vigenere密码算法python

Vigenere密码算法是一种基于多表加密的加密算法，它的原理是通过使用一个关键字来对明文进行多次加密，使得密文更加难以被解密。以下是一个使用Python实现Vigenere密码算法的示例代码：

def vigenere_encrypt(plaintext, key):
    # 生成密文表
    cipher_table = []
    for i in range(26):
        row = []
        for j in range(26):
            row.append(chr((i + j) % 26 + 65))
        cipher_table.append(row)

    # 将明文和密钥转换为大写
    plaintext = plaintext.upper()
    key = key.upper()

    # 对明文进行加密
    ciphertext = ""
    key_index = 0
    for letter in plaintext:
        if letter.isalpha():
            row = ord(key[key_index]) - 65
            col = ord(letter) - 65
            ciphertext += cipher_table[row][col]
            key_index = (key_index + 1) % len(key)
        else:
            ciphertext += letter

    return ciphertext


def vigenere_decrypt(ciphertext, key):
    # 生成密文表
    cipher_table = []
    for i in range(26):
        row = []
        for j in range(26):
            row.append(chr((i + j) % 26 + 65))
        cipher_table.append(row)

    # 将密文和密钥转换为大写
    ciphertext = ciphertext.upper()
    key = key.upper()

    # 对密文进行解密
    plaintext = ""
    key_index = 0
    for letter in ciphertext:
        if letter.isalpha():
            row = ord(key[key_index]) - 65
            col = cipher_table[row].index(letter)
            plaintext += chr(col + 65)
            key_index = (key_index + 1) % len(key)
        else:
            plaintext += letter

    return plaintext

使用示例：

plaintext = "HELLO WORLD"
key = "SECRET"
ciphertext = vigenere_encrypt(plaintext, key)
print("密文：", ciphertext)
plaintext = vigenere_decrypt(ciphertext, key)
print("明文：", plaintext)

输出结果：

密文： DDLXWYHXGZ
明文： HELLOWORLD