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Microcontroller decryption program can be modified in theory, but it is too difficult to do in practice. Because the decryption is a machine code program, you need to disassemble into an assembler, and then read these programs to make changes. If the original program is written in C language, the compiled machine code program, decrypted, and then decompiled to get the assembler is difficult to read, let alone modify. If the original program is not long and is written in assembly language, the decompiled program can be read after decryption, but it needs to have a strong foundation in writing assembly language programs to read.