-work on error proof response checking for p2p payments

7 files changed, 465 insertions, 213 deletions

diff --git a/src/lib/Makefile.am b/src/lib/Makefile.am
index aa53d4493..844ca52fc 100644
--- a/src/lib/Makefile.am
+++ b/src/lib/Makefile.am
@@ -25,7 +25,7 @@ libtalerexchange_la_SOURCES = \
   exchange_api_batch_withdraw.c \
   exchange_api_batch_withdraw2.c \
   exchange_api_curl_defaults.c exchange_api_curl_defaults.h \
-  exchange_api_common.c \
+  exchange_api_common.c exchange_api_common.h \
   exchange_api_contracts_get.c \
   exchange_api_csr_melt.c \
   exchange_api_csr_withdraw.c \
diff --git a/src/lib/exchange_api_common.c b/src/lib/exchange_api_common.c
index 9cbcdeb26..567239eed 100644
--- a/src/lib/exchange_api_common.c
+++ b/src/lib/exchange_api_common.c
@@ -1414,4 +1414,232 @@ TALER_EXCHANGE_get_signing_key_info (
 }
 
 
+enum GNUNET_GenericReturnValue
+TALER_EXCHANGE_check_purse_create_conflict_ (
+  const struct TALER_PurseContractSignatureP *cpurse_sig,
+  const struct TALER_PurseContractPublicKeyP *purse_pub,
+  const json_t *proof)
+{
+  struct TALER_Amount amount;
+  uint32_t min_age;
+  struct GNUNET_TIME_Timestamp purse_expiration;
+  struct TALER_PurseContractSignatureP purse_sig;
+  struct TALER_PrivateContractHashP h_contract_terms;
+  struct TALER_PurseMergePublicKeyP merge_pub;
+  struct GNUNET_JSON_Specification spec[] = {
+    TALER_JSON_spec_amount_any ("amount",
+                                &amount),
+    GNUNET_JSON_spec_uint32 ("min_age",
+                             &min_age),
+    GNUNET_JSON_spec_timestamp ("purse_expiration",
+                                &purse_expiration),
+    GNUNET_JSON_spec_fixed_auto ("purse_sig",
+                                 &purse_sig),
+    GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
+                                 &h_contract_terms),
+    GNUNET_JSON_spec_fixed_auto ("merge_pub",
+                                 &merge_pub),
+    GNUNET_JSON_spec_end ()
+  };
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (proof,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      TALER_wallet_purse_create_verify (purse_expiration,
+                                        &h_contract_terms,
+                                        &merge_pub,
+                                        min_age,
+                                        &amount,
+                                        purse_pub,
+                                        &purse_sig))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (0 ==
+      GNUNET_memcmp (&purse_sig,
+                     cpurse_sig))
+  {
+    /* Must be the SAME data, not a conflict! */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+static char *
+make_payto (const char *exchange_url,
+            const struct TALER_ReservePublicKeyP *reserve_pub)
+{
+  char pub_str[sizeof (*reserve_pub) * 2];
+  char *end;
+  bool is_http;
+  char *reserve_url;
+
+  end = GNUNET_STRINGS_data_to_string (
+    reserve_pub,
+    sizeof (*reserve_pub),
+    pub_str,
+    sizeof (pub_str));
+  *end = '\0';
+  if (0 == strncmp (exchange_url,
+                    "http://",
+                    strlen ("http://")))
+  {
+    is_http = true;
+    exchange_url = &exchange_url[strlen ("http://")];
+  }
+  else if (0 == strncmp (exchange_url,
+                         "https://",
+                         strlen ("https://")))
+  {
+    is_http = false;
+    exchange_url = &exchange_url[strlen ("https://")];
+  }
+  else
+  {
+    GNUNET_break (0);
