Hardware Hacking P2 | Logic Analyzers | HackTheBox Debugging Interface

We covered another hardware hacking challenge where we demonstrated an analysis of an archived file that was created by capturing data off the async serial interface of an embedded device. The objective was to decode the captured data and we used SALEAE logic analyzer to decode the data.. This was part of HackTheBox Debugging Interface challenge.

Challenge Description

We accessed the embedded device’s asynchronous serial debugging interface while it was operational and captured some messages that were being transmitted over it. Can you decode them?

File Exploration

After downloading and unzipping the challenge package, we are presented with a file named:

pythonCopyEditdebugging_interface_signal.zip

Upon extracting it:

bashCopyEditunzip debugging_interface_signal.zip

We find two files:

• metadata.sr – likely contains signal configuration or reference data
• signal_capture – a binary file that appears to be the actual serial communication dump

Let’s analyze the nature of the binary file:

bashCopyEditfile signal_capture

The result confirms that this is indeed binary data—most likely representing the captured serial communication.

Analyzing Serial Communication with Logic Analyzer

At this point, we need a tool to visualize and decode the binary signal data. One excellent choice is Logic 2, a free logic analyzer software by Saleae, widely used to interpret captured data from embedded systems.

You can find it here:
👉 https://www.saleae.com/downloads/

Download the version suitable for your OS (Linux, macOS, or Windows) and follow the installation instructions provided on the website.

Once installed:

1. Launch Logic 2.
2. Click “Open Capture” and select the signal_capture file.
3. Upon opening, you’ll see a visual block of signal data, representing voltage changes over time (serial communication).

Signal Analysis and Decoding

Zoom into the start of the first data block, typically marked around the 0.7 millisecond mark. When hovering over this section, you should see the bit width displayed — in this case, approximately 32.02 microseconds.

This corresponds to a baud rate of 31,230 bps, which is critical for decoding.

Now proceed to decode the signal:

1. Click the Analyzers tab in Logic.
2. Select “Async Serial” as the analyzer type (matching the description of the challenge).
3. Set:
   • Channel: 0
   • Bit Rate: 31230
   • Leave parity, stop bits, and other settings as default unless specified
4. Click “Save”.

Viewing the Decoded Output

To view the decoded transmission:

• Navigate to the “Terminal” panel within Logic.
• You will now see the decoded text stream , this represents the data originally transmitted over the embedded system’s serial interface.

Among the output, you’ll find the flag, clearly marked within the decoded stream.

Submitting the Flag

Once you copy the flag:

bashCopyEditSubmit it to the Hack The Box platform.

You should receive confirmation of successful challenge completion!

Video Walkthrough

Video walkthrough for HackTheBox Debugging Interface is coming soon