implement /payback parsing and signature verification

src/exchange/Makefile.am

@@ -37,6 +37,7 @@ taler_exchange_httpd_SOURCES = \
   taler-exchange-httpd_keystate.c taler-exchange-httpd_keystate.h \
   taler-exchange-httpd_mhd.c taler-exchange-httpd_mhd.h \
   taler-exchange-httpd_parsing.c taler-exchange-httpd_parsing.h \
+  taler-exchange-httpd_payback.c taler-exchange-httpd_payback.h \
   taler-exchange-httpd_refresh.c taler-exchange-httpd_refresh.h \
   taler-exchange-httpd_refund.c taler-exchange-httpd_refund.h \
   taler-exchange-httpd_reserve.c taler-exchange-httpd_reserve.h \

src/exchange/taler-exchange-httpd_db.c

@@ -2256,4 +2256,27 @@ TEH_DB_execute_track_transaction (struct MHD_Connection *connection,
 }
 
 
+/**
+ * Execute a "/payback".  The validity of the coin and signature have
+ * already been checked.  The database must now check that the coin is
+ * not (double) spent, and execute the transaction (record details,
+ * generate success or failure response).
+ *
+ * @param connection the MHD connection to handle
+ * @param coin information about the coin
+ * @param coin_bks blinding data of the coin (to be checked)
+ * @param coin_sig signature of the coin
+ * @return MHD result code
+ */
+int
+TEH_DB_execute_payback (struct MHD_Connection *connection,
+                        const struct TALER_CoinPublicInfo *coin,
+                        const struct TALER_DenominationBlindingKeyP *coin_bks,
+                        const struct TALER_CoinSpendSignatureP *coin_sig)
+{
+  GNUNET_break (0); /* not implemented (#3887) */
+  return MHD_NO;
+}
+
+
 /* end of taler-exchange-httpd_db.c */

src/exchange/taler-exchange-httpd_db.h

@@ -236,5 +236,24 @@ TEH_DB_execute_track_transaction (struct MHD_Connection *connection,
                                   const struct TALER_MerchantPublicKeyP *merchant_pub);
 
 
+/**
+ * Execute a "/payback".  The validity of the coin and signature have
+ * already been checked.  The database must now check that the coin is
+ * not (double) spent, and execute the transaction (record details,
+ * generate success or failure response).
+ *
+ * @param connection the MHD connection to handle
+ * @param coin information about the coin
+ * @param coin_bks blinding data of the coin (to be checked)
+ * @param coin_sig signature of the coin
+ * @return MHD result code
+ */
+int
+TEH_DB_execute_payback (struct MHD_Connection *connection,
+                        const struct TALER_CoinPublicInfo *coin,
+                        const struct TALER_DenominationBlindingKeyP *coin_bks,
+                        const struct TALER_CoinSpendSignatureP *coin_sig);
+
+
 #endif
 /* TALER_EXCHANGE_HTTPD_DB_H */

src/exchange/taler-exchange-httpd_keystate.c

@@ -806,6 +806,9 @@ TEH_KS_denomination_key_lookup (const struct TEH_KS_StateHandle *key_state,
       return NULL;
     }
     break;
+  case TEH_KS_DKU_PAYBACK:
+    GNUNET_break (0); /* not implemented (#3887) */
+    return NULL;
   }
   return dki;
 }

src/exchange/taler-exchange-httpd_keystate.h

@@ -92,9 +92,14 @@ enum TEH_KS_DenominationKeyUse {
   TEH_KS_DKU_WITHDRAW,
 
   /**
-   * The key is to be usd for a /deposit or /refresh (melt) operation.
+   * The key is to be used for a /deposit or /refresh (melt) operation.
    */
-  TEH_KS_DKU_DEPOSIT
+  TEH_KS_DKU_DEPOSIT,
+
+  /**
+   * The key is to be used for a /payback operation.
+   */
+  TEH_KS_DKU_PAYBACK
 
