A chip decapping attack involves physically removing the protective casing of a semiconductor device (usually an integrated circuit) to gain direct access to its internal components, such as the die and circuits. This can be done to extract sensitive information, reverse-engineer the chip, or bypass security mechanisms. Here’s a step-by-step guide on how a chip decapping attack is typically performed:
1. Preparation and Safety
- Safety Equipment: Use protective gloves, goggles, and work in a well-ventilated area or under a fume hood, as the chemicals and tools used can be hazardous.
- Tools and Materials:
- Acetone or other solvents (for cleaning)
- Nitric acid or sulfuric acid (for decapping)
- A decapping machine or hot plate
- Precision tools (tweezers, scalpels)
- Optical microscope or SEM (Scanning Electron Microscope)
2. Device Selection
- Identify the Target Chip: Choose the chip to be decapped, typically one containing sensitive data or security features.
- Documentation: Gather datasheets, package information, and any other relevant documentation to understand the chip’s layout and packaging type.
3. Chip Removal
- Desolder the Chip: If the chip is soldered onto a circuit board, carefully desolder it using a soldering iron or rework station to avoid damaging the chip or surrounding components.
- Clean the Chip: Use acetone or another solvent to clean any residual solder, adhesive, or coating from the chip.
4. Decapping Process
- Mechanical Decapping (Optional): In some cases, the top layer of the chip package can be carefully sanded or milled down to expose the underlying layers. This step is often a precursor to chemical decapping.
- Chemical Decapping:
- Acid Application: Place the chip on a heat-resistant surface or decapping machine and carefully apply nitric acid or sulfuric acid to the chip’s package. The acid will dissolve the epoxy or plastic casing.
- Heat Application: Heat may be applied to accelerate the reaction. This can be done using a hot plate or within a decapping machine.
- Monitoring: Carefully monitor the process under a microscope to ensure the die is not damaged.
- Rinse and Neutralize: Once the casing is sufficiently removed, rinse the chip thoroughly with a neutralizing solution (e.g., water or alcohol) to remove any residual acid.
5. Accessing the Die
- Clean the Die: Use precision tools to gently clean any remaining debris from the die.
- Inspect Under a Microscope: Use an optical microscope or SEM to inspect the exposed die. This allows you to analyze the layout, identify security features, or locate areas of interest such as fuses or memory cells.
6. Data Extraction and Analysis
- Probe the Die: Use microprobes to access specific points on the die for data extraction. This may involve reading stored data directly from memory cells or accessing internal communication buses.
- Reverse Engineering: Analyze the chip’s structure and operation. This can reveal proprietary algorithms, encryption keys, or other sensitive information.
7. Security Bypass
- Exploit Identified Vulnerabilities: Depending on the findings, you may be able to bypass security mechanisms, disable protections, or clone the chip.
Tools for Advanced Decapping
- Laser Decapping: Some advanced decapping processes use lasers to precisely remove chip layers without chemicals.
- Focused Ion Beam (FIB): For extremely precise decapping and circuit modification.