exchange/src/lib/exchange_api_deposit.c

/*
  This file is part of TALER
  Copyright (C) 2014, 2015, 2018, 2019 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_deposit.c
 * @brief Implementation of the /deposit request of the exchange's HTTP API
 * @author Sree Harsha Totakura <sreeharsha@totakura.in>
 * @author Christian Grothoff
 */
#include "platform.h"
#include <jansson.h>
#include <microhttpd.h> /* just for HTTP status codes */
#include <gnunet/gnunet_util_lib.h>
#include <gnunet/gnunet_json_lib.h>
#include <gnunet/gnunet_curl_lib.h>
#include "taler_json_lib.h"
#include "taler_auditor_service.h"
#include "taler_exchange_service.h"
#include "exchange_api_handle.h"
#include "taler_signatures.h"
#include "exchange_api_curl_defaults.h"


/**
 * 1:#AUDITOR_CHANCE is the probability that we report deposits
 * to the auditor.
 *
 * 2==50% of going to auditor. This is way too high, but set
 * deliberately this high for testing
 */
#define AUDITOR_CHANCE 2

/**
 * @brief A Deposit Handle
 */
struct TALER_EXCHANGE_DepositHandle
{

  /**
   * The connection to exchange this request handle will use
   */
  struct TALER_EXCHANGE_Handle *exchange;

  /**
   * The url for this request.
   */
  char *url;

  /**
   * Context for #TEH_curl_easy_post(). Keeps the data that must
   * persist for Curl to make the upload.
   */
  struct TEAH_PostContext ctx;

  /**
   * Handle for the request.
   */
  struct GNUNET_CURL_Job *job;

  /**
   * Function to call with the result.
   */
  TALER_EXCHANGE_DepositResultCallback cb;

  /**
   * Closure for @a cb.
   */
  void *cb_cls;

  /**
   * Information the exchange should sign in response.
   */
  struct TALER_DepositConfirmationPS depconf;

  /**
   * Exchange signature, set for #auditor_cb.
   */
  struct TALER_ExchangeSignatureP exchange_sig;

  /**
   * Exchange signing public key, set for #auditor_cb.
   */
  struct TALER_ExchangePublicKeyP exchange_pub;

  /**
   * Value of the /deposit transaction, including fee.
   */
  struct TALER_Amount amount_with_fee;

  /**
   * Total value of the coin being transacted with.
   */
  struct TALER_Amount coin_value;

};


/**
 * Function called for each auditor to give us a chance to possibly
 * launch a deposit confirmation interaction.
 *
 * @param cls closure
 * @param ah handle to the auditor
 * @param auditor_pub public key of the auditor
 * @return NULL if no deposit confirmation interaction was launched
 */
static struct TEAH_AuditorInteractionEntry *
auditor_cb (void *cls,
            struct TALER_AUDITOR_Handle *ah,
            const struct TALER_AuditorPublicKeyP *auditor_pub)
{
  struct TALER_EXCHANGE_DepositHandle *dh = cls;
  const struct TALER_EXCHANGE_Keys *key_state;
  const struct TALER_EXCHANGE_SigningPublicKey *spk;
  struct TALER_Amount amount_without_fee;
  struct TEAH_AuditorInteractionEntry *aie;

