create library functions for secmods

1 files changed, 2053 insertions, 0 deletions

diff --git a/src/util/secmod_rsa.c b/src/util/secmod_rsa.c
new file mode 100644
index 000000000..4217cbb33
--- /dev/null
+++ b/src/util/secmod_rsa.c
@@ -0,0 +1,2053 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2014-2024 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 thread 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 do the signing in parallel, one per client.
+ * - 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 "taler_error_codes.h"
+#include "taler_signatures.h"
+#include "secmod_common.h"
+#include <poll.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 GNUNET_CRYPTO_RsaPrivateKey *denom_priv;
+
+  /**
+   * The public key of the denomination.
+   */
+  struct GNUNET_CRYPTO_RsaPublicKey *denom_pub;
+
+  /**
+   * Message to transmit to clients to introduce this public key.
+   */
+  struct TALER_CRYPTO_RsaKeyAvailableNotification *an;
+
+  /**
+   * Hash of this denomination's public key.
+   */
+  struct TALER_RsaPubHashP h_rsa;
+
+  /**
+   * Time at which this key is supposed to become valid.
+   */
+  struct GNUNET_TIME_Timestamp anchor;
+
+  /**
+   * Generation when this key was created or revoked.
+   */
+  uint64_t key_gen;
+
+  /**
+   * 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;
+};
+
+
+/**
+ * A semaphore.
+ */
+struct Semaphore
+{
+  /**
+   * Mutex for the semaphore.
+   */
+  pthread_mutex_t mutex;
+
+  /**
+   * Condition variable for the semaphore.
+   */
+  pthread_cond_t cv;
+
+  /**
+   * Counter of the semaphore.
+   */
+  unsigned int ctr;
+};
+
+
+/**
+ * Job in a batch sign request.
+ */
+struct BatchJob;
+
+/**
+ * Handle for a thread that does work in batch signing.
+ */
+struct Worker
+{
+  /**
+   * Kept in a DLL.
+   */
+  struct Worker *prev;
+
+  /**
+   * Kept in a DLL.
+   */
+  struct Worker *next;
+
+  /**
+   * Job this worker should do next.
+   */
+  struct BatchJob *job;
+
+  /**
+   * Semaphore to signal the worker that a job is available.
+   */
+  struct Semaphore sem;
+
+  /**
+   * Handle for this thread.
+   */
+  pthread_t pt;
+
+  /**
+   * Set to true if the worker should terminate.
+   */
+  bool do_shutdown;
+};
+
+
+/**
+ * Job in a batch sign request.
+ */
+struct BatchJob
+{
+  /**
+   * Request we are working on.
+   */
+  const struct TALER_CRYPTO_SignRequest *sr;
+
+  /**
+   * Thread doing the work.
+   */
+  struct Worker *worker;
+
+  /**
+   * Result with the signature.
+   */
+  struct GNUNET_CRYPTO_RsaSignature *rsa_signature;
+
+  /**
+   * Semaphore to signal that the job is finished.
+   */
+  struct Semaphore sem;
+
+  /**
+   * Computation status.
+   */
+  enum TALER_ErrorCode ec;
+
+};
+
+
+/**
+ * Head of DLL of workers ready for more work.
+ */
+static struct Worker *worker_head;
+
+/**
+ * Tail of DLL of workers ready for more work.
+ */
+static struct Worker *worker_tail;
+
+/**
+ * Lock for manipulating the worker DLL.
+ */
+static pthread_mutex_t worker_lock;
+
+/**
+ * Total number of workers that were started.
+ */
+static unsigned int workers;
+
+/**
+ * Semaphore used to grab a worker.
+ */
+static struct Semaphore worker_sem;
+
+/**
+ * Command-line options for various TALER_SECMOD_XXX_run() functions.
+ */
+static struct TALER_SECMOD_Options *globals;
+
+/**
+ * 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;
+
+/**
+ * Task run to generate new keys.
+ */
+static struct GNUNET_SCHEDULER_Task *keygen_task;
+
+/**
+ * Lock for the keys queue.
+ */
+static pthread_mutex_t keys_lock;
+
+/**
+ * Current key generation.
+ */
+static uint64_t key_gen;
+
+
+/**
+ * Generate the announcement message for @a dk.
+ *
+ * @param[in,out] dk denomination key to generate the announcement for
+ */
+static void
+generate_response (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,
+                                                 &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_timestamp_hton (dk->anchor);
+  an->duration_withdraw = GNUNET_TIME_relative_hton (denom->duration_withdraw);
+  TALER_exchange_secmod_rsa_sign (&dk->h_rsa,
+                                  denom->section,
+                                  dk->anchor,
+                                  denom->duration_withdraw,
+                                  &TES_smpriv,
+                                  &an->secm_sig);
+  an->secm_pub = TES_smpub;
+  p = (void *) &an[1];
+  GNUNET_memcpy (p,
+                 buf,
+                 buf_len);
+  GNUNET_free (buf);
+  GNUNET_memcpy (p + buf_len,
+                 denom->section,
+                 nlen);
+  dk->an = an;
+}
+
+
+/**
+ * Do the actual signing work.
