenominationKey);
+  ndk->denom = denom;
+  ndk->anchor = dk->anchor;
+  if (GNUNET_OK !=
+      setup_key (ndk,
+                 dk))
+  {
+    GNUNET_break (0);
+    GNUNET_SCHEDULER_shutdown ();
+    global_ret = 44;
+    return;
+  }
+
+  /* get rid of the old key */
+  dk->purge = true;
+  GNUNET_assert (GNUNET_OK ==
+                 GNUNET_CONTAINER_multihashmap_remove (
+                   keys,
+                   &dk->h_denom_pub,
+                   dk));
+  GNUNET_CONTAINER_DLL_remove (denom->keys_head,
+                               denom->keys_tail,
+                               dk);
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Revocation of denomination key %s complete\n",
+              GNUNET_h2s (&rr->h_denom_pub));
+
+  /* Tell clients this key is gone */
+  {
+    struct Client *nxt;
+
+    for (struct Client *client = clients_head;
+         NULL != client;
+         client = nxt)
+    {
+      nxt = client->next;
+      if (GNUNET_OK !=
+          notify_client_dk_del (client,
+                                dk))
+        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                    "Failed to notify client about revoked key, client dropped\n");
+    }
+  }
+  if (0 == dk->rc)
+    free_dk (dk);
+}
+
+
+static void
+read_job (void *cls)
+{
+  struct Client *client = cls;
+  char buf[65536];
+  ssize_t buf_size;
+  const struct GNUNET_MessageHeader *hdr;
+  struct sockaddr_un addr;
+  socklen_t addr_size = sizeof (addr);
+
+  read_task = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                             unix_sock,
+                                             &read_job,
+                                             NULL);
+  buf_size = GNUNET_NETWORK_socket_recvfrom (unix_sock,
+                                             buf,
+                                             sizeof (buf),
+                                             (struct sockaddr *) &addr,
+                                             &addr_size);
+  if (-1 == buf_size)
+  {
+    GNUNET_log_strerror (GNUNET_ERROR_TYPE_WARNING,
+                         "recv");
+    return;
+  }
+  if (0 == buf_size)
+  {
+    return;
+  }
+  if (buf_size < sizeof (struct GNUNET_MessageHeader))
+  {
+    GNUNET_break_op (0);
+    return;
+  }
+  hdr = (const struct GNUNET_MessageHeader *) buf;
+  if (ntohs (hdr->size) != buf_size)
+  {
+    GNUNET_break_op (0);
+    free_client (client);
+    return;
+  }
+  switch (ntohs (hdr->type))
+  {
+  case TALER_HELPER_RSA_MT_REQ_INIT:
+    if (ntohs (hdr->size) != sizeof (struct GNUNET_MessageHeader))
+    {
+      GNUNET_break_op (0);
+      return;
+    }
+    {
+      struct Client *client;
+
+      client = GNUNET_new (struct Client);
+      client->addr = addr;
+      client->addr_size = addr_size;
+      GNUNET_CONTAINER_DLL_insert (clients_head,
+                                   clients_tail,
+                                   client);
+      for (struct Denomination *denom = denom_head;
+           NULL != denom;
+           denom = denom->next)
+      {
+        for (struct DenominationKey *dk = denom->keys_head;
+             NULL != dk;
+             dk = dk->next)
+        {
+          if (GNUNET_OK !=
+              notify_client_dk_add (client,
+                                    dk))
+          {
+            /* client died, skip the rest */
+            client = NULL;
+            break;
+          }
+        }
+        if (NULL == client)
+          break;
+      }
+      if (NULL != client)
+      {
+        struct GNUNET_MessageHeader synced = {
+          .type = htons (TALER_HELPER_RSA_SYNCED),
+          .size = htons (sizeof (synced))
+        };
+
+        GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                    "Sending RSA SYNCED message\n");
+        if (GNUNET_OK !=
+            transmit (&client->addr,
+                      client->addr_size,
+                      &synced))
+        {
+          GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                      "Client %s must have disconnected\n",
+                      client->addr.sun_path);
+          free_client (client);
+        }
+      }
+    }
+    break;
+  case TALER_HELPER_RSA_MT_REQ_SIGN:
+    if (ntohs (hdr->size) <= sizeof (struct TALER_CRYPTO_SignRequest))
+    {
+      GNUNET_break_op (0);
+      return;
+    }
+    handle_sign_request (&addr,
+                         addr_size,
+                         (const struct TALER_CRYPTO_SignRequest *) buf);
+    break;
+  case TALER_HELPER_RSA_MT_REQ_REVOKE:
+    if (ntohs (hdr->size) != sizeof (struct TALER_CRYPTO_RevokeRequest))
+    {
+      GNUNET_break_op (0);
+      return;
+    }
+    handle_revoke_request (&addr,
+                           addr_size,
+                           (const struct TALER_CRYPTO_RevokeRequest *) buf);
+    break;
+  default:
+    GNUNET_break_op (0);
+    return;
+  }
+}
+
+
+/**
+ * Create a new denomination key (we do not have enough).
