View source for OpenTimestamps

{{Infobox software
|                   name = OpenTimestamps
|                   logo = openTimestamps logo.png
|               logo alt = 
|           logo caption = 
|             screenshot = <!-- Image name is enough. -->
|         screenshot alt = 
|                caption = 
|            collapsible = <!-- Any text here will collapse the screenshot. -->
|                 author = 
|              developer = Open
|               released = 
|           discontinued = <!-- Set to yes if software is discontinued, otherwise omit. -->
|             ver layout = <!-- simple (default) or stacked -->
| latest release version = 0.7.2<ref name="ots-client-latest-version">{{cite web |url=https://github.com/opentimestamps/opentimestamps-client/tree/opentimestamps-client-v0.7.2 |title=OpenTimestamps client, latest version |website=[[GitHub]] |accessdate=31 December 2024 }}</ref>
|    latest release date = {{Start date and age|2024|12|31|df=yes/no}}<ref name="ots-client-latest-version" />
| latest preview version = <!-- {{Start date and age|2017|01|10|df=yes/no}} -->
|    latest preview date = <!-- {{Start date and age|YYYY|MM|DD|df=yes/no}} -->
|                   repo = {{URL|https://github.com/opentimestamps/}}
|   programming language = [[Python (programming language)|Python]], [[Java (software platform)|Java]], [[JavaScript]], [[Rust (programming language)|Rust]]
|       operating system = 
|               platform = 
|                   size = 
|               language = 
|         language count = <!-- Number only -->
|      language footnote = 
|                  genre = [[Trusted timestamping|Decentralized timestamping]]
|                license = [[GNU Lesser General Public License|LGPL3]]
|                  alexa = 
|                website = {{URL|https://opentimestamps.org}}
|               standard = 
|                   AsOf = 
}}

'''OpenTimestamps''' ('''OTS''') is an [[open-source software|open-source]]<ref>{{cite web|url=https://github.com/opentimestamps|title=OpenTimestamps code repository|website=[[GitHub]] |access-date=7 June 2018}}</ref> project that aims to provide a standard format for blockchain timestamping.<ref>{{cite web|url=https://opentimestamps.org|title=OpenTimestamps website|access-date=7 June 2018}}</ref>
With the advent of systems like [[Bitcoin]], it is possible to create and verify proofs of existence of documents (timestamps) without relying on a [[trusted third party]]; this represents an enhancement in terms of security, since it excludes the possibility of a malicious (or careless) trusted third party to compromise the timestamp.<ref>{{cite journal|last1=Gao|first1=Yuefei|last2=Applications|first2=Hajime|date=2017|title=A Decentralized Trusted Timestamping Based on Blockchains|journal=IEEJ Journal of Industry Applications|volume=6|issue=4|pages=252–257|doi=10.1541/ieejjia.6.252|doi-access=free}}</ref>

OTS defines a set of rules for conveniently creating timestamps and later independently verifying them. Currently, timestamping with Bitcoin is fully supported, however the format is flexible enough to support a variety of methods.{{efn|As of now, it is possible to timestamp also with [[Litecoin]] and [[Ethereum]], although verification is not supported.}}

Anyone could create timestamps with the permissionless blockchain by paying the transaction fees, for convenience OTS built an infrastructure that aggregates timestamp requests from users and packs them into transactions funded by public calendar servers; as a result, users can timestamp for free, in a trust-minimized setting.{{efn|The worst thing that a calendar can do is not to timestamp the users data; if that happens, then users can timestamp by themselves.}}

== What is a timestamp ==
A timestamp is a proof that some data ''d'' existed prior to a certain point in time.<ref name="ots-launch">{{cite web|url=https://petertodd.org/2016/opentimestamps-announcement|title=OpenTimestamps: Scalable, Trust-Minimized, Distributed Timestamping with Bitcoin|last=Todd|first=Peter|date=September 15, 2016|accessdate=May 5, 2018}}</ref>

To create such proof, it turns out that it is not necessary to publish ''d'' on the blockchain, which would be expensive, but it is enough to '''commit''' ''d'' to the blockchain. 
Such commitment proves that ''d'' existed prior to a certain block, in the sense that if ''d'' changes, then the proof becomes invalid and hence useless.