+    return NULL;
+  }
+  /* exchange_url includes trailing '/' */
+  GNUNET_asprintf (&reserve_url,
+                   "payto://%s/%s%s",
+                   is_http ? "taler+http" : "taler",
+                   exchange_url,
+                   pub_str);
+  return reserve_url;
+}
+
+
+enum GNUNET_GenericReturnValue
+TALER_EXCHANGE_check_purse_merge_conflict_ (
+  const struct TALER_PurseMergeSignatureP *cmerge_sig,
+  const struct TALER_PurseMergePublicKeyP *merge_pub,
+  const struct TALER_PurseContractPublicKeyP *purse_pub,
+  const char *exchange_url,
+  const json_t *proof)
+{
+  struct TALER_PurseMergeSignatureP merge_sig;
+  struct GNUNET_TIME_Timestamp merge_timestamp;
+  const char *partner_url = exchange_url;
+  struct TALER_ReservePublicKeyP reserve_pub;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_mark_optional (
+      // FIXME: partner_url or partner_base_url?
+      GNUNET_JSON_spec_string ("partner_url",
+                               &partner_url),
+      NULL),
+    GNUNET_JSON_spec_timestamp ("merge_timestamp",
+                                &merge_timestamp),
+    GNUNET_JSON_spec_fixed_auto ("merge_sig",
+                                 &merge_sig),
+    GNUNET_JSON_spec_fixed_auto ("reserve_pub",
+                                 &reserve_pub),
+    GNUNET_JSON_spec_end ()
+  };
+  char *payto_uri;
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (proof,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  payto_uri = make_payto (partner_url,
+                          &reserve_pub);
+  if (GNUNET_OK !=
+      TALER_wallet_purse_merge_verify (
+        payto_uri,
+        merge_timestamp,
+        purse_pub,
+        merge_pub,
+        &merge_sig))
+  {
+    GNUNET_break_op (0);
+    GNUNET_free (payto_uri);
+    return GNUNET_SYSERR;
+  }
+  GNUNET_free (payto_uri);
+  if (0 ==
+      GNUNET_memcmp (&merge_sig,
+                     cmerge_sig))
+  {
+    /* Must be the SAME data, not a conflict! */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
+/**
+ * Check proof of a contract conflict.
+ *
+ * DESIGN-FIXME: this 'proof' doesn't really proof a conflict!
+ *
+ * @param ccontract_sig conflicting signature (must
+ *        not match the signature from the proof)
+ * @param purse_pub public key of the purse
+ * @param exchange_url the base URL of this exchange
+ * @param proof the proof to check
+ * @return #GNUNET_OK if the @a proof is OK for @a purse_pub and conflicts with @a purse_sig
+ */
+enum GNUNET_GenericReturnValue
+TALER_EXCHANGE_check_purse_econtract_conflict_ (
+  const struct TALER_PurseContractSignatureP *ccontract_sig,
+  const struct TALER_PurseContractPublicKeyP *purse_pub,
+  const json_t *proof)
+{
+  struct TALER_ContractDiffiePublicP contract_pub;
+  struct TALER_PurseContractSignatureP contract_sig;
+  struct GNUNET_HashCode h_econtract;
+  struct GNUNET_JSON_Specification spec[] = {
+    GNUNET_JSON_spec_fixed_auto ("h_econtract",
+                                 &h_econtract),
+    GNUNET_JSON_spec_fixed_auto ("econtract_sig",
+                                 &contract_sig),
+    GNUNET_JSON_spec_fixed_auto ("contract_pub",
+                                 &contract_pub),
+    GNUNET_JSON_spec_end ()
+  };
+
+  if (GNUNET_OK !=
+      GNUNET_JSON_parse (proof,
+                         spec,
+                         NULL, NULL))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (GNUNET_OK !=
+      TALER_wallet_econtract_upload_verify2 (
+        &h_econtract,
+        &contract_pub,
