path: root/src/lib/exchange_api_age_withdraw_reveal.c

/*
  This file is part of TALER
  Copyright (C) 2023 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_age_withdraw_reveal.c
 * @brief Implementation of /age-withdraw/$ACH/reveal requests
 * @author Özgür Kesim
 */

#include "platform.h"
#include <gnunet/gnunet_common.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_curl_lib.h"
#include "taler_json_lib.h"
#include "taler_exchange_service.h"
#include "exchange_api_common.h"
#include "exchange_api_handle.h"
#include "taler_signatures.h"
#include "exchange_api_curl_defaults.h"

/**
 * Handler for a running age-withdraw-reveal  request
 */
struct TALER_EXCHANGE_AgeWithdrawRevealHandle
{

  /* The index not to be disclosed */
  uint8_t noreveal_index;

  /* The age-withdraw commitment */
  struct TALER_AgeWithdrawCommitmentHashP h_commitment;

  /* The maximum age */
  uint8_t max_age;

  /* Number of coins */
  size_t num_coins;

  /* The @e num_coins * kappa coin secrets from the age-withdraw commitment */
  const struct TALER_EXCHANGE_AgeWithdrawCoinInput *coins_input;

  /* The @e num_coins algorithm- and coin-specific parameters from the
   * previous call to /age-withdraw. */
  const struct TALER_ExchangeWithdrawValues *alg_values;

  /* The url for the reveal request */
  const char *request_url;

  /**
   * CURL handle for the request job.
   */
  struct GNUNET_CURL_Job *job;

  /**
   * Post Context
   */
  struct TALER_CURL_PostContext post_ctx;

  /* Callback */
  TALER_EXCHANGE_AgeWithdrawRevealCallback callback;

  /* Reveal */
  void *callback_cls;
};


static enum GNUNET_GenericReturnValue
reveal_coin (
  const struct TALER_PlanchetMasterSecretP *secret,
  const struct TALER_DenominationPublicKey *denom_pub,
  const struct TALER_ExchangeWithdrawValues *alg_values,
  const struct TALER_BlindedDenominationSignature *blind_sig,
  uint8_t max_age,
  struct TALER_EXCHANGE_RevealedCoinInfo *revealed_coin)
{
  enum GNUNET_GenericReturnValue ret = GNUNET_SYSERR;

#define BREAK_ON_FAILURE(call) \
  do { \
    if (GNUNET_OK != (call)) { GNUNET_break (0); break; } \
  } while(0)

  do {
    struct TALER_CoinPubHashP h_coin_pub;
    struct TALER_PlanchetDetail planchet_detail;
    const struct TALER_AgeCommitmentHash *hac = NULL;
    struct TALER_FreshCoin fresh_coin;

    TALER_planchet_setup_coin_priv (secret,
                                    alg_values,
                                    &revealed_coin->coin_priv);

    TALER_planchet_blinding_secret_create (secret,
                                           alg_values,
                                           &revealed_coin->bks);

    revealed_coin->age_commitment_proof = NULL;
    if (0 < max_age)
    {
      BREAK_ON_FAILURE (
        TALER_age_restriction_from_secret (
          secret,
          &denom_pub->age_mask,
          max_age,
          revealed_coin->age_commitment_proof));

      TALER_age_commitment_hash (
        &revealed_coin->age_commitment_proof->commitment,
        &revealed_coin->h_age_commitment);

      hac = &revealed_coin->h_age_commitment;
    }

    BREAK_ON_FAILURE (
      TALER_planchet_prepare (denom_pub,
                              alg_values,
                              &revealed_coin->bks,
                              &revealed_coin->coin_priv,
                              hac,
                              &h_coin_pub,
                              &planchet_detail));

    BREAK_ON_FAILURE (
      TALER_planchet_to_coin (denom_pub,
                              blind_sig,
                              &revealed_coin->bks,
                              &revealed_coin->coin_priv,
                              &revealed_coin->h_age_commitment,
                              &h_coin_pub,
                              alg_values,
                              &fresh_coin));

