用C++实现Vigenere密码的移位问题

#include <iostream>
#include <string>

std::string vigenereCipher(const std::string& plaintext, const std::string& keyword) {
    std::string ciphertext;
    int keywordLength = keyword.length();
    int base = 'A'; // 假设明文只包含大写字母

    for (int i = 0; i < plaintext.length(); i++) {
        char plainChar = plaintext[i];
        char keywordChar = keyword[i % keywordLength];

        int shift = keywordChar - base;
        char cipherChar = (plainChar - base + shift) % 26 + base;

        ciphertext += cipherChar;
    }

    return ciphertext;
}

int main() {
    std::string plaintext = "HELLO";
    std::string keyword = "KEY";

    std::string ciphertext = vigenereCipher(plaintext, keyword);
    std::cout << "Ciphertext: " << ciphertext << std::endl;

    return 0;
}