本文旨在解决在使用 Python 的 Crypto 库进行 AES 加密解密时，解密后得到空字符串的问题。通过分析代码，找出问题根源在于密钥处理方式不正确，并提供修正后的代码示例，确保加密和解密过程的正确性，最终实现数据的可靠保护。
在使用 Python 的 Crypto 库进行 AES 加密和解密时，有时可能会遇到解密后文本为空的情况。这通常是由于密钥处理不当造成的。以下将详细介绍如何避免这个问题，并提供正确的代码示例。
问题在于，原始代码中，当提供密钥给 AESCipher 构造函数时，错误地计算了密钥的哈希值，而正确的做法应该是对密钥进行 Base64 解码。AESCipher.get_key 方法将密钥编码为 Base64 字符串，因此在解密时需要进行逆向操作。
正确的 AESCipher 构造函数应如下所示：
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import hashlibfrom Crypto.Cipher import AESfrom Crypto import Randomfrom base64 import b64encode, b64decodeclass AESCipher(object): def __init__(self, key=None): # Initialize the AESCipher object with a key, # defaulting to a randomly generated key self.block_size = AES.block_size if key: self.key = b64decode(key.encode()) else: self.key = Random.new().read(self.block_size) def encrypt(self, plain_text): # Encrypt the provided plaintext using AES in CBC mode plain_text = self.__pad(plain_text) iv = Random.new().read(self.block_size) cipher = AES.new(self.key, AES.MODE_CBC, iv) encrypted_text = cipher.encrypt(plain_text) # Combine IV and encrypted text, then base64 encode for safe representation return b64encode(iv + encrypted_text).decode("utf-8") def decrypt(self, encrypted_text): # Decrypt the provided ciphertext using AES in CBC mode encrypted_text = b64decode(encrypted_text) iv = encrypted_text[:self.block_size] cipher = AES.new(self.key, AES.MODE_CBC, iv) plain_text = cipher.decrypt(encrypted_text[self.block_size:]) return self.__unpad(plain_text) def get_key(self): # Get the base64 encoded representation of the key return b64encode(self.key).decode("utf-8") def __pad(self, plain_text): # Add PKCS7 padding to the plaintext number_of_bytes_to_pad = self.block_size - len(plain_text) % self.block_size padding_bytes = bytes([number_of_bytes_to_pad] * number_of_bytes_to_pad) padded_plain_text = plain_text.encode() + padding_bytes return padded_plain_text @staticmethod def __unpad(plain_text): # Remove PKCS7 padding from the plaintext last_byte = plain_text[-1] return plain_text[:-last_byte] if isinstance(last_byte, int) else plain_text
关键的修改在于 __init__ 方法中，当 key 参数存在时，使用 b64decode(key.encode()) 对其进行 Base64 解码，而不是计算哈希值。
完整代码示例:
以下是包含修正后的 AESCipher 类的完整代码示例，并包含加密、解密以及保存到文件等功能。
import hashlibfrom Crypto.Cipher import AESfrom Crypto import Randomfrom base64 import b64encode, b64decodeclass AESCipher(object): def __init__(self, key=None): # Initialize the AESCipher object with a key, defaulting to a randomly generated key self.block_size = AES.block_size if key: self.key = b64decode(key.encode()) else: self.key = Random.new().read(self.block_size) def encrypt(self, plain_text): # Encrypt the provided plaintext using AES in CBC mode plain_text = self.__pad(plain_text) iv = Random.new().read(self.block_size) cipher = AES.new(self.key, AES.MODE_CBC, iv) encrypted_text = cipher.encrypt(plain_text) # Combine IV and encrypted text, then base64 encode for safe representation return b64encode(iv + encrypted_text).decode("utf-8") def decrypt(self, encrypted_text): # Decrypt the provided ciphertext using AES in CBC mode encrypted_text = b64decode(encrypted_text) iv = encrypted_text[:self.block_size] cipher = AES.new(self.key, AES.MODE_CBC, iv) plain_text = cipher.decrypt(encrypted_text[self.block_size:]) return self.__unpad(plain_text) def get_key(self): # Get the base64 encoded representation of the key return b64encode(self.key).decode("utf-8") def __pad(self, plain_text): # Add PKCS7 padding to the plaintext number_of_bytes_to_pad = self.block_size - len(plain_text) % self.block_size padding_bytes = bytes([number_of_bytes_to_pad] * number_of_bytes_to_pad) padded_plain_text = plain_text.encode() + padding_bytes return padded_plain_text @staticmethod def __unpad(plain_text): # Remove PKCS7 padding from the plaintext last_byte = plain_text[-1] return plain_text[:-last_byte] if isinstance(last_byte, int) else plain_textdef save_to_notepad(text, key, filename): # Save encrypted text and key to a file with open(filename, 'w') as file: file.write(f"Key: {key}nEncrypted text: {text}") print(f"Text and key saved to {filename}")def encrypt_and_save(): # Take user input, encrypt, and save to a file user_input = "" while not user_input: user_input = input("Enter the plaintext: ") aes_cipher = AESCipher() # Randomly generated key encrypted_text = aes_cipher.encrypt(user_input) key = aes_cipher.get_key() filename = input("Enter the filename (including .txt extension): ") save_to_notepad(encrypted_text, key, filename)def decrypt_from_file(): # Decrypt encrypted text from a file using a key filename = input("Enter the filename to decrypt (including .txt extension): ") with open(filename, 'r') as file: lines = file.readlines() key = lines[0].split(":")[1].strip() encrypted_text = lines[1].split(":")[1].strip() aes_cipher = AESCipher(key) decrypted_bytes = aes_cipher.decrypt(encrypted_text) # Decoding only if the decrypted bytes are not empty decrypted_text = decrypted_bytes.decode("utf-8") if decrypted_bytes else "" print("Decrypted Text:", decrypted_text)def encrypt_and_decrypt_in_command_line(): # Encrypt and then decrypt user input in the command line user_input = "" while not user_input: user_input = input("Enter the plaintext: ") aes_cipher = AESCipher() encrypted_text = aes_cipher.encrypt(user_input) key = aes_cipher.get_key() print("Key:", key) print("Encrypted Text:", encrypted_text) decrypted_bytes = aes_cipher.decrypt(encrypted_text) decrypted_text = decrypted_bytes.decode("utf-8") if decrypted_bytes else "" print("Decrypted Text:", decrypted_text)# Menu Interfacewhile True: print("nMenu:") print("1. Encrypt and save to file") print("2. Decrypt from file") print("3. Encrypt and decrypt in command line") print("4. Exit") choice = input("Enter your choice (1, 2, 3, or 4): ") if choice == '1': encrypt_and_save() elif choice == '2': decrypt_from_file() elif choice == '3': encrypt_and_decrypt_in_command_line() elif choice == '4': print("Exiting the program. Goodbye!") break else: print("Invalid choice. Please enter 1, 2, 3, or 4.")
注意事项：
密钥安全： 请务必安全地存储和传输密钥。避免将密钥硬编码到代码中。编码问题： 在处理文本时，确保使用一致的编码方式（如 UTF-8）。Padding： PKCS7 padding 是 AES 加密常用的填充方式，确保加密和解密都使用相同的填充方式。IV (Initialization Vector)： 每次加密都应该使用不同的 IV，以增强安全性。
总结：
通过修正 AESCipher 类的构造函数，确保在解密时正确处理密钥，可以有效解决 AES 解密后文本为空的问题。同时，注意密钥安全、编码一致性以及正确的填充方式，可以提高加密系统的安全性。
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