Introduction to Android Partitions in Forensics

Mobile device forensics presents unique challenges, primarily due to the intricate security mechanisms protecting user data. Android, being the most widely used mobile operating system, is a frequent target for forensic investigations. While unrooted devices offer limited access, a rooted Android device opens the door to a complete, block-level file system extraction, providing unparalleled depth for analysis. Understanding the various partitions on an Android device and their forensic significance is paramount for a successful investigation. This guide delves into the core Android partitions, their contents, and how to extract them from a rooted device.

The Landscape of Android Partitions

An Android device’s internal storage is divided into several partitions, each serving a specific purpose. These partitions are typically organized as block devices, similar to traditional hard drives, and contain different components of the operating system, user data, and vendor-specific files. On a rooted device, we can access these raw block devices directly.

• /boot Partition: This critical partition contains the kernel and the ramdisk. The kernel is the core of the Android OS, managing hardware resources. The ramdisk is a small root filesystem loaded into RAM during boot, containing essential files for the early boot process, including init and fstab.
• /system Partition: This partition houses the Android operating system framework, system applications, libraries, and binaries. It’s mounted read-only during normal operation. Forensic analysis of /system can reveal modifications to the OS, pre-installed malware, or custom ROMs.
• /data (or /userdata) Partition: This is arguably the most forensically rich partition. It contains all user-specific data, including installed applications, application data (databases, preference files), user files (photos, videos, documents), contacts, call logs, SMS messages, and browsing history. Accessing this partition is the primary goal in many investigations.
• /cache Partition: This partition stores frequently accessed data and temporary files to improve system performance. While often overlooked, it can contain valuable forensic artifacts such as browser cache, application temporary files, and system logs that might not be present elsewhere.
• /recovery Partition: This partition contains a recovery image that can be booted independently of the main Android system. It’s used for flashing updates, factory resets, or performing backups. Forensic analysis might reveal custom recovery images (e.g., TWRP) that indicate previous tampering or specific tools used on the device.
• /vendor Partition: Introduced with Android 8.0 Oreo, this partition contains OEM (Original Equipment Manufacturer) specific binaries and libraries, including the Hardware Abstraction Layer (HAL) implementations. It separates vendor-specific code from the core Android system, facilitating faster updates.
• /persist Partition: This partition stores critical, persistent device-specific settings that survive factory resets, such as Wi-Fi MAC addresses, Bluetooth addresses, and other calibration data. It’s essential for device identification.
• /efs (Samsung specific) / /modem / /radio Partitions: These partitions store critical radio firmware, IMEI, and other hardware-specific identifiers. While device-specific, they contain information crucial for unique device identification and verifying cellular network activity.

Why Extract Each Partition for Forensic Analysis

• /boot: Can indicate if a custom kernel was flashed (often a prerequisite for root), or if a malicious kernel module was loaded.
• /system: Reveals modifications to the core Android OS, custom ROMs, system-level malware, or traces of rooting methods. Comparing its hash to a known clean image can identify alterations.
• /data: The primary target for user activity. Contains app databases (WhatsApp, Signal, Telegram), browser history, GPS data, call logs, SMS/MMS, media files, and deleted file remnants. This is where most actionable intelligence resides.
• /cache: Often contains temporary files, web cache, app cache, and sometimes log files that provide a snapshot of recent activity or application behavior.
• /recovery: Presence of custom recovery images can indicate previous attempts to root, flash custom ROMs, or modify the device’s software state.
• /vendor: Can reveal OEM-specific vulnerabilities, custom device drivers, or modifications introduced by the manufacturer that might be relevant to the device’s behavior.
• /persist / /efs: Crucial for validating device identity (IMEI, MAC addresses) and ensuring no spoofing or tampering of these identifiers.

Step-by-Step: Extracting Partitions from a Rooted Android Device

Before proceeding, ensure your Android device is rooted, ADB (Android Debug Bridge) is installed on your workstation, and USB debugging is enabled on the device. We will use the dd command, a powerful utility for low-level data copying, available on Android’s shell.

Prerequisites:

1. Rooted Android device.
2. ADB installed and configured on your forensic workstation.
3. USB debugging enabled on the device.
4. Sufficient storage space on the device’s internal SD card (or an external one) for the partition images.

Procedure:

1. Connect your Android device to your forensic workstation.

adb devices

Ensure your device is listed and authorized.

2. Gain root shell access.

adb rootadb shell

The shell prompt should change to #, indicating root access.

3. Identify the block devices for each partition.

Android devices map logical partitions to physical block devices. You can often find these mappings in /dev/block/by-name/ or by examining /proc/partitions or /etc/fstab. The exact names (e.g., mmcblk0pX or sdaX) can vary between devices.

ls -l /dev/block/by-name/

This command will list symbolic links to the actual block devices, making it easier to identify partitions like userdata, system, boot, etc. For example, userdata -> /dev/block/mmcblk0p34.

4. Extract the desired partition using dd.

Use the dd command to create a raw image of the partition and save it to a location on the device’s internal storage (e.g., /sdcard/). It’s crucial to select a location with enough free space.

# Example for userdata partitiondd if=/dev/block/mmcblk0p34 of=/sdcard/userdata.img bs=4M

Replace /dev/block/mmcblk0p34 with the actual path to your userdata partition and userdata.img with a descriptive filename. bs=4M sets the block size to 4 megabytes for faster copying; adjust as needed.

Important: This process can take a significant amount of time, especially for large partitions like userdata. Do not interrupt the process. Repeat this step for all partitions of interest (system, boot, cache, etc.).

# Example for system partition (assuming path /dev/block/mmcblk0p33)dd if=/dev/block/mmcblk0p33 of=/sdcard/system.img bs=4M# Example for boot partition (assuming path /dev/block/mmcblk0p28)dd if=/dev/block/mmcblk0p28 of=/sdcard/boot.img bs=4M

5. Pull the image files to your forensic workstation.

Once the images are created on the device, use adb pull to transfer them to your computer for analysis.

adb pull /sdcard/userdata.img C:orensics	arget_device
aw_images
emove adb pull /sdcard/system.img C:orensics	arget_device
aw_images
emove adb pull /sdcard/boot.img C:orensics	arget_device
aw_images
emove 

It’s good practice to verify the integrity of the pulled images using hash comparisons if possible.

Post-Extraction Analysis

After successfully extracting the raw partition images, forensic tools such as Autopsy, FTK Imager, X-Ways Forensics, or specialized mobile forensic platforms can be used to mount, parse, and analyze the data. These tools allow for file carving, keyword searching, timeline analysis, and database examination, extracting actionable intelligence from the raw data. Remember to always work on copies of the extracted images to preserve the original evidence.

Conclusion

A comprehensive understanding of Android’s partition structure and the ability to perform full block-level extractions from rooted devices are invaluable skills in mobile forensics. By systematically extracting and analyzing each relevant partition, investigators can uncover a wealth of digital evidence crucial for any case. This meticulous approach ensures no stone is left unturned in the pursuit of digital truth.