Shulou(Shulou.com)06/02 Report--

Algorithm transplant encryption chip is a patented product of Lingke Xin'an Co., Ltd. Its main function is to embed the LKCOS intelligent operating system of Lingke Xin'an Company. Users can transplant some key algorithm functions of MCU programs to the chip to run. The user writes the code in standard C language, compiles and downloads it to the intelligent chip through the KEIL C compiler. In the actual operation, the program segment in the smart card chip is run by calling the function, and the running result is obtained, which is used as the input data for the further operation of the user program. Therefore, the chip has become a part of the product, and the algorithm is operated inside the chip, which can not be cracked by pirates, which fundamentally eliminates the possibility of the program being cracked.

The debugging of algorithm transplant encryption chip includes two parts: communication debugging and algorithm debugging. This time, we first analyze the common problems in communication debugging.

Common problems in communication debugging

1. Communication format setting

The data format of a frame is: 1 start bit, 8 data bits, 1 even check bit (can not be omitted), 2 stop bits, a total of 12 bits.

2. Communication rate

The communication rate of the encryption chip = external clock frequency / frequency division factor (the default frequency division coefficient is 372). If the external clock frequency is changed, the communication rate will change. Our demo circuit uses 3.579Mhz external clock, so the default communication rate is 3.579M/372, so 9600bps communication is used.

3. Reset problem

After the encryption chip is powered on, the instruction can be reset at least once. If the communication is abnormal, the reset operation can be carried out first, and then the instruction interaction can be carried out again.

4. Clock problem

An external clock must be provided. If the communication is not normal, the clock VPP and frequency should be checked first to ensure that the CLK is in a continuous and normal supply state when reset and instruction interaction is carried out. Many customer feedback communication failures are caused by clock failure, late start, discontinuous clock supply and so on. It can be observed by logic analyzer and oscilloscope.

5. Judge the source of the problem of the chip from the timing.

"Communication used to be normal, but now it's not working. What's going on?"

"I sent an order, but the encryption chip didn't reply. Is there something wrong with the chip?"

"the data I received is wrong. Is there something wrong with the algorithm running on the encryption chip?"

The contents in the above quotation marks are the real information fed back by the user. The descriptions of these problems are all superficial, and if they are still unable to locate after preliminary analysis, we need to start with the underlying time series. The timing of communication between MCU and encryption chip is captured by logic analyzer or oscilloscope, and compared with the data sent and received by MCU, so as to determine whether it is caused by the abnormal communication of encryption chip or MCU.

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