Demystifying the Hash: Is it Possible to Recreate a Document from its Hash on Blockchain?

It is a common and very important question in the world of digital signatures and Blockchain technology: "If my document's hash is part of a public Blockchain, is it possible to decrypt it to recreate my original document?".

The categorical answer is No. The hashing process is a one-way function by design, meaning it is computationally impossible to reverse a hash to obtain the original content of the document. This aspect is, in fact, the cornerstone of security and privacy in systems like Cincel.

What is a Hash function and why is it irreversible?

A cryptographic hash function, such as the SHA256 used by Cincel, is a mathematical algorithm that takes an input (in this case, your digital document of any size) and produces a fixed-length string of characters. This string is known as the "hash" or "cryptographic summary" of the document.

The key characteristics of a good hash function are:

• One-way: It is very easy to generate the hash from the document, but extremely difficult (practically impossible) to do the reverse: derive the original document from its hash.
• Determinism: A document will always produce the same hash.
• Avalanche effect: Even a tiny change in the original document (a letter, a space) will result in a completely different hash.
• Collision resistance: It is practically impossible to find two different documents that produce the same hash.

Think of the hash as a unique and unrepeatable digital fingerprint of your document. You can create the fingerprint from the finger, but you cannot recreate the finger from the fingerprint.

Cincel, the Hash, and your Document Security

At Cincel, we use blockchain technology (and public networks like Bitcoin)for a specific purpose: to prove the existence and integrity of a document at a given time, but not to expose its content.

• Hash Generation: When a document is signed and certified in Cincel, its SHA256 hash is generated. This hash is a mathematical representation of the document, not the document itself.
• Blockchain Notarization: This hash (the document's digital fingerprint) is recorded on a public blockchain, along with a timestamp. This creates an immutable and publicly verifiable record that this exact document existed on that date and time.
• Integrity Verification: If in the future someone attempts to alter the document, the newly generated hash would be different from the hash recorded on the blockchain. This would prove that the document has been modified, invalidating any manipulation attempt.
• Guaranteed Privacy: Your document's original content is never uploaded or stored on the public blockchain. Only the hash, an alphanumeric series with no meaning on its own, is what is recorded. This ensures that the privacy and confidentiality of your information remain intact.

Your information remains secure and confidential

The cryptographic design of hash functions ensures that sensitive information from your documents is not exposed on public blockchains. Blockchain notarization in Cincel reinforces the legal validity and legal certainty of your agreements by demonstrating their inalterability and existence over time, complying with security and legality standards, including NOM151 for conservation certificates.