When investigating computers for legal cases, it’s absolutely vital that any digital information we find – like emails, photos, or documents – is kept exactly as it was. No changes, big or small, are allowed.
Even the smallest alteration – imagine changing just one letter in an email, a single number in a spreadsheet, or one pixel in an image – can make the entire piece of evidence untrustworthy. This instantly makes people doubt its truthfulness and could mean a judge won’t allow it to be used as proof in a legal case.
That’s why we use something called “hash values.” Think of a hash value as a unique digital identifier, much like a super-specific fingerprint for a file or a piece of data. If you have a document and you calculate its hash value, you get a long, unique code (like e3b0c44298fc1c149afbf4c8996fb92427ae41e4649b934ca495991b7852b855). If even one tiny speck of that document changes – say, you add a comma or a space – the hash value will change completely to a totally different code.
It’s a proven, scientific method, fully accepted in courts, to guarantee that the electronic evidence has not been touched, changed, or damaged since we collected it. By comparing the hash value taken when the evidence was found with a new one taken later, we can scientifically prove that nothing has been altered.
Understanding Hash Codes – The Digital Fingerprint:
What Is A Hash Value?
Think of a hash value as a unique digital fingerprint for any piece of data. Whether you are dealing with a single email, a photo, or an entire hard drive containing terabytes of information, a hash formula creates a corresponding code.
This code is an alphanumeric string (a mix of letters and numbers) that always maintains a fixed length, regardless of how large or small the original file is. Powerful mathematical recipes, known as algorithms (like SHA-256), are used to generate these codes.
Simple Example: Imagine running a massive 10-gigabyte video file through a hash tool. The result might be a short, 64-character code. If you run a tiny 1-kilobyte text document through the same tool, the result is still exactly 64 characters long.
Proof Of No Tampering:
The most critical function of a hash value is its extreme sensitivity. This is what makes it essential for data integrity:
If you change even the smallest detail in the original data, the hash code changes completely and dramatically.
This change is not subtle. If you open a document and change just one single period (.), the resulting hash will look nothing like the original one – it will be entirely unrecognizable. This property is why hashes are the ultimate tool for proving that digital evidence has not been altered or manipulated in any way.
Role In Forensic Investigation:
In legal and forensic settings, hash values are the absolute standard for ensuring evidence integrity in court.
The process follows strict steps:
- Initial Capture: When forensic experts legally seize a piece of digital property (like a computer or phone), they immediately calculate its unique “fingerprint” (the original hash value) before doing anything else.
- Creating The Copy: The investigator then creates a perfect forensic copy, often called a disk image, of the seized device. They immediately calculate the hash value of this copy.
- Verification: The hash of the original device and the hash of the forensic copy must match perfectly. If they do not, the copy is invalid.
- Ongoing Integrity: This verification process is repeated at every stage of the investigation – when the evidence moves from the seizure location to the lab, and again before it is presented to a jury.
By consistently matching the hash codes, investigators can guarantee that the evidence analysed in the lab is an exact, unaltered duplicate of the data originally seized, preventing legal challenges that the evidence was somehow corrupted or changed.
Judicial Recognition:
Courts worldwide have recognized hash values as reliable proof of data integrity:
- India: State of Delhi v. Mohd. Afzal (2003) – Delhi High Court accepted MD5 and SHA-1 hashes for admissibility. This ruling was a crucial step because it established a judicial precedent recognizing that hash values are a valid tool for verifying that electronic records have not been tampered with. This practice has since become standard in Indian digital forensics and legal proceedings.
- United States: US v. Cartier (2007) – A landmark US case that upheld the use of SHA-1 hash values in digital forensic investigations. The court affirmed that hashing is a reliable method for authenticating digital evidence by providing a unique “digital fingerprint”, dismissing the defense’s argument regarding the theoretical risk of a “hash collision.” This ruling solidified the acceptance of cryptographic hashing for proving the integrity of digital evidence in the legal system.
- United Kingdom: R v. Shepherd (1993) – Established the foundational common law principle requiring proof of computer system reliability and the integrity of the output data for admissibility. This set the legal stage for later technological methods, like hash-based verification, which became the standard practice for forensically proving data integrity.
However, nowadays SHA-256 is used which is better than MD5 because it is far more secure and trustworthy. MD5 is an older system that has been “broken,” meaning experts can now easily create two completely different pieces of data (like two different files) that produce the exact same MD5 digital fingerprint, which is called a collision. This makes MD5 unsafe for security and legal evidence because a dishonest person could swap real evidence with a fake file that has the same hash. SHA-256, on the other hand, creates a much longer and more complex digital fingerprint, making it practically impossible to find a collision, guaranteeing that the file’s integrity and authenticity cannot be faked.
