fix cyclic dependency by combining exchange-lib and auditor-lib directories

1 files changed, 1779 insertions, 0 deletions

diff --git a/src/lib/exchange_api_handle.c b/src/lib/exchange_api_handle.c
new file mode 100644
index 000000000..9743b1f09
--- /dev/null
+++ b/src/lib/exchange_api_handle.c
@@ -0,0 +1,1779 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2014-2018 GNUnet e.V.
+
+  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 exchange-lib/exchange_api_handle.c
+ * @brief Implementation of the "handle" component of the exchange's HTTP API
+ * @author Sree Harsha Totakura <sreeharsha@totakura.in>
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include <microhttpd.h>
+#include <gnunet/gnunet_curl_lib.h>
+#include "taler_json_lib.h"
+#include "taler_exchange_service.h"
+#include "taler_auditor_service.h"
+#include "taler_signatures.h"
+#include "exchange_api_handle.h"
+#include "exchange_api_curl_defaults.h"
+#include "backoff.h"
+
+/**
+ * Which revision of the Taler protocol is implemented
+ * by this library?  Used to determine compatibility.
+ */
+#define TALER_PROTOCOL_CURRENT 2
+
+/**
+ * How many revisions back are we compatible to?
+ */
+#define TALER_PROTOCOL_AGE 0
+
+/**
+ * Current version for (local) JSON serialization of persisted
+ * /keys data.
+ */
+#define TALER_SERIALIZATION_FORMAT_VERSION 0
+
+
+/**
+ * Log error related to CURL operations.
+ *
+ * @param type log level
+ * @param function which function failed to run
+ * @param code what was the curl error code
+ */
+#define CURL_STRERROR(type, function, code)      \
+ GNUNET_log (type, "Curl function `%s' has failed at `%s:%d' with error: %s", \
+             function, __FILE__, __LINE__, curl_easy_strerror (code));
+
+/**
+ * Stages of initialization for the `struct TALER_EXCHANGE_Handle`
+ */
+enum ExchangeHandleState
+{
+  /**
+   * Just allocated.
+   */
+  MHS_INIT = 0,
+
+  /**
+   * Obtained the exchange's certification data and keys.
+   */
+  MHS_CERT = 1,
+
+  /**
+   * Failed to initialize (fatal).
+   */
+  MHS_FAILED = 2
+};
+
+
+/**
+ * Data for the request to get the /keys of a exchange.
+ */
+struct KeysRequest;
+
+
+/**
+ * Entry in list of ongoing interactions with an auditor.
+ */
+struct AuditorInteractionEntry
+{
+  /**
+   * DLL entry.
+   */
+  struct AuditorInteractionEntry *next;
+
+  /**
+   * DLL entry.
+   */
+  struct AuditorInteractionEntry *prev;
+
+  /**
+   * Interaction state.
+   */
+  struct TALER_AUDITOR_DepositConfirmationHandle *dch;
+};
+
+
+/**
+ * Entry in DLL of auditors used by an exchange.
+ */
+struct AuditorListEntry
+{
+  /**
+   * Next pointer of DLL.
+   */
+  struct AuditorListEntry *next;
+
+  /**
+   * Prev pointer of DLL.
+   */
+  struct AuditorListEntry *prev;
+
+  /**
+   * Base URL of the auditor.
+   */
+  const char *auditor_url;
+
+  /**
+   * Handle to the auditor.
+   */
+  struct TALER_AUDITOR_Handle *ah;
+
+  /**
+   * Head of DLL of interactions with this auditor.
+   */
+  struct AuditorInteractionEntry *ai_head;
+
+  /**
+   * Tail of DLL of interactions with this auditor.
+   */
+  struct AuditorInteractionEntry *ai_tail;
+
+  /**
+   * Public key of the auditor.
+   */
+  struct TALER_AuditorPublicKeyP auditor_pub;
+
+  /**
+   * Flag indicating that the auditor is available and that protocol
+   * version compatibility is given.
+   */
+  int is_up;
+
+};
+
+
+/**
+ * Handle to the exchange
+ */
+struct TALER_EXCHANGE_Handle
+{
+  /**
+   * The context of this handle
+   */
+  struct GNUNET_CURL_Context *ctx;
+
+  /**
+   * The URL of the exchange (i.e. "http://exchange.taler.net/")
+   */
+  char *url;
+
+  /**
+   * Function to call with the exchange's certification data,
+   * NULL if this has already been done.
+   */
+  TALER_EXCHANGE_CertificationCallback cert_cb;
+
+  /**
+   * Closure to pass to @e cert_cb.
+   */
+  void *cert_cb_cls;
+
+  /**
+   * Data for the request to get the /keys of a exchange,
+   * NULL once we are past stage #MHS_INIT.
+   */
+  struct KeysRequest *kr;
+
+  /**
+   * Task for retrying /keys request.
+   */
+  struct GNUNET_SCHEDULER_Task *retry_task;
+
+  /**
+   * Raw key data of the exchange, only valid if
+   * @e handshake_complete is past stage #MHS_CERT.
+   */
+  json_t *key_data_raw;
+
+  /**
+   * Head of DLL of auditors of this exchange.
+   */
+  struct AuditorListEntry *auditors_head;
+
+  /**
+   * Tail of DLL of auditors of this exchange.
+   */
+  struct AuditorListEntry *auditors_tail;
+
+  /**
+   * Key data of the exchange, only valid if
+   * @e handshake_complete is past stage #MHS_CERT.
+   */
+  struct TALER_EXCHANGE_Keys key_data;
+
+  /**
+   * Retry /keys frequency.
+   */
+  struct GNUNET_TIME_Relative retry_delay;
+
+  /**
+   * When does @e key_data expire?
+   */
+  struct GNUNET_TIME_Absolute key_data_expiration;
+
+  /**
+   * Stage of the exchange's initialization routines.
+   */
+  enum ExchangeHandleState state;
+
+};
+
+
+/* ***************** Internal /keys fetching ************* */
+
+/**
+ * Data for the request to get the /keys of a exchange.
+ */
+struct KeysRequest
+{
+  /**
+   * The connection to exchange this request handle will use
+   */
+  struct TALER_EXCHANGE_Handle *exchange;
+
+  /**
+   * The url for this handle
+   */
+  char *url;
+
+  /**
+   * Entry for this request with the `struct GNUNET_CURL_Context`.
+   */
+  struct GNUNET_CURL_Job *job;
+
+  /**
+   * Expiration time according to "Expire:" header.
+   * 0 if not provided by the server.
+   */
+  struct GNUNET_TIME_Absolute expire;
+
+};
+
+
+/**
+ * Iterate over all available auditors for @a h, calling
+ * @param ah and giving it a chance to start a deposit
+ * confirmation interaction.
+ *
+ * @param h exchange to go over auditors for
+ * @param ac function to call per auditor
+ * @param ac_cls closure for @a ac
+ */
+void
+TEAH_get_auditors_for_dc (struct TALER_EXCHANGE_Handle *h,
+			  TEAH_AuditorCallback ac,
+			  void *ac_cls)
+{
+  // FIXME!
+}
+
+
+/**
+ * Release memory occupied by a keys request.
+ * Note that this does not cancel the request
+ * itself.
+ *
+ * @param kr request to free
+ */
+static void
+free_keys_request (struct KeysRequest *kr)
+{
+  GNUNET_free (kr->url);
+  GNUNET_free (kr);
+}
+
+
+#define EXITIF(cond)                                              \
+  do {                                                            \
+    if (cond) { GNUNET_break (0); goto EXITIF_exit; }             \
+  } while (0)
+
+
+/**
+ * Parse a exchange's signing key encoded in JSON.
