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Decryption process of chip decryption
Invasive type of attack is the first step in the chip package (referred to as the "open cover" sometimes called "", English as "DECAP", decapsulation). There are two ways to achieve this goal: the first is to completely dissolve the chip package, exposed metal connections. The second is to move away from the plastic package on the silicon core. The first method requires the chip to be bound to the test fixture, with the aid of the binding platform to operate. In addition to the second methods need to have a certain knowledge of the attacker and the necessary skills, but also requires personal wisdom and patience, but it is relatively easy to operate, complete family operations.
Chip above the plastic can be opened with a knife, the epoxy resin around the chip can be corroded with concentrated nitric acid. Hot concentrated nitric acid will dissolve the chip package will not affect the chip and connection. The process generally in very dry conditions, because the presence of water may have been exposed by erosion wire connection (which may cause the decryption failure).
The chip is then cleaned with acetone in the ultrasonic bath to remove the residual nitric acid.
The final step is to find the location of the protection fuse and fuse exposed under ultraviolet light. A magnification of the microscope at least 100 times tracking in general use, from the programming voltage input pin of the connection, to find the protection fuse. If there is no microscope, the different parts of the chip will be exposed to ultraviolet light and observe the results of a simple search method. When operating, the chip is used for protecting the program memory from being erased by ultraviolet light. The fuse exposed under UV light for 5 to 10 minutes to destroy the protective effect of the protection, use a simple programmer can directly read the contents of program memory.
For the use of the protective layer to protect the EEPROM unit of the microcontroller, the use of UV reset protection circuit is not feasible. For this type of microcontroller, the general use of micro probe technology to read the contents of the memory. When the chip is packaged and opened, it is easy to find the data bus from the memory to the other parts of the circuit under the microscope. For some reason, the chip lock is positioned in the programming mode and is not locked to the memory access. Using this defect, the probe will be placed on the top of the data line to read all the desired data. In programming mode, restart the reading process and connect the probe to the other data lines to read all the information in the program and data memory.
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