Phone forensics basics and best practices for police investigators
The most successful mobile phone investigations typically combine human investigative expertise with easy-to-use software technology
By Evan Dixon
Special Contributor to PoliceOne
In the world of digital forensics, mobile phone investigations are growing exponentially. The number of cell phones investigated each year has increased nearly tenfold over the past decade. Courtrooms are relying more and more on the information inside a cell phone as vital evidence in cases of all types. Despite that, the practice of mobile phone forensics is still in its relative infancy. Many digital investigators are new to the field and are in search of a “Phone Forensics for Dummies.” Unfortunately, that book isn’t available yet, so investigators have to look elsewhere for information on how to best tackle cell phone analysis. This article by no means should serve as an academic guide. However, it can be used as a first step to gaining understanding in this area.
The History of Phone Forensics
First, it’s important to understand how we got to where we are today. In 2005, there were two billion cell phones worldwide. Today, there are more than 5 billion and that number is expected to grow nearly another billion by 2012. Translated, this means that nearly every human being on Earth carries a cell phone. These phones are not just a way to make and receive calls, but rather a resource to store information about one’s life. When a cell phone is obtained as part of a criminal investigation, an investigator is able to tell a significant amount about the owner. In many ways, the information found inside a phone is more important than a fingerprint in that it provides much more than identification. Using forensic software, digital investigators are able to see the call list, text messages, pictures, videos and much more all to serve as evidence either convicting or vindicating the suspect.
The Step-by-Step Investigation Process
Lee Reiber, lead instructor and owner of Mobile Forensics Inc., breaks up the investigation into three parts — seizure, isolation, and documentation. The seizure component primarily involves the legal ramifications. “If you do not have a legal right to examine the device or its contents then you are likely to have all the evidence suppressed no matter how hard you have worked,” says Reiber. The isolation component is the most important “because the cellular phone's data can be changed, altered and deleted over the air (OTA). Not only is the carrier capable of doing this, but the user can employ applications to remotely ‘wipe’ the data from the device.” The documentation process involves photographing the phone at the time of seizure. Reiber says the photos should show time settings, state of device and characteristics.
After the phone is taken to the digital forensics investigator, the device should be examined with a professional tool. These tools include products such as MOBILedit! Forensic, Paraben Device Seizure, Susteen SecureView, and AccessData MPE. It is absolutely a last resort to investigate phones manually. Manual investigation should only be used if no tool on the market is able to support the device. Modern cell phones are like miniature computers that require a sophisticated software program for comprehensive analysis.
When examining a cell phone, it is important to protect it from remote access and a network signal. As cell phone jammers are illegal in the United States and most of Europe, Reiber recommends “using a metallic mesh to wrap the device securely and then placing the phone into standby mode or airplane mode from transportation, photographing and then placing the phone in a state to be examined.”
Steve Bunting, Senior Forensic Consultant at Forward Discovery, lays out the process flow as follows.
• Achieve and maintain network isolation (Faraday bag, RF-shielded box, and/or RF-shielded room)
• Document thoroughly the device, noting all information available — use photography to support this documentation
• If a SIM card is in place, remove, read, and image the SIM card
• Clone the SIM card
• With the cloned SIM card installed, do a logical extraction of the cell device with a tool (i.e. MOBILedit! Forensic, AccessData MPE, etc,) — if non-SIM device, start here
• Examine the extracted data from the logical examination
• If supported by both the model and the tool, do a physical extraction of the cell device
• View parsed data from physical extraction, which will vary greatly depending on the make / model of cell phone and the tool being used
• Carve raw image for various file types or strings of data
• Report your findings
Credibility on the Stand
There are two things an investigator can do to gain credibility in the courtroom. One is cross-validation of the tools used. It is vastly important that investigators do not rely on only one tool when investigating a cell phone. Both Reiber and Bunting adamantly recommend using multiple tools for cross-validation purposes. “By crosschecking data between tools, one may validate one tool using the other,” says Bunting. Doing so adds significant credibility to the evidence.
The second way to add credibility is to make sure the investigator has a solid understanding of the evidence and how it was gathered. Many of the investigations tools are simple to use and require only a couple clicks to generate a detailed report. Reiber warns against becoming a “point and click” investigator now that the tools are so easy to use. If an investigator takes the stand and is unable to speak intelligently about the technology used to gather the evidence, his credibility will be in question.
Steve Bunting puts it like this, “The more knowledge one has of the tool’s function and the data structures and function found in any given cell device, the more credibility one will have as a witness.”
If you have zero experience and suddenly find yourself called upon to handle phone examination duties for your organization, don’t panic. I speak with individuals on a weekly basis in a similar situation looking for direction. My advice is always the same: enroll in a training course, become certified, seek the counsel of veterans, engage in online digital forensics communities and forums, and speak with representatives of software companies making investigation tools. By taking these steps, you can go from novice to expert in a short period of time.