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..
  This file is part of GNU TALER.
  Copyright (C) 2014, 2015, 2016 GNUnet e.V. and INRIA

  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 2.1, 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 Lesser General Public License for more details.

  You should have received a copy of the GNU Lesser General Public License along with
  TALER; see the file COPYING.  If not, see <http://www.gnu.org/licenses/>

  @author Christian Grothoff

=============================
The Exchange RESTful JSON API
=============================

The API specified here follows the :ref:`general conventions <http-common>`
for all details not specified in the individual requests. The :ref:`glossary`
defines all specific terms used in this section.

.. _keys:

-----------------------
Obtaining Exchange Keys
-----------------------

This API is used by wallets and merchants to obtain global information about
the exchange, such as online signing keys, available denominations and the fee
structure.  This is typically the first call any exchange client makes, as it
returns information required to process all of the other interactions with the
exchange.  The returned information is secured by (1) signature(s) from the exchange,
especially the long-term offline signing key of the exchange, which clients should
cache; (2) signature(s) from auditors, and the auditor keys should be
hard-coded into the wallet as they are the trust anchors for Taler; (3)
possibly by using HTTPS.


.. http:get:: /keys

  Get a list of all denomination keys offered by the bank,
  as well as the bank's current online signing key.

  **Response:**

  :status 200 OK:
    The exchange responds with a `ExchangeKeysResponse`_ object. This request should
    virtually always be successful.

  **Details:**

  .. _ExchangeKeysResponse:
  .. code-block:: tsref

    interface ExchangeKeysResponse {
      // EdDSA master public key of the exchange, used to sign entries in `denoms` and `signkeys`
      master_public_key: EddsaPublicKey;

      // Denomination offered by this exchange.
      denoms: Denom[];

      // The date when the denomination keys were last updated.
      list_issue_date: Timestamp;

      // Auditors of the exchange.
      auditors: Auditor[];

      // The exchange's signing keys.
      signkeys: SignKey[];

      // compact EdDSA `signature`_ (binary-only) over the SHA-512 hash of the
      // concatenation of all SHA-512 hashes of the RSA denomination public keys
      // in `denoms` in the same order as they were in `denoms`.  Note that for
      // hashing, the binary format of the RSA public keys is used, and not their
      // `base32 encoding <base32>`_.  Wallets cannot do much with this signature by itself;
      // it is only useful when multiple clients need to establish that the exchange
      // is sabotaging end-user anonymity by giving disjoint denomination keys to
      // different users.  If a exchange were to do this, this signature allows the
      // clients to demonstrate to the public that the exchange is dishonest.
      eddsa_sig: EddsaSignature;

      // Public EdDSA key of the exchange that was used to generate the signature.
      // Should match one of the exchange's signing keys from /keys.  It is given
      // explicitly as the client might otherwise be confused by clock skew as to
      // which signing key was used.
      eddsa_pub: EddsaPublicKey;
    }

  .. _tsref-type-Denom:
  .. code-block:: tsref

    interface Denom {
      // How much are coins of this denomination worth?
      value: Amount;

      // When does the denomination key become valid?
      stamp_start: Timestamp;

      // When is it no longer possible to deposit coins
      // of this denomination?
      stamp_expire_withdraw: Timestamp;

      // Timestamp indicating by when legal disputes relating to these coins must
      // be settled, as the exchange will afterwards destroy its evidence relating to
      // transactions involving this coin.
      stamp_expire_legal: Timestamp;

      // Public (RSA) key for the denomination.
      denom_pub: RsaPublicKey;

      // Fee charged by the exchange for withdrawing a coin of this denomination
      fee_withdraw: Amount;

      // Fee charged by the exchange for depositing a coin of this denomination
      fee_deposit: Amount;

      // Fee charged by the exchange for refreshing a coin of this denomination
      fee_refresh: Amount;

      // Fee charged by the exchange for refunding a coin of this denomination
      fee_refund: Amount;

      // Signature of `TALER_DenominationKeyValidityPS`_
      master_sig: EddsaSignature;
    }

  Fees for any of the operations can be zero, but the fields must still be
  present. The currency of the `fee_deposit`, `fee_refresh` and `fee_refund` must match the
  currency of the `value`.  Theoretically, the `fee_withdraw` could be in a
  different currency, but this is not currently supported by the
  implementation.

  A signing key in the `signkeys` list is a JSON object with the following fields:

  .. _tsref-type-SignKey:
  .. code-block:: tsref

    interface SignKey {
      // The actual exchange's EdDSA signing public key.
      key: EddsaPublicKey;

      // Initial validity date for the signing key.
      stamp_start: Timestamp;

      // Date when the exchange will stop using the signing key, allowed to overlap
      // slightly with the next signing key's validity to allow for clock skew.
      stamp_expire: Timestamp;

      // Date when all signatures made by the signing key expire and should
      // henceforth no longer be considered valid in legal disputes.
      stamp_end: Timestamp;

      // Signature over `key` and `stamp_expire` by the exchange master key.
      // Must have purpose TALER_SIGNATURE_MASTER_SIGNING_KEY_VALIDITY.
      master_sig: EddsaSignature;
    }

  An entry in the `auditors` list is a JSON object with the following fields:

  .. _tsref-type-Auditor:
  .. code-block:: tsref

    interface Auditor {
      // The auditor's EdDSA signing public key.
      auditor_pub: EddsaPublicKey;

      // The auditor's URL.
      auditor_url: string;