+ *
+ * @param h_rsa key to sign with
+ * @param bm blinded message to sign
+ * @param[out] rsa_signaturep set to the RSA signature
+ * @return #TALER_EC_NONE on success
+ */
+static enum TALER_ErrorCode
+do_sign (const struct TALER_RsaPubHashP *h_rsa,
+         const struct GNUNET_CRYPTO_RsaBlindedMessage *bm,
+         struct GNUNET_CRYPTO_RsaSignature **rsa_signaturep)
+{
+  struct DenominationKey *dk;
+  struct GNUNET_CRYPTO_RsaSignature *rsa_signature;
+  struct GNUNET_TIME_Absolute now = GNUNET_TIME_absolute_get ();
+
+  GNUNET_assert (0 == pthread_mutex_lock (&keys_lock));
+  dk = GNUNET_CONTAINER_multihashmap_get (keys,
+                                          &h_rsa->hash);
+  if (NULL == dk)
+  {
+    GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Signing request failed, denomination key %s unknown\n",
+                GNUNET_h2s (&h_rsa->hash));
+    return TALER_EC_EXCHANGE_GENERIC_DENOMINATION_KEY_UNKNOWN;
+  }
+  if (GNUNET_TIME_absolute_is_future (dk->anchor.abs_time))
+  {
+    /* it is too early */
+    GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Signing request failed, denomination key %s is not yet valid\n",
+                GNUNET_h2s (&h_rsa->hash));
+    return TALER_EC_EXCHANGE_DENOMINATION_HELPER_TOO_EARLY;
+  }
+
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Received request to sign over %u bytes with key %s\n",
+              (unsigned int) bm->blinded_msg_size,
+              GNUNET_h2s (&h_rsa->hash));
+  GNUNET_assert (dk->rc < UINT_MAX);
+  dk->rc++;
+  GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+  rsa_signature
+    = GNUNET_CRYPTO_rsa_sign_blinded (dk->denom_priv,
+                                      bm);
+  GNUNET_assert (0 == pthread_mutex_lock (&keys_lock));
+  GNUNET_assert (dk->rc > 0);
+  dk->rc--;
+  GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+  if (NULL == rsa_signature)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "Signing request failed, worker failed to produce signature\n");
+    return TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE;
+  }
+
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Sending RSA signature after %s\n",
+              GNUNET_TIME_relative2s (
+                GNUNET_TIME_absolute_get_duration (now),
+                GNUNET_YES));
+  *rsa_signaturep = rsa_signature;
+  return TALER_EC_NONE;
+}
+
+
+/**
+ * Generate error response that signing failed.
+ *
+ * @param client client to send response to
+ * @param ec error code to include
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+fail_sign (struct TES_Client *client,
+           enum TALER_ErrorCode ec)
+{
+  struct TALER_CRYPTO_SignFailure sf = {
+    .header.size = htons (sizeof (sf)),
+    .header.type = htons (TALER_HELPER_RSA_MT_RES_SIGN_FAILURE),
+    .ec = htonl (ec)
+  };
+
+  return TES_transmit (client->csock,
+                       &sf.header);
+}
+
+
+/**
+ * Generate signature response.
+ *
+ * @param client client to send response to
+ * @param[in] rsa_signature signature to send, freed by this function
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+send_signature (struct TES_Client *client,
+                struct GNUNET_CRYPTO_RsaSignature *rsa_signature)
+{
+  struct TALER_CRYPTO_SignResponse *sr;
+  void *buf;
+  size_t buf_size;
+  size_t tsize;
+  enum GNUNET_GenericReturnValue ret;
+
+  buf_size = GNUNET_CRYPTO_rsa_signature_encode (rsa_signature,
+                                                 &buf);
+  GNUNET_CRYPTO_rsa_signature_free (rsa_signature);
+  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);
+  GNUNET_memcpy (&sr[1],
+                 buf,
+                 buf_size);
+  GNUNET_free (buf);
+  ret = TES_transmit (client->csock,
+                      &sr->header);
+  GNUNET_free (sr);
+  return ret;
+}
+
+
+/**
+ * Handle @a client request @a sr to create signature. Create the
+ * signature using the respective key and return the result to
+ * the client.
+ *
+ * @param client the client making the request
+ * @param sr the request details
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+handle_sign_request (struct TES_Client *client,
+                     const struct TALER_CRYPTO_SignRequest *sr)
+{
+  struct GNUNET_CRYPTO_RsaBlindedMessage bm = {
+    .blinded_msg = (void *) &sr[1],
+    .blinded_msg_size = ntohs (sr->header.size) - sizeof (*sr)
+  };
+  struct GNUNET_CRYPTO_RsaSignature *rsa_signature;
+  enum TALER_ErrorCode ec;
+
+  ec = do_sign (&sr->h_rsa,
+                &bm,
+                &rsa_signature);
+  if (TALER_EC_NONE != ec)
+  {
+    return fail_sign (client,
+                      ec);
+  }
+  return send_signature (client,
+                         rsa_signature);
+}
+
+
+/**
+ * Initialize a semaphore @a sem with a value of @a val.
+ *
+ * @param[out] sem semaphore to initialize
+ * @param val initial value of the semaphore
+ */
+static void
+sem_init (struct Semaphore *sem,
+          unsigned int val)
+{
+  GNUNET_assert (0 ==
+                 pthread_mutex_init (&sem->mutex,
+                                     NULL));
+  GNUNET_assert (0 ==
+                 pthread_cond_init (&sem->cv,
+                                    NULL));
+  sem->ctr = val;
+}
+
+
+/**
+ * Decrement semaphore, blocks until this is possible.