+ *
+ * @param[out] sign_key where to return the result
+ * @param check_sigs should we check signatures?
+ * @param[in] sign_key_obj json to parse
+ * @param master_key master key to use to verify signature
+ * @return #GNUNET_OK if all is fine, #GNUNET_SYSERR if the signature is
+ *        invalid or the json malformed.
+ */
+static int
+parse_json_signkey (struct TALER_EXCHANGE_SigningPublicKey *sign_key,
+		    int check_sigs,
+                    json_t *sign_key_obj,
+                    const struct TALER_MasterPublicKeyP *master_key)
+{
+  struct TALER_ExchangeSigningKeyValidityPS sign_key_issue;
+  struct TALER_MasterSignatureP sign_key_issue_sig;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_fixed_auto ("master_sig",
+                                 &sign_key_issue_sig),
+    GNUNET_JSON_spec_fixed_auto ("key",
+                                 &sign_key->key),
+    GNUNET_JSON_spec_absolute_time ("stamp_start",
+                                    &sign_key->valid_from),
+    GNUNET_JSON_spec_absolute_time ("stamp_expire",
+                                    &sign_key->valid_until),
+    GNUNET_JSON_spec_absolute_time ("stamp_end",
+                                    &sign_key->valid_legal),
+    GNUNET_JSON_spec_end()
+  };
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (sign_key_obj,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
+  if (! check_sigs)
+    return GNUNET_OK;
+  sign_key_issue.signkey_pub = sign_key->key;
+  sign_key_issue.purpose.purpose = htonl (TALER_SIGNATURE_MASTER_SIGNING_KEY_VALIDITY);
+  sign_key_issue.purpose.size = htonl (sizeof (struct TALER_ExchangeSigningKeyValidityPS));
+  sign_key_issue.master_public_key = *master_key;
+  sign_key_issue.start = GNUNET_TIME_absolute_hton (sign_key->valid_from);
+  sign_key_issue.expire = GNUNET_TIME_absolute_hton (sign_key->valid_until);
+  sign_key_issue.end = GNUNET_TIME_absolute_hton (sign_key->valid_legal);
+  if (GNUNET_OK !=
+      GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_MASTER_SIGNING_KEY_VALIDITY,
+				  &sign_key_issue.purpose,
+				  &sign_key_issue_sig.eddsa_signature,
+				  &master_key->eddsa_pub))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  sign_key->master_sig = sign_key_issue_sig;
+  return GNUNET_OK;
+}
+
+
+/**
+ * Parse a exchange's denomination key encoded in JSON.
+ *
+ * @param[out] denom_key where to return the result
+ * @param check_sigs should we check signatures?
+ * @param[in] denom_key_obj json to parse
+ * @param master_key master key to use to verify signature
+ * @param hash_context where to accumulate data for signature verification
+ * @return #GNUNET_OK if all is fine, #GNUNET_SYSERR if the signature is
+ *        invalid or the json malformed.
+ */
+static int
+parse_json_denomkey (struct TALER_EXCHANGE_DenomPublicKey *denom_key,
+		     int check_sigs,
+                     json_t *denom_key_obj,
+                     struct TALER_MasterPublicKeyP *master_key,
+                     struct GNUNET_HashContext *hash_context)
+{
+  struct TALER_DenominationKeyValidityPS denom_key_issue;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_fixed_auto ("master_sig",
+				 &denom_key->master_sig),
+    GNUNET_JSON_spec_absolute_time ("stamp_expire_deposit",
+				    &denom_key->expire_deposit),
+    GNUNET_JSON_spec_absolute_time ("stamp_expire_withdraw",
+				    &denom_key->withdraw_valid_until),
+    GNUNET_JSON_spec_absolute_time ("stamp_start",
+				    &denom_key->valid_from),
+    GNUNET_JSON_spec_absolute_time ("stamp_expire_legal",
+				    &denom_key->expire_legal),
+    TALER_JSON_spec_amount ("value",
+			    &denom_key->value),
+    TALER_JSON_spec_amount ("fee_withdraw",
+			    &denom_key->fee_withdraw),
+    TALER_JSON_spec_amount ("fee_deposit",
+			    &denom_key->fee_deposit),
+    TALER_JSON_spec_amount ("fee_refresh",
+			    &denom_key->fee_refresh),
+    TALER_JSON_spec_amount ("fee_refund",
+			    &denom_key->fee_refund),
+    GNUNET_JSON_spec_rsa_public_key ("denom_pub",
+				     &denom_key->key.rsa_public_key),
+    GNUNET_JSON_spec_end()
+  };
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (denom_key_obj,
+                         spec,
+			 NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+
+  GNUNET_CRYPTO_rsa_public_key_hash (denom_key->key.rsa_public_key,
+                                     &denom_key->h_key);
+  if (! check_sigs)
+    return GNUNET_OK;
+  memset (&denom_key_issue,
+	  0,
+	  sizeof (denom_key_issue));
+  denom_key_issue.purpose.purpose
+    = htonl (TALER_SIGNATURE_MASTER_DENOMINATION_KEY_VALIDITY);
+  denom_key_issue.purpose.size
+    = htonl (sizeof (struct TALER_DenominationKeyValidityPS));
+  denom_key_issue.master = *master_key;
+  denom_key_issue.denom_hash = denom_key->h_key;
+  denom_key_issue.start = GNUNET_TIME_absolute_hton (denom_key->valid_from);
+  denom_key_issue.expire_withdraw = GNUNET_TIME_absolute_hton (denom_key->withdraw_valid_until);
+  denom_key_issue.expire_deposit = GNUNET_TIME_absolute_hton (denom_key->expire_deposit);
+  denom_key_issue.expire_legal = GNUNET_TIME_absolute_hton (denom_key->expire_legal);
+  TALER_amount_hton (&denom_key_issue.value,
+		     &denom_key->value);
+  TALER_amount_hton (&denom_key_issue.fee_withdraw,
+		     &denom_key->fee_withdraw);
+  TALER_amount_hton (&denom_key_issue.fee_deposit,
+		       &denom_key->fee_deposit);
+  TALER_amount_hton (&denom_key_issue.fee_refresh,
+		     &denom_key->fee_refresh);
+  TALER_amount_hton (&denom_key_issue.fee_refund,
+		     &denom_key->fee_refund);
+  EXITIF (GNUNET_SYSERR ==
+	  GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_MASTER_DENOMINATION_KEY_VALIDITY,
+				      &denom_key_issue.purpose,
+				      &denom_key->master_sig.eddsa_signature,
+				      &master_key->eddsa_pub));
+  GNUNET_CRYPTO_hash_context_read (hash_context,
+				   &denom_key_issue.denom_hash,
+				   sizeof (struct GNUNET_HashCode));
+  return GNUNET_OK;
+
+ EXITIF_exit:
+  GNUNET_JSON_parse_free (spec);
+  return GNUNET_SYSERR;
+}
+
+
+/**
+ * Parse a exchange's auditor information encoded in JSON.
+ *
+ * @param[out] auditor where to return the result
+ * @param check_sig should we check signatures
+ * @param[in] auditor_obj json to parse
+ * @param key_data information about denomination keys
+ * @return #GNUNET_OK if all is fine, #GNUNET_SYSERR if the signature is
+ *        invalid or the json malformed.
