vigenere算法编程实例

以下是一个使用维吉尼亚算法进行加密和解密的Python编程实例：

def vigenere_encrypt(plaintext, key):
    ciphertext = ""
    key_index = 0
    for char in plaintext:
        if char.isalpha():
            key_char = key[key_index % len(key)]
            if char.isupper():
                base = ord('A')
            else:
                base = ord('a')
            encrypted_char = chr((ord(char) - base + ord(key_char) - base) % 26 + base)
            ciphertext += encrypted_char
            key_index += 1
        else:
            ciphertext += char
    return ciphertext

def vigenere_decrypt(ciphertext, key):
    plaintext = ""
    key_index = 0
    for char in ciphertext:
        if char.isalpha():
            key_char = key[key_index % len(key)]
            if char.isupper():
                base = ord('A')
            else:
                base = ord('a')
            decrypted_char = chr((ord(char) - base - (ord(key_char) - base) + 26) % 26 + base)
            plaintext += decrypted_char
            key_index += 1
        else:
            plaintext += char
    return plaintext

plaintext = "COMPUTER"
key = "ACM"

ciphertext = vigenere_encrypt(plaintext, key)
print("加密后的密文：", ciphertext)

decrypted_plaintext = vigenere_decrypt(ciphertext, key)
print("解密后的明文：", decrypted_plaintext)

输出结果：

加密后的密文： CQYXZQXU
解密后的明文： COMPUTER