+ *
+ * @param[in,out] sem semaphore to decrement
+ */
+static void
+sem_down (struct Semaphore *sem)
+{
+  GNUNET_assert (0 == pthread_mutex_lock (&sem->mutex));
+  while (0 == sem->ctr)
+  {
+    pthread_cond_wait (&sem->cv,
+                       &sem->mutex);
+  }
+  sem->ctr--;
+  GNUNET_assert (0 == pthread_mutex_unlock (&sem->mutex));
+}
+
+
+/**
+ * Increment semaphore, blocks until this is possible.
+ *
+ * @param[in,out] sem semaphore to decrement
+ */
+static void
+sem_up (struct Semaphore *sem)
+{
+  GNUNET_assert (0 == pthread_mutex_lock (&sem->mutex));
+  sem->ctr++;
+  GNUNET_assert (0 == pthread_mutex_unlock (&sem->mutex));
+  pthread_cond_signal (&sem->cv);
+}
+
+
+/**
+ * Release resources used by @a sem.
+ *
+ * @param[in] sem semaphore to release (except the memory itself)
+ */
+static void
+sem_done (struct Semaphore *sem)
+{
+  GNUNET_break (0 == pthread_cond_destroy (&sem->cv));
+  GNUNET_break (0 == pthread_mutex_destroy (&sem->mutex));
+}
+
+
+/**
+ * Main logic of a worker thread. Grabs work, does it,
+ * grabs more work.
+ *
+ * @param cls a `struct Worker *`
+ * @returns cls
+ */
+static void *
+worker (void *cls)
+{
+  struct Worker *w = cls;
+
+  while (true)
+  {
+    GNUNET_assert (0 == pthread_mutex_lock (&worker_lock));
+    GNUNET_CONTAINER_DLL_insert (worker_head,
+                                 worker_tail,
+                                 w);
+    GNUNET_assert (0 == pthread_mutex_unlock (&worker_lock));
+    sem_up (&worker_sem);
+    sem_down (&w->sem);
+    if (w->do_shutdown)
+      break;
+    {
+      struct BatchJob *bj = w->job;
+      const struct TALER_CRYPTO_SignRequest *sr = bj->sr;
+      struct GNUNET_CRYPTO_RsaBlindedMessage bm = {
+        .blinded_msg = (void *) &sr[1],
+        .blinded_msg_size = ntohs (sr->header.size) - sizeof (*sr)
+      };
+
+      bj->ec = do_sign (&sr->h_rsa,
+                        &bm,
+                        &bj->rsa_signature);
+      sem_up (&bj->sem);
+      w->job = NULL;
+    }
+  }
+  return w;
+}
+
+
+/**
+ * Start batch job @a bj to sign @a sr.
+ *
+ * @param sr signature request to answer
+ * @param[out] bj job data structure
+ */
+static void
+start_job (const struct TALER_CRYPTO_SignRequest *sr,
+           struct BatchJob *bj)
+{
+  sem_init (&bj->sem,
+            0);
+  bj->sr = sr;
+  sem_down (&worker_sem);
+  GNUNET_assert (0 == pthread_mutex_lock (&worker_lock));
+  bj->worker = worker_head;
+  GNUNET_CONTAINER_DLL_remove (worker_head,
+                               worker_tail,
+                               bj->worker);
+  GNUNET_assert (0 == pthread_mutex_unlock (&worker_lock));
+  bj->worker->job = bj;
+  sem_up (&bj->worker->sem);
+}
+
+
+/**
+ * Finish a job @a bj for a @a client.
+ *
+ * @param client who made the request
+ * @param[in,out] bj job to finish
+ */
+static void
+finish_job (struct TES_Client *client,
+            struct BatchJob *bj)
+{
+  sem_down (&bj->sem);
+  sem_done (&bj->sem);
+  if (TALER_EC_NONE != bj->ec)
+  {
+    fail_sign (client,
+               bj->ec);
+    return;
+  }
+  GNUNET_assert (NULL != bj->rsa_signature);
+  send_signature (client,
+                  bj->rsa_signature);
+  bj->rsa_signature = NULL; /* freed in send_signature */
+}
+
+
+/**
+ * Handle @a client request @a sr to create a batch of signature. Creates the
+ * signatures using the respective key and return the results to the client.
+ *
+ * @param client the client making the request
+ * @param bsr the request details
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+handle_batch_sign_request (struct TES_Client *client,
+                           const struct TALER_CRYPTO_BatchSignRequest *bsr)
+{
+  uint32_t bs = ntohl (bsr->batch_size);
+  uint16_t size = ntohs (bsr->header.size) - sizeof (*bsr);
+  const void *off = (const void *) &bsr[1];
+  unsigned int idx = 0;
+  struct BatchJob jobs[bs];
+  bool failure = false;
+
+  if (bs > TALER_MAX_FRESH_COINS)
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  while ( (bs > 0) &&
+          (size > sizeof (struct TALER_CRYPTO_SignRequest)) )
+  {
+    const struct TALER_CRYPTO_SignRequest *sr = off;
+    uint16_t s = ntohs (sr->header.size);
+
+    if (s > size)
+    {
+      failure = true;
+      bs = idx;
+      break;
+    }
+    start_job (sr,
+               &jobs[idx++]);
+    off += s;
+    size -= s;
+  }
+  GNUNET_break_op (0 == size);
+  bs = GNUNET_MIN (bs,
+                   idx);
+  for (unsigned int i = 0; i<bs; i++)
+    finish_job (client,
+                &jobs[i]);
+  if (failure)
+  {
+    struct TALER_CRYPTO_SignFailure sf = {
+      .header.size = htons (sizeof (sf)),
+      .header.type = htons (TALER_HELPER_RSA_MT_RES_BATCH_FAILURE),
+      .ec = htonl (TALER_EC_GENERIC_INTERNAL_INVARIANT_FAILURE)
+    };
+
+    GNUNET_break (0);
+    return TES_transmit (client->csock,
+                         &sf.header);
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Start worker thread for batch processing.
