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Python AES 加密解密后文本为空问题的解决方案

心靈之曲

发布： 2025-10-02 18:25:01

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python aes 加密解密后文本为空问题的解决方案

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 hashlib
from Crypto.Cipher import AES
from Crypto import Random
from base64 import b64encode, b64decode


class 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

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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。

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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 hashlib
from Crypto.Cipher import AES
from Crypto import Random
from base64 import b64encode, b64decode


class 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


def 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 Interface
while 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.")

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