A blog about Blockchain technology

Electronic Signature with Blockchain

With blockchain, you can imagine a world in which documents are embedded in digital code and stored in transparent, shared databases, where they are protected from deletion, tampering, and revision. In this world every agreement, every process, every task, and every payment would have a digital record and signature that could be identified, validated, stored, and shared. Intermediaries like lawyers, brokers, and institutions might no longer be necessary. Individuals, organizations, and machines would freely transact and interact with one another with little friction. This is the immense potential of blockchain. The potential application of content decentralization and distribution is enormous: people will own their digital identity and records (think of identity or residence documents, medical records, educational or professional certificates and licenses), creating a single, immutable and verifiable record store. All these documents and their metadata can be issued on the blockchain and be digitally signed. No more fake certifications, no more degree mills, no more “photoshopped” papers. Students, for example, may apply for further study, a job, immigration to another country; they may require to prove their level of study or knowledge of language to attend university. Entities like recruiters, employers, government, universities, can verify the student’s credentials without relying on central authorities, in just minutes, and with no other intermediaries.
Certificates are issued by an authority (say, an education institute), stored on a centralized document management server, or on a distributed file system like IPFS ( and signed with a cryptographic function. The document URI and content hash (the certificate’s metadata) are then encrypted and stored on the blockchain digital ledger and attached to the user’s digital identity. The system issues a unique authenticity token, which identifies the document in a non-questionable way.
A common pattern is to generate a unique hash of the digital asset and the metadata that describes it. Those hashes are then stored on a blockchain. If authenticity of a document is ever questioned, the “off chain” file can be re-hashed at a later time and that hash compared to the “on chain” value. If the hash values match, the document is authentic, but if just a character in a document is modified, the hashes will not match, making obvious that a change has occurred.
Users who need to have their certificates verified by a third party, share the authenticity token, that is the file contract address, which contains all the necessary information to verify that the document exists and is authentic (not counterfeited).
Processing documents, but also any unstructured data, and their metadata, and integrate these with blockchain to create immutable and independent verifiable records of transactions, is proof of existence and authenticity of these digital assets. Proof of existence refers to creating an unalterable date and time stamp for a specific object. This means that you can prove that a certain information object, like an email, document, image, existed at a certain point in time. Proof of authenticity asserts that an object is authentic, i.e. it has not been changed since it was stored at the indicated time instant. This is accomplished by digitally signing an object and thus creating a hash, its unique identifier. The identifier gets then committed into the distributed blockchain ledger, and the transaction gets timestamped as well. Since every entry in the blockchain is immutable, this means that you have proof that this specific object existed at a certain point in time.
Why blockchain
Why using blockchain to sign and verify digital assets, when solutions for electronic signature already exist and are broadly adopted in the industry?
  • Without the need for a central certificate authority or central time-stamping server, which are the typical dependencies of existing e-signature systems, digital signatures stored on a blockchain live independently of the object being signed. This opens to opportunities for parallel signing and independent verification, with or without the object itself. Traditional e-signing solution store digital signatures inside the document. This means that whoever needs to check if a document is signed, will have full read access to all the content in the document.
  • Also, because the document changes with each signature, signing documents in parallel is not possible: everybody needs to sign the document sequentially. By signing documents on a blockchain, the object is not changed by the signature, which also enables you to sign documents in parallel and implement business rules based on mandates, 4-eyes, majority vote, seniority, etc.
  • Lastly, but not less important, you can register multiple actions in a sequence on a blockchain. Each registration is linked to a specific case, document and task performed by the parties involved, creating a chain of transactions: an auditable trail. This audit trail can then be verified by authorized third parties, providing transparency, compliance and, most importantly, trust.


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