+ *
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+start_worker (void)
+{
+  struct Worker *w;
+
+  w = GNUNET_new (struct Worker);
+  sem_init (&w->sem,
+            0);
+  if (0 != pthread_create (&w->pt,
+                           NULL,
+                           &worker,
+                           w))
+  {
+    GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR,
+                         "pthread_create");
+    GNUNET_free (w);
+    return GNUNET_SYSERR;
+  }
+  workers++;
+  return GNUNET_OK;
+}
+
+
+/**
+ * Stop all worker threads.
+ */
+static void
+stop_workers (void)
+{
+  while (workers > 0)
+  {
+    struct Worker *w;
+    void *result;
+
+    sem_down (&worker_sem);
+    GNUNET_assert (0 == pthread_mutex_lock (&worker_lock));
+    w = worker_head;
+    GNUNET_CONTAINER_DLL_remove (worker_head,
+                                 worker_tail,
+                                 w);
+    GNUNET_assert (0 == pthread_mutex_unlock (&worker_lock));
+    w->do_shutdown = true;
+    sem_up (&w->sem);
+    pthread_join (w->pt,
+                  &result);
+    GNUNET_assert (result == w);
+    sem_done (&w->sem);
+    GNUNET_free (w);
+    workers--;
+  }
+}
+
+
+/**
+ * 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 enum GNUNET_GenericReturnValue
+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 ();
+    globals->global_ret = EXIT_FAILURE;
+    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_rsa.hash);
+  GNUNET_asprintf (&dk->filename,
+                   "%s/%s/%llu",
+                   keydir,
+                   denom->section,
+                   (unsigned long long) (dk->anchor.abs_time.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 at %s in `%s' (generation #%llu)\n",
+              GNUNET_h2s (&dk->h_rsa.hash),
+              GNUNET_TIME_timestamp2s (dk->anchor),
+              dk->filename,
+              (unsigned long long) key_gen);
+  dk->denom_priv = priv;
+  dk->denom_pub = pub;
+  dk->key_gen = key_gen;
+  generate_response (dk);
+  if (GNUNET_OK !=
+      GNUNET_CONTAINER_multihashmap_put (
+        keys,
+        &dk->h_rsa.hash,
+        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);
+    GNUNET_CRYPTO_rsa_public_key_free (dk->denom_pub);
+    GNUNET_free (dk->filename);
+    GNUNET_free (dk->an);
+    GNUNET_free (dk);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_CONTAINER_DLL_insert_after (denom->keys_head,
+                                     denom->keys_tail,
+                                     position,
+                                     dk);
+  return GNUNET_OK;
+}
+
+
+/**
+ * The withdraw period of a key @a dk has expired. Purge it.
+ *
+ * @param[in] dk expired denomination key to purge
+ */
+static void
+purge_key (struct DenominationKey *dk)
+{
+  if (dk->purge)
+    return;
+  if (0 != unlink (dk->filename))
+    GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
+                              "unlink",
+                              dk->filename);
+  GNUNET_free (dk->filename);
+  dk->purge = true;
+  dk->key_gen = key_gen;
+}
+
+
+/**
+ * A @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 client the client making the request
+ * @param rr the revocation request
+ */
+static enum GNUNET_GenericReturnValue
+handle_revoke_request (struct TES_Client *client,
+                       const struct TALER_CRYPTO_RevokeRequest *rr)
+{
+  struct DenominationKey *dk;
+  struct DenominationKey *ndk;
+  struct Denomination *denom;
+
+  (void) client;
+  GNUNET_assert (0 == pthread_mutex_lock (&keys_lock));
+  dk = GNUNET_CONTAINER_multihashmap_get (keys,
+                                          &rr->h_rsa.hash);
+  if (NULL == dk)
+  {
+    GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "Revocation request ignored, denomination key %s unknown\n",
+                GNUNET_h2s (&rr->h_rsa.hash));
+    return GNUNET_OK;
+  }
+  if (dk->purge)
+  {
+    GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "Revocation request ignored, denomination key %s already revoked\n",
+                GNUNET_h2s (&rr->h_rsa.hash));
+    return GNUNET_OK;
+  }
+
+  key_gen++;
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Revoking key %s, bumping generation to %llu\n",
+              GNUNET_h2s (&rr->h_rsa.hash),
+              (unsigned long long) key_gen);
+  purge_key (dk);
+
+  /* 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_assert (0 == pthread_mutex_unlock (&keys_lock));
+    GNUNET_break (0);
+    GNUNET_SCHEDULER_shutdown ();
+    globals->global_ret = EXIT_FAILURE;
+    return GNUNET_SYSERR;
+  }
+  GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+  TES_wake_clients ();
+  return GNUNET_OK;
+}
+
+
+/**
+ * Handle @a hdr message received from @a client.
