diff --git a/src/exchange-tools/key-helper.c b/src/exchange-tools/key-helper.c
index 13af9f720..9fd7d50a6 100644
--- a/src/exchange-tools/key-helper.c
+++ b/src/exchange-tools/key-helper.c
@@ -105,7 +105,7 @@ get_and_check_master_key (const struct GNUNET_CONFIGURATION_Handle *cfg,
                                        sizeof (mpub_cfg)))
     {
       fprintf (stderr,
-               "MASTER_PUBLIC_KEY value `%s' specified in section [exchange] of the configuration is a valid public key\n",
+               "MASTER_PUBLIC_KEY value `%s' specified in section [exchange] of the configuration is not a valid public key\n",
                masters);
       GNUNET_free (masters);
       GNUNET_free (fn);
diff --git a/src/util/taler-helper-crypto-rsa.c b/src/util/taler-helper-crypto-rsa.c
new file mode 100644
index 000000000..3aadd0566
--- /dev/null
+++ b/src/util/taler-helper-crypto-rsa.c
@@ -0,0 +1,683 @@
+/*
+  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-helper-crypto-rsa.c
+ * @brief Standalone process to perform private key RSA operations
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include "taler_util.h"
+#include <gcrypt.h>
+
+
+/**
+ * Information we keep per denomination.
+ */
+struct Denomination;
+
+
+/**
+ * One particular denomination key.
+ */
+struct DenominationKey
+{
+
+  /**
+   * Kept in a DLL of the respective denomination.
+   */
+  struct DenominationKey *next;
+
+  /**
+   * Kept in a DLL of the respective denomination.
+   */
+  struct DenominationKey *prev;
+
+  /**
+   * Denomination this key belongs to.
+   */
+  struct Denomination *denom;
+
+  /**
+   * Denomination key details.  Note that the "dki.issue.signature"
+   * IS ALWAYS uninitialized (all zeros).  The private key is in
+   * 'dki.denom_priv.rsa_private_key' and must be free'd explicitly
+   * (as it is a pointer to a variable-size data structure).
+   */
+  struct TALER_EXCHANGEDB_DenominationKey dki;
+
+  /**
+   * Time at which this key is supposed to become valid.
+   */
+  struct GNUNET_TIME_Absolute anchor;
+
+};
+
+
+struct Denomination
+{
+
+  /**
+   * Kept in a DLL. Sorted?
+   */
+  struct Denomination *next;
+
+  /**
+   * Kept in a DLL. Sorted?
+   */
+  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 are the signatures legally valid?  Should be
+   * significantly larger than @e duration_spend (i.e. years).
+   */
+  struct GNUNET_TIME_Relative duration_legal;
+
+  /**
+   * How long can the coins be spend?  Should be significantly
+   * larger than @e duration_withdraw (i.e. years).
+   */
+  struct GNUNET_TIME_Relative duration_spend;
+
+  /**
+   * 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 value of each coin?
+   */
+  struct TALER_Amount value;
+
+  /**
+   * What is the fee charged for withdrawal?
+   */
+  struct TALER_Amount fee_withdraw;
+
+  /**
+   * What is the fee charged for deposits?
+   */
+  struct TALER_Amount fee_deposit;
+
+  /**
+   * What is the fee charged for melting?
+   */
+  struct TALER_Amount fee_refresh;
+
+  /**
+   * What is the fee charged for refunds?
+   */
+  struct TALER_Amount fee_refund;
+
+  /**
+   * Length of (new) RSA keys (in bits).
+   */
+  uint32_t rsa_keysize;
+};
+
+
+/**
+ * Return value from main().
+ */
+static int global_ret;
+
+/**
+ * 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;
+
+/**
+ * The configured currency.
+ */
+static char *currency;
+
+/**
+ * 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 - #duration_overlap apart.
+ */
+static struct GNUNET_TIME_Relative overlap_duration;
+
+/**
+ * How long should keys be legally valid?
+ */
+static struct GNUNET_TIME_Relative legal_duration;
+
+/**
+ * How long into the future do we pre-generate keys?
+ */
+static struct GNUNET_TIME_Relative lookahead_sign;
+
+/**
+ * Largest duration for spending of any key.
+ */
+static struct GNUNET_TIME_Relative max_duration_spend;
+
+/**
+ * Until what time do we provide keys?
