What is Themis?

Themis is a web application that facilitates the creation and verification of timestamps of digital information on the Ethereum blockchain. Themis allows to write arbitrary data on blockchain, such data can be metadata (that are information about data which remains private), or plain information. Themis also preserves and indexes all the metadata that have been written on blockchain through its own service, allowing anyone to search and verify it independently.
Themis stands as an intermediation platform between users and blockchains, without necessarily becoming indispensable, at the end of each operation Themis provides a receipt that allows users to be independent in verifying information directly on blockchain.

Does Themis have legal validity?

It depends on the legislative framework in which operate the parties who use this tool. Some jurisdictions recognize the timestamping of data on blockchain as legally valid, for others it is necessary to resort to a technical expertise. Usually the various national jurisdictions do not have restrictions that prohibit private legal entities from signing agreements between the parties to recognize information on blockchain as authoritative, using it as a conciliation tool to track activities related to collaborations or supply operations.

What do I need to know to understand how Themis works?

It is advised to familiarize yourself with the following concepts, please refer to the Tech Details section for further information.

• Original data: arbitrary information that you want to protect.

What types of data can Themis handle?

Themis can perform timestamping on blockchain of any type of data. For the most common data such as images, PDFs, multimedia and small files, Themis helps you to extract the data fingerprint and to identify the most appropriate metadata to include in the timestamp.

What is timestamping?

The timestamping is the possibility to insert immutable information on blockchain associated to a determined temporal instant. The information entered on blockchain can be metadata, ie data that describes, without disclosing details, other private or sensitive data, or plain data. In the case in which data are written in clear text on blockchain, it is advisable to make sure not to insert sensitive data that goes to break the restrictions imposed by regulations such as GDPR, moreover one has to deal with writing costs that can be very high.

What are metadata?

Metadata is data that describes the characteristics of other data. For example, a metadata can be the fingerprint of a file, the author's first and last name, the file's creation date, the file's title and other relevant information to reconstruct the history and ownership of the file.

What is a fingerprint?

The fingerprint is a fixed-size alphanumeric string representing an arbitrarily large data file. By changing just one bit in the data file you get a fingerprint completely different. Anyone can get the same fingerprint from the same data file, while knowing the fingerprint it is not possible to reconstruct the contents of the original data file.

Are there limits to the amount of data I can write on blockchain?

If you simply write fingerprints of aggregate data, there is no limit to the amount of data that can be timestamped on blockchain. If you decide instead to write clear information on blockchain the limit is how much you are willing to pay and wait for the entry of the data.

How are metadata written on blockchains by Themis?

Themis supports different ways of writing metadata on blockchain, in order to reconcile all the requirements of economy, confidentiality and autonomy in verification. Themis allows you to write the plain metadata, so that they are publicly readable directly by a blockchain explorer. This solution is the most expensive and is not always compatible with the confidentiality of the data and with regulations on sensitive data such as GDPR. Themis allows you to write only the fingerprint of the metadata of a single item, keeping the original metadata in your index, such metadata can optionally be restricted only to appropriate authorized users. This solution is compatible both with confidentiality scenarios and with the processing of sensitive data.
For all data intensive scenarios involving the creation of numerous items, Themis allows you to combine the fingerprints of all items into a single fingerprint that is written as a timestamp on blockchain. In this case with a single timestamp it is possible to verify an arbitrary quantity of items, this solution is extremely economical, secure and confidential but makes the verifiability more complex.

How does Themis work with GDPR?

Using Themis with single hash and coalesce hash writing modes it is possible to guarantee confidentiality, protection of sensitive data and reduction of writing costs at the same time, to the cost, however, of the simplicity of checking the data, which in these cases must pass for the Themis platform and potentially for the collaboration of the data owner.

Are there limits to the amount of data I can write on blockchain via Themis?

Themis can preserve and index metadata of limited size, as indicated by the webapp. Although there are quantity limits per single item, there are no limits on the number of items that can be timestamped.

Are there limits to the number of timestamps I can run on Themis?

Themis is a volume service that does not impose any limit to the amount of data you can write, the user pays for the storage and indexing of metadata based on volume.

Are there limits or restrictions on the type of metadata I can insert on blockchain?

There are no restrictions or particular limits, but depending on the writing method, especially with plain text metadata, it is possible to incur in significant costs. In addition, compliance issues with GDPR can arise if sensitive data is used in metadata.

Can I timestamp encrypted data?

Certainly, but if you decide to write on blockchain only the metadata of the data, which remains off-chain, it is not necessary to add further protections.

Can I timestamp compressed data?

Certainly, however, for future checks it is advisable to keep the zip file that has been used, simply keeping its contents may not be sufficient for the verification, as in certain conditions generating zip files on the same content may give rise to slightly different files, with different fingerprints.

Can I timestamp a folder of files?

Yes, by making an archive (for example a zip) of the folder and using this archive for the timestamp. The archive file must be preserved for verification.

In what ways does Themis write a timestamp on blockchain?

Themis supports different ways of writing timestamps on blockchain, as detailed in section Operating Modes. The various methods differ in terms of cost control, data confidentiality and independence from Themis for verification.

What should I do with the receipt?

In the receipt there are all the information necessary to be able to independently verify the timestamp of the data on blockchain, without requiring to access (for free) the Themis index. This receipt should be carefully kept by uses together with the original data.

I lost the file receipt, can I still perform a verification if necessary?

Yes, Themis indexes the metadata of the executed timestamps, so if you are still in possession of the original data, you can recalculate from the fingerprint and query Themis with this, which will return the references to the blockchain transaction containing the timestamp.

Does Themis keep the original data on my behalf?

Themis is limited to keep small amounts of metadata, (in text format), and the proof metadata required for the verification of the timestamping on blockchain, the original data must always be preserved by the user.

What is the best blockchain for timestamping my data?

A blockchain is as reliable as its consensus system is distributed, as greater is its international adoption and as larger is its market cap. Consensus distribution prevents few entities from deciding to alter or censor information from written in blockchain. The international adoption guarantees resilience to any restrictive interventions of a single state, the market cap guarantees stability and support to the network over time. Based on these criteria, the safest blockchains to date are Ethereum and Bitcoin.

What happens if Themis is shut down?

Themis is a facilitation service that provides users with all the information necessary to be autonomous in the provision of audits to third parties, without intermediation. Users should always preserve their timestamp receipts, in case of definitive service disposal these receipts are sufficient to produce data verification.

What is an Authority?

An Authority is either a person or a company using Themis to timestamp and optionally certify their data.

What is an Auditor?

An Auditor is a special Authority that verifies the content of data published by other Authorities and if ok signs them with a public certificate.

What does it mean data validation?

Data validation is the operation performed by an Auditor on data published by an Authority certifying that the data is correct.