+ */
+static int
+parse_json_auditor (struct TALER_EXCHANGE_AuditorInformation *auditor,
+		    int check_sigs,
+                    json_t *auditor_obj,
+                    const struct TALER_EXCHANGE_Keys *key_data)
+{
+  json_t *keys;
+  json_t *key;
+  unsigned int len;
+  unsigned int off;
+  unsigned int i;
+  const char *auditor_url;
+  struct TALER_ExchangeKeyValidityPS kv;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_fixed_auto ("auditor_pub",
+                                 &auditor->auditor_pub),
+    GNUNET_JSON_spec_string ("auditor_url",
+                             &auditor_url),
+    GNUNET_JSON_spec_json ("denomination_keys",
+                           &keys),
+    GNUNET_JSON_spec_end()
+  };
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (auditor_obj,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  auditor->auditor_url = GNUNET_strdup (auditor_url);
+  kv.purpose.purpose = htonl (TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS);
+  kv.purpose.size = htonl (sizeof (struct TALER_ExchangeKeyValidityPS));
+  GNUNET_CRYPTO_hash (auditor_url,
+                      strlen (auditor_url) + 1,
+                      &kv.auditor_url_hash);
+  kv.master = key_data->master_pub;
+  len = json_array_size (keys);
+  auditor->denom_keys = GNUNET_new_array (len,
+					  struct TALER_EXCHANGE_AuditorDenominationInfo);
+  i = 0;
+  off = 0;
+  json_array_foreach (keys, i, key) {
+    struct TALER_AuditorSignatureP auditor_sig;
+    struct GNUNET_HashCode denom_h;
+    const struct TALER_EXCHANGE_DenomPublicKey *dk;
+    unsigned int dk_off;
+    struct GNUNET_JSON_Specification kspec[] = {
+      GNUNET_JSON_spec_fixed_auto ("auditor_sig",
+                                   &auditor_sig),
+      GNUNET_JSON_spec_fixed_auto ("denom_pub_h",
+                                   &denom_h),
+      GNUNET_JSON_spec_end()
+    };
+
+    if (GNUNET_OK !=
+        GNUNET_JSON_parse (key,
+                           kspec,
+                           NULL, NULL))
+    {
+      GNUNET_break_op (0);
+      continue;
+    }
+    dk = NULL;
+    dk_off = UINT_MAX;
+    for (unsigned int j=0;j<key_data->num_denom_keys;j++)
+    {
+      if (0 == memcmp (&denom_h,
+                       &key_data->denom_keys[j].h_key,
+                       sizeof (struct GNUNET_HashCode)))
+      {
+        dk = &key_data->denom_keys[j];
+        dk_off = j;
+        break;
+      }
+    }
+    if (NULL == dk)
+    {
+      GNUNET_break_op (0);
+      continue;
+    }
+    if (check_sigs)
+    {
+      kv.start = GNUNET_TIME_absolute_hton (dk->valid_from);
+      kv.expire_withdraw = GNUNET_TIME_absolute_hton (dk->withdraw_valid_until);
+      kv.expire_deposit = GNUNET_TIME_absolute_hton (dk->expire_deposit);
+      kv.expire_legal = GNUNET_TIME_absolute_hton (dk->expire_legal);
+      TALER_amount_hton (&kv.value,
+                         &dk->value);
+      TALER_amount_hton (&kv.fee_withdraw,
+			 &dk->fee_withdraw);
+      TALER_amount_hton (&kv.fee_deposit,
+			 &dk->fee_deposit);
+      TALER_amount_hton (&kv.fee_refresh,
+			 &dk->fee_refresh);
+      TALER_amount_hton (&kv.fee_refund,
+			 &dk->fee_refund);
+      kv.denom_hash = dk->h_key;
+
+      if (GNUNET_OK !=
+	  GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_AUDITOR_EXCHANGE_KEYS,
+				      &kv.purpose,
+				      &auditor_sig.eddsa_sig,
+				      &auditor->auditor_pub.eddsa_pub))
+      {
+	GNUNET_break_op (0);
+	GNUNET_JSON_parse_free (spec);
+	return GNUNET_SYSERR;
+      }
+    }
+    auditor->denom_keys[off].denom_key_offset = dk_off;
+    auditor->denom_keys[off].auditor_sig = auditor_sig;
+    off++;
+  }
+  auditor->num_denom_keys = off;
+  GNUNET_JSON_parse_free (spec);
+  return GNUNET_OK;
+}
+
+
+/**
+ * Decode the JSON in @a resp_obj from the /keys response
+ * and store the data in the @a key_data.
+ *
+ * @param[in] resp_obj JSON object to parse
+ * @param check_sig #GNUNET_YES if we should check the signature
+ * @param[out] key_data where to store the results we decoded
+ * @param[out] where to store version compatibility data
+ * @return #GNUNET_OK on success, #GNUNET_SYSERR on error
+ * (malformed JSON)
+ */
+static int
+decode_keys_json (const json_t *resp_obj,
+		  int check_sig,
+                  struct TALER_EXCHANGE_Keys *key_data,
+		  enum TALER_EXCHANGE_VersionCompatibility *vc)
+{
+  struct TALER_ExchangeSignatureP sig;
+  struct GNUNET_HashContext *hash_context;
+  struct TALER_ExchangePublicKeyP pub;
+  unsigned int age;
+  unsigned int revision;
+  unsigned int current;
+  struct GNUNET_JSON_Specification mspec[] = {
+    GNUNET_JSON_spec_fixed_auto ("eddsa_sig",
+				 &sig),
+    GNUNET_JSON_spec_fixed_auto ("eddsa_pub",
+				 &pub),
+    /* sig and pub must be first, as we skip those if
+       check_sig is false! */
+    GNUNET_JSON_spec_fixed_auto ("master_public_key",
+				 &key_data->master_pub),
+    GNUNET_JSON_spec_absolute_time ("list_issue_date",
+				    &key_data->list_issue_date),
+    GNUNET_JSON_spec_relative_time
+      ("reserve_closing_delay",
+        &key_data->reserve_closing_delay),
+    GNUNET_JSON_spec_end()
+  };
+
+  if (JSON_OBJECT != json_typeof (resp_obj))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  /* check the version */
+  {
+    const char *ver;
+    struct GNUNET_JSON_Specification spec[] = {
+      GNUNET_JSON_spec_string ("version",
+                               &ver),
+      GNUNET_JSON_spec_end()
+    };
+
+    if (GNUNET_OK !=
+        GNUNET_JSON_parse (resp_obj,
+                           spec,
+                           NULL, NULL))
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    if (3 != sscanf (ver,
+		     "%u:%u:%u",
+		     &current,
+		     &revision,
+		     &age))
+    {
+      GNUNET_break_op (0);
+      return GNUNET_SYSERR;
+    }
+    *vc = TALER_EXCHANGE_VC_MATCH;
+    if (TALER_PROTOCOL_CURRENT < current)
+    {
+      *vc |= TALER_EXCHANGE_VC_NEWER;
+      if (TALER_PROTOCOL_CURRENT < current - age)
+	*vc |= TALER_EXCHANGE_VC_INCOMPATIBLE;
+    }
+    if (TALER_PROTOCOL_CURRENT > current)
+    {
+      *vc |= TALER_EXCHANGE_VC_OLDER;
+      if (TALER_PROTOCOL_CURRENT - TALER_PROTOCOL_AGE > current)
+	*vc |= TALER_EXCHANGE_VC_INCOMPATIBLE;
+    }
+    key_data->version = GNUNET_strdup (ver);
+  }
+
+  hash_context = NULL;
+  EXITIF (GNUNET_OK !=
+	  GNUNET_JSON_parse (resp_obj,
+			     (check_sig) ? mspec : &mspec[2],
+			     NULL, NULL));
+
+  /* parse the master public key and issue date of the response */
+  if (check_sig)
+    hash_context = GNUNET_CRYPTO_hash_context_start ();
+
+  /* parse the signing keys */
+  {
+    json_t *sign_keys_array;
+    json_t *sign_key_obj;