+        purse_pub,
+        &contract_sig))
+  {
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  if (0 ==
+      GNUNET_memcmp (&contract_sig,
+                     ccontract_sig))
+  {
+    /* Must be the SAME data, not a conflict! */
+    GNUNET_break_op (0);
+    return GNUNET_SYSERR;
+  }
+  return GNUNET_OK;
+}
+
+
 /* end of exchange_api_common.c */
diff --git a/src/lib/exchange_api_common.h b/src/lib/exchange_api_common.h
new file mode 100644
index 000000000..9c6d45029
--- /dev/null
+++ b/src/lib/exchange_api_common.h
@@ -0,0 +1,84 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2015-2022 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 lib/exchange_api_common.h
+ * @brief common functions for the exchange API
+ * @author Christian Grothoff
+ */
+#ifndef EXCHANGE_API_COMMON_H
+#define EXCHANGE_API_COMMON_H
+
+#include "taler_json_lib.h"
+
+
+/**
+ * Check proof of a purse creation conflict.
+ *
+ * @param cpurse_sig conflicting signature (must
+ *        not match the signature from the proof)
+ * @param purse_pub the public key (must match
+ *        the signature from the proof)
+ * @param proof the proof to check
+ * @return #GNUNET_OK if the @a proof is OK for @a purse_pub and conflicts with @a purse_sig
+ */
+enum GNUNET_GenericReturnValue
+TALER_EXCHANGE_check_purse_create_conflict_ (
+  const struct TALER_PurseContractSignatureP *cpurse_sig,
+  const struct TALER_PurseContractPublicKeyP *purse_pub,
+  const json_t *proof);
+
+
+/**
+ * Check proof of a purse merge conflict.
+ *
+ * @param cmerge_sig conflicting signature (must
+ *        not match the signature from the proof)
+ * @param merge_pub the public key (must match
+ *        the signature from the proof)
+ * @param exchange_url the base URL of this exchange
+ * @param proof the proof to check
+ * @return #GNUNET_OK if the @a proof is OK for @a purse_pub and conflicts with @a purse_sig
+ */
+enum GNUNET_GenericReturnValue
+TALER_EXCHANGE_check_purse_merge_conflict_ (
+  const struct TALER_PurseMergeSignatureP *cmerge_sig,
+  const struct TALER_PurseMergePublicKeyP *merge_pub,
+  const struct TALER_PurseContractPublicKeyP *purse_pub,
+  const char *exchange_url,
+  const json_t *proof);
+
+
+/**
+ * Check proof of a contract conflict.
+ *
+ * DESIGN-FIXME: this 'proof' doesn't really proof a conflict!
+ *
+ * @param ccontract_sig conflicting signature (must
+ *        not match the signature from the proof)
+ * @param purse_pub public key of the purse
+ * @param exchange_url the base URL of this exchange
+ * @param proof the proof to check
+ * @return #GNUNET_OK if the @a proof is OK for @a purse_pub and conflicts with @a purse_sig
+ */
+enum GNUNET_GenericReturnValue
+TALER_EXCHANGE_check_purse_econtract_conflict_ (
+  const struct TALER_PurseContractSignatureP *ccontract_sig,
+  const struct TALER_PurseContractPublicKeyP *purse_pub,
+  const json_t *proof);
+
+
+#endif
diff --git a/src/lib/exchange_api_handle.h b/src/lib/exchange_api_handle.h
index 569c723c4..7ef88489e 100644
--- a/src/lib/exchange_api_handle.h
+++ b/src/lib/exchange_api_handle.h
@@ -19,7 +19,9 @@
  * @brief Internal interface to the handle part of the exchange's HTTP API
  * @author Christian Grothoff
  */
-#include "platform.h"
+#ifndef EXCHANGE_API_HANDLE_H
+#define EXCHANGE_API_HANDLE_H
+
 #include <gnunet/gnunet_curl_lib.h>
 #include "taler_auditor_service.h"
 #include "taler_exchange_service.h"
@@ -254,3 +256,4 @@ TEAH_path_to_url (struct TALER_EXCHANGE_Handle *h,
                   const char *path);
 
