Being able to provide evidence that you had some piece of information at a given time and it has not changed since are important in many aspects of personal, academic, or corporate life.

It can help provide evidence

• that you had some idea already at a given time,
• that you already had a piece of code, or
• that you knew about a document at a given time.

Timestamping does not assure authorship of the idea, code, or document. It only provides evidence to the existence at a given point in time. Depending on the context, authorship might be implied, at least weakly.

zeitgitter consists of two components:

1. A timestamping client, which can add a timestamp as a digital signature to an existing git repository. Existing git mechanisms can then be used to distribute these timestamps (stored in commits or tags) or keep them private.
2. A timestamping server, which supports timestamping git repositories and stores its history of commits timestamped in a git repository as well. Anybody can operate such a timestamping server, but using an independent timestamper provides strongest evidence, as collusion is less likely.
   • Publication of the timestamps history; as well as
   • getting cross-timestamps of other independent timestampers on your timestamp history both provide mechanisms to assure that timestamping has not been done retroactively ("backstamping").

The timestamping client is called git timestamp and allows to issue timestamped, signed tags or commits.

To simplify deployment, we provide a free timestamping server at https://gitta.zeitgitter.ch. It is able to provide several million timestamps per day. However, if you or your organization plan to issue more than a hundred timestamps per day, please consider installing and using your own timestamping server and have it being cross-timestamped with other servers.

Having your own timestamping server provides several benefits:

• The number of timestamps you request, their commit ID, as well as the times at which they are stamped, remain you business alone.
• You can request as many timestamps as you like.
• If you like, you can provide a service to the community as well, by timestamping other servers in turn. This strengthens the overall trust of these timestamps.

There are currently two options for installation:

• Running a Zeitgitter timestamper in Docker (recommended; only requires setting four variables)
• Traditional install on a Linux server (more work)

• Timestamping: Why and how?
• Protocol description
• Discussion of the use of (weak) cryptography

• Docker server (recommended)
• Native server (deprecated)
• How the server works
• The server's state machine