+    unsigned int index;
+
+    EXITIF (NULL == (sign_keys_array =
+                     json_object_get (resp_obj,
+                                      "signkeys")));
+    EXITIF (JSON_ARRAY != json_typeof (sign_keys_array));
+    EXITIF (0 == (key_data->num_sign_keys =
+                  json_array_size (sign_keys_array)));
+    key_data->sign_keys
+      = GNUNET_new_array (key_data->num_sign_keys,
+                          struct TALER_EXCHANGE_SigningPublicKey);
+    index = 0;
+    json_array_foreach (sign_keys_array, index, sign_key_obj) {
+      EXITIF (GNUNET_SYSERR ==
+              parse_json_signkey (&key_data->sign_keys[index],
+				  check_sig,
+                                  sign_key_obj,
+                                  &key_data->master_pub));
+    }
+  }
+
+  /* parse the denomination keys, merging with the
+     possibly EXISTING array as required (/keys cherry picking) */
+  {
+    json_t *denom_keys_array;
+    json_t *denom_key_obj;
+    unsigned int index;
+
+    EXITIF (NULL == (denom_keys_array =
+                     json_object_get (resp_obj,
+                                      "denoms")));
+    EXITIF (JSON_ARRAY != json_typeof (denom_keys_array));
+
+    index = 0;
+    json_array_foreach (denom_keys_array, index, denom_key_obj) {
+      struct TALER_EXCHANGE_DenomPublicKey dk;
+      bool found = false;
+
+      EXITIF (GNUNET_SYSERR ==
+              parse_json_denomkey (&dk,
+                                   check_sig,
+                                   denom_key_obj,
+                                   &key_data->master_pub,
+                                   hash_context));
+      for (unsigned int j=0;j<key_data->num_denom_keys;j++)
+      {
+        if (0 == memcmp (&dk,
+                         &key_data->denom_keys[j],
+                         sizeof (dk)))
+        {
+          found = true;
+          break;
+        }
+      }
+      if (found)
+      {
+        /* 0:0:0 did not support /keys cherry picking */
+        GNUNET_break_op (0 == current);
+        continue;
+      }
+      if (key_data->denom_keys_size == key_data->num_denom_keys)
+        GNUNET_array_grow (key_data->denom_keys,
+                           key_data->denom_keys_size,
+                           key_data->denom_keys_size * 2 + 2);
+      key_data->denom_keys[key_data->num_denom_keys++] = dk;
+
+      /* Update "last_denom_issue_date" */
+      TALER_LOG_DEBUG ("Crawling DK 'valid_from': %s\n",
+                       GNUNET_STRINGS_absolute_time_to_string (dk.valid_from));
+      key_data->last_denom_issue_date
+        = GNUNET_TIME_absolute_max (key_data->last_denom_issue_date,
+                                    dk.valid_from);
+    };
+  }
+  /* parse the auditor information */
+  {
+    json_t *auditors_array;
+    json_t *auditor_info;
+    unsigned int index;
+
+    EXITIF (NULL == (auditors_array =
+                     json_object_get (resp_obj,
+				      "auditors")));
+    EXITIF (JSON_ARRAY != json_typeof (auditors_array));
+
+    /* Merge with the existing auditor information we have (/keys cherry picking) */
+    index = 0;
+    json_array_foreach (auditors_array, index, auditor_info) {
+      struct TALER_EXCHANGE_AuditorInformation ai;
+      bool found = false;
+
+      memset (&ai,
+	      0,
+	      sizeof (ai));
+      EXITIF (GNUNET_SYSERR ==
+              parse_json_auditor (&ai,
+				  check_sig,
+                                  auditor_info,
+                                  key_data));
+      for (unsigned int j=0;j<key_data->num_auditors;j++)
+      {
+        struct TALER_EXCHANGE_AuditorInformation *aix = &key_data->auditors[j];
+
+	if (0 == memcmp (&ai.auditor_pub,
+			 &aix->auditor_pub,
+			 sizeof (struct TALER_AuditorPublicKeyP)))
+	{
+	  found = true;
+          /* Merge denomination key signatures of downloaded /keys into existing
+             auditor information 'aix'. */
+          GNUNET_array_grow (aix->denom_keys,
+                             aix->num_denom_keys,
+                             aix->num_denom_keys + ai.num_denom_keys);
+          memcpy (&aix->denom_keys[aix->num_denom_keys - ai.num_denom_keys],
+                  ai.denom_keys,
+                  ai.num_denom_keys * sizeof (struct TALER_EXCHANGE_AuditorDenominationInfo));
+	  break;
+	}
+      }
+      if (found)
+        continue; /* we are done */
+      if (key_data->auditors_size == key_data->num_auditors)
+	GNUNET_array_grow (key_data->auditors,
+			   key_data->auditors_size,
+			   key_data->auditors_size * 2 + 2);
+      key_data->auditors[key_data->num_auditors++] = ai;
+    };
+  }
+
+  if (check_sig)
+  {
+    struct TALER_ExchangeKeySetPS ks;
+
+    /* Validate signature... */
+    ks.purpose.size = htonl (sizeof (ks));
+    ks.purpose.purpose = htonl (TALER_SIGNATURE_EXCHANGE_KEY_SET);
+    ks.list_issue_date = GNUNET_TIME_absolute_hton (key_data->list_issue_date);
+    GNUNET_CRYPTO_hash_context_finish (hash_context,
+				       &ks.hc);
+    hash_context = NULL;
+    EXITIF (GNUNET_OK !=
+	    TALER_EXCHANGE_test_signing_key (key_data,
+					     &pub));
+    EXITIF (GNUNET_OK !=
+	    GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_KEY_SET,
+					&ks.purpose,
+					&sig.eddsa_signature,
+					&pub.eddsa_pub));
+  }
+  return GNUNET_OK;
+ EXITIF_exit:
+
+  if (NULL != hash_context)
+    GNUNET_CRYPTO_hash_context_abort (hash_context);
+  return GNUNET_SYSERR;
+}
+
+
+/**
+ * Free key data object.
+ *
+ * @param key_data data to free (pointer itself excluded)
+ */
+static void
+free_key_data (struct TALER_EXCHANGE_Keys *key_data)
+{
+  GNUNET_array_grow (key_data->sign_keys,
+                     key_data->num_sign_keys,
+                     0);
+  for (unsigned int i=0;i<key_data->num_denom_keys;i++)
+    GNUNET_CRYPTO_rsa_public_key_free (key_data->denom_keys[i].key.rsa_public_key);
+
+  GNUNET_array_grow (key_data->denom_keys,
+                     key_data->denom_keys_size,
+                     0);
+  for (unsigned int i=0;i<key_data->num_auditors;i++)
+  {
+    GNUNET_array_grow (key_data->auditors[i].denom_keys,
+                       key_data->auditors[i].num_denom_keys,
+                       0);
+    GNUNET_free (key_data->auditors[i].auditor_url);
+  }
+  GNUNET_array_grow (key_data->auditors,
+                     key_data->auditors_size,
+                     0);
+  GNUNET_free_non_null (key_data->version);
+  key_data->version = NULL;
+}
+
+
+/**
+ * Initiate download of /keys from the exchange.
+ *
+ * @param cls exchange where to download /keys from
+ */
+static void
+request_keys (void *cls);
+
+
+/**
+ * Check if our current response for /keys is valid, and if
+ * not trigger download.
