This webpage is an interface
to create and/or verify timestamp proofs using the
OpenTimestamps
protocol and its free public Bitcoin calendar servers.
[If in a hurry, skip this introduction
and go straight away to
timestamping.]
A timestamp demonstrates that a document existed in a
specific status prior to a given point in time,
providing that document with a certain sure date (e.g., postmark).
Law requires dates to be certified by
public officials and notary services;
for digital documents, timestamping is usually based on the
digital signature of a Certification Authority (CA).
Anyway, digital data can be securely timestamped using the
attestation of its hash value
in a blockchain transaction.
The hash value 'uniquely' identifies the document
(as if it were its unique digital fingerprint),
the transaction extends its native blockchain
timestamping to the included hash value,
therefore proving its
existence at a given point in time.
As a result,
the blockchain attestation of the hash value
proves also the existence of the
original document itself prior to the timestamp moment.
Timestamping and content of a blockchain transaction
are secured by the amount of computational effort
performed after the transaction inclusion in a block of the chain.
Indeed, the more blocks are added to the chain
after a given block,
the more computationally intensive is
tampering with the data of that block; even just trying
to alter the timestamp of a transaction
becomes technically and economically prohibitive,
especially in the Bitcoin blockchain case.
Although there are many ways to realize a timestamp,
OpenTimestamps
is a vendor-independent blockchain-agnostic
open protocol that defines a
set of operations for creating provable blockchain
timestamps and later independently verifying them;
as such, it allows for third party auditability and
is suitable for regulatory prescriptions.
OpenTimestamps attestation proofs can be verified
independently from
any server, vendor, or centralized infrastructure, simply
using a local copy of the blockchain (e.g., a Bitcoin
full node).
Trust minimization is achieved because of this
distributed, decentralized, independent, uncensorable,
and cross-jurisdictional design.
This webpage interface is just a facility and,
since a webpage cannot access the local filesystem,
relies for verification
on public Bitcoin block-explorers
(e.g., blockstream.info)
instead of a local copy of the blockchain.
To avoid the inefficiency of one blockchain transaction
for every timestamp, an OpenTimestamps server
provides aggregation of multiple
document hashes
in a Merkle tree data structure
and
attests only the hash
of the Merkle tree root.
The inclusion of a
hash value leaf in a Merkel tree
can be cryptographically proved and such a proof is
part of the attestation;
as a result,
the single attestation
of the tree root implicitly attests
all the leaves.
This aggregation before attestation
approach results in
almost unlimited scalability.
While anyone could timestamp with any permissionless
blockchain by paying the appropriate transaction fees
(using the OpenTimestamps protocol
or any alternative approach),
for convenience
there are multiple public OpenTimestamps
calendar servers (e.g.,
btc.ots.dgi.io),
free to use without any registration or API key.
A single calendar server can offer its services to
multiple remote OpenTimestamps clients: verifiable
timestamp are created with no cost for the clients.
The public free OpenTimestamps calendar servers
use Bitcoin as timestamp notary,
i.e., they make a Bitcoin transactions
to attest the root hash value in the Bitcoin blockchain.