+ *
+ * @param denom denomination key to create
+ * @param now current time to use (to get many keys to use the exact same time)
+ * @return #GNUNET_OK on success
+ */
+static int
+create_key (struct Denomination *denom,
+            struct GNUNET_TIME_Absolute now)
+{
+  struct DenominationKey *dk;
+  struct GNUNET_TIME_Absolute anchor;
+
+  if (NULL == denom->keys_tail)
+  {
+    anchor = now;
+  }
+  else
+  {
+    anchor = GNUNET_TIME_absolute_add (denom->keys_tail->anchor,
+                                       GNUNET_TIME_relative_subtract (
+                                         denom->duration_withdraw,
+                                         overlap_duration));
+    if (now.abs_value_us > anchor.abs_value_us)
+      anchor = now;
+  }
+  dk = GNUNET_new (struct DenominationKey);
+  dk->denom = denom;
+  dk->anchor = anchor;
+  if (GNUNET_OK !=
+      setup_key (dk,
+                 denom->keys_tail))
+  {
+    GNUNET_free (dk);
+    GNUNET_SCHEDULER_shutdown ();
+    global_ret = 42;
+    return GNUNET_SYSERR;
+  }
+
+  return GNUNET_OK;
+}
+
+
+/**
+ * At what time does this denomination require its next action?
+ * Basically, the minimum of the withdraw expiration time of the
+ * oldest denomination key, and the withdraw expiration time of
+ * the newest denomination key minus the #lookahead_sign time.
+ *
+ * @param denom denomination to compute action time for
+ */
+static struct GNUNET_TIME_Absolute
+denomination_action_time (const struct Denomination *denom)
+{
+  return GNUNET_TIME_absolute_min (
+    GNUNET_TIME_absolute_add (denom->keys_head->anchor,
+                              denom->duration_withdraw),
+    GNUNET_TIME_absolute_subtract (
+      GNUNET_TIME_absolute_subtract (
+        GNUNET_TIME_absolute_add (denom->keys_tail->anchor,
+                                  denom->duration_withdraw),
+        lookahead_sign),
+      overlap_duration));
+}
+
+
+/**
+ * The withdraw period of a key @a dk has expired. Purge it.
+ *
+ * @param[in] dk expired denomination key to purge and free
+ */
+static void
+purge_key (struct DenominationKey *dk)
+{
+  struct Denomination *denom = dk->denom;
+  struct Client *nxt;
+
+  for (struct Client *client = clients_head;
+       NULL != client;
+       client = nxt)
+  {
+    nxt = client->next;
+    if (GNUNET_OK !=
+        notify_client_dk_del (client,
+                              dk))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                  "Failed to notify client about purged key, client dropped\n");
+    }
+  }
+  GNUNET_CONTAINER_DLL_remove (denom->keys_head,
+                               denom->keys_tail,
+                               dk);
+  GNUNET_assert (GNUNET_OK ==
+                 GNUNET_CONTAINER_multihashmap_remove (keys,
+                                                       &dk->h_denom_pub,
+                                                       dk));
+  if (0 != unlink (dk->filename))
+  {
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
+                              "unlink",
+                              dk->filename);
+  }
+  else
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Purged expired private key `%s'\n",
+                dk->filename);
+  }
+  GNUNET_free (dk->filename);
+  if (0 != dk->rc)
+  {
+    /* delay until all signing threads are done with this key */
+    dk->purge = true;
+    return;
+  }
+  GNUNET_CRYPTO_rsa_private_key_free (dk->denom_priv.rsa_private_key);
+  GNUNET_free (dk);
+}
+
+
+/**
+ * Create new keys and expire ancient keys of the given denomination @a denom.
