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README.exchange.md

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Exchange and bank setup

This section is for you if you want to operate a GNU Taler Exchange and a Bank, e.g. because you are deploying it as a local payment system for an event.

Configure your web server

Adjust and add the two files in nginx-sites to your /etc/nginx/sites-enabled. Make sure you get the HTTPS certificates right. The Android app won't talk to you over insecure HTTP.

You won't need the merchant location, feel free to remove it.

  • Replace example.org by your domain in nginx-sites/taler.
  • Replace example.org by your domain in webui/*.
  • Ensure /home/taler/webui exists (copy from webui/).

First-time setup

Build the containers:

./rebuild_containers.sh

Adjust the exchange configuration in exchange-config.skel and some of the environment variables in make_env.sh as needed.

Make sure that you start with a fresh and clean database. Having old databases around will not re-run the database setup, which can result in wrong passwords being set and general confusion. Then create a .env file with the appropriate passwords:

sudo rm -rf data  # clear database
./make_env.sh     # prepare environment etc.

Starting the system

Source the .env file and launch the containers

source .env
docker-compose up

Operating a cashdesk

Navigate to https://bank.taler.example.org/webui and register a cashier account. In the scripts/ directory, run:

./restock-cashier 1337

load 1337 currency units into the cashier account. (Feels good to be the central bank, doesn't it?)

Checking account status

In the scripts/ directory, run:

./rich-account-list

in order to get a list of all accounts with their associated balances. The total sum should be zero.

Usually, the bank account has a negative balance. If you were operating a country, this would mean that the central bank had "created" money out of nothing.

If you operate an event, then the sum of bank and cashier should hopefully be equal to the negative amount of cash in your cashdesk.

Stopping the system

docker-compose down --timeout 1

Withdrawing money, the old way

After initiating the withdrawal in your wallet, you are asked to make a wire transfer to the bank's account using a provided subject.

First, wire the transaction into the bank's account on the sandbox:

docker exec -it taler-compose_libeufin_sandbox_1 /bin/bash
root@b23bfa4a27ab:/# LIBEUFIN_SANDBOX_USERNAME=admin LIBEUFIN_SANDBOX_PASSWORD=$LIBEUFIN_SANDBOX_ADMIN_PASSWORD LIBEUFIN_SANDBOX_URL=http://localhost:5016 libeufin-cli sandbox bankaccount simulate-incoming-transaction jrluser --debtor-iban DE123456 --debtor-bic SANDBOXX --debtor-name Fnord --amount MANA:5 --subject 'Taler Withdrawal PKAWS7YEG367744F9B8B7CKTC5KFPS7YH6RMD0NY52TV9TVCED6G'

Then, fetch the transactions on the nexus:

docker exec -it taler-compose_libeufin_nexus_1 /bin/bash
root@ef194aa7d8bd:/# LIBEUFIN_NEXUS_URL=http://localhost:5017 LIBEUFIN_NEXUS_USERNAME=admin LIBEUFIN_NEXUS_PASSWORD=$ADMIN_PASSWORD libeufin-cli accounts fetch-transactions nickname

Troubleshooting

Exchange logs can be examined using

docker exec -it taler-compose_exchange_1 /bin/bash
root@53e68ae5b360:/# cat /var/log/taler-exchange-*.log

Security considerations and other limitations

This setup defeats some security features Taler offers, in order to simplify the setup

  • No separation between taler-exchange and taler-exchange-offline is made. This would enable an attacker who exploits the online exchange system to exfiltrate the exchange's master key, allowing them to impersonate the exchange forever.
  • The exchange processes are all run as root user. This allows an attacker to exfiltrate short-term keys rather than only providing them with a signing/decryption oracle.

Additionally, this setup never renews coins. Coins expire in 2024.

Setup is racy and races are mitigated using sleep. This is as reliable as it sounds.

Merchant backend

Start the container using

docker run -e TOKEN=YOUR_TOKEN_HERE -e EXCHANGE_URL=https://your-exchange.org/ --rm -it -p 8888:8888 taler-merchant