用C++实现同步流密码的加解密，其中特征多项式1为x^4+x+1

#include <stdio.h>

#define POLY1 0x13 // x^4 + x + 1

void encrypt(char* plaintext, char* key, char* ciphertext, int len){
int i, j;
char feedback = 0;
for(i = 0; i < len; i++){
feedback = (feedback << 1) | (plaintext[i] ^ key[i]);
ciphertext[i] = plaintext[i] ^ feedback;
for(j = 0; j < 8; j++){
if(feedback & 0x80){ // if the highest bit of feedback is 1
feedback = (feedback << 1) ^ POLY1; // perform XOR with the polynomial
}else{
feedback <<= 1;
}
}
}
}

void decrypt(char* ciphertext, char* key, char* plaintext, int len){
int i, j;
char feedback = 0;
for(i = 0; i < len; i++){
feedback = (feedback << 1) | (ciphertext[i] ^ key[i]);
plaintext[i] = ciphertext[i] ^ feedback;
for(j = 0; j < 8; j++){
if(feedback & 0x80){ // if the highest bit of feedback is 1
feedback = (feedback << 1) ^ POLY1; // perform XOR with the polynomial
}else{
feedback <<= 1;
}
}
}
}

int main(){
char plaintext[] = "Hello World!";
char key[] = "SecretKey";
char ciphertext[sizeof(plaintext)];

encrypt(plaintext, key, ciphertext, sizeof(plaintext));
printf("Encrypted text: %s\n", ciphertext);

char decryptedtext[sizeof(ciphertext)];
decrypt(ciphertext, key, decryptedtext, sizeof(ciphertext));
printf("Decrypted text: %s\n", decryptedtext);

return 0;
}