  if (0 != GNUNET_CRYPTO_random_u32 (GNUNET_CRYPTO_QUALITY_WEAK,
                                     AUDITOR_CHANCE))
    return NULL;
  key_state = TALER_EXCHANGE_get_keys (dh->exchange);
  spk = TALER_EXCHANGE_get_signing_key_details (key_state,
                                                &dh->exchange_pub);
  GNUNET_assert (NULL != spk);
  TALER_amount_ntoh (&amount_without_fee,
                     &dh->depconf.amount_without_fee);
  aie = GNUNET_new (struct TEAH_AuditorInteractionEntry);
  aie->dch = TALER_AUDITOR_deposit_confirmation (ah,
                                                 &dh->depconf.h_wire,
                                                 &dh->depconf.h_contract_terms,
                                                 GNUNET_TIME_absolute_ntoh (dh->depconf.timestamp),
                                                 GNUNET_TIME_absolute_ntoh (dh->depconf.refund_deadline),
                                                 &amount_without_fee,
                                                 &dh->depconf.coin_pub,
                                                 &dh->depconf.merchant,
                                                 &dh->exchange_pub,
                                                 &dh->exchange_sig,
                                                 &key_state->master_pub,
                                                 spk->valid_from,
                                                 spk->valid_until,
                                                 spk->valid_legal,
                                                 &spk->master_sig,
                                                 &TEAH_acc_confirmation_cb,
                                                 aie);
  return aie;
}


/**
 * Verify that the signature on the "200 OK" response
 * from the exchange is valid.
 *
 * @param dh deposit handle
 * @param json json reply with the signature
 * @param exchange_sig[out] set to the exchange's signature
 * @param exchange_pub[out] set to the exchange's public key
 * @return #GNUNET_OK if the signature is valid, #GNUNET_SYSERR if not
 */
static int
verify_deposit_signature_ok (struct TALER_EXCHANGE_DepositHandle *dh,
                             const json_t *json,
                             struct TALER_ExchangeSignatureP *exchange_sig,
                             struct TALER_ExchangePublicKeyP *exchange_pub)
{
  const struct TALER_EXCHANGE_Keys *key_state;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_fixed_auto ("sig", exchange_sig),
    GNUNET_JSON_spec_fixed_auto ("pub", exchange_pub),
    GNUNET_JSON_spec_end()
  };

  if (GNUNET_OK !=
      GNUNET_JSON_parse (json,
                         spec,
                         NULL, NULL))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  key_state = TALER_EXCHANGE_get_keys (dh->exchange);
  if (GNUNET_OK !=
      TALER_EXCHANGE_test_signing_key (key_state,
                                       exchange_pub))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (GNUNET_OK !=
      GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_EXCHANGE_CONFIRM_DEPOSIT,
                                  &dh->depconf.purpose,
                                  &exchange_sig->eddsa_signature,
                                  &exchange_pub->eddsa_pub))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  dh->exchange_sig = *exchange_sig;
  dh->exchange_pub = *exchange_pub;
  TEAH_get_auditors_for_dc (dh->exchange,
                            &auditor_cb,
                            dh);
  return GNUNET_OK;
}


/**
 * Verify that the signatures on the "403 FORBIDDEN" response from the
 * exchange demonstrating customer double-spending are valid.
 *
 * @param dh deposit handle
 * @param json json reply with the signature(s) and transaction history
 * @return #GNUNET_OK if the signature(s) is valid, #GNUNET_SYSERR if not
 */
static int
verify_deposit_signature_forbidden (const struct TALER_EXCHANGE_DepositHandle *dh,
                                    const json_t *json)
{
  json_t *history;
  struct TALER_Amount total;

  history = json_object_get (json,
                             "history");
  if (GNUNET_OK !=
      TALER_EXCHANGE_verify_coin_history (dh->coin_value.currency,
					  &dh->depconf.coin_pub,
					  history,
					  &total))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }
  if (GNUNET_OK !=
      TALER_amount_add (&total,
                        &total,
                        &dh->amount_with_fee))
  {
    /* clearly not OK if our transaction would have caused
       the overflow... */
    return GNUNET_OK;
  }

  if (0 >= TALER_amount_cmp (&total,
                             &dh->coin_value))
  {
    /* transaction should have still fit */
    GNUNET_break (0);
    return GNUNET_SYSERR;
  }
  /* everything OK, proof of double-spending was provided */
  return GNUNET_OK;
}