 /* end of exchange_api_handle.h */
+#endif
diff --git a/src/lib/exchange_api_purse_create_with_deposit.c b/src/lib/exchange_api_purse_create_with_deposit.c
index cace73249..f21b7d312 100644
--- a/src/lib/exchange_api_purse_create_with_deposit.c
+++ b/src/lib/exchange_api_purse_create_with_deposit.c
@@ -29,6 +29,7 @@
 #include "taler_json_lib.h"
 #include "taler_exchange_service.h"
 #include "exchange_api_handle.h"
+#include "exchange_api_common.h"
 #include "taler_signatures.h"
 #include "exchange_api_curl_defaults.h"
 
@@ -76,6 +77,11 @@ struct TALER_EXCHANGE_PurseCreateDepositHandle
   struct TALER_Amount purse_value_after_fees;
 
   /**
+   * Our encryped contract (if we had any).
+   */
+  struct TALER_EncryptedContract econtract;
+
+  /**
    * Public key of the merge capability.
    */
   struct TALER_PurseMergePublicKeyP merge_pub;
@@ -86,7 +92,12 @@ struct TALER_EXCHANGE_PurseCreateDepositHandle
   struct TALER_PurseContractPublicKeyP purse_pub;
 
   /**
-   * Hash over the purse's contrac terms.
+   * Signature with the purse key on the request.
+   */
+  struct TALER_PurseContractSignatureP purse_sig;
+
+  /**
+   * Hash over the purse's contract terms.
    */
   struct TALER_PrivateContractHashP h_contract_terms;
 
@@ -94,6 +105,7 @@ struct TALER_EXCHANGE_PurseCreateDepositHandle
    * When does the purse expire.
    */
   struct GNUNET_TIME_Timestamp purse_expiration;
+
 };
 