+ *
+ * @param exchange exchange to check keys for
+ * @param force_download #GNUNET_YES to force download even if /keys is still valid
+ * @return until when the response is current, 0 if we are re-downloading
+ */
+struct GNUNET_TIME_Absolute
+TALER_EXCHANGE_check_keys_current (struct TALER_EXCHANGE_Handle *exchange,
+                                   int force_download)
+{
+  if (NULL != exchange->kr)
+    return GNUNET_TIME_UNIT_ZERO_ABS;
+  if ( (GNUNET_NO == force_download) &&
+       (0 < GNUNET_TIME_absolute_get_remaining (exchange->key_data_expiration).rel_value_us) )
+    return exchange->key_data_expiration;
+  if (NULL == exchange->retry_task)
+    exchange->retry_task = GNUNET_SCHEDULER_add_now (&request_keys,
+                                                     exchange);
+  return GNUNET_TIME_UNIT_ZERO_ABS;
+}
+
+
+/**
+ * Callback used when downloading the reply to a /keys request
+ * is complete.
+ *
+ * @param cls the `struct KeysRequest`
+ * @param response_code HTTP response code, 0 on error
+ * @param resp_obj parsed JSON result, NULL on error
+ */
+static void
+keys_completed_cb (void *cls,
+                   long response_code,
+                   const void *resp_obj)
+{
+  struct KeysRequest *kr = cls;
+  struct TALER_EXCHANGE_Handle *exchange = kr->exchange;
+  struct TALER_EXCHANGE_Keys kd;
+  struct TALER_EXCHANGE_Keys kd_old;
+  enum TALER_EXCHANGE_VersionCompatibility vc;
+  const json_t *j = resp_obj;
+
+  GNUNET_log (GNUNET_ERROR_TYPE_INFO,
+              "Received keys from URL `%s' with status %ld.\n",
+              kr->url,
+              response_code);
+  kd_old = exchange->key_data;
+  memset (&kd,
+          0,
+          sizeof (struct TALER_EXCHANGE_Keys));
+  vc = TALER_EXCHANGE_VC_PROTOCOL_ERROR;
+  switch (response_code)
+  {
+  case 0:
+    free_keys_request (kr);
+    exchange->kr = NULL;
+    GNUNET_assert (NULL == exchange->retry_task);
+    exchange->retry_delay = EXCHANGE_LIB_BACKOFF (exchange->retry_delay);
+    exchange->retry_task = GNUNET_SCHEDULER_add_delayed (exchange->retry_delay,
+                                                         &request_keys,
+                                                         exchange);
+    return;
+  case MHD_HTTP_OK:
+    if (NULL == j)
+    {
+      response_code = 0;
+      break;
+    }
+    /* We keep the denomination keys and auditor signatures from the
+       previous iteration (/keys cherry picking) */
+    kd.num_denom_keys = kd_old.num_denom_keys;
+    kd.last_denom_issue_date = kd_old.last_denom_issue_date;
+    GNUNET_array_grow (kd.denom_keys,
+                       kd.denom_keys_size,
+                       kd.num_denom_keys);
+
+    /* First make a shallow copy, we then need another pass for the RSA key... */
+    memcpy (kd.denom_keys,
+            kd_old.denom_keys,
+            kd_old.num_denom_keys * sizeof (struct TALER_EXCHANGE_DenomPublicKey));
+    for (unsigned int i=0;i<kd_old.num_denom_keys;i++)
+      kd.denom_keys[i].key.rsa_public_key
+        = GNUNET_CRYPTO_rsa_public_key_dup (kd_old.denom_keys[i].key.rsa_public_key);
+
+    kd.num_auditors = kd_old.num_auditors;
+    kd.auditors = GNUNET_new_array (kd.num_auditors,
+                                    struct TALER_EXCHANGE_AuditorInformation);
+    /* Now the necessary deep copy... */
+    for (unsigned int i=0;i<kd_old.num_auditors;i++)
+    {
+      const struct TALER_EXCHANGE_AuditorInformation *aold = &kd_old.auditors[i];
+      struct TALER_EXCHANGE_AuditorInformation *anew = &kd.auditors[i];
+
+      anew->auditor_pub = aold->auditor_pub;
+      anew->auditor_url = GNUNET_strdup (aold->auditor_url);
+      GNUNET_array_grow (anew->denom_keys,
+                         anew->num_denom_keys,
+                         aold->num_denom_keys);
+      memcpy (anew->denom_keys,
+              aold->denom_keys,
+              aold->num_denom_keys * sizeof (struct TALER_EXCHANGE_AuditorDenominationInfo));
+    }
+
+    if (GNUNET_OK !=
+        decode_keys_json (j,
+			  GNUNET_YES,
+                          &kd,
+			  &vc))
+    {
+      TALER_LOG_ERROR ("Could not decode /keys response\n");
+      response_code = 0;
+      for (unsigned int i=0;i<kd.num_auditors;i++)
+      {
+	struct TALER_EXCHANGE_AuditorInformation *anew = &kd.auditors[i];
+
+	GNUNET_array_grow (anew->denom_keys,
+			   anew->num_denom_keys,
+			   0);
+	GNUNET_free (anew->auditor_url);
+      }
+      GNUNET_free (kd.auditors);
+      kd.auditors = NULL;
+      kd.num_auditors = 0;
+      for (unsigned int i=0;i<kd_old.num_denom_keys;i++)
+	GNUNET_CRYPTO_rsa_public_key_free (kd.denom_keys[i].key.rsa_public_key);
+      GNUNET_array_grow (kd.denom_keys,
+			 kd.denom_keys_size,
+			 0);
+      kd.num_denom_keys = 0;
+      break;
+    }
+    json_decref (exchange->key_data_raw);
+    exchange->key_data_raw = json_deep_copy (j);
+    exchange->retry_delay = GNUNET_TIME_UNIT_ZERO;
+    break;
+  default:
+    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                "Unexpected response code %u\n",
+                (unsigned int) response_code);
+    break;
+  }
+  exchange->key_data = kd;
+  TALER_LOG_DEBUG ("Last DK issue date update to: %s\n",
+                   GNUNET_STRINGS_absolute_time_to_string
+                     (exchange->key_data.last_denom_issue_date));
+
+
+  if (MHD_HTTP_OK != response_code)
+  {
+    exchange->kr = NULL;
+    free_keys_request (kr);
+    exchange->state = MHS_FAILED;
+    if (NULL != exchange->key_data_raw)
+    {
+      json_decref (exchange->key_data_raw);
+      exchange->key_data_raw = NULL;
+    }
+    free_key_data (&kd_old);
+    /* notify application that we failed */
+    exchange->cert_cb (exchange->cert_cb_cls,
+                       NULL,
+		       vc);
+    return;
+  }
+
+  exchange->kr = NULL;
+  exchange->key_data_expiration = kr->expire;
+  free_keys_request (kr);
+  exchange->state = MHS_CERT;
+  /* notify application about the key information */
+  exchange->cert_cb (exchange->cert_cb_cls,
+                     &exchange->key_data,
+		     vc);
+  free_key_data (&kd_old);
+}
+
+
+/* ********************* library internal API ********* */
+
+
+/**
+ * Get the context of a exchange.
+ *
+ * @param h the exchange handle to query
+ * @return ctx context to execute jobs in
+ */
+struct GNUNET_CURL_Context *
+TEAH_handle_to_context (struct TALER_EXCHANGE_Handle *h)
+{
+  return h->ctx;
+}
+
+
+/**
+ * Check if the handle is ready to process requests.
+ *
+ * @param h the exchange handle to query
+ * @return #GNUNET_YES if we are ready, #GNUNET_NO if not
+ */
+int
+TEAH_handle_is_ready (struct TALER_EXCHANGE_Handle *h)
+{
+  return (MHS_CERT == h->state) ? GNUNET_YES : GNUNET_NO;
+}
+
+
+/**
+ * Obtain the URL to use for an API request.