    /* success */
    revealed_coin->sig = fresh_coin.sig;
    ret = GNUNET_OK;
  } while(0);

  return ret;
#undef BREAK_ON_FAILURE
}


/**
 * We got a 200 OK response for the /age-withdraw/$ACH/reveal operation.
 * Extract the signed blindedcoins and return it to the caller.
 *
 * @param awrh operation handle
 * @param j_response reply from the exchange
 * @param num_coins The (expected) number of revealed coins
 * @param[in,out] revealed_coins The @e num_coins revealed coins to populate
 * @return #GNUNET_OK on success, #GNUNET_SYSERR on errors
 */
static enum GNUNET_GenericReturnValue
age_withdraw_reveal_ok (
  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh,
  const json_t *j_response)
{
  struct TALER_EXCHANGE_AgeWithdrawRevealResponse response = {
    .hr.reply = j_response,
    .hr.http_status = MHD_HTTP_OK,
  };
  const json_t *j_sigs;
  struct GNUNET_JSON_Specification spec[] = {
    GNUNET_JSON_spec_array_const ("ev_sigs",
                                  &j_sigs),
    GNUNET_JSON_spec_end ()
  };

  if (GNUNET_OK != GNUNET_JSON_parse (j_response,
                                      spec,
                                      NULL, NULL))
  {
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }

  if (awrh->num_coins != json_array_size (j_sigs))
  {
    /* Number of coins generated does not match our expectation */
    GNUNET_break_op (0);
    return GNUNET_SYSERR;
  }

  {
    struct TALER_EXCHANGE_RevealedCoinInfo revealed_coins[awrh->num_coins];

    /* Reconstruct the coins and unblind the signatures */
    for (size_t n = 0; n < awrh->num_coins; n++)
    {
      enum GNUNET_GenericReturnValue ret;
      struct TALER_BlindedDenominationSignature blinded_sig;
      json_t *j_sig = json_array_get (j_sigs, n);
      struct GNUNET_JSON_Specification spec[] = {
        GNUNET_JSON_spec_fixed_auto ("", &blinded_sig),
        GNUNET_JSON_spec_end ()
      };

      GNUNET_assert (NULL != j_sig);
      if (GNUNET_OK != GNUNET_JSON_parse (j_sig,
                                          spec,
                                          NULL, NULL))
      {
        GNUNET_break_op (0);
        return GNUNET_SYSERR;
      }
      ret = reveal_coin (&awrh->coins_input[n].secrets[awrh->noreveal_index],
                         &awrh->coins_input[n].denom_pub->key,
                         &awrh->alg_values[n],
                         &blinded_sig,
                         awrh->max_age,
                         &revealed_coins[n]);

      if (GNUNET_OK != ret)
        return ret;
    }

    response.details.ok.num_coins = awrh->num_coins;
    response.details.ok.revealed_coins = revealed_coins;
    awrh->callback (awrh->callback_cls,
                    &response);
    /* Make sure the callback isn't called again */
    awrh->callback = NULL;
  }

  return GNUNET_OK;
}


/**
 * Function called when we're done processing the
 * HTTP /age-withdraw/$ACH/reveal request.
 *
 * @param cls the `struct TALER_EXCHANGE_AgeWithdrawRevealHandle`
 * @param response_code The HTTP response code
 * @param response response data
 */
static void
handle_age_withdraw_reveal_finished (
  void *cls,
  long response_code,
  const void *response)
{
  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh = cls;
  const json_t *j_response = response;
  struct TALER_EXCHANGE_AgeWithdrawRevealResponse awr = {
    .hr.reply = j_response,
    .hr.http_status = (unsigned int) response_code
  };

  awrh->job = NULL;
  /* FIXME[oec]: Only handle response-codes that are in the spec */
  switch (response_code)
  {
  case 0:
    awr.hr.ec = TALER_EC_GENERIC_INVALID_RESPONSE;
    break;
  case MHD_HTTP_OK:
    {
      enum GNUNET_GenericReturnValue ret;

      ret = age_withdraw_reveal_ok (awrh,
                                    j_response);
      if (GNUNET_OK != ret)
      {
        GNUNET_break_op (0);
        awr.hr.http_status = 0;
        awr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
        break;
      }
      GNUNET_assert (NULL == awrh->callback);
      TALER_EXCHANGE_age_withdraw_reveal_cancel (awrh);
      return;
    }
  case MHD_HTTP_UNAVAILABLE_FOR_LEGAL_REASONS:
    /* only validate reply is well-formed */
    {
      uint64_t ptu;
      struct GNUNET_JSON_Specification spec[] = {
        GNUNET_JSON_spec_uint64 ("legitimization_uuid",
                                 &ptu),
        GNUNET_JSON_spec_end ()
      };

