What is a Hash Function?

In the digital world, a hash function is like the unique fingerprint of any file or data set. It takes an input of any size (a document, an image, a text, etc.) and transforms it into a fixed-length alphanumeric string, known as a hash or cryptographic digest.

This process, called hashing, is fundamental to guarantee the integrity and security of digital information, and is a technological pillar in services like Cincel.

How does a Hash Function work?

Imagine you have a document. A hash function processes every bit of that document and generates a compact "fingerprint." If you change even a single character in the original document, the hash function will generate a completely different fingerprint.

The main characteristics of a good cryptographic hash function, such as the one used by Cincel (for example, SHA256), are:

• One-Way (Unidireccionality): It is computationally impossible to reverse the hash to obtain the original document. It works in only one direction: from the document to the hash.

• Determinism: For the same input document, exactly the same hash will always be generated.

• Collision Resistance: It is extremely difficult (almost impossible) to find two different documents that generate the same hash.

• Avalanche Effect: A minimal change in the original document (such as adding or removing a comma) results in a completely different hash, making any alteration evident.

Why are Hash Functions important in Cincel?

Hash functions are essential for the security and legal validity of the documents you sign in Cincel and are applied as follows:

• Document Integrity Verification: When a document is signed in Cincel, its hash is generated. This hash is recorded in the Audit Trail and is used for notarization with Blockchain. If the original document were modified after signing, its hash would change, immediately demonstrating its alteration. This guarantees that the document that was signed is exactly the one being presented.

• Basis for the NOM-151 Certificate: The document hash is a fundamental component within the Data Message Conservation Certificate (NOM-151). This certificate, issued by an authorized PSC, uses the hash to certify the existence and integrity of the document at a specific date and time (granting it "Certain Date"), complying with Mexican regulations.

• Security and Non-Repudiation: By cryptographically associating the document hash with the user's signature (especially with e.firma), the principle of non-repudiation is reinforced, which means that the signer cannot deny having signed the document.