      // An array of denomination keys the auditor affirms with its signature.
      // Note that the message only includes the hash of the public key, while the
      // signature is actually over the expanded information including expiration
      // times and fees.  The exact format is described below.
      denomination_keys: DenominationKey[];
    }

  .. _tsref-type-DenominationKey:
  .. code-block:: tsref

    interface DenominationKey {
      // hash of the public RSA key used to sign coins of the respective
      // denomination.  Note that the auditor's signature covers more than just
      // the hash, but this other information is already provided in `denoms` and
      // thus not repeated here.
      denom_pub_h: HashCode;

      // Signature of `TALER_ExchangeKeyValidityPS`_
      auditor_sig: EddsaSignature;
    }

  The same auditor may appear multiple times in the array for different subsets
  of denomination keys, and the same denomination key hash may be listed
  multiple times for the same or different auditors.  The wallet or merchant
  just should check that the denomination keys they use are in the set for at
  least one of the auditors that they accept.

  .. note::

    Both the individual denominations *and* the denomination list is signed,
    allowing customers to prove that they received an inconsistent list.

.. _wire-req:

-----------------------------------
Obtaining wire-transfer information
-----------------------------------

.. http:get:: /wire

  Returns a list of payment methods supported by the exchange.  The idea is that wallets may use this information to instruct users on how to perform wire transfers to top up their wallets.

  **Response:**

  :status 200: The exchange responds with a `WireResponse`_ object. This request should virtually always be successful.

  **Details:**

  .. _WireResponse:
  .. _tsref-type-WireResponse:
  .. code-block:: tsref

    interface WireResponse {
      // The key is a supported method (i.e. "sepa" or "test").
      // The value is a method-specific JSON object with account details
      // (i.e. IBAN number, owner name, bank address, etc.).
      // The value objects may also contain signatures (if applicable).
      //
      // A single /wire response can contain an arbitrary number of these
      // string-object pairs.  However, the keys must be unique.
      string: Object;
     }

  Possible encodings for the objects are right now the following:

  .. _WireTestResponse:
  .. _tsref-type-WireTestResponse:
  .. code-block:: tsref

    interface WireTestResponse {
      // Mandatory indicator that this is a TEST wire response.
      type: "test";

      // Account number at the bank
      account_number: number;

      // URI of the bank
      bank_uri: string;

      // Name of the account's owner
      name: string;

      // Salt used to sign, `base32`_ encoded
      salt: string;

      // Signaure of `TALER_MasterWireDetailsPS`_ with purpose TALER_SIGNATURE_MASTER_TEST_DETAILS
      // Note that the `h_sepa_details` field of `TALER_MasterWireDetailsPS`_ is computed
      // by concatenating all of the above fields (in the same order they appear) and then
      // by hashing the obtained concatenation.
      sig: EddsaSignature;
    }

  .. _WireSepaResponse:
  .. _tsref-type-WireSepaResponse:
  .. code-block:: tsref

    interface WireSepaResponse {
      // Mandatory indicator that this is a SEPA wire response.
      type: "sepa";

      // Legal name of the owner of the account
      receiver_name: string;

      // IBAN account number.
      iban: string;

      // BIC of the bank.
      bic: string;

      // Signaure of `TALER_MasterWireDetailsPS`_ with purpose TALER_SIGNATURE_MASTER_SEPA_DETAILS
      // Note that the `h_sepa_details` field of `TALER_MasterWireDetailsPS`_ is computed
      // by concatenating all of the above fields (in the same order they appear) and then
      // by hashing the obtained concatenation.
      sig: EddsaSignature;
    }

----------
Withdrawal
----------

This API is used by the wallet to obtain digital coins.

When transfering money to the exchange such as via SEPA transfers, the exchange creates
a *reserve*, which keeps the money from the customer.  The customer must
specify an EdDSA reserve public key as part of the transfer, and can then
withdraw digital coins using the corresponding private key.  All incoming and
outgoing transactions are recorded under the corresponding public key by the
exchange.

  .. note::

     Eventually the exchange will need to advertise a policy for how long it will keep transaction histories for inactive or even fully drained reserves.  We will therefore need some additional handler similar to `/keys` to advertise those terms of service.


.. http:get:: /reserve/status

  Request information about a reserve.

  .. note::
    The client currently does not have to demonstrate knowledge of the private
    key of the reserve to make this request, which makes the reserve's public
    key privileged information known only to the client, their bank, and the
    exchange.  In future, we might wish to revisit this decision to improve
    security, such as by having the client EdDSA-sign an ECDHE key to be used
    to derive a symmetric key to encrypt the response.  This would be useful if
    for example HTTPS were not used for communication with the exchange.

  **Request:**

  :query reserve_pub: EdDSA reserve public key identifying the reserve.

  **Response:**

  :status 200 OK:
    The exchange responds with a `ReserveStatus`_ object;  the reserve was known to the exchange,
  :status 404 Not Found: The reserve key does not belong to a reserve known to the exchange.