+ */
+static struct GNUNET_TIME_Absolute lookahead_sign_stamp;
+
+/**
+ * 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 *lsock;
+
+/**
+ * Task run to accept new inbound connections.
+ */
+static struct GNUNET_SCHEDULER_Task *accept_task;
+
+/**
+ * Task run to generate new keys.
+ */
+static struct GNUNET_SCHEDULER_Task *keygen_task;
+
+
+/**
+ * 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,
+                                           "exchange",
+                                           "LEGAL_DURATION",
+                                           &legal_duration))
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               "exchange",
+                               "LEGAL_DURATION",
+                               "fails to specify valid timeframe");
+    return GNUNET_SYSERR;
+  }
+  GNUNET_TIME_round_rel (&legal_duration);
+
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (kcfg,
+                                           "exchangedb",
+                                           "OVERLAP_DURATION",
+                                           &overlap_duration))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "exchangedb",
+                               "OVERLAP_DURATION");
+    return GNUNET_SYSERR;
+  }
+  GNUNET_TIME_round_rel (&overlap_duration);
+
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (kcfg,
+                                           "exchange",
+                                           "LOOKAHEAD_SIGN",
+                                           &lookahead_sign))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "exchange",
+                               "LOOKAHEAD_SIGN");
+    return GNUNET_SYSERR;
+  }
+  GNUNET_TIME_round_rel (&lookahead_sign);
+
+  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)
+{
+  const char *dir;
+  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 (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (kcfg,
+                                           ct,
+                                           "DURATION_SPEND",
+                                           &denom->duration_spend))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               ct,
+                               "DURATION_SPEND");
+    return GNUNET_SYSERR;
+  }
+  GNUNET_TIME_round_rel (&denom->duration_spend);
+  max_duration_spend = GNUNET_TIME_relative_max (max_duration_spend,
+                                                 denom->duration_spend);
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_time (kcfg,
+                                           ct,
+                                           "DURATION_LEGAL",
+                                           &denom->duration_legal))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               ct,
+                               "DURATION_LEGAL");
+    return GNUNET_SYSERR;
+  }
+  GNUNET_TIME_round_rel (&denom->duration_legal);
+  if (duration_overlap.rel_value_us >=
+      denom->duration_withdraw.rel_value_us)
+  {
+    GNUNET_log_config_invalid (GNUNET_ERROR_TYPE_ERROR,
+                               "exchangedb",
+                               "DURATION_OVERLAP",
+                               "Value given for DURATION_OVERLAP 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,
+                               "exchangedb",
+                               "RSA_KEYSIZE",
+                               "Given RSA keysize outside of permitted range [1024,8192]\n");
+    return GNUNET_SYSERR;
+  }
+  denom->rsa_keysize = (unsigned int) rsa_keysize;
+  if (GNUNET_OK !=
+      TALER_config_get_amount (kcfg,
+                               ct,
+                               "VALUE",
+                               &denom->value))
+  {
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      TALER_config_get_amount (kcfg,
+                               ct,
+                               "FEE_WITHDRAW",
+                               &denom->fee_withdraw))
+  {
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      TALER_config_get_amount (kcfg,
+                               ct,
+                               "FEE_DEPOSIT",
+                               &denom->fee_deposit))
+  {
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      TALER_config_get_amount (kcfg,
+                               ct,
+                               "FEE_REFRESH",
+                               &denom->fee_refresh))
+  {
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      TALER_config_get_amount (kcfg,
+                               ct,
+                               "fee_refund",
+                               &denom->fee_refund))
+  {
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Generate new denomination signing keys for the denomination type of the given @a
+ * denomination_alias.
+ *
+ * @param cls a `int *`, 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)
+{
+  int *ret = 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))
+  {
+    *ret = GNUNET_SYSERR;
+    GNUNET_free (denom);
+    return;
+  }
+  GNUNET_CONTAINER_DLL_insert (denom_head,
+                               denom_tail,
+                               denom);
+  // FIXME: load all existing denomination keys for this denom from disk!
+}
+
+
+/**
+ * Function run to accept incoming connections on #sock.