/**
 * Function called when we're done processing the
 * HTTP /deposit request.
 *
 * @param cls the `struct TALER_EXCHANGE_DepositHandle`
 * @param response_code HTTP response code, 0 on error
 * @param response parsed JSON result, NULL on error
 */
static void
handle_deposit_finished (void *cls,
                         long response_code,
                         const void *response)
{
  struct TALER_EXCHANGE_DepositHandle *dh = cls;
  struct TALER_ExchangeSignatureP exchange_sig;
  struct TALER_ExchangePublicKeyP exchange_pub;
  struct TALER_ExchangeSignatureP *es = NULL;
  struct TALER_ExchangePublicKeyP *ep = NULL;
  const json_t *j = response;

  dh->job = NULL;
  switch (response_code)
  {
  case 0:
    break;
  case MHD_HTTP_OK:
    if (GNUNET_OK !=
        verify_deposit_signature_ok (dh,
                                     j,
				     &exchange_sig,
                                     &exchange_pub))
    {
      GNUNET_break_op (0);
      response_code = 0;
    }
    else
    {
      es = &exchange_sig;
      ep = &exchange_pub;
    }
    break;
  case MHD_HTTP_BAD_REQUEST:
    /* This should never happen, either us or the exchange is buggy
       (or API version conflict); just pass JSON reply to the application */
    break;
  case MHD_HTTP_FORBIDDEN:
    /* Double spending; check signatures on transaction history */
    if (GNUNET_OK !=
        verify_deposit_signature_forbidden (dh,
                                            j))
    {
      GNUNET_break_op (0);
      response_code = 0;
    }
    break;
  case MHD_HTTP_UNAUTHORIZED:
    /* Nothing really to verify, exchange says one of the signatures is
       invalid; as we checked them, this should never happen, we
       should pass the JSON reply to the application */
    break;
  case MHD_HTTP_NOT_FOUND:
    /* Nothing really to verify, this should never
       happen, we should pass the JSON reply to the application */
    break;
  case MHD_HTTP_INTERNAL_SERVER_ERROR:
    /* Server had an internal issue; we should retry, but this API
       leaves this to the application */
    break;
  default:
    /* unexpected response code */
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Unexpected response code %u\n",
                (unsigned int) response_code);
    GNUNET_break (0);
    response_code = 0;
    break;
  }
  dh->cb (dh->cb_cls,
          response_code,
	  TALER_JSON_get_error_code (j),
	  es,
          ep,
          j);
  TALER_EXCHANGE_deposit_cancel (dh);
}


/**
 * Verify signature information about the deposit.
 *
 * @param dki public key information
 * @param amount the amount to be deposited
 * @param h_wire hash of the merchant’s account details
 * @param h_contract_terms hash of the contact of the merchant with the customer (further details are never disclosed to the exchange)
 * @param coin_pub coin’s public key
 * @param denom_pub denomination key with which the coin is signed
 * @param denom_pub_hash hash of @a denom_pub
 * @param denom_sig exchange’s unblinded signature of the coin
 * @param timestamp timestamp when the deposit was finalized
 * @param merchant_pub the public key of the merchant (used to identify the merchant for refund requests)
 * @param refund_deadline date until which the merchant can issue a refund to the customer via the exchange (can be zero if refunds are not allowed)
 * @param coin_sig the signature made with purpose #TALER_SIGNATURE_WALLET_COIN_DEPOSIT made by the customer with the coin’s private key.
 * @return #GNUNET_OK if signatures are OK, #GNUNET_SYSERR if not
 */
static int
verify_signatures (const struct TALER_EXCHANGE_DenomPublicKey *dki,
                   const struct TALER_Amount *amount,
                   const struct GNUNET_HashCode *h_wire,
                   const struct GNUNET_HashCode *h_contract_terms,
                   const struct TALER_CoinSpendPublicKeyP *coin_pub,
                   const struct TALER_DenominationSignature *denom_sig,
                   const struct TALER_DenominationPublicKey *denom_pub,
                   const struct GNUNET_HashCode *denom_pub_hash,
                   struct GNUNET_TIME_Absolute timestamp,
                   const struct TALER_MerchantPublicKeyP *merchant_pub,
                   struct GNUNET_TIME_Absolute refund_deadline,
                   const struct TALER_CoinSpendSignatureP *coin_sig)
{
  struct TALER_DepositRequestPS dr;
  struct TALER_CoinPublicInfo coin_info;