  **Details:**

  .. _ReserveStatus:
  .. code-block:: tsref

    interface ReserveStatus {
      // Balance left in the reserve.
      balance: Amount;

      // Transaction history for this reserve
      history: TransactionHistoryItem[];
    }

  Objects in the transaction history have the following format:

  .. _tsref-type-TransactionHistoryItem:
  .. code-block:: tsref

    interface TransactionHistoryItem {
      // Either "WITHDRAW" or "DEPOSIT"
      type: string;

      // The amount that was withdrawn or deposited.
      amount: Amount;

      // Sender account details, only present if type is "DEPOSIT".
      sender_account_details?: any;

      // Transfer details uniquely identifying the transfer, only present if type is "DEPOSIT".
      transfer_details?: any;

      // `base32`_ encoding of `TALER_WithdrawRequestPS`_ with purpose TALER_SIGNATURE_WALLET_RESERVE_WITHDRAW. This field appears only if `type` is "WITHDRAW".
      details?: string;

      // Signature of `TALER_WithdrawRequestPS`_ created with the `reserves's private key <reserve-priv>`_.  Only present if type is "WITHDRAW".
      signature?: EddsaSignature;
    }


.. http:post:: /reserve/withdraw

  Withdraw a coin of the specified denomination.  Note that the client should
  commit all of the request details, including the private key of the coin and
  the blinding factor, to disk *before* issuing this request, so that it can
  recover the information if necessary in case of transient failures, like
  power outage, network outage, etc.

  **Request:** The request body must be a `WithdrawRequest`_ object.

  **Response:**

  :status 200 OK:
    The request was succesful, and the response is a `WithdrawResponse`.  Note that repeating exactly the same request
    will again yield the same response, so if the network goes down during the
    transaction or before the client can commit the coin signature to disk, the
    coin is not lost.
  :status 401 Unauthorized: The signature is invalid.
  :status 404 Not Found:
    The denomination key or the reserve are not known to the exchange.  If the
    denomination key is unknown, this suggests a bug in the wallet as the
    wallet should have used current denomination keys from `/keys`.  If the
    reserve is unknown, the wallet should not report a hard error yet, but
    instead simply wait for up to a day, as the wire transaction might simply
    not yet have completed and might be known to the exchange in the near future.
    In this case, the wallet should repeat the exact same request later again
    using exactly the same blinded coin.
  :status 403 Forbidden:
    The balance of the reserve is not sufficient to withdraw a coin of the indicated denomination.
    The response is `WithdrawError`_ object.


  **Details:**

  .. _WithdrawRequest:
  .. code-block:: tsref

    interface WithdrawRequest {
      // Denomination public key (RSA), specifying the type of coin the client
      // would like the exchange to create.
      denom_pub: RsaPublicKey;

      // coin's blinded public key, should be (blindly) signed by the exchange's
      // denomination private key
      coin_ev: CoinEnvelope;

      // `public (EdDSA) key <reserve-pub>`_ of the reserve from which the coin should be
      // withdrawn.  The total amount deducted will be the coin's value plus the
      // withdrawal fee as specified with the denomination information.
      reserve_pub: EddsaPublicKey;

      // Signature of `TALER_WithdrawRequestPS`_ created with the `reserves's private key <reserve-priv>`_
      reserve_sig: EddsaSignature;
    }


  .. _WithdrawResponse:
  .. code-block:: tsref

    interface WithdrawResponse {
      // The blinded RSA signature over the `coin_ev`, affirms the coin's
      // validity after unblinding.
      ev_sig: BlindedRsaSignature;
    }

  .. _WithdrawError:
  .. code-block:: tsref

    interface WithdrawError {
      // Constant "Insufficient funds"
      error: string;

      // Amount left in the reserve
      balance: Amount;

      // History of the reserve's activity, in the same format as returned by /reserve/status.
      history: TransactionHistoryItem[]
    }

.. _deposit-par:

-------
Deposit
-------

Deposit operations are requested by a merchant during a transaction. For the
deposit operation, the merchant has to obtain the deposit permission for a coin
from their customer who owns the coin.  When depositing a coin, the merchant is
credited an amount specified in the deposit permission, possibly a fraction of
the total coin's value, minus the deposit fee as specified by the coin's
denomination.


.. _deposit:

.. http:POST:: /deposit

  Deposit the given coin and ask the exchange to transfer the given :ref:`amount`
  to the merchants bank account.  This API is used by the merchant to redeem
  the digital coins.  The request should contain a JSON object with the
  following fields:

  **Request:** The request body must be a `DepositRequest`_ object.

  **Response:**

  :status 200 Ok:
    The operation succeeded, the exchange confirms that no double-spending took place.  The response will include a `DepositSuccess`_ object.
  :status 401 Unauthorized:
    One of the signatures is invalid.
  :status 403 Forbidden:
    The deposit operation has failed because the coin has insufficient
    residual value; the request should not be repeated again with this coin.
    In this case, the response is a `DepositDoubleSpendError`_.
  :status 404:
    Either the denomination key is not recognized (expired or invalid) or
    the wire type is not recognized.

  **Details:**

  .. _DepositRequest:
  .. code-block:: tsref

    interface DepositRequest {
      // Amount to be deposited, can be a fraction of the
      // coin's total value.
      f: Amount;

      // The merchant's account details. This must be a JSON object whose format
      // must correspond to one of the supported wire transfer formats of the exchange.
      // See `wireformats`_.
      wire: Object;

      // SHA-512 hash of the merchant's payment details from `wire`.  Although
      // strictly speaking redundant, this helps detect inconsistencies.
      H_wire: HashCode;

      // SHA-512 hash of the contact of the merchant with the customer.  Further
      // details are never disclosed to the exchange.
      H_contract: HashCode;

      // `coin's public key <eddsa-coin-pub>`_, both ECDHE and EdDSA.
      coin_pub: CoinPublicKey;

      // denomination RSA key with which the coin is signed
      denom_pub: RsaPublicKey;

      // exchange's unblinded RSA signature of the coin
      ub_sig: RsaSignature;

      // timestamp when the contract was finalized, must match approximately the
      // current time of the exchange
      timestamp: Timestamp;

      // indicative time by which the exchange undertakes to transfer the funds to
      // the merchant, in case of successful payment.
      pay_deadline: Timestamp;

      // 64-bit transaction id for the transaction between merchant and customer
      transaction_id: number;

      // EdDSA `public key of the merchant <merchant-pub>`_, so that the client can identify the
      // merchant for refund requests.
      merchant_pub: EddsaPublicKey;

      // date until which the merchant can issue a refund to the customer via the
      // exchange, possibly zero if refunds are not allowed.
      refund_deadline: Timestamp;

      // Signature of `TALER_DepositRequestPS`_, made by the customer with the `coin's private key <coin-priv>`_
      coin_sig: EddsaSignature;
    }

  The deposit operation succeeds if the coin is valid for making a deposit and
  has enough residual value that has not already been deposited or melted.