      if (GNUNET_OK !=
          GNUNET_JSON_parse (j_response,
                             spec,
                             NULL, NULL))
      {
        GNUNET_break_op (0);
        awr.hr.http_status = 0;
        awr.hr.ec = TALER_EC_GENERIC_REPLY_MALFORMED;
        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 */
    awr.hr.ec = TALER_JSON_get_error_code (j_response);
    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
    break;
  case MHD_HTTP_FORBIDDEN:
    GNUNET_break_op (0);
    /**
     * This should never happen, as we don't sent any signatures
     * to the exchange to verify.  We should simply pass the JSON reply
     * to the application
     **/
    awr.hr.ec = TALER_JSON_get_error_code (j_response);
    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
    break;
  case MHD_HTTP_NOT_FOUND:
    /* Nothing really to verify, the exchange basically just says
       that it doesn't know this age-withraw commitment. */
    awr.hr.ec = TALER_JSON_get_error_code (j_response);
    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
    break;
  case MHD_HTTP_CONFLICT:
    /* An age commitment for one of the coins did not fulfill
     * the required maximum age requirement of the corresponding
     * reserve.
     * Error code: TALER_EC_EXCHANGE_GENERIC_COIN_AGE_REQUIREMENT_FAILURE.
     */
    awr.hr.ec = TALER_JSON_get_error_code (j_response);
    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
    break;
  case MHD_HTTP_GONE:
    /* could happen if denomination was revoked */
    /* Note: one might want to check /keys for revocation
       signature here, alas tricky in case our /keys
       is outdated => left to clients */
    awr.hr.ec = TALER_JSON_get_error_code (j_response);
    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
    break;
  case MHD_HTTP_INTERNAL_SERVER_ERROR:
    /* Server had an internal issue; we should retry, but this API
       leaves this to the application */
    awr.hr.ec = TALER_JSON_get_error_code (j_response);
    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
    break;
  default:
    /* unexpected response code */
    GNUNET_break_op (0);
    awr.hr.ec = TALER_JSON_get_error_code (j_response);
    awr.hr.hint = TALER_JSON_get_error_hint (j_response);
    GNUNET_log (GNUNET_ERROR_TYPE_ERROR,
                "Unexpected response code %u/%d for exchange age-withdraw\n",
                (unsigned int) response_code,
                (int) awr.hr.ec);
    break;
  }
  awrh->callback (awrh->callback_cls,
                  &awr);
  TALER_EXCHANGE_age_withdraw_reveal_cancel (awrh);
}


/**
 * Prepares the request URL for the age-withdraw-reveal request
 *
 * @param exchange_url The base-URL to the exchange
 * @param[in,out] awrh The handler
 * @return GNUNET_OK on success, GNUNET_SYSERR otherwise
 */
static
enum GNUNET_GenericReturnValue
prepare_url (
  const char *exchange_url,
  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh)
{
  char arg_str[sizeof (struct TALER_AgeWithdrawCommitmentHashP) * 2 + 32];
  char pub_str[sizeof (struct TALER_AgeWithdrawCommitmentHashP) * 2];
  char *end;

  end = GNUNET_STRINGS_data_to_string (&awrh->h_commitment,
                                       sizeof (awrh->h_commitment),
                                       pub_str,
                                       sizeof (pub_str));
  *end = '\0';
  GNUNET_snprintf (arg_str,
                   sizeof (arg_str),
                   "age-withraw/%s/reveal",
                   pub_str);

  awrh->request_url = TALER_url_join (exchange_url,
                                      arg_str,
                                      NULL);
  if (NULL == awrh->request_url)
  {
    GNUNET_break (0);
    TALER_EXCHANGE_age_withdraw_reveal_cancel (awrh);
    return GNUNET_SYSERR;
  }

  return GNUNET_OK;
}


/**
 * Call /age-withdraw/$ACH/reveal
 *
 * @param curl_ctx The context for CURL
 * @param awrh The handler
 * @param reveal_inputs The secrets of the coin candidates
 */
static
void
perform_protocol (
  struct GNUNET_CURL_Context *curl_ctx,
  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh)
{
  CURL *curlh = NULL;
  json_t *j_request_body = NULL;
  json_t *j_array_of_secrets = NULL;
  json_t *j_secrets = NULL;
  json_t *j_sec = NULL;