+ * Removes the @a denom from the #denom_head DLL and re-insert its at the
+ * correct location sorted by next maintenance activity.
+ *
+ * @param[in,out] denom denomination to update material for
+ * @param now current time to use (to get many keys to use the exact same time)
+ */
+static void
+update_keys (struct Denomination *denom,
+             struct GNUNET_TIME_Absolute now)
+{
+  /* create new denomination keys */
+  while ( (NULL == denom->keys_tail) ||
+          (0 ==
+           GNUNET_TIME_absolute_get_remaining (
+             GNUNET_TIME_absolute_subtract (
+               GNUNET_TIME_absolute_subtract (
+                 GNUNET_TIME_absolute_add (denom->keys_tail->anchor,
+                                           denom->duration_withdraw),
+                 lookahead_sign),
+               overlap_duration)).rel_value_us) )
+    if (GNUNET_OK !=
+        create_key (denom,
+                    now))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                  "Failed to create keys for `%s'\n",
+                  denom->section);
+      return;
+    }
+  /* remove expired denomination keys */
+  while ( (NULL != denom->keys_head) &&
+          (0 ==
+           GNUNET_TIME_absolute_get_remaining
+             (GNUNET_TIME_absolute_add (denom->keys_head->anchor,
+                                        denom->duration_withdraw)).rel_value_us) )
+    purge_key (denom->keys_head);
+
+  /* Update position of 'denom' in #denom_head DLL: sort by action time */
+  {
+    struct Denomination *before;
+    struct GNUNET_TIME_Absolute at;
+
+    at = denomination_action_time (denom);
+    GNUNET_CONTAINER_DLL_remove (denom_head,
+                                 denom_tail,
+                                 denom);
+    before = NULL;
+    for (struct Denomination *pos = denom_head;
+         NULL != pos;
+         pos = pos->next)
+    {
+      if (denomination_action_time (pos).abs_value_us >= at.abs_value_us)
+        break;
+      before = pos;
+    }
+
+    GNUNET_CONTAINER_DLL_insert_after (denom_head,
+                                       denom_tail,
+                                       before,
+                                       denom);
+  }
+}
+
+
+/**
+ * Task run periodically to expire keys and/or generate fresh ones.
+ *
+ * @param cls NULL
+ */
+static void
+update_denominations (void *cls)
+{
+  struct Denomination *denom;
+  struct GNUNET_TIME_Absolute now;
+
+  (void) cls;
+  now = GNUNET_TIME_absolute_get ();
+  (void) GNUNET_TIME_round_abs (&now);
+  keygen_task = NULL;
+  do {
+    denom = denom_head;
+    update_keys (denom,
+                 now);
+  } while (denom != denom_head);
+  keygen_task = GNUNET_SCHEDULER_add_at (denomination_action_time (denom),
+                                         &update_denominations,
+                                         NULL);
+}
+
+
+/**
+ * Parse private key of denomination @a denom in @a buf.