  dr.purpose.purpose = htonl (TALER_SIGNATURE_WALLET_COIN_DEPOSIT);
  dr.purpose.size = htonl (sizeof (struct TALER_DepositRequestPS));
  dr.h_contract_terms = *h_contract_terms;
  dr.h_wire = *h_wire;
  dr.timestamp = GNUNET_TIME_absolute_hton (timestamp);
  dr.refund_deadline = GNUNET_TIME_absolute_hton (refund_deadline);
  TALER_amount_hton (&dr.amount_with_fee,
                     amount);
  TALER_amount_hton (&dr.deposit_fee,
                     &dki->fee_deposit);
  dr.merchant = *merchant_pub;
  dr.coin_pub = *coin_pub;
  if (GNUNET_OK !=
      GNUNET_CRYPTO_eddsa_verify (TALER_SIGNATURE_WALLET_COIN_DEPOSIT,
                                  &dr.purpose,
                                  &coin_sig->eddsa_signature,
                                  &coin_pub->eddsa_pub))
  {
    GNUNET_break_op (0);
    TALER_LOG_WARNING ("Invalid coin signature on /deposit request!\n");
    {
      TALER_LOG_DEBUG ("... amount_with_fee was %s\n",
                       TALER_amount2s (amount));
      TALER_LOG_DEBUG ("... deposit_fee was %s\n",
                       TALER_amount2s (&dki->fee_deposit));
    }

    return GNUNET_SYSERR;
  }

  /* check coin signature */
  coin_info.coin_pub = *coin_pub;
  coin_info.denom_pub_hash = *denom_pub_hash;
  coin_info.denom_sig = *denom_sig;
  if (GNUNET_YES !=
      TALER_test_coin_valid (&coin_info,
                             denom_pub))
  {
    GNUNET_break_op (0);
    TALER_LOG_WARNING ("Invalid coin passed for /deposit\n");
    return GNUNET_SYSERR;
  }
  if (0 < TALER_amount_cmp (&dki->fee_deposit,
                            amount))
  {
    GNUNET_break_op (0);
    TALER_LOG_WARNING ("Deposit amount smaller than fee\n");
    return GNUNET_SYSERR;
  }
  return GNUNET_OK;
}


