C语言怎么实现gsm加密算法

???GSM????,????????:

1. ??GSM????:GSM????????????,???????????(Linear Feedback Shift Register, LFSR)??????,???????????????

2. ??LFSR??:??GSM???????LFSR????????,??LFSR?????????

3. ??????:????????????????????,?????

????????????:

#include 

// LFSR????????
unsigned char lfsr(unsigned char state) {
    unsigned char lsb = state & 1;
    state >>= 1;
    if (lsb)
        state ^= 0x1B;  // GMS??????????
    return state;
}

// GSM????
void gsmEncrypt(unsigned char* key, unsigned char* plaintext, unsigned char* ciphertext, int length) {
    unsigned char state = 0x1;  // ????
    int i;
    for (i = 0; i < length; i++) {
        state = lfsr(state);
        ciphertext[i] = key[i] ^ state ^ plaintext[i];
    }
}

int main() {
    unsigned char key[] = {0x7C, 0x5B, 0xCD, 0x27, 0x51, 0x8D, 0x8, 0x68};  // ??
    unsigned char plaintext[] = {0x12, 0x34, 0x56, 0x78};  // ??
    int length = sizeof(plaintext) / sizeof(unsigned char);
    unsigned char ciphertext[length];  // ??

    gsmEncrypt(key, plaintext, ciphertext, length);

    printf("Ciphertext: ");
    for (int i = 0; i < length; i++) {
        printf("X ", ciphertext[i]);
    }
    printf("\n");

    return 0;
}

????????,???GSM???????LFSR???(0x1B)?????(0x1)??????????????????,???????????16???????

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