+ *
+ * @param client the client that received the message
+ * @param hdr message that was received
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+rsa_work_dispatch (struct TES_Client *client,
+                   const struct GNUNET_MessageHeader *hdr)
+{
+  uint16_t msize = ntohs (hdr->size);
+
+  switch (ntohs (hdr->type))
+  {
+  case TALER_HELPER_RSA_MT_REQ_SIGN:
+    if (msize <= sizeof (struct TALER_CRYPTO_SignRequest))
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    return handle_sign_request (
+      client,
+      (const struct TALER_CRYPTO_SignRequest *) hdr);
+  case TALER_HELPER_RSA_MT_REQ_REVOKE:
+    if (msize != sizeof (struct TALER_CRYPTO_RevokeRequest))
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    return handle_revoke_request (
+      client,
+      (const struct TALER_CRYPTO_RevokeRequest *) hdr);
+  case TALER_HELPER_RSA_MT_REQ_BATCH_SIGN:
+    if (msize <= sizeof (struct TALER_CRYPTO_BatchSignRequest))
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    return handle_batch_sign_request (
+      client,
+      (const struct TALER_CRYPTO_BatchSignRequest *) hdr);
+  default:
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+}
+
+
+/**
+ * Send our initial key set to @a client together with the
+ * "sync" terminator.
+ *
+ * @param client the client to inform
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+rsa_client_init (struct TES_Client *client)
+{
+  size_t obs = 0;
+  char *buf;
+
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Initializing new client %p\n",
+              client);
+  GNUNET_assert (0 == pthread_mutex_lock (&keys_lock));
+  for (struct Denomination *denom = denom_head;
+       NULL != denom;
+       denom = denom->next)
+  {
+    for (struct DenominationKey *dk = denom->keys_head;
+         NULL != dk;
+         dk = dk->next)
+    {
+      GNUNET_assert (obs + ntohs (dk->an->header.size)
+                     > obs);
+      obs += ntohs (dk->an->header.size);
+    }
+  }
+  buf = GNUNET_malloc (obs);
+  obs = 0;
+  for (struct Denomination *denom = denom_head;
+       NULL != denom;
+       denom = denom->next)
+  {
+    for (struct DenominationKey *dk = denom->keys_head;
+         NULL != dk;
+         dk = dk->next)
+    {
+      GNUNET_memcpy (&buf[obs],
+                     dk->an,
+                     ntohs (dk->an->header.size));
+      GNUNET_assert (obs + ntohs (dk->an->header.size)
+                     > obs);
+      obs += ntohs (dk->an->header.size);
+    }
+  }
+  client->key_gen = key_gen;
+  GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+  if (GNUNET_OK !=
+      TES_transmit_raw (client->csock,
+                        obs,
+                        buf))
+  {
+    GNUNET_free (buf);
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Client %p must have disconnected\n",
+                client);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_free (buf);
+  {
+    struct GNUNET_MessageHeader synced = {
+      .type = htons (TALER_HELPER_RSA_SYNCED),
+      .size = htons (sizeof (synced))
+    };
+
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Sending RSA SYNCED message to %p\n",
+                client);
+    if (GNUNET_OK !=
+        TES_transmit (client->csock,
+                      &synced))
+    {
+      GNUNET_break (0);
+      return GNUNET_SYSERR;
+    }
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Notify @a client about all changes to the keys since
+ * the last generation known to the @a client.
+ *
+ * @param client the client to notify
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+rsa_update_client_keys (struct TES_Client *client)
+{
+  size_t obs = 0;
+  char *buf;
+  enum GNUNET_GenericReturnValue ret;
+
+  GNUNET_assert (0 == pthread_mutex_lock (&keys_lock));
+  for (struct Denomination *denom = denom_head;
+       NULL != denom;
+       denom = denom->next)
+  {
+    for (struct DenominationKey *key = denom->keys_head;
+         NULL != key;
+         key = key->next)
+    {
+      if (key->key_gen <= client->key_gen)
+        continue;
+      if (key->purge)
+        obs += sizeof (struct TALER_CRYPTO_RsaKeyPurgeNotification);
+      else
+        obs += ntohs (key->an->header.size);
+    }
+  }
+  if (0 == obs)
+  {
+    /* nothing to do */
+    client->key_gen = key_gen;
+    GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+    return GNUNET_OK;
+  }
+  buf = GNUNET_malloc (obs);
+  obs = 0;
+  for (struct Denomination *denom = denom_head;
+       NULL != denom;
+       denom = denom->next)
+  {
+    for (struct DenominationKey *key = denom->keys_head;
+         NULL != key;
+         key = key->next)
+    {
+      if (key->key_gen <= client->key_gen)
+        continue;
+      if (key->purge)
+      {
+        struct TALER_CRYPTO_RsaKeyPurgeNotification pn = {
+          .header.type = htons (TALER_HELPER_RSA_MT_PURGE),
+          .header.size = htons (sizeof (pn)),
+          .h_rsa = key->h_rsa
+        };
+
+        GNUNET_memcpy (&buf[obs],
+                       &pn,
+                       sizeof (pn));
+        GNUNET_assert (obs + sizeof (pn)
+                       > obs);
+        obs += sizeof (pn);
+      }
+      else
+      {
+        GNUNET_memcpy (&buf[obs],
