You can timestamp any type of digital document. It could be texts, audio, photos, videos, source code, zip files containing several documents, etc.
No, tangible.io never sees your document. All you share is a digital "fingerprint" of your document in the form of a cryptographic hash (a 64 character long string of letters and numbers). The hash is calculated by your web browser without sharing the document with tangible.io. If you prefer you can calculate the hash using offline tools and manually enter it into the search field.
To verify a timestamp you will need to present an exact copy of your original (i.e. whose hash is the same as the hash you timestamped). Any change to the document, including to document meta data, will result in a different hash for the document. To avoid accidentally modifying an already timestamped document it a good idea to save your timestamped originals in a safe place and never open them directly. Always make a copy of an original before viewing it. Also remember to always save your tangible.io receipt.
Your timestamped document must itself contain a reference to you. One way to achieve this is to timestamp a zip file containing your originals together with a file identifying who you are. If you are in possession of the wallet that purchased the timestamp, then it is also possible to prove that you control the private key that signed the timestamp transaction.
Your transaction containing the document hash will always be stored in the bitcoin blockchain and can't be removed regardless of the fate of this site. Your timestamp receipt contains the bitcoin transaction ID for the transaction containing your document hash. You can look it up using blockchain explorers such as blockchain.info.
For fingerprinting documents tangible.io uses a cryptographic hash called SHA256. The hash consists of a 64 character long string of letters and numbers. A cryptographic checksum has such mathematical properties that it can be considered a unique identifier for a document.
All bitcoin transactions are saved in the bitcoin blockchain. Its purpose is to keep track of transactions and their timing. There is currently several billions USD worth of bitcoin relying on the blockchain performing this task correctly. Just as bitcoin transactions are protected from tampering, so are your timestamps.
Timestamps are paid for with bitcoin. A wallet supporting the bitcoin payment protocol (BIP 70/71/72) is needed. It is fairly recent and not all wallets support it properly yet. Currently, the following wallets are confirmed to work with this site:
Additional questions can be sent to firstname.lastname@example.org.