/**
 * Submit a deposit permission to the exchange and get the exchange's response.
 * Note that while we return the response verbatim to the caller for
 * further processing, we do already verify that the response is
 * well-formed (i.e. that signatures included in the response are all
 * valid).  If the exchange's reply is not well-formed, we return an
 * HTTP status code of zero to @a cb.
 *
 * We also verify that the @a coin_sig is valid for this deposit
 * request, and that the @a ub_sig is a valid signature for @a
 * coin_pub.  Also, the @a exchange must be ready to operate (i.e.  have
 * finished processing the /keys reply).  If either check fails, we do
 * NOT initiate the transaction with the exchange and instead return NULL.
 *
 * @param exchange the exchange handle; the exchange must be ready to operate
 * @param amount the amount to be deposited
 * @param wire_deadline date until which the merchant would like the exchange to settle the balance (advisory, the exchange cannot be
 *        forced to settle in the past or upon very short notice, but of course a well-behaved exchange will limit aggregation based on the advice received)
 * @param wire_details the merchant’s account details, in a format supported by the exchange
 * @param h_contract_terms hash of the contact of the merchant with the customer (further details are never disclosed to the exchange)
 * @param coin_pub coin’s public key
 * @param denom_pub denomination key with which the coin is signed
 * @param denom_sig exchange’s unblinded signature of the coin
 * @param timestamp timestamp when the contract was finalized, must not be too far in the future
 * @param merchant_pub the public key of the merchant (used to identify the merchant for refund requests)
 * @param refund_deadline date until which the merchant can issue a refund to the customer via the exchange (can be zero if refunds are not allowed); must not be after the @a wire_deadline
 * @param coin_sig the signature made with purpose #TALER_SIGNATURE_WALLET_COIN_DEPOSIT made by the customer with the coin’s private key.
 * @param cb the callback to call when a reply for this request is available
 * @param cb_cls closure for the above callback
 * @return a handle for this request; NULL if the inputs are invalid (i.e.
 *         signatures fail to verify).  In this case, the callback is not called.
 */
struct TALER_EXCHANGE_DepositHandle *
TALER_EXCHANGE_deposit (struct TALER_EXCHANGE_Handle *exchange,
                        const struct TALER_Amount *amount,
                        struct GNUNET_TIME_Absolute wire_deadline,
                        json_t *wire_details,
                        const struct GNUNET_HashCode *h_contract_terms,
                        const struct TALER_CoinSpendPublicKeyP *coin_pub,
                        const struct TALER_DenominationSignature *denom_sig,
                        const struct TALER_DenominationPublicKey *denom_pub,
                        struct GNUNET_TIME_Absolute timestamp,
                        const struct TALER_MerchantPublicKeyP *merchant_pub,
                        struct GNUNET_TIME_Absolute refund_deadline,
                        const struct TALER_CoinSpendSignatureP *coin_sig,
                        TALER_EXCHANGE_DepositResultCallback cb,
                        void *cb_cls)
{
  const struct TALER_EXCHANGE_Keys *key_state;
  const struct TALER_EXCHANGE_DenomPublicKey *dki;
  struct TALER_EXCHANGE_DepositHandle *dh;
  struct GNUNET_CURL_Context *ctx;
  json_t *deposit_obj;
  CURL *eh;
  struct GNUNET_HashCode h_wire;
  struct GNUNET_HashCode denom_pub_hash;
  struct TALER_Amount amount_without_fee;

  (void) GNUNET_TIME_round_abs (&wire_deadline);
  (void) GNUNET_TIME_round_abs (&refund_deadline);
  GNUNET_assert (refund_deadline.abs_value_us <= wire_deadline.abs_value_us);
  GNUNET_assert (GNUNET_YES ==
		 TEAH_handle_is_ready (exchange));
  /* initialize h_wire */
  if (GNUNET_OK !=
      TALER_JSON_merchant_wire_signature_hash (wire_details,
                                               &h_wire))
  {
    GNUNET_break (0);
    return NULL;
  }
  key_state = TALER_EXCHANGE_get_keys (exchange);
  dki = TALER_EXCHANGE_get_denomination_key (key_state,
                                             denom_pub);
  GNUNET_assert (NULL != dki);
  GNUNET_assert (GNUNET_SYSERR !=
                 TALER_amount_subtract (&amount_without_fee,
                                        amount,
                                        &dki->fee_deposit));
  GNUNET_CRYPTO_rsa_public_key_hash (denom_pub->rsa_public_key,
                                     &denom_pub_hash);
  if (GNUNET_OK !=
      verify_signatures (dki,
                         amount,
                         &h_wire,
                         h_contract_terms,
                         coin_pub,
                         denom_sig,
                         denom_pub,
                         &denom_pub_hash,
                         timestamp,
                         merchant_pub,
                         refund_deadline,
                         coin_sig))
  {
    GNUNET_break_op (0);
    return NULL;
  }