+ *
+ * @param[out] denom denomination of the key
+ * @param filename name of the file we are parsing, for logging
+ * @param buf key material
+ * @param buf_size number of bytes in @a buf
+ */
+static void
+parse_key (struct Denomination *denom,
+           const char *filename,
+           const void *buf,
+           size_t buf_size)
+{
+  struct GNUNET_CRYPTO_RsaPrivateKey *priv;
+  char *anchor_s;
+  char dummy;
+  unsigned long long anchor_ll;
+  struct GNUNET_TIME_Absolute anchor;
+
+  anchor_s = strrchr (filename,
+                      '/');
+  if (NULL == anchor_s)
+  {
+    /* File in a directory without '/' in the name, this makes no sense. */
+    GNUNET_break (0);
+    return;
+  }
+  anchor_s++;
+  if (1 != sscanf (anchor_s,
+                   "%llu%c",
+                   &anchor_ll,
+                   &dummy))
+  {
+    /* Filenames in KEYDIR must ONLY be the anchor time in seconds! */
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "Filename `%s' invalid for key file, skipping\n",
+                filename);
+    return;
+  }
+  anchor.abs_value_us = anchor_ll * GNUNET_TIME_UNIT_SECONDS.rel_value_us;
+  if (anchor_ll != anchor.abs_value_us / GNUNET_TIME_UNIT_SECONDS.rel_value_us)
+  {
+    /* Integer overflow. Bad, invalid filename. */
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "Filename `%s' invalid for key file, skipping\n",
+                filename);
+    return;
+  }
+  priv = GNUNET_CRYPTO_rsa_private_key_decode (buf,
+                                               buf_size);
+  if (NULL == priv)
+  {
+    /* Parser failure. */
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "File `%s' is malformed, skipping\n",
+                filename);
+    return;
+  }
+
+  {
+    struct GNUNET_CRYPTO_RsaPublicKey *pub;
+    struct DenominationKey *dk;
+    struct DenominationKey *before;
+
+    pub = GNUNET_CRYPTO_rsa_private_key_get_public (priv);
+    if (NULL == pub)
+    {
+      GNUNET_break (0);
+      GNUNET_CRYPTO_rsa_private_key_free (priv);
+      return;
+    }
+    dk = GNUNET_new (struct DenominationKey);
+    dk->denom_priv.rsa_private_key = priv;
+    dk->denom = denom;
+    dk->anchor = anchor;
+    dk->filename = GNUNET_strdup (filename);
+    GNUNET_CRYPTO_rsa_public_key_hash (pub,
+                                       &dk->h_denom_pub);
+    dk->denom_pub.rsa_public_key = pub;
+    if (GNUNET_OK !=
+        GNUNET_CONTAINER_multihashmap_put (
+          keys,
+          &dk->h_denom_pub,
+          dk,
+          GNUNET_CONTAINER_MULTIHASHMAPOPTION_UNIQUE_ONLY))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                  "Duplicate private key %s detected in file `%s'. Skipping.\n",
+                  GNUNET_h2s (&dk->h_denom_pub),
+                  filename);
+      GNUNET_CRYPTO_rsa_private_key_free (priv);
+      GNUNET_CRYPTO_rsa_public_key_free (pub);
+      GNUNET_free (dk);
+      return;
+    }
+    before = NULL;
+    for (struct DenominationKey *pos = denom->keys_head;
+         NULL != pos;
+         pos = pos->next)
+    {
+      if (pos->anchor.abs_value_us > anchor.abs_value_us)
+        break;
+      before = pos;
+    }
+    GNUNET_CONTAINER_DLL_insert_after (denom->keys_head,
+                                       denom->keys_tail,
+                                       before,
+                                       dk);
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Imported key %s from `%s'\n",
+                GNUNET_h2s (&dk->h_denom_pub),
+                filename);
+  }
+}
+
+
+/**
+ * Import a private key from @a filename for the denomination
+ * given in @a cls.