  .. _`tsref-type-DepositSuccess`:
  .. _DepositSuccess:
  .. code-block:: tsref

     interface DepositSuccess {
      // The string constant "DEPOSIT_OK"
      status: string;

      // the EdDSA signature of `TALER_DepositConfirmationPS`_ using a current
      // `signing key of the exchange <sign-key-priv>`_ affirming the successful
      // deposit and that the exchange will transfer the funds after the refund
      // deadline, or as soon as possible if the refund deadline is zero.
      sig: EddsaSignature;

      // `public EdDSA key of the exchange <sign-key-pub>`_ that was used to
      // generate the signature.
      // Should match one of the exchange's signing keys from /keys.  It is given
      // explicitly as the client might otherwise be confused by clock skew as to
      // which signing key was used.
      pub: EddsaPublicKey;
      }

  .. _DepositDoubleSpendError:
  .. code-block:: tsref

    interface DepositDoubleSpendError {
      // The string constant "insufficient funds"
      error: string;

      // Transaction history for the coin that is
      // being double-spended
      history: CoinSpendHistoryItem[];
    }

  .. _`tsref-type-CoinSpendHistoryItem`:
  .. _CoinSpendHistoryItem:
  .. code-block:: tsref

    interface CoinSpendHistoryItem {
      // Either "deposit" or "melt" or "refund"
      type: string;

      // The total amount of the coin's value absorbed (or restored in the case of a refund) by this transaction.
      // Note that for deposit and melt, this means the amount given includes
      // the transaction fee, while for refunds the amount given excludes
      // the transaction fee. The current coin value can thus be computed by
      // subtracting deposit and melt amounts and adding refund amounts from
      // the coin's denomination value.
      amount: Amount;

      // `base32`_ binary encoding of the transaction data as a
      // `TALER_DepositRequestPS`_ or `TALER_RefreshMeltCoinAffirmationPS`_
      // or `TALER_RefundRequestPS`_
      details: string;

      // `EdDSA Signature <eddsa-sig>`_ of what we got in `details`.
      // Note that in the case of a 'refund', the signature is made with
      // the `public key of the merchant <merchant-pub>`_, and not `that of the coin <eddsa-coin-pub>`_
      signature: EddsaSignature;
    }

----------
Refreshing
----------

Refreshing creates `n` new coins from `m` old coins, where the sum of
denominations of the new coins must be smaller than the sum of the old coins'
denominations plus melting (refresh) and withdrawal fees charged by the exchange.
The refreshing API can be used by wallets to melt partially spent coins, making
transactions with the freshly exchangeed coins unlinkabe to previous transactions
by anyone except the wallet itself.

However, the new coins are linkable from the private keys of all old coins
using the /refresh/link request.  While /refresh/link must be implemented by
the exchange to achieve taxability, wallets do not really ever need that part of
the API during normal operation.

.. _refresh:
.. http:post:: /refresh/melt

  "Melts" coins.  Invalidates the coins and prepares for exchangeing of fresh
  coins.  Taler uses a global parameter `kappa` for the cut-and-choose
  component of the protocol, for which this request is the commitment.  Thus,
  various arguments are given `kappa`-times in this step.  At present `kappa`
  is always 3.


  :status 401 Unauthorized:
    One of the signatures is invalid.
  :status 200 OK:
    The request was succesful.  The response body is `MeltResponse`_ in this case.
  :status 403 Forbidden:
    The operation is not allowed as at least one of the coins has insufficient funds.  The response
    is `MeltForbiddenResponse`_ in this case.
  :status 404:
    the exchange does not recognize the denomination key as belonging to the exchange,
    or it has expired

  **Details:**


  .. code-block:: tsref

    interface MeltRequest {
      // Array of `n` new denominations to order.
      new_denoms: RsaPublicKey[];

      // Information about coin being melted.
      melt_coin: MeltCoin;

      // The outer dimension of the 2d array has `kappa` entries
      // for the cut-and-choose protocol.
      // The inner array contains `n` entries with blinded coins,
      // matching the respective entries in `new_denoms`.
      coin_evs: CoinEnvelope[][];

      // `kappa` transfer public keys (ephemeral ECDHE keys)
      transfer_pubs: EddsaPublicKey[];

    }

  For details about the HKDF used to derive the new coin private keys and
  the blinding factors from ECDHE between the transfer public keys and
  the private key of the melted coin, please refer to the
  implementation in `libtalerutil`. The `melt_coin` field is a list of JSON
  objects with the following fields:


  .. _tsref-type-MeltCoin:
  .. code-block:: tsref

    interface MeltCoin {
      // `Coin public key <eddsa-coin-pub>`_, uniquely identifies the coin
      coin_pub: string;

      // The denomination public key allows the exchange to determine total coin value.
      denom_pub: RsaPublicKey;

      // Signature over the `coin public key <eddsa-coin-pub>`_ by the denomination.
      denom_sig: RsaSignature;

      // Signature by the `coin <coin-priv>`_ over the session public key.
      confirm_sig: EddsaSignature;

      // Amount of the value of the coin that should be melted as part of
      // this refresh operation, including melting fee.
      value_with_fee: Amount;
    }

  Errors such as failing to do proper arithmetic when it comes to calculating
  the total of the coin values and fees are simply reported as bad requests.
  This includes issues such as melting the same coin twice in the same session,
  which is simply not allowed.  However, theoretically it is possible to melt a
  coin twice, as long as the `value_with_fee` of the two melting operations is
  not larger than the total remaining value of the coin before the melting
  operations. Nevertheless, this is not really useful.