Forensic Procedure:
Investigators follow a strict chain of custody:
- Seizure: Devices secured and documented.
- Imaging: Bit-by-bit copies created.
- Hashing: MD5/SHA-256 applied to both original and image.
- Verification: Comparison confirms integrity.
- Courtroom: Reports submitted with hash values for judicial scrutiny.
Tools For Hash Calculation:
Write Blockers:
Write blockers prevent any alteration to original media during acquisition. Commonly used hardware write blockers in India include: Write Blocker (Brand), Tableau T356789iu, WiebeTech USB 3.0 WB and Digital Intelligence UltraBlock. Their cost in the Indian market is approximately Rs 55,000 to Rs 70,000.
FTK Imager – The Trusted Tool For Copying And Fingerprinting Digital Evidence:
FTK Imager is one of the most reliable tools that digital investigators use. Its main job is to create perfect copies of digital evidence and immediately prove those copies haven’t been touched.
Trusted By Courts: FTK Imager uses standard, approved methods (like MD5 and SHA-256) to create a unique digital fingerprint (a hash) for the evidence. Because of this, the reports it generates are widely accepted in courts as proof of evidence integrity.
How Ftk Imager Guarantees Data Is Pure:
Imagine a detective needs to copy a suspect’s hard drive to use as evidence in a fraud case. Here are the simple steps they would follow:
- Start The Program: The detective launches FTK Imager.
- Pick The Evidence: They tell the program what to copy (this is called “Adding an Evidence Item”).
Example: They select the suspect’s computer hard drive. - Make A Perfect Copy (The Image): They choose to “Create a Forensic Image.” They pick a standard copy format (like E01). Crucially, they turn on the option to “Calculate hash values.” This tells the tool to immediately create the digital fingerprint for the original data and the copy.
- Proof Is Automatic: FTK Imager makes the copy and then automatically generates and checks the hash codes.
Example: It gives the hard drive copy a unique code like a1b2c3d4…. The tool then records that code in a summary report. This report is the official document that says: “This copy is exactly the same as the original.” - Check Individual Files: If the investigator later needs to prove that one specific email or document inside that copy is also untouched, they can export a file hash list. This gives them the individual fingerprint for every single file, allowing for easy, one-by-one verification.
The entire process guarantees that the digital evidence presented in court is an exact, untainted, and trustworthy twin of the original.
Hashing – The Unbreakable Digital Fingerprint For Evidence Integrity:
Imagine a special code for every piece of digital information. This code, called a “hash,” is unique, like a fingerprint for data. If even one tiny part of the information changes, the hash code changes completely. This makes hashing incredibly valuable when we need to prove that digital evidence hasn’t been altered.
It’s used in many serious situations to guarantee that digital files, documents, or records are exactly as they were found, with no hidden changes.
Case Applications:
- In Cyber Fraud Cases: Hash values protect against claims of planted or altered evidence. When investigators look into complex financial crimes, they deal with lots of digital paperwork—bank statements, emails, transaction records. They use hashing to create a unique code for each piece of digital evidence the moment they get it. This code acts as unbreakable proof that the evidence is original and hasn’t been tampered with. It stops anyone from claiming that a file was secretly changed or added after the investigation started. It’s like sealing the evidence with a digital stamp that can’t be faked.
- In Terrorism Trials: In very important court cases, such as those involving national security or terrorism, digital experts carefully copy data from devices like computers or phones. Right after copying, they create a hash for the copied data. They then write reports showing these hash codes. This is vital because it tells the judge and jury that the digital information presented in court is an exact, untouched copy of what was originally found. There’s no doubt that the evidence is pure and authentic.
- In Corporate Investigations: If a company needs to investigate an employee’s computer—perhaps for a policy violation or audit—they first make a perfect duplicate of the computer’s hard drive. Immediately after making this copy, they generate a hash code for it. This digital fingerprint proves that the copy is an exact twin of the original. Only then do the HR or legal teams start sifting through the data. This way, everyone knows the information they are examining is a true and unaltered copy, ensuring fairness and accuracy in the investigation.
Conclusion:
Hash values are incredibly important, not just for technical reasons, but also as a core legal part of looking into digital crimes. They use mathematical methods to prove that no one has changed any digital evidence. This makes investigations trustworthy and strong enough to stand up to close examination by judges. When used with special tools, like write blockers (which stop data from being altered) and software such as FTK Imager (which makes perfect copies of data), hash values make sure that digital information is truly original, dependable, and acceptable as evidence in courts all over the world.
