Forensic Labs, Mobile Devices

Cost-Effective Tools For Small Mobile Forensic Labs

by Alex Moeller

As the costs associated with running a mobile devices forensic laboratory can be considered to be high, this article is aimed at providing alternative options for small organisations or individuals looking to reduce overheads. 

Case Management Tools

There are numerous case management systems available online which are free to download, and premium features offered by some of the paid software are not worth losing coin over at the small business stage.

These case management systems, however, are a double-edged sword. Although many have built-in data loss mitigation features such as real-time backup, the feature requires a constant internet connection. This can open up your system to possible attacks and manipulation of case information.

Although lacking in features compared to the online programs, Microsoft Excel [1] is a viable option which can be used to design a functional case management system with little skill. The added bonus of services such as Air Tables [2] is that you can download premade templates into Excel, skipping all the messing around with fonts and table making. 

Mobile Forensic Tools

Now, this is the big saver part, and as most of us probably know, any decent software used in digital forensics is expensive. So how do you break up costs?

Building a PC that can handle Cellebrite [3] or XRY [4] will cost you around £500.00 if you’re smart, and while an expensive graphics card is not required, a decent amount of RAM and processing speed is.

Write blockers aren’t required unless you wish to perform SD card extractions. The usage of SD cards by mobile phones has generally decreased as a result of their more substantial internal storage capabilities. If you are required to examine an SD card then NIST [5] provides free validation test reports on multiple software write blockers, thus ensuring the most suitable tool is used for the work. 

SIM card readers themselves don’t cost a lot and can be purchased on Amazon for around £10.00. 

Extraction

Mobile phone extraction software can seem expensive, but it doesn’t have to be. The main difference between the more expensive ones versus the cheaper ones is ease of use. Tools like Cellebrite and XRY are great at combining lots of different mobile extraction methods into a streamlined and efficient solution. The less expensive tools require slightly more training and time spent becoming familiar with the steps involved, but practice makes perfect. Starting with the simple task of being able to extract only images or texts until your requirements outgrow the tool, at which point the more expensive software becomes the more viable tool.

Adb [6]–[8] is an option for Android devices, but you run the risk of breaking the phone if you don’t learn the correct commands.

Autopsy [9] is an option that should be considered as it is capable of extracting text messages (SMS / MMS), call logs, contacts, and GPS data. The downside to these types of software is that they have limited coverage as each device can have a different OS version. The aforementioned software will therefore only work on specific mobile devices.

A document entitled “Open Source Mobile Device Forensics” authored by Heather Mahalik in 2014 provides further options to consider when looking at open source solutions [10].

Analysis

As with the extraction stage, cheaper options are available for the analysis of data. The presentation of extracted data for analysis is crucial as there is a vast amount of data available to an examiner and it needs to be presented in a logical fashion. 

In most mobile phone extractions, however, large amounts of data are recovered, and so subsequently require a more professional touch. This can be achieved by using a software which inputs the raw data extracted from the phone and outputs it in graphical displays. 

Autopsy[11] has a GUI interface which comes with features like Timeline Analysis, Hash Filtering, File System Analysis and Keyword Searching out of the box, and has the ability to add other modules for extended functionality. 

Services like Splunk [12] offer a great way to transform messy looking data sets into clear and understandable models and tables. 

Validation

Validation of tools and methods is a massive, exhaustive process which never seems to end. 

But keep calm and keep validating. 

To ensure reproducibility and repeatability a laboratory must be able to validate results by demonstrating the reliability of the tools used to ascertain those results. For example, if instructed to locate a specific image stored on a mobile device, an examiner should be able to extract an image and confirm the hash checksum. A useful tool to accomplish this task is Jacksum [10], which is free open-source software that calculates a variety of hash checksums and can be incorporated into Microsoft Windows and accessed by simply right-clicking on a file. Another great tool for image analysis is Image Magick [11], which is also free and can provide detailed analysis of specific aspects of an image.

Validation needs to be tackled in an efficient manner with an appropriate strategy that meets your end-user requirements. Mobile phone validation can seem like a daunting task at first, but breaking it down into smaller parts will make it easier. First validating the fundamental features which exist on every make and model of phone such as contacts, SMS messages and call logs can set you on the right path, and the scope can be increased later on.