The proof consists in a sequence of commitment operations, such as <code>sha256</code>, <code>append</code>, <code>prepend</code>.{{efn|Note how, by conveniently combining these commitment operations, it is possible to traverse a [[Merkle tree]]. Similarly to Bitcoin, OTS makes use of this commitment structure to pack several timestamps in one transaction.}} 
These operations are the cryptographic path that proves that ''d'' commits to a certain block header. In other words, that ''d'' caused the block header to have its value, indeed, if ''d'' were different then, due to the mathematical properties of commitment operations, the block header would be different. 
To verify the commitment, the operations are applied in sequence to the data ''d'', then the result, which should be the transaction merkle root, is checked to be equal to the one observed in the blockchain; if the check goes fine, then one can assert that ''d'' existed prior to the block.

For the timestamped file <code>hello.txt</code>, the OTS proof is encoded in a file named <code>hello.txt.ots</code> which contains:
* the hash of the timestamped file;
* the commitment operations;
* one or more attestations on the blockchain.{{efn|A timestamps is in form of a tree: from the starting hash, multiple branches leads to different attestations. This provides the redundancy that protect users in case a calendar is down.}}
With this information, a challenger can independently verify that <code>hello.txt</code> existed prior to a certain block.

== Usage ==
OTS provides users multiple and easy ways to create and independently verify timestamps:{{Citation needed|date=September 2022}}
* With [https://github.com/opentimestamps/opentimestamps-client opentimestamps-client] in Python;
* With [https://github.com/opentimestamps/java-opentimestamps java-opentimestamps];
* With [https://github.com/opentimestamps/javascript-opentimestamps javascript-opentimestamps];
* On {{URL|https://opentimestamps.org}}.{{efn|The website is the easiest method to create and verify timestamps but it is the less secure: differently from the previous ones, users cannot verify independently the timestamp, since the verification is made by a third party.}}
In the following sections it is shown an example of the usage of the Python client.

=== Timestamp creation ===
The ''stamp'' operation creates the first version of the timestamp. It is applied to the file for which you want to prove its existence (original file).

<syntaxhighlight lang="console">
$ cat hello.txt
Hello World!
$ ots stamp hello.txt
Submitting to remote calendar https://a.pool.opentimestamps.org
Submitting to remote calendar https://b.pool.opentimestamps.org
Submitting to remote calendar https://a.pool.eternitywall.com
</syntaxhighlight>

The ''stamp'' operation calculates the [[SHA-2|SHA256 hash]] of the original file, [[concatenation|concatenates]] a random 128-bit [[cryptographic nonce|nonce]] to maintain privacy, and recalculates the SHA256 hash, sending this unique value to the calendar servers. Each of the calendar servers will add the received hash to its [[Merkle tree]] and return the necessary response to generate the initial OTS file. This OTS file is still incomplete because it does not yet contain the record in the blockchain.<ref name="ots1">{{cite web|url=https://pg.443.co.za/autots.pdf|title=Practical Application of Distributed Ledger Technology in Support of Digital Evidence Integrity Verification Processes|last=Weilbach|first=William Thomas|date=December 11, 2017|archive-url=https://web.archive.org/web/20180418161102/https://pg.443.co.za/autots.pdf|archive-date=18 April 2018|url-status=dead|accessdate=May 5, 2018}}</ref>

Once a reasonable time has elapsed, the user will run the ''upgrade'' operation on the same OTS file. This will communicate with the calendar servers and update the OTS file with the Bitcoin block header attestation.<ref name="ots-launch" />

<syntaxhighlight lang="console">
$ ots upgrade hello.txt.ots
Success! Timestamp complete
</syntaxhighlight>

It is also possible to create timestamps for several different files simultaneously. In that case, the ''stamp'' operation will send a single request to the calendar servers with a Merkle root derived from the original files, and later, that same operation will calculate the Merkle tree paths and create the timestamps for each one of the original files.