 };
 

src/exchange/taler-exchange-httpd_payback.c

@@ -0,0 +1,180 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2017 Inria and GNUnet e.V.
+
+  TALER is free software; you can redistribute it and/or modify it under the
+  terms of the GNU Affero 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 Affero General Public License for more details.
+
+  You should have received a copy of the GNU Affero General Public License along with
+  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file taler-exchange-httpd_payback.c
+ * @brief Handle /payback requests; parses the POST and JSON and
+ *        verifies the coin signature before handing things off
+ *        to the database.
+ * @author Christian Grothoff
+ */
+#include "platform.h"
+#include <gnunet/gnunet_util_lib.h>
+#include <gnunet/gnunet_json_lib.h>
+#include <jansson.h>
+#include <microhttpd.h>
+#include <pthread.h>
+#include "taler_json_lib.h"
+#include "taler-exchange-httpd_parsing.h"
+#include "taler-exchange-httpd_payback.h"
+#include "taler-exchange-httpd_responses.h"
+#include "taler-exchange-httpd_keystate.h"
+#include "taler-exchange-httpd_validation.h"
+
+
+/**
+ * We have parsed the JSON information about the payback request. Do
+ * some basic sanity checks (especially that the signature on the
+ * request and coin is valid) and then execute the payback operation.
+ * Note that we need the DB to check the fee structure, so this is not
+ * done here.
+ *
+ * @param connection the MHD connection to handle
+ * @param coin information about the coin
+ * @param coin_bks blinding data of the coin (to be checked)
+ * @param coin_sig signature of the coin
+ * @return MHD result code
+ */
+static int
+verify_and_execute_payback (struct MHD_Connection *connection,
+                            const struct TALER_CoinPublicInfo *coin,
+                            const struct TALER_DenominationBlindingKeyP *coin_bks,
+                            const struct TALER_CoinSpendSignatureP *coin_sig)
+{
+  struct TEH_KS_StateHandle *key_state;
+  const struct TALER_EXCHANGEDB_DenominationKeyIssueInformation *dki;
+  struct TALER_PaybackRequestPS pr;
+
+
+  /* check denomination exists and is in payback mode */
+  key_state = TEH_KS_acquire ();
+  dki = TEH_KS_denomination_key_lookup (key_state,
+                                        &coin->denom_pub,
+					TEH_KS_DKU_PAYBACK);
+  if (NULL == dki)
+  {
+    TEH_KS_release (key_state);
+    TALER_LOG_WARNING ("Denomination key in /payback request not in payback mode\n");
+    return TEH_RESPONSE_reply_arg_unknown (connection,
+					   TALER_EC_PAYBACK_DENOMINATION_KEY_UNKNOWN,
+                                           "denom_pub");
+  }
+
+  /* check denomination signature */
+  if (GNUNET_YES !=
+      TALER_test_coin_valid (coin))
+  {
+    TALER_LOG_WARNING ("Invalid coin passed for /payback\n");
+    TEH_KS_release (key_state);
+    return TEH_RESPONSE_reply_signature_invalid (connection,
+						 TALER_EC_PAYBACK_DENOMINATION_SIGNATURE_INVALID,
+                                                 "denom_sig");
+  }
+
+  /* check payback request signature */
+  pr.purpose.purpose = htonl (TALER_SIGNATURE_WALLET_COIN_PAYBACK);
+  pr.purpose.size = htonl (sizeof (struct TALER_PaybackRequestPS));
+  pr.coin_pub = coin->coin_pub;
+  pr.h_denom_pub = dki->issue.properties.denom_hash;
+  pr.coin_blind = *coin_bks;
+
+  TEH_KS_release (key_state);
+
+  if (GNUNET_OK !=
+      GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_WALLET_COIN_PAYBACK,
+                                  &pr.purpose,
+                                  &coin_sig->eddsa_signature,
+                                  &coin->coin_pub.eddsa_pub))
+  {
+    TALER_LOG_WARNING ("Invalid signature on /payback request\n");
+    return TEH_RESPONSE_reply_signature_invalid (connection,
+						 TALER_EC_PAYBACK_SIGNATURE_INVALID,
+                                                 "coin_sig");
+  }
+
+  return TEH_DB_execute_payback (connection,
+                                 coin,
+                                 coin_bks,
+                                 coin_sig);
+}
+
+
+/**
+ * Handle a "/payback" request.  Parses the JSON, and, if successful,
+ * passes the JSON data to #parse_and_handle_payback_request() to
+ * further check the details of the operation specified.  If
+ * everything checks out, this will ultimately lead to the "/refund"
+ * being executed, or rejected.
+ *
+ * @param rh context of the handler
+ * @param connection the MHD connection to handle
+ * @param[in,out] connection_cls the connection's closure (can be updated)
+ * @param upload_data upload data
+ * @param[in,out] upload_data_size number of bytes (left) in @a upload_data
+ * @return MHD result code
+  */
+int
+TEH_PAYBACK_handler_payback (struct TEH_RequestHandler *rh,
+                             struct MHD_Connection *connection,
+                             void **connection_cls,
+                             const char *upload_data,
+                             size_t *upload_data_size)
+{
+  json_t *json;
+  int res;
+  struct TALER_CoinPublicInfo coin;
+  struct TALER_DenominationBlindingKeyP coin_bks;
+  struct TALER_CoinSpendSignatureP coin_sig;
+  struct GNUNET_JSON_Specification spec[] = {
+    TALER_JSON_spec_denomination_public_key ("denom_pub",
+                                             &coin.denom_pub),
+    TALER_JSON_spec_denomination_signature ("ub_sig",
+                                            &coin.denom_sig),
+    GNUNET_JSON_spec_fixed_auto ("coin_pub",
+                                 &coin.coin_pub),
+    GNUNET_JSON_spec_fixed_auto ("coin_blind_key_secret",
+                                 &coin_bks),
+    GNUNET_JSON_spec_fixed_auto ("coin_sig",
+                                 &coin_sig),
+    GNUNET_JSON_spec_end ()
+  };
+
+  res = TEH_PARSE_post_json (connection,
+                             connection_cls,
+                             upload_data,
+                             upload_data_size,
+                             &json);
+  if (GNUNET_SYSERR == res)
+    return MHD_NO;
+  if ( (GNUNET_NO == res) || (NULL == json) )
+    return MHD_YES;
+  res = TEH_PARSE_json_data (connection,
+                             json,
+                             spec);
+  json_decref (json);
+  if (GNUNET_SYSERR == res)
+    return MHD_NO; /* hard failure */
+  if (GNUNET_NO == res)
+    return MHD_YES; /* failure */
+  res = verify_and_execute_payback (connection,
+                                    &coin,
+                                    &coin_bks,
+                                    &coin_sig);
+  GNUNET_JSON_parse_free (spec);
+  return res;
+}
+
+
+/* end of taler-exchange-httpd_payback.c */