+ *
+ * @param cls NULL
+ */
+static void
+accept_job (void *cls)
+{
+  struct GNUNET_NETWORK_Handle *sock;
+  struct sockaddr_storage addr;
+  socklen_t alen;
+
+  accept_task = NULL;
+  alen = sizeof (addr);
+  sock = GNUNET_NETWORK_socket_accept (lsock,
+                                       (struct sockaddr *) &addr,
+                                       &alen);
+  // FIXME: add to list of managed connections;
+  // then send all known keys;
+  // start to listen for incoming requests;
+
+  accept_task = GNUNET_SCHEDULER_add_read (GNUNET_TIME_UNIT_FOREVER_REL,
+                                           lsock,
+                                           &accept_job,
+                                           NULL);
+}
+
+
+/**
+ * Function run on shutdown. Stops the various jobs (nicely).
+ *
+ * @param cls NULL
+ */
+static void
+do_shutdown (void *cls)
+{
+  (void) cls;
+  if (NULL != accept_task)
+  {
+    GNUNET_SCHEDULER_cancel (accept_task);
+    accept_task = NULL;
+  }
+  if (NULL != lsock)
+  {
+    GNUNET_break (0 ==
+                  GNUNET_NETWORK_socket_close (lsock));
+    lsock = NULL;
+  }
+  if (NULL != keygen_task)
+  {
+    GNUNET_SCHEDULER_cancel (keygen_task);
+    keygen_task = NULL;
+  }
+}
+
+
+/**
+ * Main function that will be run.
+ *
+ * @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 (GNUNET_OK !=
+      TALER_config_get_currency (cfg,
+                                 &currency))
+  {
+    global_ret = 1;
+    return;
+  }
+  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);
+  if (GNUNET_OK !=
+      load_durations ())
+  {
+    global_ret = 1;
+    return;
+  }
+  if (GNUNET_OK !=
+      GNUNET_CONFIGURATION_get_value_filename (kcfg,
+                                               "exchange",
+                                               "KEYDIR",
+                                               &exchange_directory))
+  {
+    GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                               "exchange",
+                               "KEYDIR");
+    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;
+      char *unixpath;
+
+      if (GNUNET_OK !=
+          GNUNET_CONFIGURATION_get_value_filename (kcfg,
+                                                   "exchange-helper-crypto-rsa",
+                                                   "UNIXPATH",
+                                                   &unixpath))
+      {
+        GNUNET_log_config_missing (GNUNET_ERROR_TYPE_ERROR,
+                                   "exchange-helper-crypto-rsa",
+                                   "UNIXPATH");
+        global_ret = 3;
+        return;
+      }
+      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;
+      }
+    }
+    lsock = GNUNET_NETWORK_socket_box_native (sock);
+  }
+
+  GNUNET_SCHEDULER_add_shutdown (&do_shutdown,
+                                 NULL);
+  /* FIXME: start job to accept incoming requests on 'sock' */
+  accept_task = GNUNET_SCHEDULER_add_read_net (GNUNET_TIME_UNIT_FOREVER_REL,
+                                               lsock,
+                                               &accept_job,
+                                               NULL);
+
+  /* Load denominations */
+  keys = GNUNET_CONTAINER_multihashmap_create (65536,
+                                               GNUNET_NO);
+  {
+    int ok;
+
+    ok = GNUNET_OK;
+    GNUNET_CONFIGURATION_iterate_sections (kcfg,
+                                           &load_denominations,
+                                           &ok);
+    if (GNUNET_OK != ok)
+    {
+      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;
+  }
+
+  // FIXME: begin job to create additional denomination keys based on
+  // next needs!
+  // FIXME: same job or extra job for private key expiration/purge?
+}
+
+
+int
+main (int argc,
+      char **argv)
+{
+  struct GNUNET_GETOPT_CommandLineOption options[] = {
+    GNUNET_GETOPT_option_timetravel ('T',
+                                     "timetravel"),
+    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;
+
+  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 */
+  (void) TALER_project_data_default ();
+  GNUNET_assert (GNUNET_OK ==
+                 GNUNET_log_setup ("taler-helper-crypto-rsa",
+                                   "WARNING",
+                                   NULL));
+  now = now_tmp = GNUNET_TIME_absolute_get ();
+  ret = GNUNET_PROGRAM_run (argc, argv,
+                            "taler-helper-crypto-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;
+}