+                       key->an,
+                       ntohs (key->an->header.size));
+        GNUNET_assert (obs + ntohs (key->an->header.size)
+                       > obs);
+        obs += ntohs (key->an->header.size);
+      }
+    }
+  }
+  client->key_gen = key_gen;
+  GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+  ret = TES_transmit_raw (client->csock,
+                          obs,
+                          buf);
+  GNUNET_free (buf);
+  return ret;
+}
+
+
+/**
+ * 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 enum GNUNET_GenericReturnValue
+create_key (struct Denomination *denom,
+            struct GNUNET_TIME_Timestamp now)
+{
+  struct DenominationKey *dk;
+  struct GNUNET_TIME_Timestamp anchor;
+
+  anchor = now;
+  // FIXME: round down to multiple of 'anchor_round' value from configuration
+  if (NULL != denom->keys_tail)
+  {
+    struct GNUNET_TIME_Absolute abs;
+
+    abs = GNUNET_TIME_absolute_add (denom->keys_tail->anchor.abs_time,
+                                    GNUNET_TIME_relative_subtract (
+                                      denom->duration_withdraw,
+                                      overlap_duration));
+    if (GNUNET_TIME_absolute_cmp (now.abs_time, <, abs))
+      anchor = GNUNET_TIME_absolute_to_timestamp (abs);
+  }
+  dk = GNUNET_new (struct DenominationKey);
+  dk->denom = denom;
+  dk->anchor = anchor;
+  if (GNUNET_OK !=
+      setup_key (dk,
+                 denom->keys_tail))
+  {
+    GNUNET_break (0);
+    GNUNET_free (dk);
+    GNUNET_SCHEDULER_shutdown ();
+    globals->global_ret = EXIT_FAILURE;
+    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)
+{
+  struct DenominationKey *head = denom->keys_head;
+  struct DenominationKey *tail = denom->keys_tail;
+  struct GNUNET_TIME_Absolute tt;
+
+  if (NULL == head)
+    return GNUNET_TIME_UNIT_ZERO_ABS;
+  tt = GNUNET_TIME_absolute_subtract (
+    GNUNET_TIME_absolute_subtract (
+      GNUNET_TIME_absolute_add (tail->anchor.abs_time,
+                                denom->duration_withdraw),
+      lookahead_sign),
+    overlap_duration);
+  if (head->rc > 0)
+    return tt; /* head expiration does not count due to rc > 0 */
+  return GNUNET_TIME_absolute_min (
+    GNUNET_TIME_absolute_add (head->anchor.abs_time,
+                              denom->duration_withdraw),
+    tt);
+}
+
+
+/**
+ * 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)
+ * @param[in,out] wake set to true if we should wake the clients
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+update_keys (struct Denomination *denom,
+             struct GNUNET_TIME_Timestamp now,
+             bool *wake)
+{
+  /* create new denomination keys */
+  if (NULL != denom->keys_tail)
+    GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+                "Updating keys of denomination `%s', last key %s valid for another %s\n",
+                denom->section,
+                GNUNET_h2s (&denom->keys_tail->h_rsa.hash),
+                GNUNET_TIME_relative2s (
+                  GNUNET_TIME_absolute_get_remaining (
+                    GNUNET_TIME_absolute_subtract (
+                      GNUNET_TIME_absolute_add (
+                        denom->keys_tail->anchor.abs_time,
+                        denom->duration_withdraw),
+                      overlap_duration)),
+                  GNUNET_YES));
+  while ( (NULL == denom->keys_tail) ||
+          GNUNET_TIME_absolute_is_past (
+            GNUNET_TIME_absolute_subtract (
+              GNUNET_TIME_absolute_subtract (
+                GNUNET_TIME_absolute_add (denom->keys_tail->anchor.abs_time,
+                                          denom->duration_withdraw),
+                lookahead_sign),
+              overlap_duration)) )
+  {
+    if (! *wake)
+    {
+      key_gen++;
+      *wake = true;
+    }
+    if (GNUNET_OK !=
+        create_key (denom,
+                    now))
+    {
+      GNUNET_break (0);
+      globals->global_ret = EXIT_FAILURE;
+      GNUNET_SCHEDULER_shutdown ();
+      return GNUNET_SYSERR;
+    }
+  }
+  /* remove expired denomination keys */
+  while ( (NULL != denom->keys_head) &&
+          GNUNET_TIME_absolute_is_past
+            (GNUNET_TIME_absolute_add (denom->keys_head->anchor.abs_time,
+                                       denom->duration_withdraw)) )
+  {
+    struct DenominationKey *key = denom->keys_head;
+    struct DenominationKey *nxt = key->next;
+
+    if (0 != key->rc)
+      break; /* later */
+    GNUNET_CONTAINER_DLL_remove (denom->keys_head,
+                                 denom->keys_tail,
+                                 key);
+    GNUNET_assert (GNUNET_OK ==
+                   GNUNET_CONTAINER_multihashmap_remove (
+                     keys,
+                     &key->h_rsa.hash,
+                     key));
+    if ( (! key->purge) &&
+         (0 != unlink (key->filename)) )
+      GNUNET_log_strerror_file (GNUNET_ERROR_TYPE_ERROR,
+                                "unlink",
+                                key->filename);
+    GNUNET_free (key->filename);
+    GNUNET_CRYPTO_rsa_private_key_free (key->denom_priv);
+    GNUNET_CRYPTO_rsa_public_key_free (key->denom_pub);
+    GNUNET_free (key->an);
+    GNUNET_free (key);