  .. _tsref-type-MeltResponse:
  .. _MeltResponse:
  .. code-block:: tsref

    interface MeltResponse {
      // Which of the `kappa` indices does the client not have to reveal.
      noreveal_index: number;

      // Signature of `TALER_RefreshMeltConfirmationPS`_ whereby the exchange
      // affirms the successful melt and confirming the `noreveal_index`
      exchange_sig: EddsaSignature;

      // `public EdDSA key <sign-key-pub>`_ of the exchange that was used to generate the signature.
      // Should match one of the exchange's signing keys from /keys.  Again given
      // explicitly as the client might otherwise be confused by clock skew as to
      // which signing key was used.
      exchange_pub: EddsaPublicKey;
    }


  .. _tsref-type-MeltForbiddenResponse:
  .. _MeltForbiddenResponse:
  .. code-block:: tsref

    interface MeltForbiddenResponse {
      // Always "insufficient funds"
      error: string;

      // public key of a melted coin that had insufficient funds
      coin_pub: EddsaPublicKey;

      // original total value of the coin
      original_value: Amount;

      // remaining value of the coin
      residual_value: Amount;

      // amount of the coin's value that was to be melted
      requested_value: Amount;

      // The transaction list of the respective coin that failed to have sufficient funds left.
      // Note that only the transaction history for one bogus coin is given,
      // even if multiple coins would have failed the check.
      history: CoinSpendHistoryItem[];
    }


.. http:post:: /refresh/reveal

  Reveal previously commited values to the exchange, except for the values
  corresponding to the `noreveal_index` returned by the /exchange/melt step.
  Request body contains a JSON object with the following fields:


  :status 200 OK:
    The transfer private keys matched the commitment and the original request was well-formed.
    The response body is a `RevealResponse`_
  :status 409 Conflict:
    There is a problem between the original commitment and the revealed private
    keys.  The returned information is proof of the missmatch, and therefore
    rather verbose, as it includes most of the original /refresh/melt request,
    but of course expected to be primarily used for diagnostics.
    The response body is a `RevealConflictResponse`_.



  .. code-block:: tsref

    interface RevealRequest {
      // Hash over most of the arguments to the /exchange/melt step.  Used to
      // identify the corresponding melt operation.  For details on which elements
      // must be hashed in which order, please consult the source code of the exchange
      // reference implementation.
      session_hash: HashCode;

      // Array of `kappa - 1` ECDHE transfer private keys.
      // The exchange will use those to decrypt the transfer secrets,
      // and then decrypt the private keys and blinding factors
      // of the coins to be generated and check all this against the commitments.
      transfer_privs: EddsaPrivateKey[];
    }


  .. _RevealResponse:
  .. code-block:: tsref

    interface RevealResponse {
      // List of the exchange's blinded RSA signatures on the new coins.  Each
      // element in the array is another JSON object which contains the signature
      // in the "ev_sig" field.
      ev_sigs: BlindedRsaSignature[];
    }


  .. _RevealConflictResponse:
  .. code-block:: tsref

    interface RevealConflictResponse {
      // Constant "commitment violation"
      error: string;

      // Signature of the coin over the melting operation.
      coin_sig: EddsaSignature;

      // Coin that we failed to successfully melt.
      coin_pub: EddsaPublicKey;

      // Amount of the value of the coin to be melted in the refresh session.
      melt_amount_with_fee: Amount;

      // Fee that was due for the melting for the coin.
      melt_fee: Amount;

      // Denomination keys to be used for the coins to be withdrawn.
      newcoin_infos: RsaPublicKey[];

      // Array of blinded coins to be withdrawn.  Same length as
      // `newcoin_infos`.
      commit_infos: CoinEnvelope[];

      // Transfer public key at index `gamma`.
      gamma_tp: EddsaPublicKey;

      // Specific `gamma` value chosen by the exchange.
      gamma: number;

    }


  .. _tsref-type-LinkInfo:
  .. code-block:: tsref

    interface LinkInfo {
      // the transfer ECDHE public key
      transfer_pub: EddsaPublicKey;

    }

  .. _tsref-type-CommitInfo:
  .. code-block:: tsref

    interface CommitInfo {
      coin_ev: BlindedRsaSignature;

    }


.. http:get:: /refresh/link

  Link the old public key of a melted coin to the coin(s) that were exchangeed during the refresh operation.

  **Request:**

  :query coin_pub: melted coin's public key

  **Response:**

  :status 200 OK:
    All commitments were revealed successfully.  The exchange returns an array,
    typically consisting of only one element, in which each each element contains
    information about a melting session that the coin was used in.
  :status 404 Not Found:
    The exchange has no linkage data for the given public key, as the coin has not
    yet been involved in a refresh operation.

