Technical solution


Integrate the blockchain technology into iText 7, enabling you to store digital signatures in a blockchain instead of in the PDF document.


Blockchain with iText 7

Blockchain has become well-known because of its use with Bitcoin, but there are several lesser known applications of Blockchain and Distributed Ledger Technology (DLT).

By integrating the blockchain technology into iText 7, you secure your invoices and digital signatures in your PDF documents, and are also able to store digital signatures in a blockchain instead of in the PDF document.


Why should you use iText & Blockchain

You have sent out some contracts in PDF to your clients and would like to be able to track real time who has already signed the document, and with whom it is now. 

You've paid a digital invoice of your supplier, and afterwards it seemed to be fake - you were a victim of invoicing fraud.

These issues and many more can now be solved by Blockchain. Continue reading to discover more.

Cost reduction

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  • Speed up interactions between clients and stakeholders.

  • Reduce your papertrail.

  • Automate your processes.

Better and secured communication

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  • Pass sensitive information through with risk or leakes, gets lost or is distorted along the way.

  • Clear and quick internal communication in case of frequent changes of prices, conversion rates, etc.   

Track real time

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  • See who already signed, with whom the document is now, etc.

  • For logistics track where the package is at the moment.

Key features

Core Capabilities of Blockchain with iText 7

A blockchain holds data. It collects this data in units called 'blocks'. There is a mechanism to prove a block has not been tampered with. And over time, blocks get chained together. This chaining organically enables a kind of 'history'.

A blockchain supersedes older technology that deals with authentication and nonrepudiation. First, there are many ways you can digitally sign a document. Typically by "signing" we mean creating a hash of a document, creating a signature from that hash with a private key, and storing the signature. This has two effects:

  • the signature identifies the person who signed the document.
  • the signature, when decrypted, identifies the file from which it was computed.

Once such a signature is stored in a blockchain, it can not be changed or deleted. This gives you an extra advantage: the fact that your signature is in the blockchain gives you a point in time when the operation was done.


Data in a blockchain

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  • Can be signed using known PKI-infrastructure.
  • Is automatically validated and timestamped.
  • Can be viewed by everyone
  • Can live separately from the physical (real world) data it references.

Relation to PDF

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  • PDF documents can be digitally signed.
  • Web of trust
  • Integrity: “The document has this exact content.”
  • Authentication: “I created this document. And I can prove it.”
  • Non-repudiation: “He created this document. And I can prove it.”
  • Timestamp

Secure digital signatures

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  • Requires Certificate Authority (centralized).
  • Requires timeserver (centralized).
  • Cannot be signed in parallel.
  • Signatures live in the document.

Theoretical usecase - high level

On a high level, the idea is to separate the functionality of signing and integrity from a pdf, and bring those into the blockchain. Imagine an example use case.

  • The document is created, and the document ID (along with its hash, and the name of the hashing algorithm) gets put on a public blockchain. This does not cause any problems, since the hash typically does not allow you to rebuild the entire document. We put the hashing algorithm on the chain as well to ensure long term validation.
  • Now imagine that this document is an invoice. Bob has had some work done on his house, and the renovation company sends him an invoice.
  • Bob wants to sign the invoice to indicate he agrees with the price and will pay. Bob's private key is then used to encrypt the hash-value of the document. This signature (comprising the ID of the document, the original hash-value, the signed hash-value, as well as the names of the hashing algorithm and signing algorithm) are stored on the blockchain.
  • Alice, who works for the renovation company wants to check whether Bob has signed already. She can easily look up all records on the blockchain for a given ID (the document ID). One of these records ought to be the record Bob created earlier. Since the record contains the original hash, and the names of all the algorithms involved, Alice can verify 2 things:
    • it was Bob that signed, using the hash, the signed hash, and Bob's public key.
    • Bob signed the exact document she sent him, using the document ID and the hash.
    Blockchain high level use case


    Theoretical usecase - low level


    The interfaces we impose on blockchain implementations are minimal, yet they provide us with the needed abstraction to enable us to build complex applications and workflows on top of them. We abstract a blockchain as a multimap, allowing end-users to store an object (represented by Record, which is HashMap) and tying it to a key (String).

    public interface IBlockChain {
         * Put data on the blockchain
         * @param key  the key being used to put the data on the blockchain
         * @param data the data being put on the blockchain
        public boolean put(String key, Record data);
         * Get data from the blockchain
         * @param key the key being queried
         * @return
        public List<Record> get(String key);
         * Get all data from the blockchain
         * @return
        public List<Record> all();

    Concrete implementation using JSON-RPC and MultiChain

    As a proof of concept we have provided an implementation of the interface IBlockchain using JSON-RPC (remote procedure call) and MultiChain.

    If you want to learn more about setting up a blockchain instance with MultiChain, check out their website for more resources, in particular the getting started guide here.

    Blockchain low level use case


    An example of iText & Blockchain

     this example, we will show you how to put a document on the blockchain, with signature:

           IBlockChain mc = new MultiChain(
            InputStream keystoreInputStream = BasicFunctionalityTest.class.getClassLoader().getResourceAsStream("ks");
            InputStream inputFileStream = BasicFunctionalityTest.class.getClassLoader().getResourceAsStream("input.pdf");
            AbstractExternalSignature sgn = new DefaultExternalSignature(keystoreInputStream, "demo", "password");
            PdfChain chain = new PdfChain(mc, sgn);
            // put a document on the chain
            boolean wasAdded = chain.put(inputFileStream);
            // check whether the chain now contains this value
            boolean isEmpty = chain.get("z�L{�Wd=��\u007F\u0010��G�").isEmpty();

    You can retrieve information about a document from the blockchain like this:

      IBlockChain mc = new MultiChain(
            PdfChain chain = new PdfChain(mc);
            for(Record record : chain.get(new File("example_file.pdf")))
                for(Map.Entry<String,Object> en : record.entrySet())
                    System.out.println(en.getKey() + "\t" + en.getValue().toString());


    Still have questions about PDF solutions with blockchain?

    We're happy to help! Send your questions to us, and we'll get back to you a.s.a.p.

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