Prevent yourself from designing circuit to be copied

As far as we know it, it is not only a technical issue to prevent copying, but also a game process. When designing a product, the technology that cannot be copied can be pursued without cost. Instead, the appropriate anti-copying method should be selected according to the product characteristics to increase the complexity of the copying board, thereby making the cost of copying board unacceptable and effectively avoiding hardware. Being pirated.

Copying board and anti-copying board is a problem of "attack and defense". Only by knowing how to "attack" can we better "anti-". To solve this problem, in addition to consulting professional PCB designers and online search, it also uses the company or individual who provides the buyer's identity and provides copying services to understand the market of PCB copying and chip decryption.

The following is the investigation of PCB copy board and chip decryption:

In TB choose a circuit module (size: 6X6cm, double layer), by consulting related copy board enterprises, learned that the price of this module is about 400 yuan, can provide PCB file and component list, plus 200 yuan can provide Schematic file, and to ensure the correctness of the board. Through continued communication, the company can not copy high-frequency PCB boards and flexible boards, which is difficult. If the chip LOGO is polished on the PCB, you need to find a professional to identify the model, which is charged separately.

Then consulted a domestic professional chip decryption company, learned that when deciphering a 51 MCU, its asking price is 20,000 yuan. If the program in the chip is encrypted while downloading the program, the decryption will be more difficult. And this chip model is relatively new, has not been decrypted before, can not guarantee 100% decryption. Then I proposed that because the chip uses anti-copy board technology, the ID number is required at power-on. The response is that this requires a disassembly operation that cannot complete this task.

From the above communication, the difficulty level of "hardware piracy" is from low to high: roughly reverse the PCB file or schematic file from the board, high-frequency PCB or soft PCB copy board, infer that there is no LOGO. The component model, the decryption chip obtains a binary file, disassembles the encrypted binary file, and the like.

The following is a brief introduction to the methods of anti-copying that can be used:

1, the PCB copy board prevention means

1. Polish the LOGO on the chip, use components without device identification, and place interference components without affecting the function. These measures are taken to increase the reverse PCB file from the board.

2, sealing, painting. This method can only simply increase the difficulty of copying the board.

3. The PCB adopts the buried hole and blind hole technology to make the via hole hidden in the board. This method has high cost and is only suitable for high-end products.

4. For the high-frequency board, the characteristics of the PCB can be utilized, and the parameters such as the distributed capacitance are used, so that the parameters after the copying are different, and the board cannot work normally.

In general, the current reverse design can use a low-cost operation process to copy the PCB, so the precautions that can be made on the PCB are only to increase the difficulty of copying and copying the board.

2, the chip decryption means

1. Polish the chip LOGO and print the LOGO of other chips. Select the chip with the same power layout and grounding layout (the easiest way is to select the LOGO of different models of the same company). This can mislead the decryption company and make the decrypted chip not working properly. Need to rework, re-analyze the part number and increase the cost of decryption.

2. Use some relatively unfamiliar and unpopular single-chip microcomputers to increase the difficulty of counterfeit purchases and avoid the situation where the chips used have been decrypted by some companies.

3. The main control chip selects a chip with better encryption performance and more difficult decryption. Or directly adopt a SoC with high security performance.

4. Under the condition that the design cost is allowed, the smart card chip with hardware self-destruction function should be selected to effectively deal with physical attacks.

5, using CPU cartoon with COS protection technology or open CPU card encryption coprocessor technology.

6. The program of the main control chip adopts the soft encryption method when downloading.

7. In the program area, mark your unit, development time and imitation and other signs, in order to obtain legal protection.

Decryption of the chip is relatively difficult and costly. The use of simple precautions can greatly increase the difficulty of "hardware piracy", thereby increasing the cost of decryption.

3, the combination of software and hardware

1. The simplest means of prevention is password authentication. At present, the mainstream processor chip will have a unique ID number. After the system is powered on, the ID number is first read to confirm that the ID number is within the authorized range, thereby ensuring the validity of the hardware. This method basically does not increase the development cost, and can achieve a certain protection effect. For added security, the ID number can be encrypted. But the way this password is transmitted directly will be easily cracked.

2, dynamic password authentication protection technology, can be achieved through a dedicated protection chip. The operational flow and hardware connection to the processor are shown below:

The basic principle is that the protection chip and the MCU have the same key and the same symmetric algorithm. The random number is used as the communication data, and the MCU determines whether the calculation result of the protection chip is correct or not to determine whether the program continues to run. This product and technology solves the plaintext transmission of passwords during the authentication process, which can effectively avoid "hardware piracy". DM2016 uses OTP ROM to save the key. Since the decryption of OTP ROM is more difficult than the decryption of Flash, it improves the performance of "hardware piracy". The disadvantage is that it increases the hardware cost and takes up the PCB area.

3. The dedicated SoC chip is used to integrate the encryption module and the processor into an MCU. The chip, such as ESPU0808, integrates an encryption processing unit and an 8051 core.

In general, the combination of hardware and software technology can effectively prevent "hardware piracy" behavior, greatly increasing the cost of piracy. But in terms of technology, it can still be solved by technical means.

4. One of my ideas

At present, a combination of software and hardware can achieve better security performance. To decrypt this hardware, you can bypass hardware authentication, obtain key and disassemble and other technical means. So you can take measures from the following aspects.

1, in order to bypass the hardware certification, hardware certification is best not to concentrate only on a part of the code on the system. Authentication can be performed using a random function + timer method.

2. In order to avoid the key being acquired, it is best to use dynamic password authentication. This avoids the direct transmission of the key, making it difficult for the decryption software or the dedicated detection device to extract the key from the binary file obtained in the chip.

3. Disassembly is the most destructive technical means for software encryption. At present, many MCUs use some encryption measures to prevent the decrypter from obtaining binary files from the MCU's Flash. But this method will still be overcome by the decryptor through non-intrusive, intrusive or semi-intrusive means. And if the program is downloaded by encryption, it can avoid direct disassembly. Obtaining keys and encryption algorithms from encrypted binary files or bypassing hardware authentication is difficult, which effectively prevents the product from being pirated.