Proof of Existence allows users store an online distributed proof of existence for any document anonymously and securely on the Bitcoin blockchain. Documents themselves are not stored. Instead, Proof of Existence stores a cryptographic digest of each file along with the time of upload for verification purposes. This allows users to prove that they have certain information without having to reveal their data or themselves.
Proof of Existence provides decentralized proof that no third party or government can tamper with. Validation is provided through the Bitcoin blockchain, allowing users to access the cryptographic digest for a file even if the Proof of Existence site is damaged or down.