What is “Digital Hashing”?
Digital hashing is the process of using a secure algorithm to map a set of electronic data into a single, large string of numbers and letters. This string is called the hash value. Since no two electronic files can have the same hash value, it is like a secure signature or fingerprint for that data.
The smallest change in the original data produces a large, random change in the hash value. For example, if just one pixel is changed in a digital image, the new hash value for the data will be dramatically different. This makes it obvious if the data has been modified.
For forensic digital evidence, hashing is considered similar to a Bates Stamp used for paper documents. Not only can the hash value be used to identify the specific data, it also guarantees the authenticity of the original data set.
The FARO® FocusS and FocusM Laser Scanners and the FARO ScanPlan calculate a hash value for the data every time a scan is captured.
The Importance of Hashing for Public Safety Users
It is well known that electronic data can be modified – even laser scan data. When laser scan data is submitted in a court case as evidence, the opposing side may question if it has been tampered with. For example, if there is an objection to the chain of custody record for the scan data, it may be necessary to verify that the submitted scans are identical to the data that was originally collected. This is easy to do if a hash value was calculated when the laser scans were first captured.
In the United States, and many other countries, hashing is the accepted method to validate that the data has not been modified since it was collected. In 2017, the US Federal Rule of Evidence 902 was amended to say “…data copied from electronic devices, storage media, and electronic files are ordinarily authenticated by “hash value.”
In India’s Information Technology Act of 2000, verification of a digital hash is required for ALL electronic data files submitted as evidence in court. Hashing is recognized as the most effective way to prove that laser scans of a forensic scene have not been tampered with.
How Does FARO Apply Digital Hashing?
FARO has a patented process that uses digital hashing to secure data captured with the FARO FocusS and FocusM Laser Scanners and the ScanPlan. The Focus Laser Scanners automatically calculate a hash value for the data every time a scan is captured. There is no way for a user to forget to hash the data. It only takes about one second for each scan to be hashed.
FARO uses the SHA-2 hashing algorithm with a signature width of 256 bit. This algorithm is accepted by the US Federal Rules of Evidence for hashing data submitted as evidence in court.
The FARO Scan Verification Tool is used to calculate the current hash values of a scan project and compare them to the original hash values when the scans were captured. Using this tool, it can be validated at any time that the original, raw scans have not been modified.
FARO Scan Verification Tool
The Scan Verification Tool is a free software application that allows you to verify a scan's authenticity by comparing its current hash value to the value calculated when the data was captured. When scan verification is finished, the tool will display a list of the scans with status icons to the right. If desired, a detailed report is generated that shows the verification status for the selected scans.
The Scan Verification Tool only compares the original, raw scan data. If the scan data is registered and filters applied in SCENE software, the SCENE project would have a different hash value. The revision history maintained by SCENE software can be used to verify modifications made to the project after the scans were first captured.
The Scan Verification Tool can be downloaded from this link: Scan Verification Tool Download and Manual
For more information on using the Scan Verification Tool, refer to these articles: