Hackaday · Creativity & design

Extracting Device Firmware Using a Logic Analyzer

A method has been developed to extract firmware from devices without physically removing the flash chip, using a logic analyzer to capture SPI read operations during boot time.

This technique allows for firmware extraction by monitoring the SPI bus, which is used to load firmware from chips like the W25Q-series. The process involves identifying, capturing, and decoding the SPI read operations.

While not capturing the entire chip's contents, this method sniffs what the CPU reads, offering a significant advancement for reverse engineering.

The author explains the fundamentals of SPI communication, detailing how to interpret signals using a logic analyzer and flash chip datasheets. This section serves as a primer on SPI for those interested in chip communication.

Captured SPI data is then decoded using Scapy, a Python tool typically used for network packets. Scapy is adapted to process logic analyzer capture files, converting them into image files for further analysis.

An issue was discovered where the extracted firmware image had a gap for the filesystem. This was because the CPU switches to a faster Quad-SPI mode for the filesystem, utilizing additional data lines.

Further capturing and processing were required to address the Quad-SPI data. The two resulting image files were merged into a single file using a 'dd' command.

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