#define FAIL_IF(cond) \
  do { \
    if ((cond)) \
    { \
      GNUNET_break (! (cond)); \
      goto ERROR; \
    } \
  } while(0)

  for (size_t n = 0; n < awrh->num_coins; n++)
  {
    const struct TALER_PlanchetMasterSecretP *secrets =
      awrh->coins_input[n].secrets;

    j_secrets = json_array ();
    FAIL_IF (NULL == j_secrets);

    for (uint8_t k = 0; k < TALER_CNC_KAPPA; k++)
    {
      const struct TALER_PlanchetMasterSecretP *secret = &secrets[k];
      if (awrh->noreveal_index == k)
        continue;

      j_sec = GNUNET_JSON_PACK (
        GNUNET_JSON_pack_data_auto (NULL, secret));

      FAIL_IF (NULL == j_sec);
      FAIL_IF (0 < json_array_append_new (j_secrets,
                                          j_sec));
    }

    FAIL_IF (0 < json_array_append_new (j_array_of_secrets,
                                        j_secrets));
  }
  j_request_body = GNUNET_JSON_PACK (
    GNUNET_JSON_pack_array_steal ("disclosed_coin_secrets",
                                  j_array_of_secrets));
  FAIL_IF (NULL == j_request_body);

  curlh = TALER_EXCHANGE_curl_easy_get_ (awrh->request_url);
  FAIL_IF (NULL == curlh);
  FAIL_IF (GNUNET_OK !=
           TALER_curl_easy_post (&awrh->post_ctx,
                                 curlh,
                                 j_request_body));
  json_decref (j_request_body);
  j_request_body = NULL;

  awrh->job = GNUNET_CURL_job_add2 (curl_ctx,
                                    curlh,
                                    awrh->post_ctx.headers,
                                    &handle_age_withdraw_reveal_finished,
                                    awrh);
  FAIL_IF (NULL == awrh->job);

  /* No error, return */
  return;

ERROR:
  if (NULL != j_sec)
    json_decref (j_sec);
  if (NULL != j_secrets)
    json_decref (j_secrets);
  if (NULL != j_array_of_secrets)
    json_decref (j_array_of_secrets);
  if (NULL != j_request_body)
    json_decref (j_request_body);
  if (NULL != curlh)
    curl_easy_cleanup (curlh);
  TALER_EXCHANGE_age_withdraw_reveal_cancel (awrh);
  return;
#undef FAIL_IF
}


struct TALER_EXCHANGE_AgeWithdrawRevealHandle *
TALER_EXCHANGE_age_withdraw_reveal (
  struct GNUNET_CURL_Context *curl_ctx,
  const char *exchange_url,
  size_t num_coins,
  const struct TALER_EXCHANGE_AgeWithdrawCoinInput coins_input[static
                                                               num_coins],
  const struct TALER_ExchangeWithdrawValues alg_values[static num_coins],
  uint8_t noreveal_index,
  const struct TALER_AgeWithdrawCommitmentHashP *h_commitment,
  uint8_t max_age,
  TALER_EXCHANGE_AgeWithdrawRevealCallback reveal_cb,
  void *reveal_cb_cls)
{
  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh =
    GNUNET_new (struct TALER_EXCHANGE_AgeWithdrawRevealHandle);
  awrh->noreveal_index = noreveal_index;
  awrh->callback = reveal_cb;
  awrh->callback_cls = reveal_cb_cls;
  awrh->h_commitment = *h_commitment;
  awrh->num_coins = num_coins;
  awrh->coins_input = coins_input;
  awrh->alg_values = alg_values;
  awrh->max_age = max_age;


  if (GNUNET_OK !=
      prepare_url (exchange_url,
                   awrh))
    return NULL;

  perform_protocol (curl_ctx, awrh);

  return awrh;
}


void
TALER_EXCHANGE_age_withdraw_reveal_cancel (
  struct TALER_EXCHANGE_AgeWithdrawRevealHandle *awrh)
{
  if (NULL != awrh->job)
  {
    GNUNET_CURL_job_cancel (awrh->job);
    awrh->job = NULL;
  }
  TALER_curl_easy_post_finished (&awrh->post_ctx);
  /* FIXME[oec]: anything else left to cleanup!? */
  GNUNET_free (awrh);
}


/* exchange_api_age_withdraw_reveal.c */