+ *
+ * @param[in,out] cls a `struct Denomiantion`
+ * @param filename name of a file in the directory
+ */
+static int
+import_key (void *cls,
+            const char *filename)
+{
+  struct Denomination *denom = cls;
+  struct GNUNET_DISK_FileHandle *fh;
+  struct GNUNET_DISK_MapHandle *map;
+  void *ptr;
+  int fd;
+  struct stat sbuf;
+
+  {
+    struct stat lsbuf;
+
+    if (0 != lstat (filename,
+                    &lsbuf))
+    {
+      GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                                "lstat",
+                                filename);
+      return GNUNET_OK;
+    }
+    if (! S_ISREG (lsbuf.st_mode))
+    {
+      GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                  "File `%s' is not a regular file, which is not allowed for private keys!\n",
+                  filename);
+      return GNUNET_OK;
+    }
+  }
+
+  fd = open (filename,
+             O_CLOEXEC);
+  if (-1 == fd)
+  {
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                              "open",
+                              filename);
+    return GNUNET_OK;
+  }
+  if (0 != fstat (fd,
+                  &sbuf))
+  {
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                              "stat",
+                              filename);
+    return GNUNET_OK;
+  }
+  if (! S_ISREG (sbuf.st_mode))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "File `%s' is not a regular file, which is not allowed for private keys!\n",
+                filename);
+    return GNUNET_OK;
+  }
+  if (0 != (sbuf.st_mode & (S_IWUSR | S_IRWXG | S_IRWXO)))
+  {
+    /* permission are NOT tight, try to patch them up! */
+    if (0 !=
+        fchmod (fd,
+                S_IRUSR))
+    {
+      GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                                "fchmod",
+                                filename);
+      /* refuse to use key if file has wrong permissions */
+      GNUNET_break (0 == close (fd));
+      return GNUNET_OK;
+    }
+  }
+  fh = GNUNET_DISK_get_handle_from_int_fd (fd);
+  if (NULL == fh)
+  {
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                              "open",
+                              filename);
+    GNUNET_break (0 == close (fd));
+    return GNUNET_OK;
+  }
+  if (sbuf.st_size > 2048)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "File `%s' to big to be a private key\n",
+                filename);
+    GNUNET_DISK_file_close (fh);
+    return GNUNET_OK;
+  }
+  ptr = GNUNET_DISK_file_map (fh,
+                              &map,
+                              GNUNET_DISK_MAP_TYPE_READ,
+                              (size_t) sbuf.st_size);
+  if (NULL == ptr)
+  {
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                              "mmap",
+                              filename);
+    GNUNET_DISK_file_close (fh);
+    return GNUNET_OK;
+  }
+  parse_key (denom,
+             filename,
+             ptr,
+             (size_t) sbuf.st_size);
+  GNUNET_DISK_file_unmap (map);
+  GNUNET_DISK_file_close (fh);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Parse configuration for denomination type parameters.  Also determines
+ * our anchor by looking at the existing denominations of the same type.
+ *
+ * @param ct section in the configuration file giving the denomination type parameters
+ * @param[out] denom set to the denomination parameters from the configuration
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR if the configuration is invalid
+ */
+static int
+parse_denomination_cfg (const char *ct,
+                        struct Denomination *denom)
+{
+  unsigned long long rsa_keysize;
+
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (kcfg,
+                                           ct,
+                                           "DURATION_WITHDRAW",
+                                           &denom->duration_withdraw))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               ct,
+                               "DURATION_WITHDRAW");
+    return GNUNET_SYSERR;
+  }
+  GNUNET_TIME_round_rel (&denom->duration_withdraw);
+  if (overlap_duration.rel_value_us >=
+      denom->duration_withdraw.rel_value_us)
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               "taler-exchange-secmod-rsa",
+                               "OVERLAP_DURATION",
+                               "Value given must be smaller than value for DURATION_WITHDRAW!");
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_number (kcfg,
+                                             ct,
+                                             "RSA_KEYSIZE",
+                                             &rsa_keysize))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               ct,
+                               "RSA_KEYSIZE");
+    return GNUNET_SYSERR;
+  }
+  if ( (rsa_keysize > 4 * 2048) ||
+       (rsa_keysize < 1024) )
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               ct,
+                               "RSA_KEYSIZE",
+                               "Given RSA keysize outside of permitted range [1024,8192]\n");
+    return GNUNET_SYSERR;
+  }
+  denom->rsa_keysize = (unsigned int) rsa_keysize;
+  denom->section = GNUNET_strdup (ct);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Closure for #load_denominations.
+ */
+struct LoadContext
+{
+  /**
+   * Current time to use.