=== Timestamp verification ===
The verification of the OTS proof requires both the OTS file and the original file. The user must also have an up-to-date Bitcoin [[node (networking)|node]]{{efn|It is not strictly required a full node, indeed the attestation are on the block header, thus a pruned node is enough to verify a timestamp. Note that a SPV node has the whole ''block header chain'', so, in theory, it could verify timestamps, however it does not verify blocks and thus has a much lower security compared to pruned nodes.}} on their own machine to perform the verification without relying on trusted third parties.<ref>{{cite web|url=https://github.com/opentimestamps/opentimestamps-client|title=OpenTimestamps client repository|website=[[GitHub]]|accessdate=June 7, 2018}}</ref>

<syntaxhighlight lang="console">
$ ots verify hello.txt.ots
Assuming target filename is 'hello.txt'
Success! Bitcoin attests data existed as of Mon Apr 16 01:15:16 2018 CEST
</syntaxhighlight>

=== Show timestamp information ===
{{Infobox file format
| name = OpenTimestamps
| icon = 
| iconcaption = 
| icon_size = 
| screenshot = 
| screenshot_size = 
| caption = 
| extension = .ots
| mime = 
| type_code = 
| uniform_type = 
| conforms_to = 
| magic = <code>\x00</code>&nbsp;<code>O</code>&nbsp;<code>p</code>&nbsp;<code>e</code>&nbsp;<code>n</code>&nbsp;<code>T</code>&nbsp;<code>i</code>&nbsp;<code>m</code>&nbsp;<code>e</code>&nbsp;<code>s</code>&nbsp;<code>t</code>&nbsp;<code>a</code>&nbsp;<code>m</code>&nbsp;<code>p</code>&nbsp;<code>s</code> <code>\x00</code>&nbsp;<code>\x00</code>&nbsp;<code>P</code>&nbsp;<code>r</code>&nbsp;<code>o</code>&nbsp;<code>o</code>&nbsp;<code>f</code> <code>\x00</code>&nbsp;<code>\xbf</code>&nbsp;<code>\x89</code>&nbsp;<code>\xe2</code>&nbsp;<code>\xe8</code>&nbsp;<code>\x84</code>&nbsp;<code>\xe8</code>&nbsp;<code>\x92</code>&nbsp;<code>\x94</code>
| max_size = 
| developer = 
| released =                <!-- {{start date and age|YYYY|mm|dd|df=yes/no}} -->
| latest_release_version = 
| latest_release_date =     <!-- {{start date and age|YYYY|mm|dd|df=yes/no}} -->
| type = 
| container_for = 
| contained_by = 
| extended_from = 
| extended_to = 
| standard =                <!-- or: | standards = -->
| free = 
| open = 
| url = {{URL|https://opentimestamps.org/}}
}}
The basic structure of a timestamp is divided into three main sections:<ref name="ots1" />
# File hash
# Merkle tree construction
# Bitcoin block header attestation

The timestamp is saved in a [[binary file]] to save space and avoid problems of interpretation, [[character encoding|encoding]] and compatibility between systems.<ref name="ots1" /> Generally, this file has a <samp>.ots</samp> [[filename extension|extension]] and its [[magic number (programming)|magic number]] is <code>\x00</code>&nbsp;<code>O</code>&nbsp;<code>p</code>&nbsp;<code>e</code>&nbsp;<code>n</code>&nbsp;<code>T</code>&nbsp;<code>i</code>&nbsp;<code>m</code>&nbsp;<code>e</code>&nbsp;<code>s</code>&nbsp;<code>t</code>&nbsp;<code>a</code>&nbsp;<code>m</code>&nbsp;<code>p</code>&nbsp;<code>s</code> <code>\x00</code>&nbsp;<code>\x00</code>&nbsp;<code>P</code>&nbsp;<code>r</code>&nbsp;<code>o</code>&nbsp;<code>o</code>&nbsp;<code>f</code> <code>\x00</code>&nbsp;<code>\xbf</code>&nbsp;<code>\x89</code>&nbsp;<code>\xe2</code>&nbsp;<code>\xe8</code>&nbsp;<code>\x84</code>&nbsp;<code>\xe8</code>&nbsp;<code>\x92</code>&nbsp;<code>\x94</code>.<ref>{{cite web |url=https://github.com/opentimestamps/python-opentimestamps/blob/master/opentimestamps/core/timestamp.py#L273 |title=Header magic definition in python-opentimestamps |website=[[GitHub]] |accessdate=7 June 2018 }}</ref>

The ''info'' operation presents the content of the timestamp on a human-readable format. In this case, a single attestation of the <samp>hello.txt</samp> file is shown, which hashes all the way to the Bitcoin block header at block 518387.