  deposit_obj = json_pack ("{s:o, s:O," /* f/wire */
                           " s:o, s:o," /* H_wire, h_contract_terms */
                           " s:o, s:o," /* coin_pub, denom_pub */
                           " s:o, s:o," /* ub_sig, timestamp */
                           " s:o," /* merchant_pub */
                           " s:o, s:o," /* refund_deadline, wire_deadline */
                           " s:o}",     /* coin_sig */
                           "contribution", TALER_JSON_from_amount (amount),
                           "wire", wire_details,
                           "H_wire", GNUNET_JSON_from_data_auto (&h_wire),
                           "h_contract_terms", GNUNET_JSON_from_data_auto (h_contract_terms),
                           "coin_pub", GNUNET_JSON_from_data_auto (coin_pub),
                           "denom_pub_hash", GNUNET_JSON_from_data_auto (&denom_pub_hash),
                           "ub_sig", GNUNET_JSON_from_rsa_signature (denom_sig->rsa_signature),
                           "timestamp", GNUNET_JSON_from_time_abs (timestamp),
                           "merchant_pub", GNUNET_JSON_from_data_auto (merchant_pub),
                           "refund_deadline", GNUNET_JSON_from_time_abs (refund_deadline),
                           "wire_transfer_deadline", GNUNET_JSON_from_time_abs (wire_deadline),
                           "coin_sig", GNUNET_JSON_from_data_auto (coin_sig)
                           );
  if (NULL == deposit_obj)
  {
    GNUNET_break (0);
    return NULL;
  }

  dh = GNUNET_new (struct TALER_EXCHANGE_DepositHandle);
  dh->exchange = exchange;
  dh->cb = cb;
  dh->cb_cls = cb_cls;
  dh->url = TEAH_path_to_url (exchange, "/deposit");
  dh->depconf.purpose.size = htonl (sizeof (struct TALER_DepositConfirmationPS));
  dh->depconf.purpose.purpose = htonl (TALER_SIGNATURE_EXCHANGE_CONFIRM_DEPOSIT);
  dh->depconf.h_contract_terms = *h_contract_terms;
  dh->depconf.h_wire = h_wire;
  dh->depconf.timestamp = GNUNET_TIME_absolute_hton (timestamp);
  dh->depconf.refund_deadline = GNUNET_TIME_absolute_hton (refund_deadline);
  TALER_amount_hton (&dh->depconf.amount_without_fee,
                     &amount_without_fee);
  dh->depconf.coin_pub = *coin_pub;
  dh->depconf.merchant = *merchant_pub;
  dh->amount_with_fee = *amount;
  dh->coin_value = dki->value;

  eh = TEL_curl_easy_get (dh->url);
  if (GNUNET_OK !=
      TALER_curl_easy_post (&dh->ctx,
                           eh,
                           deposit_obj))
  {
    GNUNET_break (0);
    curl_easy_cleanup (eh);
    json_decref (deposit_obj);
    GNUNET_free (dh->url);
    GNUNET_free (dh);
    return NULL;
  }
  json_decref (deposit_obj);
  GNUNET_log (GNUNET_ERROR_TYPE_DEBUG,
              "URL for deposit: `%s'\n",
              dh->url);
  ctx = TEAH_handle_to_context (exchange);
  dh->job = GNUNET_CURL_job_add2 (ctx,
                                  eh,
                                  dh->ctx.headers,
                                  &handle_deposit_finished,
                                  dh);
  return dh;
}


/**
 * Cancel a deposit permission request.  This function cannot be used
 * on a request handle if a response is already served for it.
 *
 * @param deposit the deposit permission request handle
 */
void
TALER_EXCHANGE_deposit_cancel (struct TALER_EXCHANGE_DepositHandle *deposit)
{
  if (NULL != deposit->job)
  {
    GNUNET_CURL_job_cancel (deposit->job);
    deposit->job = NULL;
  }
  GNUNET_free (deposit->url);
  TALER_curl_easy_post_finished (&deposit->ctx);
  GNUNET_free (deposit);
}


/* end of exchange_api_deposit.c */