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diff --git a/operate-exchange.rst b/operate-exchange.rst new file mode 100644 index 00000000..b276d06d --- /dev/null +++ b/operate-exchange.rst @@ -0,0 +1,155 @@ +.. + 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 + +====================== +Operating the Exchange +====================== + ++++++++++++++ +Configuration ++++++++++++++ + +The following data and facilities have to be set up, in order to run an exchange: + +* Keying +* Serving +* Currency +* Bank account +* Coins +* Database + +In this document, we assume that ``$HOME/.config/taler.conf`` is being customized. + +------ +Keying +------ + +The exchange works with three types of keys: + +* `master key` +* `sign keys` +* `denomination keys` (see section `Coins`) + +`master key`: in section `[exchange]`, edit the two following values: + +* `master_priv_file`: Path to the exchange's master private file. +* `master_public_key`: Must specify the exchange's master public key. + +`sign keys`: the following two options under `[exchange_keys]` section control `sign keys`: + +* `lookahead_sign`: How long should one signing key be used? +* `signkey_duration`: How much time we want to cover with our `signkeys`? Note that if `signkey_duration` is bigger than `lookahead_sign`, `taler-exchange-keyup` will generate a quantity of `signkeys` which is sufficient to cover all the gap. + +.. note:: + `signkeys` will be used in future versions of Taler. + +------- +Serving +------- + +The exchange can serve HTTP over both TCP and UNIX domain socket. It needs this +configuration *twice*, because it opens one connection for ordinary REST calls, and one +for "/admin" and "/test" REST calls, because the operator may want to restrict the access to "/admin". + +The following values are to be configured under the section `[exchange]` and `[exchange-admin]`: + +* `SERVE`: must be set to `tcp` to serve HTTP over TCP, or `unix` to serve HTTP over a UNIX domain socket +* `PORT`: set to the TCP port to listen on if `SERVE` is `tcp`. +* `UNIXPATH`: set to the UNIX domain socket path to listen on if `SERVE` is `unix` +* `UNIXPATH_MODE`: number giving the mode with the access permission mask for the `UNIXPATH` (i.e. 660 = rw-rw----). + +The exchange can be started with the `-D` option to disable the administrative +functions entirely. It is recommended that the administrative API is only +accessible via a properly protected UNIX domain socket. + +-------- +Currency +-------- + +The exchange supports only one currency. This data is set under the respective +option `currency` in section `[taler]`. + +------------ +Bank account +------------ + +The command line tool `taler-exchange-wire` is used to create a file with +the JSON response to /wire requests using the exchange's offline +master key. The resulting file's path needs to be added to the configuration +under the respective option for the wire transfer method, i.e. +`sepa_response_file` in section `[exchange-wire-incoming-sepa]` when the +`wireformat` option in the configuration file allows `sepa` transactions. For example, +the utility may be invoked as follows:: + + taler-exchange-wire -j '{"name": "The Exchange", "account_number": 10, "bank_uri": "https://bank.demo.taler.net", "type": "test"}' -t test -o exchange.json + +Note that the value given to option `-t` must match the value in the JSON's field ``"type"``. `exchange.json` will be the same JSON given to ``-j`` plus the field +``"sig"``, which holds the signature of the JSON given in option ``-j`` made with exchange's master key. Finally, if `taler-exchange-wire` will not find any master +key at the location mentioned in `master_priv_file`, it will automatically generate (and use) one. + +-------- +Database +-------- + +The option `db` under section `[exchange]` gets the DB backend's name the exchange +is going to use. So far, only `db = postgres` is supported. After choosing the backend, +it is mandatory to supply the connection string (namely, the database name). This is +possible in two ways: + +* via an environment variable: `TALER_EXCHANGEDB_POSTGRES_CONFIG`. +* via configuration option `db_conn_str`, under section `[exchangedb-BACKEND]`. For example, the demo exchange is configured as follows: + +.. code-block:: text + + [exchange] + ... + db = postgres + ... + + [exchange-postgres] + db_conn_str = postgres:///talerdemo + +------------------------- +Coins (denomination keys) +------------------------- + +Sections specifying denomination (coin) information start with "coin\_". By convention, the name continues with "$CURRENCY_[$SUBUNIT]_$VALUE", i.e. `[coin_eur_ct_10]` for a 10 cent piece. However, only the "coin\_" prefix is mandatory. Each "coin\_"-section must then have the following options: + +* `value`: How much is the coin worth, the format is CURRENCY:VALUE.FRACTION. For example, a 10 cent piece is "EUR:0.10". +* `duration_withdraw`: How long can a coin of this type be withdrawn? This limits the losses incurred by the exchange when a denomination key is compromised. +* `duration_overlap`: What is the overlap of the withdrawal timespan for this coin type? +* `duration_spend`: How long is a coin of the given type valid? Smaller values result in lower storage costs for the exchange. +* `fee_withdraw`: What does it cost to withdraw this coin? Specified using the same format as `value`. +* `fee_deposit`: What does it cost to deposit this coin? Specified using the same format as `value`. +* `fee_refresh`: What does it cost to refresh this coin? Specified using the same format as `value`. +* `rsa_keysize`: How many bits should the RSA modulus (product of the two primes) have for this type of coin. + +----------------------- +Keys duration +----------------------- + +Both `signkeys` and `denom keys` have a :ref:`starting date <keys-duration>`. +The option `lookahead_provide`, under section `[exchange_keys]`, is such that only keys whose starting date is +younger than `lookahead_provide` will be issued by the exchange. + ++++++++++ +Utilities ++++++++++ + +------------------ +Reserve management +------------------ + +Incoming transactions to the exchange's provider result in the creation or update of reserves, identified by their withdrawal key. +The command line tool `taler-exchange-reservemod` allows create and add money to reserves in the exchange's database. |