Why Hash Values Are Crucial in Digital Evidence Authentication

Before hashing or hash values became common in legal settings, proving the authenticity of digital evidence could be tricky — especially if opposing counsel was determined to exclude the evidence.

It was often contested that screenshot evidence, for example, could have been manipulated with basic photo editing tools. Without authentication like hash value verification, legal teams had to spend significant time and resources providing a sponsoring witness who could testify to the authenticity of digital evidence.

That's just one reason why hash values are crucial in digital evidence authentication. In this article, we’ll dig into what a hash value is, their role in digital forensics, and how you can authenticate your digital evidence with hash verification.

Key Takeaways

• A hash value is a unique string of numbers and letters generated from a digital file that acts as its digital fingerprint. If even a single pixel on a file changes, the hash value will change, demonstrating it has been altered.
  
• Hash values help authenticate digital evidence by showing whether a file has been altered since its hash was generated.
  
• Hashing algorithms vary in security and purpose. Common examples include MD5, SHA-1, CRC32, SHA-2, and SHA-256, with SHA-256 offering stronger security for modern applications.
  
• Hash values can be generated with hashing tools that apply a selected algorithm to a digital file and produce a value that can later be used to verify the file’s integrity.

What Is a Hash Value ?

A hash value is a fixed-length string of numbers and letters generated by a mathematical algorithm from a digital file or other data. It acts like a digital fingerprint: if the underlying data changes, even slightly, the resulting hash value will also change.

In digital forensics, hash values are used to verify that digital evidence has remained unchanged since it was collected. Matching hash values can demonstrate that two copies of a file are identical and help establish the integrity and authenticity of digital evidence.

What Is a Hash Value or Hash Function in Digital Forensics?

A hash function is a mathematical algorithm that converts digital data into a fixed-length hash value. The same input produces the same hash value, while even a small change to the input produces a different result.

The Cybersecurity and Infrastructure Security Agency (CISA) defines hash value(s) or hash function(s) as:

A fixed-length string of numbers and letters generated from a mathematical algorithm and an arbitrarily sized file such as an email, document, picture, or other type of data. 

This generated string is unique to the file being hashed and is a one-way function—a computed hash cannot be reversed to find other files that may generate the same hash value.

In simple terms, a hash value or hash function is a specific number string that is associated with one particular file, created through a hashing algorithm.

If the file is altered in any way, the hashing algorithm will produce a different number string.

It’s impossible to change the file without changing the associated hash value as well. So if you have two copies of a file, and they both have the same hash value, you can be certain that they are identical.

The Federal Rules of Evidence Amendments for Digital Evidence Authentication

Thanks to the Federal Rules of Evidence Amendments 902(13) and (14), witness testimony to the authenticity of digital evidence has been replaced by certification.

To streamline evidence submission and authentication, electronically stored information (ESI), like social media posts and comments, cellphone images, text messages, and website content can now be submitted as machine-generated authenticated evidence.

Hash values are often used to certify this data, illustrating what a hash value is in digital forensics.

To understand what this means in a practical sense, let’s take a closer look at the amendments themselves:

FRE 902(13): Certified Records Generated by an Electronic Process or System

 A record generated by an electronic process or system that produces an accurate result, as shown by a certification of a qualified person that complies with the certification requirements of Rule 902(11) or (12). The proponent must also meet the notice requirements of Rule 902(11). 

This rule allows for the certification of records by a qualified person who can verify the accuracy of the process or system that generated the records, eliminating the need for in-court testimony to establish authenticity.

FRE 902(14): Certified Data Copied from an Electronic Device, Storage Medium, or File

Data copied from an electronic device, storage medium, or file, if authenticated by a process of digital identification, as shown by a certification of a qualified person that complies with the certification requirements of Rule (902(11) or (12). The proponent also must meet the notice requirements of Rule 902 (11).

Amendment 902(14) allows for data copies to be authenticated through a process of digital identification—typically using hash values, which demonstrate the hash value meaning and show what a hash value is in digital forensics. Like 902(13), this rule requires a certification by a qualified person who can attest to the integrity of the process used to copy the data.

What The Federal Rules of Evidence Amendments Say About Hash Values for Evidence Authentication

While the amendments themselves don’t mention any specific ‘electronic process or system that produces an accurate result,’ references to hash values are made in accompanying comments provided by the Standing Committee on Federal Rules in the 2017 Amendment:

Today, data copied from electronic devices, storage media, and electronic files are ordinarily authenticated by "hash value."

A hash value is a number that is often represented as a sequence of characters and is produced by an algorithm based upon the digital contents of a drive, medium, or file.

If the hash values for the original and copy are different, then the copy is not identical to the original. If the hash values for the original and copy are the same, it is highly improbable that the original and copy are not identical.

Thus, identical hash values for the original and copy reliably attest to the fact that they are exact duplicates.

The Importance of Hash Values in Digital Forensics

The hash value meaning is fundamental to digital forensics, providing a reliable, efficient, and secure method for verifying the integrity and authenticity of digital evidence. By incorporating hash values into their investigative processes, forensic experts can ensure that digital evidence is trustworthy and defensible in court.

