In this article by Heather Mahalik and Rohit Tamma, authors of the book Practical Mobile Forensics, Second Edition, we will cover the following topics:
- Introduction to mobile forensics
- Challenges in mobile forensics
(For more resources related to this topic, see here.)
Why do we need mobile forensics?
In 2015, there were more than 7 billion mobile cellular subscriptions worldwide, up from less than 1 billion in 2000, says International Telecommunication Union (ITU). The world is witnessing technology and user migration from desktops to mobile phones. The following figure sourced from statista.com shows the actual and estimated growth of smartphones from the year 2009 to 2018.
Growth of smartphones from 2009 to 2018 in million units
Gartner Inc. reports that global mobile data traffic reached 52 million terabytes (TB) in 2015, an increase of 59 percent from 2014, and the rapid growth is set to continue through 2018, when mobile data levels are estimated to reach 173 million TB. Smartphones of today, such as the Apple iPhone, Samsung Galaxy series, and BlackBerry phones, are compact forms of computers with high performance, huge storage, and enhanced functionalities. Mobile phones are the most personal electronic device that a user accesses. They are used to perform simple communication tasks, such as calling and texting, while still providing support for Internet browsing, e-mail, taking photos and videos, creating and storing documents, identifying locations with GPS services, and managing business tasks. As new features and applications are incorporated into mobile phones, the amount of information stored on the devices is continuously growing. Mobiles phones become portable data carriers, and they keep track of all your moves. With the increasing prevalence of mobile phones in peoples' daily lives and in crime, data acquired from phones become an invaluable source of evidence for investigations relating to criminal, civil, and even high-profile cases. It is rare to conduct a digital forensic investigation that does not include a phone. Mobile device call logs and GPS data were used to help solve the attempted bombing in Times Square, New York, in 2010. The details of the case can be found at http://www.forensicon.com/forensics-blotter/cell-phone-email-forensics-i....
The science behind recovering digital evidence from mobile phones is called mobile forensics. Digital evidence is defined as information and data that is stored on, received, or transmitted by an electronic device that is used for investigations. Digital evidence encompasses any and all digital data that can be used as evidence in a case.
Digital forensics is a branch of forensic science focusing on the recovery and investigation of raw data residing in electronic or digital devices. The goal of the process is to extract and recover any information from a digital device without altering the data present on the device. Over the years, digital forensics grew along with the rapid growth of computers and various other digital devices. There are various branches of digital forensics based on the type of digital device involved such as computer forensics, network forensics, mobile forensics, and so on.
Mobile forensics is a branch of digital forensics related to the recovery of digital evidence from mobile devices. Forensically sound is a term used extensively in the digital forensics community to qualify and justify the use of particular forensic technology or methodology. The main principle for a sound forensic examination of digital evidence is that the original evidence must not be modified. This is extremely difficult with mobile devices. Some forensic tools require a communication vector with the mobile device, thus a standard write protection will not work during forensic acquisition. Other forensic acquisition methods may involve removing a chip or installing a bootloader on the mobile device prior to extract data for forensic examination. In cases where the examination or data acquisition is not possible without changing the configuration of the device, the procedure and the changes must be tested, validated, and documented. Following proper methodology and guidelines is crucial in examining mobile devices as it yields the most valuable data. As with any evidence gathering, not following the proper procedure during the examination can result in loss or damage of evidence or render it inadmissible in court.
The mobile forensics process is broken into three main categories: seizure, acquisition, and examination/analysis. Forensic examiners face some challenges while seizing the mobile device as a source of evidence. At the crime scene, if the mobile device is found switched off, the examiner should place the device in a faraday bag to prevent changes should the device automatically power on. As shown in the following figure, Faraday bags are specifically designed to isolate the phone from the network.
A Faraday bag (Image courtesy: http://www.amazon.com/Black-Hole-Faraday-Bag-Isolation/dp/B0091WILY0)
If the phone is found switched on, switching it off has a lot of concerns attached to it. If the phone is locked by a PIN or password or encrypted, the examiner will be required to bypass the lock or determine the PIN to access the device. Mobile phones are networked devices and can send and receive data through different sources, such as telecommunication systems, Wi-Fi access points, and Bluetooth. So, if the phone is in a running state, a criminal can securely erase the data stored on the phone by executing a remote wipe command. When a phone is switched on, it should be placed in a faraday bag. If possible, prior to placing the mobile device in the faraday bag, disconnect it from the network to protect the evidence by enabling the flight mode and disabling all network connections (Wi-Fi, GPS, Hotspots, and so on). This will also preserve the battery, which will drain while in a faraday bag and protect against leaks in the faraday bag. Once the mobile device is seized properly, the examiner may need several forensic tools to acquire and analyze the data stored on the phone.
