Guide to Capturing PCAP Files on Android Devices

This guide provides detailed instructions for capturing network traffic on both rooted and non-rooted Android devices, including options for using Termux with relevant tools. Capturing traffic is essential for log analysis and debugging purposes. Let's break it down.

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1. Rooted Devices

Rooted devices provide full access to system files and network interfaces, enabling robust packet capture capabilities.

1.1 Using tcpdump

tcpdump is a command-line tool for capturing network packets. Here’s how to use it on a rooted Android device.

Step-by-Step Instructions:

1. Install tcpdump:

• Download the tcpdump binary compatible with Android from a trusted source (e.g., https://www.tcpdump.org).
• Transfer the binary to your device:

  adb push tcpdump /data/local/tmp
  

• Change permissions to make it executable:

  adb shell
  su
  chmod 755 /data/local/tmp/tcpdump
  

Another way to install tcpdump:

• Download the tcpdump binary:

  wget https://www.tcpdump.org/release/tcpdump-(version).tar.gz
  

• Extract and install:

  tar -xvf tcpdump-(version).tar.gz
  cd tcpdump-(version)
  ./configure
  make
  make install
  

• Alternatively, you can copy a precompiled tcpdump binary to your phone using ADB:

  adb push tcpdump /data/local/tmp/
  adb shell chmod +x /data/local/tmp/tcpdump

1. Capture Network Traffic:

   • Run tcpdump to start capturing traffic:

     /data/local/tmp/tcpdump -i any -w /sdcard/capture.pcap
     

     • -i any: Captures traffic from all interfaces.
     • -w: Specifies the output file in PCAP format.

2. Stop the Capture:

   • Use Ctrl+C in the terminal to stop the capture.

3. Transfer PCAP File:

   • Transfer the file to your computer for analysis:

     adb pull /sdcard/capture.pcap
     

1.2 Using Shark for Root

Shark for Root is a GUI-based frontend for tcpdump.

Steps:

1. Download and install Shark for Root from a trusted source.
2. Grant root permissions when prompted.
3. Start capturing traffic using the app’s interface.
4. Save the PCAP file and transfer it for analysis.

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2. Non-Rooted Devices

For non-rooted devices, you can use apps that leverage VPN-based traffic capturing.

2.1 Using Packet Capture App

The Packet Capture app uses a local VPN to intercept traffic.

Steps:

1. Install Packet Capture:

   • Download the app from the Play Store.

2. Configure SSL Decryption (Optional):

   • Install the app’s SSL certificate to capture HTTPS traffic.
   • Follow the app’s instructions to add the certificate to your device.

3. Start Capturing Traffic:

   • Open the app and start the VPN service.
   • Perform network activities you want to analyze.

4. Export PCAP File:

   • Stop the capture and export the file in PCAP format.
   • Transfer the file for analysis.

2.2 Using tPacketCapture

tPacketCapture is another app that operates similarly to Packet Capture.

Steps:

1. Install the app from the Play Store.
2. Launch the app and start the capture.
3. Perform network activities and stop the capture.
4. Export the PCAP file.

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3. Using Termux (Rooted or Non-Rooted)

Termux is a terminal emulator for Android that can work with various tools, including tcpdump.

3.1 Installing tcpdump in Termux

Steps:

1. Install Termux:

   • Download Termux from the Play Store or F-Droid.

2. Install Required Packages:

   • Update and install packages:

     pkg update && pkg upgrade
     pkg install tsu tcpdump
     

3. Capture Traffic:

   • For rooted devices:

     tsu
     tcpdump -i any -w /sdcard/capture.pcap
     

   • For non-rooted devices (limited to Termux session traffic):

     tcpdump -i any -w capture.pcap
     

4. Stop the Capture:

   • Use Ctrl+C to stop capturing traffic.

5. Transfer File:

   • Use ADB or cloud storage to move the PCAP file to your computer.

3.2 Combining with Other Tools

You can use additional tools with Termux for enhanced capabilities:

• OpenVPN: To route traffic through a VPN and capture it.
• SSLsplit: To decrypt HTTPS traffic (requires root).

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4. Analyzing the PCAP File

Once you’ve captured the traffic, transfer the PCAP file to a computer for analysis using tools like Wireshark or tshark.

Steps for Wireshark:

1. Open Wireshark on your computer.
2. Load the PCAP file:
   • File > Open > Select the PCAP file.
3. Analyze the captured traffic using Wireshark’s filters and visualization tools.

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5. Troubleshooting

No Traffic Captured:

• Ensure permissions are granted for storage and internet access.
• For non-rooted devices, verify the VPN is active.

Incomplete Traffic (HTTPS):

• Install and configure an SSL certificate for the capture tool.

PCAP File Not Found:

• Check the output path specified in the capture tool.
• Ensure the tool has write permissions.

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This guide provides a detailed approach for both rooted and non-rooted Android devices.