<syntaxhighlight lang="console">
$ ots info hello.txt.ots
File sha256 hash: 03ba204e50d126e4674c005e04d82e84c21366780af1f43bd54a37816b6ab340
Timestamp:
append 72d8a09f54b12580b48c2f7c7dea4ce0
sha256
 -> append fe0d089c9bfe5289c3ee579904af3551
    sha256
    prepend 5ad3d92b
    append 8fefb42191040403
    verify PendingAttestation('https://alice.btc.calendar.opentimestamps.org')
    sha256
    prepend f0e8b62a519b0b8fad763c33c558e0179a43b8d89cb4130b6dbaa91e3d3252f6
    sha256
    prepend beca183da3f86784a7d54778bc48e78c570245d51474f32475e6d1851989b140
    sha256
    append a95879c35c15ace7dc5fd1d2cf0a7d9b0e4110b5b8a74da4c64082835f6f6a2e
    sha256
    append cf9b259e4506235f97225706f3a675f51ecf2657814639d87e4e6f42d8581ae7
    sha256
    prepend e3b7ff694e1b14b4420556ca77ea8e9509e44b7fbed0dc9a3b67c00fcf016ca2
    sha256
    prepend 01000000017230dffb1edd7cae0c8feb3fec7c91c34b33b22fdfac071b83e790ce34254b340000000017160014a4282cbf0f17fd6d51b61da f7cf4d56e32183b60fdffffff02d7c062000000000017a914365c46ff772b9f1da73efeb2c559777e1a2c33b4870000000000000000226a20
    append f2e80700
    # Bitcoin transaction id 7e6e5aafa1fc9d933992621a7ac321dc7b9368d0e1baa72ff77665b07b75315f
    sha256
    sha256
    append d67f1615f986694d707d7d044883c7885f3dded2ac9df5f6b9270a5bdda38aa3
    sha256
    sha256
    append e551a80b2bdd88f417fc95014662f7a65d8c0c4d833b6df034bc12f1af35b953
    sha256
    sha256
    append 0902830fc37fde4996c350de40c0ae621c739ce002a7be4b3725d7e281fc02a3
    sha256
    sha256
    append 7ac1e262423598f1477825882f78ededc98b44bf0136f059e438391aa0e7a686
    sha256
    sha256
    prepend 9ee83975bef756160275a336203059109fd4336572e5e47e9a3edadb82a8934c
    sha256
    sha256
    append 7a3229b63fc7a88d4edde4aa5b855416265842120fde246462271e5418f895bd
    sha256
    sha256
    prepend a4c712ca130f63862f329874f11466eb74ee7b505c191344ee11b30d14ca4946
    sha256
    sha256
    append 13bf98cdb708ed3321b8d48ff290c5bdbefa6fb9be34717e97a3f3cfa9b87994
    sha256
    sha256
    prepend d2aec8bd2edf2d6d10606df92f1b8b53a97362d7aba7d3fa15bf55c0aab94e35
    sha256
    sha256
    verify BitcoinBlockHeaderAttestation(518387)
    # Bitcoin block merkle root b4f71191dc633cfb125543211022b1059d78b42a359408da5958fc15231ef6de
</syntaxhighlight>

== Use cases ==
Applications include [[defensive publication]]s.<ref>{{cite journal |title=Bitcoin for the biological literature |author=Douglas Heaven |journal=Nature |editor=[[Nature (journal)|Nature]] |date=February 4, 2019 |volume=566 |issue=7742 |pages=141–142 |doi=10.1038/d41586-019-00447-9 |pmid=30718888 |bibcode=2019Natur.566..141H |s2cid=256769716 |doi-access=free }}</ref>

== Notes ==

{{Notelist|30em}}

==References==
{{Reflist}}

{{Bitcoin}}

[[Category:Bitcoin]]
[[Category:Blockchains]]