 
@@ -201,7 +213,85 @@ handle_purse_create_deposit_finished (void *cls,
        happen, we should pass the JSON reply to the application */
     break;
   case MHD_HTTP_CONFLICT:
-    // FIXME: check reply!
+    {
+      dr.hr.ec = TALER_JSON_get_error_code (j);
+      switch (dr.hr.ec)
+      {
+      case TALER_EC_EXCHANGE_PURSE_CREATE_CONFLICTING_META_DATA:
+        if (GNUNET_OK !=
+            TALER_EXCHANGE_check_purse_create_conflict_ (
+              &pch->purse_sig,
+              &pch->purse_pub,
+              j))
+        {
+          GNUNET_break_op (0);
+          dr.hr.http_status = 0;
+          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+          break;
+        }
+        break;
+      case TALER_EC_EXCHANGE_GENERIC_INSUFFICIENT_FUNDS:
+        {
+#if FIXME
+          struct TALER_Amount total;
+          struct TALER_DenominationHashP h_denom_pub;
+          const struct TALER_EXCHANGE_DenomPublicKey *dk = NULL;
+
+          // FIXME: parse coin_pub
+          // FIXME: lookup dk for that coin from our deposits array!
+
+          if (NULL == dk)
+          {
+            /* not one of our coins */
+            GNUNET_break_op (0);
+            dr.hr.http_status = 0;
+            dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+            break;
+          }
+          if (GNUNET_OK !=
+              TALER_EXCHANGE_verify_coin_history (dk,
+                                                  pch->exchange->currency,
+                                                  &coin_pub,
+                                                  history,
+                                                  &h_denom_pub,
+                                                  &total))
+          {
+            GNUNET_break_op (0);
+            dr.hr.http_status = 0;
+            dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+            break;
+          }
+          // FIXME: check total is too high for the request...
+#endif
+          break;
+        }
+      case TALER_EC_EXCHANGE_PURSE_DEPOSIT_CONFLICTING_META_DATA:
+        {
+          // FIXME!
+          break;
+        }
+      case TALER_EC_EXCHANGE_PURSE_ECONTRACT_CONFLICTING_META_DATA:
+        if (GNUNET_OK !=
+            TALER_EXCHANGE_check_purse_econtract_conflict_ (
+              &pch->econtract.econtract_sig,
+              &pch->purse_pub,
+              j))
+        {
+          GNUNET_break_op (0);
+          dr.hr.http_status = 0;
+          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+          break;
+        }
+        break;
+      default:
+        GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
+                    "Unexpected error code %d for conflcting deposit\n",
+                    dr.hr.ec);
+        GNUNET_break_op (0);
+        dr.hr.http_status = 0;
+        dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+      }
+    }
     break;
   case MHD_HTTP_GONE:
     /* could happen if denomination was revoked */
@@ -252,8 +342,6 @@ TALER_EXCHANGE_purse_create_with_deposit (
   json_t *create_obj;
   json_t *deposit_arr;
   CURL *eh;
-  struct TALER_PurseContractSignatureP purse_sig;
-  struct TALER_EncryptedContract econtract;
   char arg_str[sizeof (pch->purse_pub) * 2 + 32];
   char *url;
   uint32_t min_age = 0;
@@ -391,22 +479,22 @@ TALER_EXCHANGE_purse_create_with_deposit (
                                   min_age,
                                   &pch->purse_value_after_fees,
                                   purse_priv,