Validating every phone you encounter would be ridiculous. It would literally never end as new models are hitting the market quicker than we are able to validate. Instead, initially focus on a specific type of phone, or do a Google search for the most commonly purchased phones and pick a nice selection which represents a sample of the market. Commonly used phones can be expensive, so look for second-hand ones and perform a factory reset. Before conducting any tests perform an extraction of the phone and make note of any remaining data so it can be ignored in tests.

Buying new phones should be avoided not only to reduce costs, but also because second-hand devices have the advantage of being more closely aligned with the types of devices used in casework.

Documents published by NIST [13], [14] provide validation results [15] for you to set acceptable pass criteria for your own testing. The FSR [16] has also published guidance regarding validation, as has the Scientific Working Group on Digital Forensics [16] [17]. Combining these documents can help provide a solid overview when creating validation plans.

Digital Storage

Digital storage goes hand in hand with a good case management system. It’s crucial that exhibits for a specific case are kept as one and are not lost, and this can be achieved by keeping your case management system in sync with exhibit logs. Exhibit logs should state where an exhibit is being kept and if it has been returned to the instructing party.

The security of physical exhibits is as vital as the safety of any digital exhibits and should be made a priority. Depending on your work environment you will need a safe, stored within an area of restricted access. Ensuring only workstations with no internet capabilities have access to case data, and using only encrypted USB flash drives, will ensure safety from most outside dangers. 

A NAS system can be of great use but can cost a lot, so again, either look for cheaper alternatives like simply swapping out hard drives, or browse eBay until the right one comes up for a reasonable price. 

If that’s too expensive you can build your own, but consider that whatever route you take will require validation testing. Security is yet another key aspect to consider when using a NAS, as you can never be too careful in digital forensics. Most extracted data have the potential to contain viruses or malware which could compromise confidential files. The best way to ensure the safety of these files is to keep the NAS separated from the internet completely, but if you do need to connect to the NAS remotely an article by How-to Geek describes the necessary steps to keep it safe [19].

Report Writing

Reporting the results of a case needs to be completed with no grammatical errors and should be accessible to the reader. One way of ensuring this is by using software that picks up any grammatical errors found in reports, thus preventing any misunderstandings. Software like Grammarly [20] is free to use and offers a premium option for more advanced grammatical errors that perhaps Microsoft Word might not pick up. However, this and similar software require an internet connection to function, leaving you again open to any online attacks. With that being said, a few ways around this are available.

The first option would be to set up a low specification workstation for running internet searches and to operate Word with Grammarly installed. The finished report can then be put onto an encrypted memory stick, thus minimising the risk.

A safer option would be to make some tweaks to the spellcheck available within Word [21] and create your own dictionary of keywords and phrases you wish Word not to pick up on.

Peer Review

Peer reviewing of each other’s work is obviously a free thing to do if you work with someone else with a similar skill set, but if you work alone then you must make some friends who work in your area of expertise. Peer review is essential in ensuring reliability and error mitigation and is advised to ensure compliance with the FSR Codes of Practice [22].

When peer reviewing work, don’t waste time and money (and trees) printing out forms. Try using the comment feature in Word for areas that need addressing. This could also be a good way of recording improvement actions to show how your company finds errors and makes improvements. 

Delivery

Sending confidential documents online can be a risky game, so procedures should be put in place to mitigate against said risks. Tresorit [23] and Sophos [24] provide end-to-end encrypted file-sharing services and each offer free trials which should be taken full advantage of before making a decision on which to commit.

Transporting important case data via an external device requires security while in transit. This can be achieved by using strong encryption with software such as VeraCrypt [25], a free tool for encrypting hard drives and USB flash drives. 

Conclusion

It’s currently a difficult time for smaller laboratories to compete against larger ones, due to the stress of ISO 17025 accreditation looming over us all every second of our already stressful day-to-day lives. The chance to cut costs should be seized at every opportunity, to save money for those accreditation visits and rainy days. Not everything has to be state-of-the-art, cutting-edge tech. If you learn the necessary skills and are prepared to accept fewer flashy features, then try some of these alternative methods instead of forking out cash at every turn. I want my final words in this article to be positive and push for more cooperation between smaller digital forensic laboratories, as I believe that this will not only benefit everyone in setting a higher standard, but will also significantly improve our justice system. 