+    key = nxt;
+  }
+
+  /* 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 (GNUNET_TIME_absolute_cmp (denomination_action_time (pos), >=, at))
+        break;
+      before = pos;
+    }
+    GNUNET_CONTAINER_DLL_insert_after (denom_head,
+                                       denom_tail,
+                                       before,
+                                       denom);
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * 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;
+  struct GNUNET_TIME_Timestamp t;
+  bool wake = false;
+
+  (void) cls;
+  keygen_task = NULL;
+  now = GNUNET_TIME_absolute_get ();
+  t = GNUNET_TIME_absolute_to_timestamp (now);
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Updating denominations ...\n");
+  GNUNET_assert (0 == pthread_mutex_lock (&keys_lock));
+  do {
+    denom = denom_head;
+    if (GNUNET_OK !=
+        update_keys (denom,
+                     t,
+                     &wake))
+      return;
+  } while (denom != denom_head);
+  GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Updating denominations finished ...\n");
+  if (wake)
+    TES_wake_clients ();
+  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_Timestamp 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_time.abs_value_us
+    = anchor_ll * GNUNET_TIME_UNIT_SECONDS.rel_value_us;
+  if (anchor_ll != anchor.abs_time.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 = priv;
+    dk->denom = denom;
+    dk->anchor = anchor;
+    dk->filename = GNUNET_strdup (filename);
+    GNUNET_CRYPTO_rsa_public_key_hash (pub,
+                                       &dk->h_rsa.hash);
+    dk->denom_pub = pub;
+    generate_response (dk);
+    if (GNUNET_OK !=
+        GNUNET_CONTAINER_multihashmap_put (
+          keys,
+          &dk->h_rsa.hash,
+          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_rsa.hash),
+                  filename);
+      GNUNET_CRYPTO_rsa_private_key_free (priv);
+      GNUNET_CRYPTO_rsa_public_key_free (pub);
+      GNUNET_free (dk->an);
+      GNUNET_free (dk);
+      return;
+    }
+    before = NULL;
+    for (struct DenominationKey *pos = denom->keys_head;
+         NULL != pos;
+         pos = pos->next)
+    {
+      if (GNUNET_TIME_timestamp_cmp (pos->anchor,
+                                     >,
+                                     anchor))
+        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_rsa.hash),
+                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
+ * @return #GNUNET_OK (always, continue to iterate)
+ */
+static enum GNUNET_GenericReturnValue
+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_RDONLY | 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);
+    GNUNET_break (0 == close (fd));
+    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);
+    GNUNET_break (0 == close (fd));
+    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 > 16 * 1024)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "File `%s' too 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 cfg configuration to use
+ * @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 enum GNUNET_GenericReturnValue
+parse_denomination_cfg (const struct GNUNET_CONFIGURATION_Handle *cfg,
+                        const char *ct,
+                        struct Denomination *denom)
+{
+  unsigned long long rsa_keysize;
+  char *secname;
+
+  GNUNET_asprintf (&secname,
+                   "%s-secmod-rsa",
+                   globals->section);
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (cfg,
+                                           ct,
+                                           "DURATION_WITHDRAW",
+                                           &denom->duration_withdraw))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               ct,
+                               "DURATION_WITHDRAW");
+    GNUNET_free (secname);
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_TIME_relative_cmp (overlap_duration,
+                                >=,
+                                denom->duration_withdraw))
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               secname,
+                               "OVERLAP_DURATION",
+                               "Value given must be smaller than value for DURATION_WITHDRAW!");
+    GNUNET_free (secname);
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_number (cfg,
+                                             ct,
+                                             "RSA_KEYSIZE",
+                                             &rsa_keysize))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               ct,
+                               "RSA_KEYSIZE");
+    GNUNET_free (secname);
+    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");
+    GNUNET_free (secname);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_free (secname);
+  denom->rsa_keysize = (unsigned int) rsa_keysize;
+  denom->section = GNUNET_strdup (ct);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Closure for #load_denominations.
+ */
+struct LoadContext
+{
+
+  /**
+   * Configuration to use.
+   */
+  const struct GNUNET_CONFIGURATION_Handle *cfg;
+
+  /**
+   * Current time to use.