Here are four fundamental ways hash values ensure the authenticity, integrity, and reliability of digital evidence:

1. Ensuring Data Integrity

As we’ve discussed, one of the primary functions of hashing in digital forensics is to verify the integrity of data. According to the Federal Rules of Evidence (FRE) amendments 902(13) and 902(14), digitally stored information can be submitted as authenticated evidence without the need for witness testimony, provided it has been properly hashed and certified.

2. Authenticating Evidence

When digital evidence is collected, a hash value is generated from the original data using a hashing function like SHA-256. This hash value acts as a unique digital fingerprint for that specific piece of evidence.

Now, at any point in the investigation, the collected evidence can be hashed again and compared to the original hash value.

If the hashes match, the data has remained unchanged. Any discrepancy between the hash values indicates tampering or corruption, alerting forensic analysts to potential issues with the evidence. In court, the hash value can be used to demonstrate that the evidence has not been altered since its collection.

3. Preventing and Detecting Tampering

Digital evidence is vulnerable to tampering, either intentionally or unintentionally. Hash values provide a robust mechanism for detecting any changes to the evidence.

Even the smallest alteration to a file will result in a completely different hash value. Forensic tools that generate and compare hash values can quickly detect such changes, ensuring the immutability of the evidence. This feature is particularly useful for identifying unauthorized access or malicious modifications.

4. Facilitating Evidence Comparison

In cases involving multiple copies of digital evidence, hash values simplify the process of comparing these copies to ensure they are identical.

Rather than manually examining the contents of each file, forensic analysts can compare the hash values of the original and duplicate files. Matching hash values confirm that the copies are identical, streamlining the verification process and reducing the risk of human error.

How Do Hash Values Authenticate Digital Evidence?

Digital evidence authentication is the process of establishing that digital evidence is what it claims to be.

Hash values authenticate digital evidence by verifying that the evidence has not changed since it was collected. When evidence is collected through purpose-built evidence collection tools, a hash value is generated and recorded.

The file can later be hashed again and the resulting hash value can be compared to the original. Matching hashes indicate the evidence is unchanged, while different hashes indicate it has been altered or corrupted.

A hash value guarantees authenticity thanks to five particular characteristics:

1. Hash values are deterministic.

A specific input (or file) will always deliver the same hash value (number string). This means that it is easy to verify the authenticity of a file. If two people independently (and correctly) check the hash value of a file, they will always get the same answer.

2. The odds of “collisions” are low. 

If you’re using hashing algorithms like SHA-265 chances of two different inputs (files) coincidentally having the exact same hash value are incredibly small—practically non-existent.

3. A hash can be calculated quickly. 

Generating a hash value is quick and easy (provided you have the right tool). The size of the file in question is also irrelevant—generating a hash value for a large file is as simple as creating one for a small file.

4. Any change to the input will change the output. 

Even the smallest change to the input file will result in a change to the resulting hash value. This means that it is impossible to alter a file without changing the associated hash value, which makes it very easy to prove (or disprove) the authenticity of a piece of digital evidence.

5. It’s secure. 

Because of what is called ‘pre-image resistance’ hash values should be computationally infeasible to reverse, meaning you cannot derive the original input given only the hash output.

The video below from the Computerphile YouTube channel offers a great explanation of how hashing and hash values are used in the realm of digital signatures and data authentication.

What are the Main Differences Between Popular Hashing Algorithms MD5, SHA-1, CRC32, SHA-2, and SHA-256?

Not all hashing algorithms are created equal. Though we’ll save you the in-depth technical details, it’s valuable to have a basic understanding of which algorithms are useful for digital forensics and which hashing algorithms are obsolete.

MD5 (Message-Digest Algorithm 5)

• Developed in 1991 by Ronald Rivest.
• Was used primarily for data security and encryption, but because of its vulnerability to security breaches, the primary use today is authentication.
• Due to susceptibility to collision attacks, MD5 is not suitable for cryptographic security in new systems.

SHA-1 (Secure Hash Algorithm 1)

• Developed in 1993 by the National Security Agency (NSA).
• Formerly a staple in security applications like SSL certificates, officially retired in 2022 in favor of more secure options.
• Vulnerable to collision attacks, making it inadequate for modern cryptographic requirements.

CRC32 (Cyclic Redundancy Check)

• Primarily used to detect accidental changes to raw data in digital networks and storage devices. It’s common in file compression, file verification, and in applications where fast and simple error-detection is needed.
• NOT suitable for cryptographic security because it is not designed to withstand malicious alterations.

SHA-2 (Secure Hash Algorithm 2)

• Set of hash functions developed in 2001 by the NSA.
• Variants include SHA-224, SHA-256, SHA-384, SHA-512, SHA-512/224, SHA-512/256.
• Recommended for current cryptographic applications, including compliance with security standards.
• Highly secure against known cryptographic attacks.