src/exchange/taler-exchange-httpd_payback.h

@@ -0,0 +1,51 @@
+/*
+  This file is part of TALER
+  Copyright (C) 2017 GNUnet e.V.
+
+  TALER is free software; you can redistribute it and/or modify it under the
+  terms of the GNU Affero 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 Affero General Public License for more details.
+
+  You should have received a copy of the GNU Affero General Public License along with
+  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>
+*/
+/**
+ * @file taler-exchange-httpd_payback.h
+ * @brief Handle /payback requests
+ * @author Christian Grothoff
+ */
+#ifndef TALER_EXCHANGE_HTTPD_PAYBACK_H
+#define TALER_EXCHANGE_HTTPD_PAYBACK_H
+
+#include <gnunet/gnunet_util_lib.h>
+#include <microhttpd.h>
+#include "taler-exchange-httpd.h"
+
+
+/**
+ * Handle a "/payback" request.  Parses the JSON, and, if successful,
+ * passes the JSON data to #parse_and_handle_payback_request() to
+ * further check the details of the operation specified.  If
+ * everything checks out, this will ultimately lead to the "/refund"
+ * being executed, or rejected.
+ *
+ * @param rh context of the handler
+ * @param connection the MHD connection to handle
+ * @param[in,out] connection_cls the connection's closure (can be updated)
+ * @param upload_data upload data
+ * @param[in,out] upload_data_size number of bytes (left) in @a upload_data
+ * @return MHD result code
+  */
+int
+TEH_PAYBACK_handler_payback (struct TEH_RequestHandler *rh,
+                             struct MHD_Connection *connection,
+                             void **connection_cls,
+                             const char *upload_data,
+                             size_t *upload_data_size);
+
+
+#endif

src/include/taler_error_codes.h

@@ -831,6 +831,27 @@ enum TALER_ErrorCode
    */
   TALER_EC_TRACK_TRANSACTION_MERCHANT_SIGNATURE_INVALID = 1804,
 
+  /**
+   * The given denomination key is not in the "payback" set of the
+   * exchange right now.  This response is provided with an
+   * HTTP status code of MHD_HTTP_NOT_FOUND.
+   */
+  TALER_EC_PAYBACK_DENOMINATION_KEY_UNKNOWN = 1850,
+
+  /**
+   * The given coin signature is invalid for the request.
+   * This response is provided with an
+   * HTTP status code of MHD_HTTP_UNAUTHORIZED.
+   */
+  TALER_EC_PAYBACK_SIGNATURE_INVALID = 1851,
+
+  /**
+   * The signature of the denomination key over the coin is not valid.
+   * This response is provided with HTTP status code
+   * MHD_HTTP_BAD_REQUEST.
+   */
+  TALER_EC_PAYBACK_DENOMINATION_SIGNATURE_INVALID = 1852,
+
 
   /* *********** Merchant backend error codes ********* */