Understanding the role of hashing in electronic timestamping

Hashing plays a decisive role in safeguarding digital documents. By generating a unique fingerprint for each file, it becomes possible to verify its integrity and to provide reliable evidence of its condition at a specific moment in time. This fingerprint is used in electronic timestamping to link a document to a certified date and time, without ever exposing the original content.
Understanding how hashing works, the algorithms involved, and its benefitsoffers a clearer view of its place in digital proof and regulatory compliance.

This article outlines the principles of hashing, its practical applications, its limitations, and the recommended approaches that help strengthen document security within a timestamping framework.

Sommaire

• Definition of hashing
• How does hashing work?
• The role of hashing in electronic timestamping
• Hashing and data security: the importance of integrity
• The advantages of hashing in electronic timestamping
• Use cases for hashing in timestamping
• Limitations and challenges of hashing in electronic timestamping
• Common mistakes to avoid in hashing and timestamping processes

Key points about hashing

• Hashing generates a unique, irreversible fingerprint that enables the integrity of a document to be verified without disclosing its content.
• Any alteration to the file immediately changes the fingerprint, making attempts at tampering detectable at once.
• Modern algorithms such as SHA-256 are required to produce a dependable proof, whereas MD5 is now considered inadequate and insecure.
• In electronic timestamping, only the fingerprint is timestamped, preserving confidentiality, ensuring traceability, and meeting regulatory requirements such as eIDAS.
• Hashing is widely used across the legal, financial, public and healthcare sectors to certify document integrity and maintain reliable evidence over time.
• Evidency’s qualified timestamping service applies hashing to link a document’s fingerprint to a certified date and time, providing lasting and legally sound proof.

Definition of hashing

What is a hash?

Hashing converts a file, a text or any other piece of data into a fixed-length digital fingerprint, often referred to as a hash value or digest. This process relies on an algorithm that applies the same calculation each time, ensuring that identical content always produces the same fingerprint.

It offers a condensed representation of the data, making verification straightforward without revealing the original document.

If the file is altered, even slightly, the fingerprint changes automatically. Hashing is also non-reversible, meaning that the original data cannot be reconstructed from the hash value. These characteristics are what make hashing so valuable for information security, maintaining document integrity and supporting electronic timestamping.

Main hashing algorithms

SHA-256 is one of the most widely used hashing algorithms today. It is employed in blockchain systems and in qualified timestamping, as it produces a stable digital fingerprint that makes integrity verification straightforward. Its ability to generate a consistent result for identical content makes it well suited to creating long-term digital evidence. Thanks to its reliability, SHA-256 is recommended in environments where traceability and the authenticity of documents must be assured.

MD5 belongs to an older family of algorithms and now presents vulnerabilities that limit the reliability of any evidence derived from it. The French cybersecurity agency ANSSI no longer considers it suitable for applications requiring a high level of security, notably because of the risk of collisions. Its use should therefore be restricted to non-sensitive contexts. In regulated environments, or whenever a document carries legal or contractual implications, it is advisable to select algorithms recognised as secure, such as those in the SHA-2 or SHA-3 families, whose output length is at least 256 bits in line with current recommendations.

How does hashing work?

The principle behind a hash

Hashing operates by compressing a text, a file or any piece of data using a dedicated function that produces a digital fingerprint known as a hash value. This fingerprint keeps the same length whatever the document, offering a condensed representation of the original content.

A hashing function follows a precise and reproducible mathematical process: identical input will always generate the same fingerprint. These values may be stored in a hash table to simplify the organisation or comparison of multiple fingerprints. This approach offers a quick and efficient way to verify a document’s integrity without needing direct access to its content.

Characteristics of hashing

A hash has three fundamental characteristics:

• Uniqueness: in practice, the same data will always generate the same fingerprint, while any alteration to the file produces a different result.
• Non-reversibility: the fingerprint cannot be used to reconstruct the original content, which protects sensitive information.
• Tamper indication: if a recalculated fingerprint differs from the one previously recorded, the document has been altered.

These characteristics are precisely what make hashing a natural component of qualified timestamping.

The role of hashing in electronic timestamping

Electronic timestamping links a document to a certified date and time. To preserve the confidentiality of the file, only its hash fingerprint is sent to the timestamping service, which records it together with a verifiable date and time. If the document is altered at a later stage, its fingerprint will no longer match the one originally timestamped, making it straightforward to confirm whether its integrity has been maintained.

Consider the example of a digital contract signed between two organisations. At the time of signing, a fingerprint is generated and timestamped. Several months later, a simple recalculation of the hash is enough to confirm that the stored file has remained unchanged. This mechanism applies to a broad range of use cases, including contracts, reports, legal archives and regulatory documents.

Hashing and data security: the importance of integrity

Hashing makes it possible to verify that a file has not been altered since its creation or since it was timestamped.