  **Details:**

  .. _tsref-type-LinkResponse:
  .. code-block:: tsref

    interface LinkResponse {
      // transfer ECDHE public key corresponding to the `coin_pub`, used to
      // decrypt the `secret_enc` in combination with the private key of
      // `coin_pub`.
      transfer_pub: EcdhePublicKey;

      // ECDHE-encrypted link secret that, once decrypted, can be used to
      // decrypt/unblind the `new_coins`.
      secret_enc: Base32;

      // array with (encrypted/blinded) information for each of the coins
      // exchangeed in the refresh operation.
      new_coins: NewCoinInfo[];
    }

  .. _tsref-type-NewCoinInfo:
  .. code-block:: tsref

    interface NewCoinInfo {
      // RSA public key of the exchangeed coin.
      denom_pub: RsaPublicKey;

      // Exchange's blinded signature over the exchangeed coin.
      ev_sig: BlindedRsaSignature;
    }




-----------------------
Tracking wire transfers
-----------------------

This API is used by merchants that need to find out which wire
transfers (from the exchange to the merchant) correspond to which deposit
operations.  Typically, a merchant will receive a wire transfer with a
**wire transfer identifier** and want to know the set of deposit
operations that correspond to this wire transfer.  This is the
preferred query that merchants should make for each wire transfer they
receive.  If a merchant needs to investigate a specific deposit
operation (i.e. because it seems that it was not paid), then the
merchant can also request the wire transfer identifier for a deposit
operation.

Sufficient information is returned to verify that the coin signatures
are correct. This also allows governments to use this API when doing
a tax audit on merchants.

Naturally, the returned information may be sensitive for the merchant.
We do not require the merchant to sign the request, as the same requests
may also be performed by the government auditing a merchant.
However, wire transfer identifiers should have sufficient entropy to
ensure that obtaining a successful reply by brute-force is not practical.
Nevertheless, the merchant should protect the wire transfer identifiers
from his bank statements against unauthorized access, least his income
situation is revealed to an adversary. (This is not a major issue, as
an adversary that has access to the line-items of bank statements can
typically also view the balance.)


.. http:get:: /track/transfer

  Provides deposits associated with a given wire transfer.

  **Request:**

  :query wtid: raw wire transfer identifier identifying the wire transfer (a base32-encoded value)

  **Response:**

  :status 200 OK:
    The wire transfer is known to the exchange, details about it follow in the body.
    The body of the response is a `TrackTransferResponse`_.
  :status 404 Not Found:
    The wire transfer identifier is unknown to the exchange.

  .. _TrackTransferResponse:
  .. _tsref-type-TrackTransferResponse:
  .. code-block:: tsref

    interface TrackTransferResponse {
      // Total amount transferred
      total: Amount;

      // public key of the merchant (identical for all deposits)
      merchant_pub: EddsaPublicKey;

      // hash of the wire details (identical for all deposits)
      H_wire: HashCode;

      // Time of the execution of the wire transfer by the exchange
      execution_time: Timestamp;

      // details about the deposits
      deposits: TrackTransferDetail[];

      // signature from the exchange made with purpose
      // `TALER_SIGNATURE_EXCHANGE_CONFIRM_WIRE_DEPOSIT`
      exchange_sig: EddsaSignature;

      // public EdDSA key of the exchange that was used to generate the signature.
      // Should match one of the exchange's signing keys from /keys.  Again given
      // explicitly as the client might otherwise be confused by clock skew as to
      // which signing key was used.
      exchange_pub: EddsaSignature;
    }

  .. _tsref-type-TrackTransferDetail:
  .. code-block:: tsref

    interface TrackTransferDetail {
      // SHA-512 hash of the contact of the merchant with the customer.
      H_contract: HashCode;

      // 64-bit transaction id for the transaction between merchant and
      // customer
      transaction_id: number;

      // coin's public key, both ECDHE and EdDSA.
      coin_pub: CoinPublicKey;

      // The total amount the original deposit was worth.
      deposit_value: Amount;

      // applicable fees for the deposit
      deposit_fee: Amount;

    }

.. http:post:: /track/transaction

  Provide the wire transfer identifier associated with an (existing) deposit operation.

  **Request:** The request body must be a `TrackTransactionRequest`_ JSON object.

  **Response:**

  :status 200 OK:
    The deposit has been executed by the exchange and we have a wire transfer identifier.
    The response body is a `TrackTransactionResponse`_ object.
  :status 202 Accepted:
    The deposit request has been accepted for processing, but was not yet
    executed.  Hence the exchange does not yet have a wire transfer identifier.  The
    merchant should come back later and ask again.
    The response body is a `TrackTransactionAcceptedResponse`_.
  :status 401 Unauthorized: The signature is invalid.
  :status 404 Not Found: The deposit operation is unknown to the exchange

  **Details:**

  .. _tsref-type-TrackTransactionRequest:
  .. _TrackTransactionRequest:
  .. code-block:: tsref

    interface TrackTransactionRequest {
      // SHA-512 hash of the merchant's payment details.
      H_wire: HashCode;

      // SHA-512 hash of the contact of the merchant with the customer.
      H_contract: HashCode;

      // coin's public key, both ECDHE and EdDSA.
      coin_pub: CoinPublicKey;

      // 64-bit transaction id for the transaction between merchant and customer
      transaction_id: number;

      // the EdDSA public key of the merchant, so that the client can identify
      // the merchant for refund requests.
      merchant_pub: EddsaPublicKey;