+   */
+  struct GNUNET_TIME_Absolute now;
+
+  /**
+   * Status, to be set to #GNUNET_SYSERR on failure
+   */
+  int ret;
+};
+
+
+/**
+ * Generate new denomination signing keys for the denomination type of the given @a
+ * denomination_alias.
+ *
+ * @param cls a `struct LoadContext`, with 'ret' to be set to #GNUNET_SYSERR on failure
+ * @param denomination_alias name of the denomination's section in the configuration
+ */
+static void
+load_denominations (void *cls,
+                    const char *denomination_alias)
+{
+  struct LoadContext *ctx = cls;
+  struct Denomination *denom;
+
+  if (0 != strncasecmp (denomination_alias,
+                        "coin_",
+                        strlen ("coin_")))
+    return; /* not a denomination type definition */
+  denom = GNUNET_new (struct Denomination);
+  if (GNUNET_OK !=
+      parse_denomination_cfg (denomination_alias,
+                              denom))
+  {
+    ctx->ret = GNUNET_SYSERR;
+    GNUNET_free (denom);
+    return;
+  }
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Loading keys for denomination %s\n",
+              denom->section);
+  {
+    char *dname;
+
+    GNUNET_asprintf (&dname,
+                     "%s/%s",
+                     keydir,
+                     denom->section);
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_DISK_directory_create (dname));
+    GNUNET_DISK_directory_scan (dname,
+                                &import_key,
+                                denom);
+    GNUNET_free (dname);
+  }
+  GNUNET_CONTAINER_DLL_insert (denom_head,
+                               denom_tail,
+                               denom);
+  update_keys (denom,
+               ctx->now);
+}
+
+
+/**
+ * Load the various duration values from #kcfg.
+ *
+ * @return #GNUNET_OK on success
+ */
+static int
+load_durations (void)
+{
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (kcfg,
+                                           "taler-exchange-secmod-rsa",
+                                           "OVERLAP_DURATION",
+                                           &overlap_duration))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "taler-exchange-secmod-rsa",
+                               "OVERLAP_DURATION");
+    return GNUNET_SYSERR;
+  }
+  GNUNET_TIME_round_rel (&overlap_duration);
+
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (kcfg,
+                                           "taler-exchange-secmod-rsa",
+                                           "LOOKAHEAD_SIGN",
+                                           &lookahead_sign))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "taler-exchange-secmod-rsa",
+                               "LOOKAHEAD_SIGN");
+    return GNUNET_SYSERR;
+  }
+  GNUNET_TIME_round_rel (&lookahead_sign);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Function run on shutdown. Stops the various jobs (nicely).
+ *
+ * @param cls NULL
+ */
+static void
+do_shutdown (void *cls)
+{
+  (void) cls;
+  if (NULL != read_task)
+  {
+    GNUNET_SCHEDULER_cancel (read_task);
+    read_task = NULL;
+  }
+  if (NULL != unix_sock)
+  {
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_NETWORK_socket_close (unix_sock));
+    unix_sock = NULL;
+  }
+  if (0 != unlink (unixpath))
+  {
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                              "unlink",
+                              unixpath);
+  }
+  GNUNET_free (unixpath);
+  if (NULL != keygen_task)
+  {
+    GNUNET_SCHEDULER_cancel (keygen_task);
+    keygen_task = NULL;
+  }
+  if (NULL != done_task)
+  {
+    GNUNET_SCHEDULER_cancel (done_task);
+    done_task = NULL;
+  }
+  /* shut down worker threads */
+  GNUNET_assert (0 == pthread_mutex_lock (&work_lock));
+  in_shutdown = true;
+  GNUNET_assert (0 == pthread_cond_broadcast (&work_cond));
+  GNUNET_assert (0 == pthread_mutex_unlock (&work_lock));
+  for (unsigned int i = 0; i<num_workers; i++)
+    GNUNET_assert (0 == pthread_join (workers[i],
+                                      NULL));
+  if (NULL != done_signal)
+  {
+    GNUNET_break (GNUNET_OK ==
+                  GNUNET_NETWORK_socket_close (done_signal));
+    done_signal = NULL;
+  }
+}
+
+
+/**
+ * Main function that will be run under the GNUnet scheduler.