SHA-256 (Part of SHA-2 family)

• Key in blockchain technologies and digital signatures, underscoring its robustness and reliability.
• Inherits SHA-2’s strong security features, providing solid protection against cryptographic threats.
• Provides stronger security than legacy algorithms such as MD5 and SHA-1 and is commonly used for modern data integrity and authentication purposes

SHA-3 (Secure Hash Algorithm 3)

• Standardized by NIST in 2015 as an alternative to the SHA-2 family
  
• Uses a different cryptographic design than SHA-2 and includes SHA3-224, SHA3-256, SHA3-384, and SHA3-512
  
• Considered secure for modern cryptographic applications and provides an alternative to SHA-2 algorithms such as SHA-256

Here is a comparison table showing each algorithm, what makes it unique, and any security features/issues.

Why Is SHA-256 Preferred Today?

 SHA-256 remains a strong choice for modern hashing applications because it provides significantly greater collision resistance than legacy algorithms such as MD5 and SHA-1.

NIST continues to recognize SHA-256 and other SHA-2 and SHA-3 algorithms for secure hashing applications, while SHA-1 is being phased out. 

How To Use Free Online Tools to Generate or Verify a Hash Value for a Digital File

To generate a hash that’s associated with a particular file is fairly easy, and can be done with an online tool in a few simple steps: 

1. Visit https://www.toolsley.com/hash.html
2. Upload the file that you want to generate a hash value for
3. Select the hashing algorithms you want to use (we recommend SHA-256)
4. The hash value will automatically appear next to your selected algorithms.
5. To verify the hash, you can click on the green link icon next to the hash value. A window will pop up with a web address you can copy. 
   

   

6. Paste the web address into a new tab in your browser.
7. If you upload the same file as you generated the hash value for, you’ll get a green bar that says, “VALID”.
8. If you edit your original file in any way (change one letter even) and try to validate it, the bar will be red and say, “INVALID”.

DISCLAIMER: Risks with Using Free Online Tools to Generate Hash Values for Authenticating Evidence

As we’ve discussed, hash values act as a digital signature or fingerprint that can authenticate digital evidence. Understanding the hash value meaning is crucial when using these tools.

However, if the original was tampered with before assigning a hash value, the hash value would still generate – it would not be able to flag that the evidence was already tampered with. 

That is why it is crucial to make sure evidence is, “generated by an electronic process or system that produces an accurate result, as shown by a certification of a qualified person” as is required in FRE 902 (13) & (14). The process used to generate or copy the data must be certified by a qualified person who can attest to the integrity of the process. 

So, as long as a piece of evidence was correctly collected and processed, anyone using the same algorithm to authenticate it at a later stage will see that exact same resulting hash value. 

Any change to the data will result in the hash value changing — making the evidence easy to authenticate. 

However, if hashing is not done correctly, opposing counsel will quickly question the authenticity. 

This means collecting and attempting to authenticate evidence yourself using free hashing tools, as we’ve shown you above, may be risky. 

And if you’re trying to process many pieces of digital evidence and relying on copy-paste to keep track of which hash value is associated with which document, it would be easy to miss errors or lose track. 

The bottom line: If you’re submitting this evidence in court, you’ll want to make use of only the most reliable hashing methods and tools.

This is where purpose-built digital evidence collection tools can help. By capturing online evidence and generating supporting authentication information as part of the collection process, legal teams can reduce the risks associated with manually collecting evidence.

How to Generate Defensible Self-Authenticating Digital Evidence with Hash Values

If you want to generate defensible self-authenticating digital evidence, there’s quite a lot to consider. We’ve created a free reference guide that summarizes hundreds of pages of documentation, explaining how you can generate self-authenticating evidence that will stand up in court.

You can download this free paper by clicking on the button below.

How Pagefreezer Can Help You Generate Defensible Digital Evidence with Hash Values

 Through our work helping legal teams and investigators collect online evidence, we know that defensibility depends on more than simply generating a hash value. The collection process must also preserve the content and associated metadata in a way that allows its integrity to be verified later.

If you want to generate hash values for evidence you’re collecting online from websites, social media platforms, team collaboration platforms like MS Teams or Slack, we can help. 

Not only can we help you authenticate digital evidence with the highest standard of hashing algorithms, SHA-256, our software also allows you to simplify the process of collecting ESI from online data sources. You’ll be able to:

• Capture dynamic online media like YouTube and Instagram videos 
• Automate website, social media, and other evidence collection
• Capture all associated metadata revealing key information
• Easily search and organize collected evidence
• Export in a variety of formats, complete with hash values, digital signatures, and metadata

If you’d like to learn more about our digital evidence collection services, watch the video below or visit our evidence collection page here.  

Building Confidence in Digital Evidence

As digital evidence becomes more central to investigations and litigation, it is critical that you be able to demonstrate that the evidence you collected has not been tampered with.

That confidence starts with a defensible collection process. Hash values provide an important layer of verification, but they’re most effective when combined with reliable capture methods, preserved metadata, and clear documentation.

Webpreserver helps legal teams collect online evidence in a way that preserves this critical information from the start.

Explore our WebPreserver digital evidence collection solution to see how you can build a more defensible evidence workflow.