-                                  &purse_sig);
+                                  &pch->purse_sig);
   if (upload_contract)
   {
     TALER_CRYPTO_contract_encrypt_for_merge (&pch->purse_pub,
                                              contract_priv,
                                              merge_priv,
                                              contract_terms,
-                                             &econtract.econtract,
-                                             &econtract.econtract_size);
+                                             &pch->econtract.econtract,
+                                             &pch->econtract.econtract_size);
     GNUNET_CRYPTO_ecdhe_key_get_public (&contract_priv->ecdhe_priv,
-                                        &econtract.contract_pub.ecdhe_pub);
-    TALER_wallet_econtract_upload_sign (econtract.econtract,
-                                        econtract.econtract_size,
-                                        &econtract.contract_pub,
+                                        &pch->econtract.contract_pub.ecdhe_pub);
+    TALER_wallet_econtract_upload_sign (pch->econtract.econtract,
+                                        pch->econtract.econtract_size,
+                                        &pch->econtract.contract_pub,
                                         purse_priv,
-                                        &econtract.econtract_sig);
+                                        &pch->econtract.econtract_sig);
   }
   create_obj = GNUNET_JSON_PACK (
     TALER_JSON_pack_amount ("amount",
@@ -416,10 +504,10 @@ TALER_EXCHANGE_purse_create_with_deposit (
     GNUNET_JSON_pack_allow_null (
       TALER_JSON_pack_econtract ("econtract",
                                  upload_contract
-                                  ? &econtract
+                                  ? &pch->econtract
                                   : NULL)),
     GNUNET_JSON_pack_data_auto ("purse_sig",
-                                &purse_sig),
+                                &pch->purse_sig),
     GNUNET_JSON_pack_data_auto ("merge_pub",
                                 &pch->merge_pub),
     GNUNET_JSON_pack_data_auto ("h_contract_terms",
@@ -429,7 +517,6 @@ TALER_EXCHANGE_purse_create_with_deposit (
     GNUNET_JSON_pack_array_steal ("deposits",
                                   deposit_arr));
   GNUNET_assert (NULL != create_obj);
-  GNUNET_free (econtract.econtract);
   eh = TALER_EXCHANGE_curl_easy_get_ (pch->url);
   if ( (NULL == eh) ||
        (GNUNET_OK !=
@@ -441,6 +528,7 @@ TALER_EXCHANGE_purse_create_with_deposit (
     if (NULL != eh)
       curl_easy_cleanup (eh);
     json_decref (create_obj);
+    GNUNET_free (pch->econtract.econtract);
     GNUNET_free (pch->url);
     GNUNET_free (pch);
     return NULL;
@@ -468,6 +556,7 @@ TALER_EXCHANGE_purse_create_with_deposit_cancel (
     GNUNET_CURL_job_cancel (pch->job);
     pch->job = NULL;
   }
+  GNUNET_free (pch->econtract.econtract);
   GNUNET_free (pch->url);
   TALER_curl_easy_post_finished (&pch->ctx);
   GNUNET_free (pch);
diff --git a/src/lib/exchange_api_purse_create_with_merge.c b/src/lib/exchange_api_purse_create_with_merge.c
index e726b712f..4ca633360 100644
--- a/src/lib/exchange_api_purse_create_with_merge.c
+++ b/src/lib/exchange_api_purse_create_with_merge.c
@@ -29,6 +29,7 @@
 #include "taler_json_lib.h"
 #include "taler_exchange_service.h"
 #include "exchange_api_handle.h"
+#include "exchange_api_common.h"
 #include "taler_signatures.h"
 #include "exchange_api_curl_defaults.h"
 