+ *
+ * @param cls closure
+ * @param args remaining command-line arguments
+ * @param cfgfile name of the configuration file used (for saving, can be NULL!)
+ * @param cfg configuration
+ */
+static void
+run (void *cls,
+     char *const *args,
+     const char *cfgfile,
+     const struct GNUNET_CONFIGURATION_Handle *cfg)
+{
+  (void) cls;
+  (void) args;
+  (void) cfgfile;
+  kcfg = cfg;
+  if (now.abs_value_us != now_tmp.abs_value_us)
+  {
+    /* The user gave "--now", use it! */
+    now = now_tmp;
+  }
+  else
+  {
+    /* get current time again, we may be timetraveling! */
+    now = GNUNET_TIME_absolute_get ();
+  }
+  GNUNET_TIME_round_abs (&now);
+
+  {
+    char *pfn;
+
+    if (GNUNET_OK !=
+        GNUNET_CONFIGURATION_get_value_filename (kcfg,
+                                                 "taler-exchange-secmod-rsa",
+                                                 "SM_PRIV_KEY",
+                                                 &pfn))
+    {
+      GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                                 "taler-exchange-secmod-rsa",
+                                 "SM_PRIV_KEY");
+      global_ret = 1;
+      return;
+    }
+    if (GNUNET_SYSERR ==
+        GNUNET_CRYPTO_eddsa_key_from_file (pfn,
+                                           GNUNET_YES,
+                                           &smpriv.eddsa_priv))
+    {
+      GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                                 "taler-exchange-secmod-rsa",
+                                 "SM_PRIV_KEY",
+                                 "Could not use file to persist private key");
+      GNUNET_free (pfn);
+      global_ret = 1;
+      return;
+    }
+    GNUNET_free (pfn);
+    GNUNET_CRYPTO_eddsa_key_get_public (&smpriv.eddsa_priv,
+                                        &smpub.eddsa_pub);
+  }
+
+  if (GNUNET_OK !=
+      load_durations ())
+  {
+    global_ret = 1;
+    return;
+  }
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_filename (kcfg,
+                                               "taler-exchange-secmod-rsa",
+                                               "KEY_DIR",
+                                               &keydir))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "taler-exchange-secmod-rsa",
+                               "KEY_DIR");
+    global_ret = 1;
+    return;
+  }
+
+  /* open socket */
+  {
+    int sock;
+
+    sock = socket (PF_UNIX,
+                   SOCK_DGRAM,
+                   0);
+    if (-1 == sock)
+    {
+      GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR,
+                           "socket");
+      global_ret = 2;
+      return;
+    }
+    {
+      struct sockaddr_un un;
+
+      if (GNUNET_OK !=
+          GNUNET_CONFIGURATION_get_value_filename (kcfg,
+                                                   "taler-exchange-secmod-rsa",
+                                                   "UNIXPATH",
+                                                   &unixpath))
+      {
+        GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                                   "taler-exchange-secmod-rsa",
+                                   "UNIXPATH");
+        global_ret = 3;
+        return;
+      }
+      if (GNUNET_OK !=
+          GNUNET_DISK_directory_create_for_file (unixpath))
+      {
+        GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                                  "mkdir(dirname)",
+                                  unixpath);
+      }
+      if (0 != unlink (unixpath))
+      {
+        if (ENOENT != errno)
+          GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_WARNING,
+                                    "unlink",
+                                    unixpath);
+      }
+      memset (&un,
+              0,
+              sizeof (un));
+      un.sun_family = AF_UNIX;
+      strncpy (un.sun_path,
+               unixpath,
+               sizeof (un.sun_path));
+      if (0 != bind (sock,
+                     (const struct sockaddr *) &un,
+                     sizeof (un)))
+      {
+        GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
+                                  "bind",
+                                  unixpath);
+        global_ret = 3;
+        GNUNET_break (0 == close (sock));
