GitCash: A Git based payment system

GitCash is a Git based payment system primarily targeted at hackerspaces and similar groups. It is being developed by Coredump in collaboration with other Swiss hackerspaces.

High-Level Goals

• Money enters the system by putting cash into a cash box and crediting yourself that amount in the payment system. That credit can then be used to pay for goods.
• Decentralized storage format for transactions in a repository.
• Insecure but transparent: There is no authentication, but all transactions are transparent and public (if you have access to the repository).

How it works

Transactions are stored as TOML snippets in Git commit messages. Every commit contains 1 transaction (or none at all).

This has a few advantages:

• We an use a regular Git server (GitLab, Gitea or even just a repo reachable by SSH)
• The integrity is ensured through Git hashes
• The transactions are ordered in the Git DAG
• Transactions can be validated using a pre-push hook on the server
• Conflicts can be resolved by merging
• You could create transactions "by hand"
• Commits could be signed

Transactions in the repository can be created or analyzed by any node that has access to the repository.

Use cases for nodes

• Fridge: Pay for drinks at the fridge by scanning the barcode
• Laser Cutter: Pay for laser cutter time by starting and stopping your session on a touch panel
• 3D Printer: Pay for your 3D prints by putting your print on an electronic scale and entering your name and the material on a touch panel
• Notification Monitor: Whenever money is deduced from your account, you get a notification
• ... and many more!

Not all nodes might have the processing power to be a "full node" that can parse the Git repository. For these use cases, a small server could accept new transactions over a simple API and write them to the repository.

Storage format / specification

See docs/spec.md.

Demo repository

See https://github.com/coredump-ch/gitcash-demo-repo.

SDK and reference implementation

• libgitcash: Library / SDK that can be used for processing a GitCash repository
• gitcash: A CLI client for GitCash

History

GitCash was brainstormed and initially developed at CCC Camp 2023. Special thanks to some of the people from Luxeria for giving feedback on the initial design!

License

Licensed under the AGPL version 3 or later. See LICENSE.md file.

Copyright (C) 2023 Coredump Rapperswil-Jona

This program is free software: you can redistribute it and/or modify
it under the terms of the GNU Affero General Public License as
published by the Free Software Foundation, either version 3 of the
License, or (at your option) any later version.

This program 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 Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License
along with this program.  If not, see <https://www.gnu.org/licenses/>.