+ *
+ * @param h handle for the exchange
+ * @param path Taler API path (i.e. "/reserve/withdraw")
+ * @return the full URL to use with cURL
+ */
+char *
+TEAH_path_to_url (struct TALER_EXCHANGE_Handle *h,
+                 const char *path)
+{
+  return TEAH_path_to_url2 (h->url,
+                           path);
+}
+
+
+/**
+ * Obtain the URL to use for an API request.
+ *
+ * @param base_url base URL of the exchange (i.e. "http://exchange/")
+ * @param path Taler API path (i.e. "/reserve/withdraw")
+ * @return the full URL to use with cURL
+ */
+char *
+TEAH_path_to_url2 (const char *base_url,
+                  const char *path)
+{
+  char *url;
+
+  if ( ('/' == path[0]) &&
+       (0 < strlen (base_url)) &&
+       ('/' == base_url[strlen (base_url) - 1]) )
+    path++; /* avoid generating URL with "//" from concat */
+  GNUNET_asprintf (&url,
+                   "%s%s",
+                   base_url,
+                   path);
+  return url;
+}
+
+
+/**
+ * Parse HTTP timestamp.
+ *
+ * @param date header to parse header
+ * @param at where to write the result
+ * @return #GNUNET_OK on success
+ */
+static int
+parse_date_string (const char *date,
+                   struct GNUNET_TIME_Absolute *at)
+{
+  struct tm now;
+  time_t t;
+  const char *end;
+
+  memset (&now,
+          0,
+          sizeof (now));
+  end = strptime (date,
+                  "%a, %d %b %Y %H:%M:%S %Z", /* RFC-1123 standard spec */
+                  &now);
+  if ( (NULL == end) ||
+       ( (*end != '\n') &&
+         (*end != '\r') ) )
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  t = mktime (&now);
+  if (((time_t) -1) == t)
+  {
+    GNUNET_log_strerror (GNUNET_ERROR_TYPE_ERROR,
+                         "mktime");
+    return GNUNET_SYSERR;
+  }
+  if (t < 0)
+    t = 0; /* can happen due to timezone issues if date was 1.1.1970 */
+  at->abs_value_us = 1000LL * 1000LL * t;
+  return GNUNET_OK;
+}
+
+
+/**
+ * Function called for each header in the HTTP /keys response.
+ * Finds the "Expire:" header and parses it, storing the result
+ * in the "expire" field fo the keys request.
+ *
+ * @param buffer header data received
+ * @param size size of an item in @a buffer
+ * @param nitems number of items in @a buffer
+ * @param userdata the `struct KeysRequest`
+ * @return `size * nitems` on success (everything else aborts)
+ */
+static size_t
+header_cb (char *buffer,
+           size_t size,
+           size_t nitems,
+           void *userdata)
+{
+  struct KeysRequest *kr = userdata;
+  size_t total = size * nitems;
+  char *val;
+
+  if (total < strlen (MHD_HTTP_HEADER_EXPIRES ": "))
+    return total;
+  if (0 != strncasecmp (MHD_HTTP_HEADER_EXPIRES ": ",
+                        buffer,
+                        strlen (MHD_HTTP_HEADER_EXPIRES ": ")))
+    return total;
+  val = GNUNET_strndup (&buffer[strlen (MHD_HTTP_HEADER_EXPIRES ": ")],
+                        total - strlen (MHD_HTTP_HEADER_EXPIRES ": "));
+  if (GNUNET_OK !=
+      parse_date_string (val,
+                         &kr->expire))
+  {
+    GNUNET_log (GNUNET_ERROR_TYPE_WARNING,
+                "Failed to parse %s-header `%s'\n",
+                MHD_HTTP_HEADER_EXPIRES,
+                val);
+    kr->expire = GNUNET_TIME_UNIT_ZERO_ABS;
+  }
+  GNUNET_free (val);
+  return total;
+}
+
+
+/* ********************* public API ******************* */
+
+
+/**
+ * Deserialize the key data and use it to bootstrap @a exchange to
+ * more efficiently recover the state.  Errors in @a data must be
+ * tolerated (i.e. by re-downloading instead).
+ *
+ * @param exchange which exchange's key and wire data should be deserialized
+ * @return data the data to deserialize
+ */
+static void
+deserialize_data (struct TALER_EXCHANGE_Handle *exchange,
+		  const json_t *data)
+{
+  enum TALER_EXCHANGE_VersionCompatibility vc;
+  json_t *keys;
+  const char *url;
+  uint32_t version;
+  struct GNUNET_TIME_Absolute expire;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_uint32 ("version",
+			     &version),
+    GNUNET_JSON_spec_json ("keys",
+			   &keys),
+    GNUNET_JSON_spec_string ("url",
+			     &url),
+    GNUNET_JSON_spec_absolute_time ("expire",
+                                    &expire),
+    GNUNET_JSON_spec_end()
+  };
+  struct TALER_EXCHANGE_Keys key_data;
+
+  if (NULL == data)
+    return;
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (data,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return;
+  }
+  if (0 != version)
+    return; /* unsupported version */
+  if (0 != strcmp (url,
+		   exchange->url))
+  {
+    GNUNET_break (0);
+    return;
+  }
+  memset (&key_data,
+	  0,
+          sizeof (struct TALER_EXCHANGE_Keys));
+  if (GNUNET_OK !=
+      decode_keys_json (keys,
+			GNUNET_NO,
+			&key_data,
+			&vc))
+    {
+      GNUNET_break (0);
+      return;
+    }
+  /* decode successful, initialize with the result */
+  GNUNET_assert (NULL == exchange->key_data_raw);
+  exchange->key_data_raw = json_deep_copy (keys);
+  exchange->key_data = key_data;
+  exchange->key_data_expiration = expire;
+  exchange->state = MHS_CERT;
+  /* notify application about the key information */
+  exchange->cert_cb (exchange->cert_cb_cls,
+                     &exchange->key_data,
+		     vc);
+}
+
+
+/**
+ * Serialize the latest key data from @a exchange to be persisted on
+ * disk (to be used with #TALER_EXCHANGE_OPTION_DATA to more
+ * efficiently recover the state).
