维吉尼亚密码(Vigenere)

# write by 2021/7/12
# 维吉尼亚密码
DIC = "abcdefghijklmnopqrstuvwxyz"
def judge_key(key):
    if not key:
        return 0
    for i in key:
        if i not in DIC:
            return 0
    return 1
def encrypt_vigenere(string, key):
    if not judge_key(key):
        return -1
    ciphertext = ""
    key_index = 0
    key_len = len(key)
    for i in string:
        if i not in DIC:
            ciphertext += i
        else:
            ciphertext += DIC[(DIC.index(i)+DIC.index(key[key_index % key_len])) % 26]
            key_index += 1
    return ciphertext
def decrypt_vigenere(string, key):
    if not judge_key(key):
        return -1
    plaintext = ""
    key_index = 0
    key_len = len(key)
    for i in string:
        if i not in DIC:
            plaintext += i
        else:
            plaintext += DIC[(DIC.index(i)-DIC.index(key[key_index % key_len])) % 26]
            key_index += 1
    return plaintext
if __name__ == '__main__':
    key_ = "linux"
    ciphertext_ = encrypt_vigenere("i love you", key_)
    plaintext_ = decrypt_vigenere(ciphertext_, key_)
    print(f"{plaintext_}: {ciphertext_}")