References

[1] Microsoft, ‘Microsoft Excel’. [Online]. Available: https://products.office.com/en-gb/excel. [Accessed: 13-Aug-2019].

[2] Air Tables, ‘Air Tables’. [Online]. Available: https://airtable.com/templates. [Accessed: 13-Aug-2019].

[3] Cellebrite, ‘Cellebrite’. [Online]. Available: https://www.cellebrite.com/en/home/. [Accessed: 15-Aug-2019].

[4] MSAB, ‘MSAB’. [Online]. Available: https://www.msab.com/. [Accessed: 15-Aug-2019].

[5] NIST, ‘DHS Reports — Test Results Software Write Block’. [Online]. Available: https://www.nist.gov/itl/ssd/software-quality-group/computer-forensics-tool-testing-program-cftt/cftt-technical/software. [Accessed: 17-Oct-2019].

[6] Android, ‘Android Debug Bridge (adb)’. [Online]. Available: https://developer.android.com/studio/command-line/adb#copyfiles. [Accessed: 15-Aug-2019].

[7] Chris Hoffman, ‘How to Install and Use ADB, the Android Debug Bridge Utility’. [Online]. Available: https://www.howtogeek.com/125769/how-to-install-and-use-abd-the-android-debug-bridge-utility/. [Accessed: 16-Aug-2019].

[8] Doug Lynch, ‘How to Install ADB on Windows, macOS, and Linux’. .

[9] Autopsy, ‘Autopsy’. [Online]. Available: https://www.autopsy.com/. [Accessed: 15-Aug-2019].

[10] Heather Mahalik, ‘Open Source Mobile Device Forensics’, 2014.

[11] Autopsy, ‘Sleuth Kit’. [Online]. Available: https://www.sleuthkit.org/autopsy/. [Accessed: 29-Sep-2019].

[12] Michael Baum, Rob Das, Erik Swan, ‘Splunk’. [Online]. Available: https://www.splunk.com/. [Accessed: 18-Aug-2019].

[13] NIST, ‘NIST (CFTT)’. [Online]. Available: https://www.nist.gov/itl/ssd/software-quality-group/computer-forensics-tool-testing-program-cftt/cftt-technical/mobile. [Accessed: 20-Sep-2019].

[14] NIST, ‘Mobile Device Data Population Setup Guide’. [Online]. Available: https://www.nist.gov/sites/default/files/documents/2017/05/09/mobile_device_data_population_setup_guide.pdf. [Accessed: 15-Sep-2019].

[15] NIST, ‘Test Results for Mobile Device Acquisition Tool Cellebrite’.

[16] FSR, ‘Validation Guidance’. FSR, 2014.

[17] SWGDE, ‘SWGDE Minimum Requirements for Testing Tools used in Digital and Multimedia Forensics’. 2018.

[18] SWGDE, ‘SWGDE Recommended Guidelines for Validation Testing’. 2014.

[19] Craig Lloyd, ‘6 Things You Should Do to Secure Your NAS’. [Online]. Available: https://www.howtogeek.com/350919/6-things-you-should-do-to-secure-your-nas/. [Accessed: 17-Aug-2019].

[20] Grammarly, ‘Grammarly’. [Online]. Available: https://www.grammarly.com. [Accessed: 17-Aug-2019].

[21] Microsoft, ‘Word’. [Online]. Available: https://products.office.com/en-us/word. [Accessed: 13-Aug-2019].

[22] FSR, ‘FSR Codes of Practice and Conduct’. 2017.

[23] Tresorit, ‘Tresorit’. [Online]. Available: https://tresorit.com/. [Accessed: 19-Sep-2019].

[24] Sophos, ‘Sophos’. [Online]. Available: https://www.sophos.com/en-us.aspx. [Accessed: 19-Sep-2019].

[25] Veracrypt, ‘Veracrypt’. [Online]. Available: https://archive.codeplex.com/?p=veracrypt. [Accessed: 05-Sep-2019].

About the Author

Alex Moeller is a Mobile Phone Forensics Examiner at Verden Forensics in Birmingham, UK, and has experience in conducting examinations in a variety of cases, both criminal and civil. He holds a degree in Forensic Computing from Birmingham City University and is currently preparing the laboratory for ISO 17025 accreditation in Mobile Device Forensics. 

About Scar de Courcier

Scar de Courcier is Senior Editor at Forensic Focus.

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