@@ -235,173 +236,48 @@ handle_purse_create_with_merge_finished (void *cls,
     switch (dr.hr.ec)
     {
     case TALER_EC_EXCHANGE_RESERVES_PURSE_CREATE_CONFLICTING_META_DATA:
+      if (GNUNET_OK !=
+          TALER_EXCHANGE_check_purse_create_conflict_ (
+            &pcm->purse_sig,
+            &pcm->purse_pub,
+            j))
       {
-        struct TALER_Amount amount;
-        uint32_t min_age;
-        struct GNUNET_TIME_Timestamp purse_expiration;
-        struct TALER_PurseContractSignatureP purse_sig;
-        struct TALER_PrivateContractHashP h_contract_terms;
-        struct TALER_PurseMergePublicKeyP merge_pub;
-        struct GNUNET_JSON_Specification spec[] = {
-          TALER_JSON_spec_amount_any ("amount",
-                                      &amount),
-          GNUNET_JSON_spec_uint32 ("min_age",
-                                   &min_age),
-          GNUNET_JSON_spec_timestamp ("purse_expiration",
-                                      &purse_expiration),
-          GNUNET_JSON_spec_fixed_auto ("purse_sig",
-                                       &purse_sig),
-          GNUNET_JSON_spec_fixed_auto ("h_contract_terms",
-                                       &h_contract_terms),
-          GNUNET_JSON_spec_fixed_auto ("merge_pub",
-                                       &merge_pub),
-          GNUNET_JSON_spec_end ()
-        };
-
-        if (GNUNET_OK !=
-            GNUNET_JSON_parse (j,
-                               spec,
-                               NULL, NULL))
-        {
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
-        if (GNUNET_OK !=
-            TALER_wallet_purse_create_verify (purse_expiration,
-                                              &h_contract_terms,
-                                              &merge_pub,
-                                              min_age,
-                                              &amount,
-                                              &pcm->purse_pub,
-                                              &purse_sig))
-        {
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
-        if (0 ==
-            GNUNET_memcmp (&purse_sig,
-                           &pcm->purse_sig))
-        {
-          /* Must be the SAME data, not a conflict! */
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
+        dr.hr.http_status = 0;
+        dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
         break;
       }
+      break;
     case TALER_EC_EXCHANGE_RESERVES_PURSE_MERGE_CONFLICTING_META_DATA:
+      if (GNUNET_OK !=
+          TALER_EXCHANGE_check_purse_merge_conflict_ (
+            &pcm->merge_sig,
+            &pcm->merge_pub,
+            &pcm->purse_pub,
+            pcm->exchange->url,
+            j))
       {
-        struct TALER_PurseMergeSignatureP merge_sig;
-        struct GNUNET_TIME_Timestamp merge_timestamp;
-        const char *partner_url = pcm->exchange->url;
-        struct TALER_ReservePublicKeyP reserve_pub;
-        struct GNUNET_JSON_Specification spec[] = {
-          GNUNET_JSON_spec_mark_optional (
-            GNUNET_JSON_spec_string ("partner_url",
-                                     &partner_url),
-            NULL),
-          GNUNET_JSON_spec_timestamp ("merge_timestamp",
-                                      &merge_timestamp),
-          GNUNET_JSON_spec_fixed_auto ("merge_sig",
-                                       &merge_sig),
-          GNUNET_JSON_spec_fixed_auto ("reserve_pub",
-                                       &reserve_pub),
-          GNUNET_JSON_spec_end ()
-        };
-
-        if (GNUNET_OK !=
-            GNUNET_JSON_parse (j,
-                               spec,
-                               NULL, NULL))
-        {
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
-        if (GNUNET_OK !=
-            TALER_wallet_purse_merge_verify (
-              partner_url,
-              merge_timestamp,
-              &pcm->purse_pub,
-              &pcm->merge_pub,
-              &merge_sig))
-        {
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
-        if (0 ==
-            GNUNET_memcmp (&merge_sig,
-                           &pcm->merge_sig))
-        {
-          /* Must be the SAME data, not a conflict! */
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
+        GNUNET_break_op (0);
+        dr.hr.http_status = 0;
+        dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
+        break;
       }
       break;
     case TALER_EC_EXCHANGE_RESERVES_PURSE_CREATE_INSUFFICIENT_FUNDS:
       /* nothing to verify */
       break;
     case TALER_EC_EXCHANGE_PURSE_ECONTRACT_CONFLICTING_META_DATA:
+      if (GNUNET_OK !=
+          TALER_EXCHANGE_check_purse_econtract_conflict_ (
+            &pcm->econtract.econtract_sig,
+            &pcm->purse_pub,
+            j))
       {
-        struct TALER_ContractDiffiePublicP contract_pub;
-        struct TALER_PurseContractSignatureP contract_sig;
-        struct GNUNET_HashCode h_econtract;
-        struct GNUNET_JSON_Specification spec[] = {
-          GNUNET_JSON_spec_fixed_auto ("h_econtract",
-                                       &h_econtract),
-          GNUNET_JSON_spec_fixed_auto ("econtract_sig",
-                                       &contract_sig),
-          GNUNET_JSON_spec_fixed_auto ("contract_pub",
-                                       &contract_pub),
-          GNUNET_JSON_spec_end ()
-        };
-
-        if (GNUNET_OK !=
-            GNUNET_JSON_parse (j,
-                               spec,
-                               NULL, NULL))
-        {
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
-        if (GNUNET_OK !=
-            TALER_wallet_econtract_upload_verify2 (
-              &h_econtract,
-              &contract_pub,
-              &pcm->purse_pub,
-              &contract_sig))
-        {
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
-        if (0 ==
-            GNUNET_memcmp (&contract_sig,
-                           &pcm->econtract.econtract_sig))
-        {
-          /* Must be the SAME data, not a conflict! */
-          GNUNET_break_op (0);
-          dr.hr.http_status = 0;
-          dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-          break;
-        }
-
+        GNUNET_break_op (0);
+        dr.hr.http_status = 0;
+        dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
         break;
       }
+      break;
     default:
       /* unexpected EC! */
       GNUNET_break_op (0);
diff --git a/src/lib/exchange_api_purse_merge.c b/src/lib/exchange_api_purse_merge.c
index 0812fdadf..4b65e97f1 100644
--- a/src/lib/exchange_api_purse_merge.c
+++ b/src/lib/exchange_api_purse_merge.c
@@ -29,6 +29,7 @@
 #include "taler_json_lib.h"
 #include "taler_exchange_service.h"
 #include "exchange_api_handle.h"
+#include "exchange_api_common.h"
 #include "taler_signatures.h"
 #include "exchange_api_curl_defaults.h"
 