+ *
+ * @param exchange which exchange's key and wire data should be
+ *        serialized
+ * @return NULL on error (i.e. no current data available);
+ *         otherwise JSON object owned by the caller
+ */
+json_t *
+TALER_EXCHANGE_serialize_data (struct TALER_EXCHANGE_Handle *exchange)
+{
+  const struct TALER_EXCHANGE_Keys *kd = &exchange->key_data;
+  struct GNUNET_TIME_Absolute now;
+  json_t *keys;
+  json_t *signkeys;
+  json_t *denoms;
+  json_t *auditors;
+
+  now = GNUNET_TIME_absolute_get ();
+  signkeys = json_array ();
+  for (unsigned int i=0;i<kd->num_sign_keys;i++)
+  {
+    const struct TALER_EXCHANGE_SigningPublicKey *sk = &kd->sign_keys[i];
+    json_t *signkey;
+
+    if (now.abs_value_us > sk->valid_until.abs_value_us)
+      continue; /* skip keys that have expired */
+    signkey = json_pack ("{s:o, s:o, s:o, s:o, s:o}",
+			 "key",
+			 GNUNET_JSON_from_data_auto (&sk->key),
+			 "master_sig",
+			 GNUNET_JSON_from_data_auto (&sk->master_sig),
+			 "stamp_start",
+			 GNUNET_JSON_from_time_abs (sk->valid_from),
+			 "stamp_expire",
+			 GNUNET_JSON_from_time_abs (sk->valid_until),
+			 "stamp_end",
+			 GNUNET_JSON_from_time_abs (sk->valid_legal));
+    if (NULL == signkey)
+    {
+      GNUNET_break (0);
+      continue;
+    }
+    json_array_append_new (signkeys,
+			   signkey);
+  }
+  denoms = json_array ();
+  for (unsigned int i=0;i<kd->num_denom_keys;i++)
+  {
+    const struct TALER_EXCHANGE_DenomPublicKey *dk = &kd->denom_keys[i];
+    json_t *denom;
+
+    if (now.abs_value_us > dk->expire_deposit.abs_value_us)
+      continue; /* skip keys that have expired */
+    denom = json_pack ("{s:o, s:o, s:o, s:o, s:o "
+		       ",s:o, s:o, s:o, s:o, s:o "
+		       ",s:o}",
+		       "stamp_expire_deposit",
+		       GNUNET_JSON_from_time_abs (dk->expire_deposit),
+		       "stamp_expire_withdraw",
+		       GNUNET_JSON_from_time_abs (dk->withdraw_valid_until),
+		       "stamp_start",
+		       GNUNET_JSON_from_time_abs (dk->valid_from),
+		       "stamp_expire_legal",
+		       GNUNET_JSON_from_time_abs (dk->expire_legal),
+		       "value",
+		       TALER_JSON_from_amount (&dk->value),
+		       "fee_withdraw",
+		       /* #6 */
+		       TALER_JSON_from_amount (&dk->fee_withdraw),
+		       "fee_deposit",
+		       TALER_JSON_from_amount (&dk->fee_deposit),
+		       "fee_refresh",
+		       TALER_JSON_from_amount (&dk->fee_refresh),
+		       "fee_refund",
+		       TALER_JSON_from_amount (&dk->fee_refund),
+		       "master_sig",
+		       GNUNET_JSON_from_data_auto (&dk->master_sig),
+		       /* #10 */
+		       "denom_pub",
+		       GNUNET_JSON_from_rsa_public_key (dk->key.rsa_public_key));
+    if (NULL == denom)
+    {
+      GNUNET_break (0);
+      continue;
+    }
+    json_array_append_new (denoms,
+			   denom);
+  }
+  auditors = json_array ();
+  for (unsigned int i=0;i<kd->num_auditors;i++)
+  {
+    const struct TALER_EXCHANGE_AuditorInformation *ai = &kd->auditors[i];
+    json_t *a;
+    json_t *adenoms;
+
+    adenoms = json_array ();
+    for (unsigned int j=0;j<ai->num_denom_keys;j++)
+    {
+      const struct TALER_EXCHANGE_AuditorDenominationInfo *adi = &ai->denom_keys[j];
+      const struct TALER_EXCHANGE_DenomPublicKey *dk = &kd->denom_keys[adi->denom_key_offset];
+      json_t *k;
+
+      if (now.abs_value_us > dk->expire_deposit.abs_value_us)
+	continue; /* skip auditor signatures for denomination keys that have expired */
+      GNUNET_assert (adi->denom_key_offset < kd->num_denom_keys);
+      k = json_pack ("{s:o, s:o}",
+		     "denom_pub_h",
+		     GNUNET_JSON_from_data_auto (&dk->h_key),
+		     "auditor_sig",
+		     GNUNET_JSON_from_data_auto (&adi->auditor_sig));
+      if (NULL == k)
+      {
+	GNUNET_break (0);
+	continue;
+      }
+      json_array_append_new (adenoms,
+			     k);
+    }
+
+    a = json_pack ("{s:o, s:s, s:o}",
+		   "auditor_pub",
+		   GNUNET_JSON_from_data_auto (&ai->auditor_pub),
+		   "auditor_url",
+		   ai->auditor_url,
+		   "denomination_keys",
+		   adenoms);
+    if (NULL == a)
+    {
+      GNUNET_break (0);
+      continue;
+    }
+    json_array_append_new (auditors,
+			   a);
+  }
+  keys = json_pack ("{s:s, s:o, s:o, s:o, s:o"
+		    ",s:o, s:o}",
+		    /* 1 */
+		    "version",
+		    kd->version,
+		    "master_public_key",
+		    GNUNET_JSON_from_data_auto (&kd->master_pub),
+		    "reserve_closing_delay",
+		    GNUNET_JSON_from_time_rel (kd->reserve_closing_delay),
+		    "list_issue_date",
+		    GNUNET_JSON_from_time_abs (kd->list_issue_date),
+		    "signkeys",
+		    signkeys,
+		    /* #6 */
+		    "denoms",
+		    denoms,
+		    "auditors",
+		    auditors);
+  if (NULL == keys)
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  return json_pack ("{s:I, s:o, s:s, s:o}",
+		    "version",
+		    (json_int_t) TALER_SERIALIZATION_FORMAT_VERSION,
+		    "expire",
+		    GNUNET_JSON_from_time_abs (exchange->key_data_expiration),
+		    "url",
+		    exchange->url,
+		    "keys",
+		    keys);
+}
+
+
+/**
+ * Initialise a connection to the exchange. Will connect to the
+ * exchange and obtain information about the exchange's master
+ * public key and the exchange's auditor.
+ * The respective information will be passed to the @a cert_cb
+ * once available, and all future interactions with the exchange
+ * will be checked to be signed (where appropriate) by the
+ * respective master key.
+ *
+ * @param ctx the context
+ * @param url HTTP base URL for the exchange
+ * @param cert_cb function to call with the exchange's
+ *        certification information
+ * @param cert_cb_cls closure for @a cert_cb
+ * @param ... list of additional arguments,
+ *        terminated by #TALER_EXCHANGE_OPTION_END.
+ * @return the exchange handle; NULL upon error
+ */
+struct TALER_EXCHANGE_Handle *
+TALER_EXCHANGE_connect
+  (struct GNUNET_CURL_Context *ctx,
+   const char *url,
+   TALER_EXCHANGE_CertificationCallback cert_cb,
+   void *cert_cb_cls,
+   ...)
+{
+  struct TALER_EXCHANGE_Handle *exchange;
+  va_list ap;
+  enum TALER_EXCHANGE_Option opt;
+
+  exchange = GNUNET_new (struct TALER_EXCHANGE_Handle);
+  exchange->ctx = ctx;
+  exchange->url = GNUNET_strdup (url);
+  exchange->cert_cb = cert_cb;
+  exchange->cert_cb_cls = cert_cb_cls;
+  exchange->retry_task = GNUNET_SCHEDULER_add_now (&request_keys,
+                                                   exchange);
+  va_start (ap, cert_cb_cls);
+  while (TALER_EXCHANGE_OPTION_END !=
+	 (opt = va_arg (ap, int)))
+  {
+    switch (opt) {
+    case TALER_EXCHANGE_OPTION_END:
+      GNUNET_assert (0);
+      break;
+    case TALER_EXCHANGE_OPTION_DATA:
+    {
+      const json_t *data = va_arg (ap, const json_t *);
+
+      deserialize_data (exchange,
+			data);
+      break;
+    }
+    default:
+      GNUNET_assert (0);
+      break;
+    }
+  }
+  va_end (ap);
+  return exchange;
+}
+
+
+/**
+ * Initiate download of /keys from the exchange.
