  Trusted timestamping is a process for proving that certain information
existed at a given point in time. This paper presents a trusted timestamping
concept and its implementation in form of a web-based service that uses the
decentralized Bitcoin block chain to store anonymous, tamper-proof timestamps
for digital content. The service allows users to hash files, such as text,
photos or videos, and store the created hashes in the Bitcoin block chain.
Users can then retrieve and verify the timestamps that have been committed to
the block chain. The non-commercial service enables anyone, e.g., researchers,
authors, journalists, students, or artists, to prove that they were in
possession of certain information at a given point in time. Common use cases
include proving that a contract has been signed, a photo taken, a video
recorded, or a task completed prior to a certain date. All procedures maintain
complete privacy of the user's data.