Mobile phones are dynamic systems that present a lot of challenges to the examiner in extracting and analyzing digital evidence. The rapid increase in the number of different kinds of mobile phones from different manufacturers makes it difficult to develop a single process or tool to examine all types of devices. Mobile phones are continuously evolving as existing technologies progress and new technologies are introduced. Furthermore, each mobile is designed with a variety of embedded operating systems. Hence, special knowledge and skills are required from forensic experts to acquire and analyze the devices.
Challenges in mobile forensics
One of the biggest forensic challenges when it comes to the mobile platform is the fact that data can be accessed, stored, and synchronized across multiple devices. As the data is volatile and can be quickly transformed or deleted remotely, more effort is required for the preservation of this data. Mobile forensics is different from computer forensics and presents unique challenges to forensic examiners.
Law enforcement and forensic examiners often struggle to obtain digital evidence from mobile devices. The following are some of the reasons:
- Hardware differences: The market is flooded with different models of mobile phones from different manufacturers. Forensic examiners may come across different types of mobile models, which differ in size, hardware, features, and operating system. Also, with a short product development cycle, new models emerge very frequently. As the mobile landscape is changing each passing day, it is critical for the examiner to adapt to all the challenges and remain updated on mobile device forensic techniques across various devices.
- Mobile operating systems: Unlike personal computers where Windows has dominated the market for years, mobile devices widely use more operating systems, including Apple's iOS, Google's Android, RIM's BlackBerry OS, Microsoft's Windows Mobile, HP's webOS, Nokia's Symbian OS, and many others. Even within these operating systems, there are several versions which make the task of forensic investigator even more difficult.
- Mobile platform security features: Modern mobile platforms contain built-in security features to protect user data and privacy. These features act as a hurdle during the forensic acquisition and examination. For example, modern mobile devices come with default encryption mechanisms from the hardware layer to the software layer. The examiner might need to break through these encryption mechanisms to extract data from the devices.
- Lack of resources: As mentioned earlier, with the growing number of mobile phones, the tools required by a forensic examiner would also increase. Forensic acquisition accessories, such as USB cables, batteries, and chargers for different mobile phones, have to be maintained in order to acquire those devices.
- Preventing data modification: One of the fundamental rules in forensics is to make sure that data on the device is not modified. In other words, any attempt to extract data from the device should not alter the data present on that device. But this is practically not possible with mobiles because just switching on a device can change the data on that device. Even if a device appears to be in an off state, background processes may still run. For example, in most mobiles, the alarm clock still works even when the phone is switched off. A sudden transition from one state to another may result in the loss or modification of data.
- Anti-forensic techniques: Anti-forensic techniques, such as data hiding, data obfuscation, data forgery, and secure wiping, make investigations on digital media more difficult.
- Dynamic nature of evidence: Digital evidence may be easily altered either intentionally or unintentionally. For example, browsing an application on the phone might alter the data stored by that application on the device.
- Accidental reset: Mobile phones provide features to reset everything. Resetting the device accidentally while examining may result in the loss of data.
- Device alteration: The possible ways to alter devices may range from moving application data, renaming files, and modifying the manufacturer's operating system. In this case, the expertise of the suspect should be taken into account.
- Passcode recovery: If the device is protected with a passcode, the forensic examiner needs to gain access to the device without damaging the data on the device. While there are techniques to bypass the screen lock, they may not work always on all the versions.
- Communication shielding: Mobile devices communicate over cellular networks, Wi-Fi networks, Bluetooth, and Infrared. As device communication might alter the device data, the possibility of further communication should be eliminated after seizing the device.
- Lack of availability of tools: There is a wide range of mobile devices. A single tool may not support all the devices or perform all the necessary functions, so a combination of tools needs to be used. Choosing the right tool for a particular phone might be difficult.
- Malicious programs: The device might contain malicious software or malware, such as a virus or a Trojan. Such malicious programs may attempt to spread over other devices over either a wired interface or a wireless one.
- Legal issues: Mobile devices might be involved in crimes, which can cross geographical boundaries. In order to tackle these multijurisdictional issues, the forensic examiner should be aware of the nature of the crime and the regional laws.
Mobile devices store a wide range of information such as SMS, call logs, browser history, chat messages, location details, and so on. Mobile device forensics includes many approaches and concepts that fall outside of the boundaries of traditional digital forensics. Extreme care should be taken while handling the device right from evidence intake phase to archiving phase. Examiners responsible for mobile devices must understand the different acquisition methods and the complexities of handling the data during analysis. Extracting data from a mobile device is half the battle. The operating system, security features, and type of smartphone will determine the amount of access you have to the data. It is important to follow sound forensic practices and make sure that the evidence is unaltered during the investigation.
Resources for Article:
- Forensics Recovery [article]
- Mobile Phone Forensics – A First Step into Android Forensics [article]
- Mobility [article]