### 设计基于Python的文件加密系统 为了实现一个安全可靠的文件加密系统，可以采用高级加密标准（AES），这是广泛接受的数据加密方法之一。下面是一个简单的例子来展示如何创建这样的系统。 #### 使用PyCryptodome库进行文件加解密操作 安装所需的库可以通过pip完成： ```bash pip install pycryptodome ``` 定义用于处理文件读取、写入以及执行实际加密和解码过程的功能函数如下所示： ```python from Crypto.Cipher import AES import os from base64 import b64encode, b64decode def pad(data): """Padding function.""" padding_length = AES.block_size - (len(data) % AES.block_size) return data + bytes([padding_length]) * padding_length def unpad(padded_data): """Unpadding function.""" unpadder = padded_data[-1] if unpadder > AES.block_size or any(i != unpadder for i in padded_data[-unpadder:]): raise ValueError('Invalid padding') return padded_data[:-unpadder] class FileEncryptorDecryptor: def __init__(self, key): self.key = key # Must be either 16, 24, or 32 bytes long def encrypt_file(self, input_filename, output_filename=None): """ Encrypts an entire file. :param str input_filename: Path to the source file that needs to be encrypted. :param str|None output_filename: Optional path where the ciphertext should be saved; defaults to appending '.enc' extension. """ cipher = AES.new(pad(self.key), AES.MODE_CBC) try: with open(input_filename, 'rb') as f_in: plaintext = f_in.read() iv = cipher.iv ciphertext = cipher.encrypt(pad(plaintext)) enc_output_filename = output_filename or f"{input_filename}.enc" with open(enc_output_filename, 'wb') as f_out: f_out.write(iv + ciphertext) except Exception as e: print(f"Error during encryption process: {e}") def decrypt_file(self, input_filename, output_filename=None): """ Decrypts previously encrypted files back into their original form. :param str input_filename: Path to the .enc file containing the ciphertext. :param str|None output_filename: Destination filename/path after decryption completes successfully; default behavior removes '.enc'. """ try: with open(input_filename, 'rb') as f_in: raw_ciphertext = f_in.read() iv = raw_ciphertext[:AES.block_size] actual_ciphertext = raw_ciphertext[AES.block_size:] decipher = AES.new(pad(self.key), AES.MODE_CBC, iv=iv) decrypted_padded_plaintext = decipher.decrypt(actual_ciphertext) dec_output_filename = output_filename or '.'.join( part for part in input_filename.split('.')[:-1]) with open(dec_output_filename, 'wb') as f_out: f_out.write(unpad(decrypted_padded_plaintext)) except Exception as e: print(f"Decryption failed due to error: {e}") ``` 此代码片段展示了怎样利用`pycryptodome`包中的工具构建基本的文件加密/解密机制[^1]。需要注意的是，在真实环境中部署之前还需要考虑更多因素如异常情况下的恢复策略等以增强系统的健壮性[^3]。