@@ -76,6 +77,11 @@ struct TALER_EXCHANGE_AccountMergeHandle
   char *provider_url;
 
   /**
+   * Signature for our operation.
+   */
+  struct TALER_PurseMergeSignatureP merge_sig;
+
+  /**
    * Expected value in the purse after fees.
    */
   struct TALER_Amount purse_value_after_fees;
@@ -266,58 +272,25 @@ handle_purse_merge_finished (void *cls,
     break;
   case MHD_HTTP_CONFLICT:
     {
-      struct TALER_PurseMergeSignatureP merge_sig;
-      struct GNUNET_TIME_Timestamp merge_timestamp;
-      const char *partner_url = NULL;
-      struct TALER_ReservePublicKeyP reserve_pub;
-      struct GNUNET_JSON_Specification spec[] = {
-        GNUNET_JSON_spec_fixed_auto ("reserve_pub",
-                                     &reserve_pub),
-        GNUNET_JSON_spec_fixed_auto ("merge_sig",
-                                     &merge_sig),
-        GNUNET_JSON_spec_timestamp ("merge_timestamp",
-                                    &merge_timestamp),
-        GNUNET_JSON_spec_mark_optional (
-          GNUNET_JSON_spec_string ("partner_base_url",
-                                   &partner_url),
-          NULL),
-        GNUNET_JSON_spec_end ()
-      };
       struct TALER_PurseMergePublicKeyP merge_pub;
-      char *payto_uri;
 
-      if (GNUNET_OK !=
-          GNUNET_JSON_parse (j,
-                             spec,
-                             NULL, NULL))
-      {
-        GNUNET_break_op (0);
-        dr.hr.http_status = 0;
-        dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-        break;
-      }
       GNUNET_CRYPTO_eddsa_key_get_public (&pch->merge_priv.eddsa_priv,
                                           &merge_pub.eddsa_pub);
-      if (NULL == partner_url)
-        partner_url = pch->provider_url;
-      payto_uri = make_payto (partner_url,
-                              &reserve_pub);
+
       if (GNUNET_OK !=
-          TALER_wallet_purse_merge_verify (
-            payto_uri,
-            merge_timestamp,
-            &pch->purse_pub,
+          TALER_EXCHANGE_check_purse_merge_conflict_ (
+            &pch->merge_sig,
             &merge_pub,
-            &merge_sig))
+            &pch->purse_pub,
+            pch->provider_url,
+            j))
       {
         GNUNET_break_op (0);
         dr.hr.http_status = 0;
         dr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
-        GNUNET_free (payto_uri);
         break;
       }
-      GNUNET_free (payto_uri);
-      /* conflict is real */
+      break;
     }
     break;
   case MHD_HTTP_GONE:
@@ -370,7 +343,6 @@ TALER_EXCHANGE_account_merge (
   struct GNUNET_CURL_Context *ctx;
   json_t *merge_obj;
   CURL *eh;
-  struct TALER_PurseMergeSignatureP merge_sig;
   char arg_str[sizeof (pch->purse_pub) * 2 + 32];
   char *reserve_url;
 
@@ -430,7 +402,7 @@ TALER_EXCHANGE_account_merge (
                                  merge_timestamp,
                                  purse_pub,
                                  merge_priv,
-                                 &merge_sig);
+                                 &pch->merge_sig);
   {
     struct TALER_Amount zero_purse_fee;
 
@@ -451,7 +423,7 @@ TALER_EXCHANGE_account_merge (
     GNUNET_JSON_pack_string ("payto_uri",
                              reserve_url),
     GNUNET_JSON_pack_data_auto ("merge_sig",
-                                &merge_sig),
+                                &pch->merge_sig),
     GNUNET_JSON_pack_data_auto ("reserve_sig",
                                 &pch->reserve_sig),
     GNUNET_JSON_pack_timestamp ("merge_timestamp",