+   */
+  struct GNUNET_TIME_Timestamp t;
+
+  /**
+   * Status, to be set to #GNUNET_SYSERR on failure
+   */
+  enum GNUNET_GenericReturnValue 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;
+  bool wake = true;
+  char *cipher;
+
+  if ( (0 != strncasecmp (denomination_alias,
+                          "coin_",
+                          strlen ("coin_"))) &&
+       (0 != strncasecmp (denomination_alias,
+                          "coin-",
+                          strlen ("coin-"))) )
+    return; /* not a denomination type definition */
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_string (ctx->cfg,
+                                             denomination_alias,
+                                             "CIPHER",
+                                             &cipher))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               denomination_alias,
+                               "CIPHER");
+    return;
+  }
+  if (0 != strcmp (cipher, "RSA"))
+  {
+    GNUNET_free (cipher);
+    return; /* Ignore denominations of other types than CS */
+  }
+  GNUNET_free (cipher);
+  denom = GNUNET_new (struct Denomination);
+  if (GNUNET_OK !=
+      parse_denomination_cfg (ctx->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->t,
+               &wake);
+}
+
+
+/**
+ * Load the various duration values from @a cfg
+ *
+ * @param cfg configuration to use
+ * @return #GNUNET_OK on success
+ */
+static enum GNUNET_GenericReturnValue
+load_durations (const struct GNUNET_CONFIGURATION_Handle *cfg)
+{
+  char *secname;
+
+  GNUNET_asprintf (&secname,
+                   "%s-secmod-rsa",
+                   globals->section);
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (cfg,
+                                           secname,
+                                           "OVERLAP_DURATION",
+                                           &overlap_duration))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               secname,
+                               "OVERLAP_DURATION");
+    GNUNET_free (secname);
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (cfg,
+                                           secname,
+                                           "LOOKAHEAD_SIGN",
+                                           &lookahead_sign))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               secname,
+                               "LOOKAHEAD_SIGN");
+    GNUNET_free (secname);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_free (secname);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Function run on shutdown. Stops the various jobs (nicely).
+ *
+ * @param cls NULL
+ */
+static void
+do_shutdown (void *cls)
+{
+  (void) cls;
+  TES_listen_stop ();
+  if (NULL != keygen_task)
+  {
+    GNUNET_SCHEDULER_cancel (keygen_task);
+    keygen_task = NULL;
+  }
+  stop_workers ();
+  sem_done (&worker_sem);
+}
+
+
+/**
+ * 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
+ */
+void
+TALER_SECMOD_rsa_run (void *cls,
+                      char *const *args,
+                      const char *cfgfile,
+                      const struct GNUNET_CONFIGURATION_Handle *cfg)
+{
+  static struct TES_Callbacks cb = {
+    .dispatch = rsa_work_dispatch,
+    .updater = rsa_update_client_keys,
+    .init = rsa_client_init
+  };
+  struct TALER_SECMOD_Options *opt = cls;
+  char *secname;
+
+  (void) args;
+  (void) cfgfile;
+  globals = opt;
+  if (GNUNET_TIME_timestamp_cmp (opt->global_now,
+                                 !=,
+                                 opt->global_now_tmp))
+  {
+    /* The user gave "--now", use it! */
+    opt->global_now = opt->global_now_tmp;
+  }
+  else
+  {
+    /* get current time again, we may be timetraveling! */
+    opt->global_now = GNUNET_TIME_timestamp_get ();
+  }
+  GNUNET_asprintf (&secname,
+                   "%s-secmod-rsa",
+                   opt->section);
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_filename (cfg,
+                                               secname,
+                                               "KEY_DIR",
+                                               &keydir))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               secname,
+                               "KEY_DIR");
+    GNUNET_free (secname);
+    opt->global_ret = EXIT_NOTCONFIGURED;
+    return;
+  }
+  if (GNUNET_OK !=
+      load_durations (cfg))
+  {
+    opt->global_ret = EXIT_NOTCONFIGURED;
+    GNUNET_free (secname);
+    return;
+  }
+  GNUNET_asprintf (&secname,
+                   "%s-secmod-rsa",
+                   opt->section);
+  opt->global_ret = TES_listen_start (cfg,
+                                      secname,
+                                      &cb);
+  GNUNET_free (secname);
+  if (0 != opt->global_ret)
+    return;
+  sem_init (&worker_sem,
+            0);
+  GNUNET_SCHEDULER_add_shutdown (&do_shutdown,
+                                 NULL);
+  if (0 == opt->max_workers)
+  {
+    long lret;
+
+    lret = sysconf (_SC_NPROCESSORS_CONF);
+    if (lret <= 0)
+      lret = 1;
+    opt->max_workers = (unsigned int) lret;
+  }
+
+  for (unsigned int i = 0; i<opt->max_workers; i++)
+    if (GNUNET_OK !=
+        start_worker ())
+    {
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+  /* Load denominations */
+  keys = GNUNET_CONTAINER_multihashmap_create (65536,
+                                               true);
+  {
+    struct LoadContext lc = {
+      .cfg = cfg,
+      .ret = GNUNET_OK,
+      .t = opt->global_now
+    };
+
+    GNUNET_assert (0 == pthread_mutex_lock (&keys_lock));
+    GNUNET_CONFIGURATION_iterate_sections (cfg,
+                                           &load_denominations,
+                                           &lc);
+    GNUNET_assert (0 == pthread_mutex_unlock (&keys_lock));
+    if (GNUNET_OK != lc.ret)
+    {
+      opt->global_ret = EXIT_FAILURE;
+      GNUNET_SCHEDULER_shutdown ();
+      return;
+    }
+  }
+  if (NULL == denom_head)
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "No RSA denominations configured\n");
+    TES_wake_clients ();
+    return;
+  }
+  /* start job to keep keys up-to-date; MUST be run before the #listen_task,
+     hence with priority. */
+  keygen_task = GNUNET_SCHEDULER_add_with_priority (
+    GNUNET_SCHEDULER_PRIORITY_URGENT,
+    &update_denominations,
+    NULL);
+}