+ *
+ * @param cls exchange where to download /keys from
+ */
+static void
+request_keys (void *cls)
+{
+  struct TALER_EXCHANGE_Handle *exchange = cls;
+  struct KeysRequest *kr;
+  CURL *eh;
+
+  exchange->retry_task = NULL;
+  GNUNET_assert (NULL == exchange->kr);
+  kr = GNUNET_new (struct KeysRequest);
+  kr->exchange = exchange;
+  if (GNUNET_YES ==
+      TEAH_handle_is_ready (exchange))
+  {
+    char *arg;
+
+    TALER_LOG_DEBUG ("Last DK issue date (before GETting /keys): %s\n",
+                     GNUNET_STRINGS_absolute_time_to_string (exchange->key_data.last_denom_issue_date));
+    GNUNET_asprintf (&arg,
+                     "/keys?last_issue_date=%llu",
+                     (unsigned long long) exchange->key_data.last_denom_issue_date.abs_value_us / 1000000LLU);
+    kr->url = TEAH_path_to_url (exchange,
+                                arg);
+    GNUNET_free (arg);
+  }
+  else
+  {
+    kr->url = TEAH_path_to_url (exchange,
+                                "/keys");
+  }
+  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
+              "Requesting keys with URL `%s'.\n",
+              kr->url);
+  eh = TEL_curl_easy_get (kr->url);
+  GNUNET_assert (CURLE_OK ==
+                 curl_easy_setopt (eh,
+                                   CURLOPT_VERBOSE,
+                                   0));
+  GNUNET_assert (CURLE_OK ==
+                 curl_easy_setopt (eh,
+                                   CURLOPT_TIMEOUT,
+                                   (long) 300));
+  GNUNET_assert (CURLE_OK ==
+                 curl_easy_setopt (eh,
+                                   CURLOPT_HEADERFUNCTION,
+                                   &header_cb));
+  GNUNET_assert (CURLE_OK ==
+                 curl_easy_setopt (eh,
+                                   CURLOPT_HEADERDATA,
+                                   kr));
+  kr->job = GNUNET_CURL_job_add (exchange->ctx,
+                                 eh,
+                                 GNUNET_YES,
+                                 &keys_completed_cb,
+                                 kr);
+  exchange->kr = kr;
+}
+
+
+/**
+ * Disconnect from the exchange
+ *
+ * @param exchange the exchange handle
+ */
+void
+TALER_EXCHANGE_disconnect (struct TALER_EXCHANGE_Handle *exchange)
+{
+  if (NULL != exchange->kr)
+  {
+    GNUNET_CURL_job_cancel (exchange->kr->job);
+    free_keys_request (exchange->kr);
+    exchange->kr = NULL;
+  }
+  free_key_data (&exchange->key_data);
+  if (NULL != exchange->key_data_raw)
+  {
+    json_decref (exchange->key_data_raw);
+    exchange->key_data_raw = NULL;
+  }
+  if (NULL != exchange->retry_task)
+  {
+    GNUNET_SCHEDULER_cancel (exchange->retry_task);
+    exchange->retry_task = NULL;
+  }
+  GNUNET_free (exchange->url);
+  GNUNET_free (exchange);
+}
+
+
+/**
+ * Lookup the given @a pub in @a keys.
+ *
+ * @param keys the exchange's key set
+ * @param pub claimed current online signing key for the exchange
+ * @return NULL if @a pub was not found
+ */
+const struct TALER_EXCHANGE_SigningPublicKey *
+TALER_EXCHANGE_get_signing_key_details (const struct TALER_EXCHANGE_Keys *keys,
+					const struct TALER_ExchangePublicKeyP *pub)
+{
+  for (unsigned int i=0;i<keys->num_sign_keys;i++)
+  {
+    struct TALER_EXCHANGE_SigningPublicKey *spk = &keys->sign_keys[i];
+
+    if (0 == memcmp (pub,
+		     &spk->key,
+		     sizeof (struct TALER_ExchangePublicKeyP)))
+      return spk;
+  }
+  return NULL;
+}
+
+
+/**
+ * Test if the given @a pub is a the current signing key from the exchange
+ * according to @a keys.
+ *
+ * @param keys the exchange's key set
+ * @param pub claimed current online signing key for the exchange
+ * @return #GNUNET_OK if @a pub is (according to /keys) a current signing key
+ */
+int
+TALER_EXCHANGE_test_signing_key (const struct TALER_EXCHANGE_Keys *keys,
+                                 const struct TALER_ExchangePublicKeyP *pub)
+{
+  struct GNUNET_TIME_Absolute now;
+
+  /* we will check using a tolerance of 1h for the time */
+  now = GNUNET_TIME_absolute_get ();
+  for (unsigned int i=0;i<keys->num_sign_keys;i++)
+    if ( (keys->sign_keys[i].valid_from.abs_value_us <= now.abs_value_us + 60 * 60 * 1000LL * 1000LL) &&
+         (keys->sign_keys[i].valid_until.abs_value_us > now.abs_value_us - 60 * 60 * 1000LL * 1000LL) &&
+         (0 == memcmp (pub,
+                       &keys->sign_keys[i].key,
+                       sizeof (struct TALER_ExchangePublicKeyP))) )
+      return GNUNET_OK;
+  return GNUNET_SYSERR;
+}
+
+
+/**
+ * Get exchange's base URL.
+ *
+ * @param exchange exchange handle.
+ * @return the base URL from the handle.
+ */
+const char *
+TALER_EXCHANGE_get_base_url (const struct TALER_EXCHANGE_Handle *exchange)
+{
+  return exchange->url;
+}
+
+
+/**
+ * Obtain the denomination key details from the exchange.
+ *
+ * @param keys the exchange's key set
+ * @param pk public key of the denomination to lookup
+ * @return details about the given denomination key, NULL if the key is
+ * not found
+ */
+const struct TALER_EXCHANGE_DenomPublicKey *
+TALER_EXCHANGE_get_denomination_key (const struct TALER_EXCHANGE_Keys *keys,
+                                     const struct TALER_DenominationPublicKey *pk)
+{
+  for (unsigned int i=0;i<keys->num_denom_keys;i++)
+    if (0 == GNUNET_CRYPTO_rsa_public_key_cmp (pk->rsa_public_key,
+                                               keys->denom_keys[i].key.rsa_public_key))
+      return &keys->denom_keys[i];
+  return NULL;
+}
+
+
+/**
+ * Obtain the denomination key details from the exchange.
+ *
+ * @param keys the exchange's key set
+ * @param hc hash of the public key of the denomination to lookup
+ * @return details about the given denomination key
+ */
+const struct TALER_EXCHANGE_DenomPublicKey *
+TALER_EXCHANGE_get_denomination_key_by_hash (const struct TALER_EXCHANGE_Keys *keys,
+                                             const struct GNUNET_HashCode *hc)
+{
+  for (unsigned int i=0;i<keys->num_denom_keys;i++)
+    if (0 == memcmp (hc,
+                     &keys->denom_keys[i].h_key,
+                     sizeof (struct GNUNET_HashCode)))
+      return &keys->denom_keys[i];
+  return NULL;
+}
+
+
+/**
+ * Obtain the keys from the exchange.
+ *
+ * @param exchange the exchange handle
+ * @return the exchange's key set
+ */
+const struct TALER_EXCHANGE_Keys *
+TALER_EXCHANGE_get_keys (struct TALER_EXCHANGE_Handle *exchange)
+{
+  (void) TALER_EXCHANGE_check_keys_current (exchange,
+                                            GNUNET_NO);
+  return &exchange->key_data;
+}
+
+
+/**
+ * Obtain the keys from the exchange in the
+ * raw JSON format
+ *
+ * @param exchange the exchange handle
+ * @return the exchange's keys in raw JSON
+ */
+json_t *
+TALER_EXCHANGE_get_keys_raw (struct TALER_EXCHANGE_Handle *exchange)
+{
+  (void) TALER_EXCHANGE_check_keys_current (exchange,
+                                            GNUNET_NO);
+  return json_deep_copy (exchange->key_data_raw);
+}
+
+
+/* end of exchange_api_handle.c */