+        return;
+      }
+    }
+    unix_sock = GNUNET_NETWORK_socket_box_native (sock);
+  }
+
+  GNUNET_SCHEDULER_add_shutdown (&do_shutdown,
+                                 NULL);
+
+  /* Load denominations */
+  keys = GNUNET_CONTAINER_multihashmap_create (65536,
+                                               GNUNET_YES);
+  {
+    struct LoadContext lc = {
+      .ret = GNUNET_OK,
+      .now = GNUNET_TIME_absolute_get ()
+    };
+
+    (void) GNUNET_TIME_round_abs (&lc.now);
+    GNUNET_CONFIGURATION_iterate_sections (kcfg,
+                                           &load_denominations,
+                                           &lc);
+    if (GNUNET_OK != lc.ret)
+    {
+      global_ret = 4;
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+  }
+  if (NULL == denom_head)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "No denominations configured\n");
+    global_ret = 5;
+    GNUNET_SCHEDULER_shutdown ();
+    return;
+  }
+
+  /* start job to accept incoming requests on 'sock' */
+  read_task = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                             unix_sock,
+                                             &read_job,
+                                             NULL);
+  /* start job to keep keys up-to-date; MUST be run before the #read_task,
+     hence with priority. */
+  keygen_task = GNUNET_SCHEDULER_add_with_priority (
+    GNUNET_SCHEDULER_PRIORITY_URGENT,
+    &update_denominations,
+    NULL);
+
+  /* start job to handle completed work */
+  {
+    int fd;
+
+    fd = eventfd (0,
+                  EFD_NONBLOCK | EFD_CLOEXEC);
+    if (-1 == fd)
+    {
+      GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR,
+                           "eventfd");
+      global_ret = 6;
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+    done_signal = GNUNET_NETWORK_socket_box_native (fd);
+  }
+  done_task = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                             done_signal,
+                                             &handle_done,
+                                             NULL);
+
+  /* start crypto workers */
+  if (0 == num_workers)
+    num_workers = sysconf (_SC_NPROCESSORS_CONF);
+  workers = GNUNET_new_array (num_workers,
+                              pthread_t);
+  for (unsigned int i = 0; i<num_workers; i++)
+    GNUNET_assert (0 ==
+                   pthread_create (&workers[i],
+                                   NULL,
+                                   &sign_worker,
+                                   NULL));
+}
+
+
+/**
+ * The entry point.
+ *
+ * @param argc number of arguments in @a argv
+ * @param argv command-line arguments
+ * @return 0 on normal termination
+ */
+int
+main (int argc,
+      char **argv)
+{
+  struct GNUNET_GETOPT_CommandLineOption options[] = {
+    GNUNET_GETOPT_option_timetravel ('T',
+                                     "timetravel"),
+    GNUNET_GETOPT_option_uint ('p',
+                               "parallelism",
+                               "NUM_WORKERS",
+                               "number of worker threads to use",
+                               &num_workers),
+    GNUNET_GETOPT_option_absolute_time ('t',
+                                        "time",
+                                        "TIMESTAMP",
+                                        "pretend it is a different time for the update",
+                                        &now_tmp),
+    GNUNET_GETOPT_OPTION_END
+  };
+  int ret;
+
+  (void) umask (S_IWGRP | S_IROTH | S_IWOTH | S_IXOTH);
+  /* force linker to link against libtalerutil; if we do
+   not do this, the linker may "optimize" libtalerutil
+   away and skip #TALER_OS_init(), which we do need */
+  GNUNET_OS_init (TALER_project_data_default ());
+  now = now_tmp = GNUNET_TIME_absolute_get ();
+  ret = GNUNET_PROGRAM_run (argc, argv,
+                            "taler-exchange-secmod-rsa",
+                            "Handle private RSA key operations for a Taler exchange",
+                            options,
+                            &run,
+                            NULL);
+  if (GNUNET_NO == ret)
+    return 0;
+  if (GNUNET_SYSERR == ret)
+    return 1;
+  return global_ret;
+}
-- 
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