c++实现维吉尼亚加解密

可以使用以下代码实现维吉尼亚加解密：

#include <stdio.h>
#include <string.h>

void vigenere_encrypt(char *plaintext, char *key, char *ciphertext) {
    int i, j, k;
    int plaintext_len = strlen(plaintext);
    int key_len = strlen(key);
    for (i = 0, j = 0; i < plaintext_len; i++, j++) {
        if (j == key_len) {
            j = 0;
        }
        k = (plaintext[i] + key[j]) % 26;
        ciphertext[i] = k + 'A';
    }
    ciphertext[i] = '\0';
}

void vigenere_decrypt(char *ciphertext, char *key, char *plaintext) {
    int i, j, k;
    int ciphertext_len = strlen(ciphertext);
    int key_len = strlen(key);
    for (i = 0, j = 0; i < ciphertext_len; i++, j++) {
        if (j == key_len) {
            j = 0;
        }
        k = (ciphertext[i] - key[j] + 26) % 26;
        plaintext[i] = k + 'A';
    }
    plaintext[i] = '\0';
}

int main() {
    char plaintext[] = "HELLO";
    char key[] = "WORLD";
    char ciphertext[strlen(plaintext)];
    char decrypted_plaintext[strlen(plaintext)];
    vigenere_encrypt(plaintext, key, ciphertext);
    printf("Ciphertext: %s\n", ciphertext);
    vigenere_decrypt(ciphertext, key, decrypted_plaintext);
    printf("Decrypted plaintext: %s\n", decrypted_plaintext);
    return 0;
}

这段代码实现了维吉尼亚加解密，其中 plaintext 是明文，key 是密钥，ciphertext 是密文，decrypted_plaintext 是解密后的明文。