Question

You need to establish a procedure for your organization on how to validate a new forensics software package. Write two to three pages outlining the procedure you plan to use in your lab. Be sure to cite references, such as the ISO standard or NIST, to support your procedure.

Answer 1

Setting the Standard: Standards and Legal Baselines for Software/Tool Validation
According to the National Institute of Standards and Technology (NIST), test results must be repeatable and reproducible to be considered admissible as electronic evidence. Digital forensics test results are repeatable when the same results are obtained using the same methods in the same testing environment. Digital forensics test results are reproducible when the same test results are obtained using the same method in a different testing environment (different mobile phone, hard drive, and so on). NIST specifically defines these terms as follows:

Repeatability refers to obtaining the same results when using the same method on identical test items in the same laboratory by the same operator using the same equipment within short intervals of time.

Reproducibility refers to obtaining the same results being obtained when using the same method on identical test items in different laboratories with different operators utilizing different equipment.

1) Develop the Plan
Developing the scope of the plan may involve background and defining what the software or tool should do in a detailed fashion. Developing the scope of the plan also involves creating a protocol for testing by outlining the steps, tools, and requirements of such tools to be used during the test. This may include evaluation of multiple test scenarios for the same software or tool. To illustrate, if validating a particular forensic software imaging tool, that tool could be tested to determine whether or not it successfully creates, hashes, and verifies a particular baseline image that has been previously setup. There are several publically available resources and guides that can be useful in establishing what a tool should do such as those available from NIST’s Computer Forensic Tool Testing Project (CFTT) available from http://www.cftt.nist.gov. The CFTT also publishes detailed validation reports on various types of forensic hardware and software ranging from mobile phones to disk imaging tools. In addition to CFTT, Marshall University has published various software and tool validation reports that are publically available for download from http://forensics.marshall.edu/Digital/Digital-Publications.html. These detailed reports can be used to get a feel for how your own internal protocol should be drafted. The scope of the plan may also include items such as: tool version, testing manufacturer, and how often the tests will be done. These factors should be established based on your organization standards. Typically, technology within a lab setting is re-validated quarterly or biannually at the very least.

2) Develop a Controlled Data Set
This area may be the longest and most difficult part of the validation process as it is the most involved. This is because it involves setting-up specific devices and baseline images and then adding data to the specific areas of the media or device. Acquisitions would then need to be performed and documented after each addition to validate the primary baseline. This baseline may include a dummy mobile phone, USB thumb drive, or hard drive depending on the software or hardware tool you are testing.

3) Conduct the Tests in a Controlled Environment
Outside all the recommendations and standards set forth by NIST and the legal community, it only makes sense that a digital forensics examiner would perform an internal validation of the software and tools being used in the laboratory. In some cases these validations are arbitrary and can occur either in a controlled or uncontrolled environment. Since examiners are continuously bearing enormous caseloads and work responsibilities, consistent and proper validations sometimes fall through the cracks and are validated in a somewhat uncontrolled “on-the-fly” manner. It’s also a common practice in digital forensics for examiners to “borrow” validations from other laboratories and fail to validate their own software and tools. Be very careful with letting this happen. Keep in mind that in order for digital forensics to be practicing true scientific principles, the processes used must be proven to be repeatable and reproducible. In order for this to occur, the validation should occur within a controlled environment within your laboratory with the tools that you will be using. If the examiner uses a process, software, or even a tool that is haphazard or too varied from one examination to the next, the science then becomes more of an arbitrary art. Simply put, validations not only protect the integrity of the evidence, they may also protect your credibility. As stated previously, using a repeatable, consistent, scientific method in drafting these validations is always recommended.

4) Validate the Test Results against Known and Expected Results
At this point, testing is conducted against the requirements set forth for the software or tool in the previous steps. Keep in mind that results generated through the experimentation and validation stage must be repeatable. Validation should go beyond a simple surface scan when it comes to the use of those technologies in a scientific process. With that said, it is recommended that each requirement be tested at least three times. If there are any variables that may affect the outcome of the validation (e.g. failure to write-block, software bugs) they should be determined after three test runs. There may be cases, however, where more or fewer test runs may be required to generate valid results.

It’s also important to realize that you are probably not the first to use and validate a particular software or tool, so chances are that if you are experiencing inconsistent results, the community may be experiencing the same results as well. Utilizing peer review may be a valuable asset when performing these validations. Organizations such as the High Technology Crime Investigation Association (HTCIA) and the International Association of Computer Investigative Specialists (IACIS) maintain active member e-mail lists for members that can be leveraged for peer review. There are also various lists and message boards pertaining to mobile phone forensics that can be quite helpful when validating a new mobile technology. In addition, most forensic software vendors maintain message boards for software, which can be used to research bugs or inconsistencies arising during validation testing.

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