      // the EdDSA signature of the merchant made with purpose
      // `TALER_SIGNATURE_MERCHANT_TRACK_TRANSACTION` , affirming that it is really the
      // merchant who requires obtaining the wire transfer identifier.
      merchant_sig: EddsaSignature;
    }


  .. _tsref-type-TrackTransactionResponse:
  .. _TrackTransactionResponse:
  .. code-block:: tsref

    interface TrackTransactionResponse {
      // raw wire transfer identifier of the deposit.
      wtid: Base32;

      // when was the wire transfer given to the bank.
      execution_time: Timestamp;

      // The contribution of this coin to the total (without fees)
      coin_contribution: Amount;

      // Total amount transferred
      total_amount: Amount;

      // binary-only Signature_ for purpose `TALER_SIGNATURE_EXCHANGE_CONFIRM_WIRE`
      // whereby the exchange affirms the successful wire transfer.
      exchange_sig: EddsaSignature;

      // public EdDSA key of the exchange that was used to generate the signature.
      // Should match one of the exchange's signing keys from /keys.  Again given
      // explicitly as the client might otherwise be confused by clock skew as to
      // which signing key was used.
      exchange_pub: EddsaPublicKey;
    }

  .. _tsref-type-TrackTransactionAcceptedResponse:
  .. _TrackTransactionAcceptedResponse:
  .. code-block:: tsref

    interface TrackTransactionAcceptedResponse {
      // time by which the exchange currently thinks the deposit will be executed.
      execution_time: Timestamp;
    }


-------
Refunds
-------

  .. note::

     Refunds are currently not implemented (#3641), this documentation is thus a bit preliminary and may still change.

.. _refund:
.. http:POST:: /refund

  Undo deposit of the given coin, restoring its value.

  **Request:** The request body must be a `RefundRequest`_ object.

  **Response:**

  :status 200 Ok:
    The operation succeeded, the exchange confirms that the coin can now be refreshed.  The response will include a `RefundSuccess`_ object.
  :status 401 Unauthorized:
    Merchant signature is invalid.
  :status 404 Not found:
    The refund operation failed as we could not find a matching deposit operation (coin, contract, transaction ID and merchant public key must all match).
  :status 410 Gone:
    It is too late for a refund by the exchange, the money was already sent to the merchant.

  **Details:**

  .. _RefundRequest:
  .. code-block:: tsref

     interface RefundRequest {

      // Amount to be refunded, can be a fraction of the
      // coin's total deposit value (including deposit fee);
      // must be larger than the refund fee.
      refund_amount: Amount;

      // Refund fee associated with the given coin.
      // must be smaller than the refund amount.
      refund_fee: Amount;

      // SHA-512 hash of the contact of the merchant with the customer.
      H_contract: HashCode;

      // coin's public key, both ECDHE and EdDSA.
      coin_pub: CoinPublicKey;

      // 64-bit transaction id of the original transaction between merchant and customer
      transaction_id: number;

      // 64-bit transaction id of the refund transaction between merchant and customer
      rtransaction_id: number;

      // EdDSA public key of the merchant.
      merchant_pub: EddsaPublicKey;

      // EdDSA signature of the merchant affirming the refund.
      merchant_sig: EddsaPublicKey;

    }

  .. _RefundSuccess:
  .. code-block:: tsref

    interface RefundSuccess {
      // The string constant "REFUND_OK"
      status: string;

      // the EdDSA :ref:`signature` (binary-only) with purpose
      // `TALER_SIGNATURE_EXCHANGE_CONFIRM_REFUND` using a current signing key of the
      // exchange affirming the successful refund
      sig: EddsaSignature;

      // public EdDSA key of the exchange that was used to generate the signature.
      // Should match one of the exchange's signing keys from /keys.  It is given
      // explicitly as the client might otherwise be confused by clock skew as to
      // which signing key was used.
      pub: EddsaPublicKey;
   }

------------------------------
Administrative API: Key update
------------------------------

  .. note::

     This is not yet implemented (no bug number yet, as we are not sure we will
     implement this; for now, adding new files to the directory and sending a
     signal to the exchange process seems to work fine).

New denomination and signing keys can be uploaded to the exchange via the
HTTP interface.  It is, of course, only possible to upload keys signed
by the exchange's master key.  Furthermore, this API should probably only
be used via loopback, as we want to protect the private keys from
interception.

.. http:POST:: /admin/add/denomination_key

  Upload a new denomination key.

  **Request:**

  .. code-block:: tsref

    {
      // Public part of the denomination key
      denom_info: any:

      // Private RSA key
      denom_priv: RsaPrivateKey;
    }


.. http:POST:: /admin/add/sign_key

  Upload a new signing key.

  **Request:**

  .. code-block:: tsref

    {
      // Public part of the signing key
      sign_info: any;

      // Private EdDSA key
      sign_priv: EddsaPrivateKey;
    }

.. _add-incoming:

-------------------------------------
Administrative API: Bank transactions
-------------------------------------

.. http:POST:: /admin/add/incoming

  Notify exchange of an incoming transaction to fill a reserve.

  **Request:**

  .. code-block:: tsref

    {
      // Reserve public key
      reserve_pub: EddsaPublicKey;

      // Amount transferred to the reserve
      amount: Amount;

      // When was the transaction executed
      execution_date: Timestamp;

      // Sender's wire account details, so that the exchange knows from whom the
      // money comes from (and can possibly refund it).  The details
      // given here must be in a wire format supported by the exchange.
      sender_account_details: any;

      // The wire details given here should include an unique identifier
      // for each transaction. The exchange will check that the details
      // given are unique, and if the wire details are identical to previous
      // wire details will treat the request as a duplicate and not actually
      // do any update. This is true even if the amount or execution date
      // differs.
      //
      // Note that the exchange does not interpret these details in any
      // way, other than for "being unique". They are stored for diagnostics
      // and auditing.
      transfer_details: any;
    }

  **Response:**

  :status 200:
    The operation succeeded. The body is an `AddIncomingResponse`_ object.
  :status 403:
    the client is not permitted to add incoming transactions. The request may
    be disallowed by the configuration in general or restricted to certain IP
    addresses (i.e. loopback-only).


  .. _AddIncomingResponse:
  .. code-block:: tsref

    interface AddIncomingResponse {
      // The string constant `NEW` or `DUP` to indicate whether the transaction
      // was truly added to the DB or whether it already existed in the DB
      status: string;
    }

.. http:POST:: /admin/add/outgoing

  Notify exchange about the completion of an outgoing transaction satisfying a
  /deposit request.  In the future, this will allow merchants to obtain details
  about the /deposit requests they send to the exchange.

  .. note::

     This is not yet implemented (no bug number yet either).

  **Request:**

  .. code-block:: tsref

    {
      coin_pub: CoinPublicKey;

      // Amount transferred to the merchant
      amount: Amount;

      // Transaction identifier in the wire details
      transaction: number;

      // `Wire transaction details <wireformats>`_, as originally specified by the merchant
      wire: Object;
    }

  **Response**

  :status 200: The request was successful.
  :status 403: the client is not permitted to add outgoing transactions

  If the request was successful, the response has the following format:

  .. code-block:: tsref

    {
      // The string constant `NEW` or `DUP` to indicate whether the transaction
      // was truly added to the DB or whether it already existed in the DB
      status: string;
    }

------------
The Test API
------------

The test API is not there to test the exchange, but to allow
clients of the exchange (merchant and wallet implementations)
to test if their implemenation of the cryptography is
binary-compatible with the implementation of the exchange.

.. http:POST:: /test/base32

  Test hashing and Crockford :ref:`base32` encoding.

  **Request:**

  .. code-block:: tsref

    {
      // some base32-encoded value
      input: Base32;
    }

  **Response:**

  .. code-block:: tsref

    {
      // the base32_-encoded hash of the input value
      output: Base32;
    }

.. http:POST:: /test/encrypt

  Test symmetric encryption.

  **Request:**

  .. code-block:: tsref

    {
      // Some `base32`_-encoded value
      input: Base32;

      // some `base32`_-encoded hash that is used to derive the symmetric key and
      // initialization vector for the encryption using the HKDF with "skey" and
      // "iv" as the salt.
      key_hash: Base32;
    }

  **Response:**


  .. code-block:: tsref

    {
      // the encrypted value
      output: Base32;
    }

.. http:POST:: /test/hkdf

  Test Hash Key Deriviation Function.

  **Request:**


  .. code-block:: tsref

    {
      // Some `base32`_-encoded value
      input: Base32;
    }

  **Response:**


  .. code-block:: tsref

    {
      // the HKDF of the input using "salty" as salt
      output: Base32;
    }

.. http:POST:: /test/ecdhe

  Test ECDHE.

  **Request:**

  .. code-block:: tsref

    {
      ecdhe_pub: EcdhePublicKey;
      ecdhe_priv: EcdhePrivateKey;
    }

  **Response:**

  .. code-block:: tsref

    {
      // ECDH result from the two keys
      ecdhe_hash: HashCode;
    }


.. http:POST:: /test/eddsa

  Test EdDSA.

  **Request:**

  .. code-block:: tsref

    {
      eddsa_pub: EddsaPublicKey;

      // EdDSA signature using purpose TALER_SIGNATURE_CLIENT_TEST_EDDSA. Note:
      // the signed payload must be empty, we sign just the purpose here.
      eddsa_sig: EddsaSignature;
    }

  **Response:**

  :status 200: the signature was valid
  :status 401 Unauthorized: the signature was invalid

  The exchange responds with another valid signature, which gives the
  client the opportunity to test its signature verification implementation.

  .. code-block:: tsref

    {
      // Another EdDSA public key
      eddsa_pub: EddsaPublicKey;

      // EdDSA signature using purpose TALER_SIGNATURE_EXCHANGE_TEST_EDDSA
      eddsa_sig: EddsaSignature;
    }


.. http:GET:: /test/rsa/get

  Obtain the RSA public key used for signing in /test/rsa/sign.

  **Response:**

  .. code-block:: tsref

    {
      // The RSA public key the client should use when blinding a value for the /test/rsa/sign API.
      rsa_pub: RsaPublicKey;
    }

.. http:POST:: /test/rsa/sign

  Test RSA blind signatures.

  **Request:**

  .. code-block:: tsref

    {
      // Blinded value to sign.
      blind_ev: BlindedRsaSignature;
    }

  **Response:**


  .. code-block:: tsref

    {
      // Blind RSA signature over the `blind_ev` using the private key
      // corresponding to the RSA public key returned by /test/rsa/get.
      rsa_blind_sig: BlindedRsaSignature;
    }

.. http:POST:: /test/transfer

  Test Transfer decryption.

  **Request:**

  .. code-block:: tsref

    {
      // Private transfer key
      trans_priv: string;

      // `Coin public key <eddsa-coin-pub>`_
      coin_pub: EddsaPublicKey;
    }

  **Response:**

  :status 200: the operation succeeded

  .. code-block:: tsref

    {
      // Decrypted transfer secret
      secret: string;
    }