The generated fingerprint becomes a simple and reliable point of comparison: if the recalculated value matches the original one, the document remains intact.

Because even the slightest modification produces a different fingerprint, falsifying a file without detection becomes extremely difficult. This characteristic strengthens trust in digital exchanges and is suited to many areas where documents must remain stable over time, such as contract management, legal records, public archives or the financial reports submitted to supervisory authorities.

The advantages of hashing in electronic timestamping

Efficiency and speed

Hashing enables the integrity of a document to be verified in a matter of moments. Instead of comparing the entire file, one simply compares two digital fingerprints: the one created at the time of timestamping and the one recalculated during verification. As the fingerprint always retains the same size, the comparison remains fast even when documents are large or have been stored for long periods. This approach streamlines routine checks within document platforms and digital archiving systems, while ensuring immediate detection of any alteration.

Reliability and compliance

Hashing supports compliance with regulatory frameworks, including the eIDAS regulation.

The fingerprint generated during timestamping becomes an evidential element that attests to the exact state of the document at the moment it was certified. By relying on this reference, it is possible to verify the continuity of evidence over time, which strengthens the legal validity of documents and enhances the security of contractual processes as well as archive management.

Use cases for hashing in timestamping

When combined with electronic timestamping, hashing provides reliable proof of a document’s integrity, which explains its adoption across sectors where traceability and authentication are required. As a trusted service provider, Evidency support these needs by delivering qualified timestamping that meets both the operational and regulatory expectations of these environments.

Sectors of application

Hashing and timestamping are used in many environments where the traceability and integrity of documents must remain verifiable over time. Several sectors rely on these mechanisms to secure their exchanges and maintain lasting evidence of the state of their files. Among the most common applications are:

• Financial sector: certification of transaction statements, verification of reports submitted to supervisory authorities, and the protection of documents linked to internal compliance.
• Legal field: assurance of integrity for contracts, official records, materials filed within a case, or documents exchanged during legal proceedings.
• Healthcare and social services: traceability of patient records, verification of the integrity of sensitive reports, and secure management of regulated documents.
• Public administration: preservation of regulatory archives, certification of administrative decisions, and secure transmission of documents between departments.
• Businesses and internal audit: monitoring the stability of internal registers, audit reports, documents carrying legal or operational responsibility, or those requiring consistent evidence over time.

A certified digital contract, an archived file or a report submitted to a regulator can therefore be verified at any point, strengthening the reliability of exchanges and supporting informed decision-making. 

Limitations and challenges of hashing in electronic timestamping

Using hashing within electronic timestamping provides a high degree of reliability, but some aspects must be properly managed to ensure the quality of the evidence. Two points require particular attention: the risk of collisions and the choice of algorithm. These factors directly influence the system’s ability to associate a fingerprint with a document in a reliable and enduring manner.

Collision issues

Collisions occur when two different documents generate the same hash value. Although this phenomenon is uncommon, it can undermine the precision of the evidence when the algorithm used is outdated or insufficiently secure. A collision arises when distinct content produces an identical fingerprint; however, modern algorithms are designed to make this occurrence extremely rare. Reducing this risk is vital to ensure that each hash corresponds to one document only.

Algorithm security

The reliability of hashing depends directly on the algorithm selected. Some algorithms meet today’s requirements for electronic timestamping, while others now show clear limitations. Recent algorithms such as SHA-256 provide stronger resistance to attacks, whereas older algorithms such as MD5 have well-known vulnerabilities. To ensure lasting evidence, it is advisable to use an algorithm that is recognised as secure.

Common mistakes to avoid in hashing and timestamping processes

Specific practices can weaken the reliability of a hashing and electronic timestamping system. Identifying these mistakes helps preserve the quality of the evidence and the security of the documents.

• Using an outdated hashing algorithm: Older algorithms such as MD5 have well-known weaknesses and should no longer be used for sensitive documents. More recent functions, such as SHA-256, provide a higher level of security.
• Failing to carry out regular system tests: Without periodic checks, it becomes difficult to detect inconsistencies in the calculation of fingerprints. Regular testing ensures that the process remains reliable over time.
• Overlooking regulatory requirements: Electronic timestamping operates within a framework defined by rules such as eIDAS. Ignoring these requirements can undermine the legal value of the evidence produced.
• Storing the fingerprint in an unsecured environment: Even though the hash does not reveal the document’s content, it must be stored in a protected space to ensure the continuity of the evidence.

The role of hashing in electronic timestamping and digital evidence

Hashing lies at the core of timestamping, as it enables the integrity of a document to be verified and confirms that it has not been altered after its timestamp was issued. With a unique and non-reversible fingerprint, it becomes possible to establish reliable, long-term evidence suited to a wide range of uses, including contracts, archives and regulatory documents.

Evidency’s qualified timestamping service applies hashing beforehand to link a document’s fingerprint to a certified date and time, ensuring the confidentiality of its content and the long-term consistency of the evidence.