Python toolbox series (12)

In the computer world there is only binary.Only humans can make type and value judgments about data.例如,Some files are considered to be text files、是WORD/EXCELfiles or pictures.The same is true for encryption algorithms,Encryption and decryption algorithms only deal with byte streams,Don't care about the so-called file type at all.对于文件来说,The following basic operations exist：

◆ open

◆ close

◆ read

◆ write

◆ delete

在Unix世界中,It takes the concept of files to the extreme,Think of everything as a file,Both can be opened in a basically similar way,Also known as primitives.python也不例外,Provides built-in file manipulation functions.The code below demonstrates how toword文档进行加密.假设我们用WORDThe document writes a paragraph of text,内容如下图所示.

This is of course a famous poem by Cao Cao,我们使用AESalgorithm to encrypt and decrypt.AESIs a very mature、安全、Internationally used encryption and decryption algorithm for symmetric ciphers,供AESAn important parameter for encryption and decryption is the key.This key is just a random string,通常是128位或256位字长.AESThe key used for encryption and decryption is no different from other cryptographic algorithms.废话不说,直接上代码.

import os
import struct
from Crypto.Cipher import AES
from Crypto.Util.Padding import pad, unpad

defaultsize = 64*1024

def encrypt_file(key, in_filename, out_filename=None, chunksize=defaultsize):
    """
    对文件进行加密

    Args:
        key (str): 16字节密钥
        in_filename (str): 待加密文件
        out_filename (str, optional): The encrypted output file
        chunksize (int, optional): 块大小,缺省64k
    """
    if not out_filename:
        out_filename = in_filename + '.enc'
    iv = os.urandom(16)
    encryptor = AES.new(key, AES.MODE_CBC, iv)
    filesize = os.path.getsize(in_filename)
    with open(in_filename, 'rb') as infile:
        with open(out_filename, 'wb') as outfile:
            outfile.write(struct.pack('<Q', filesize))
            outfile.write(iv)
            pos = 0
            while pos < filesize:
                chunk = infile.read(chunksize)
                pos += len(chunk)
                if pos == filesize:
                    chunk = pad(chunk, AES.block_size)
                outfile.write(encryptor.encrypt(chunk))


def decrypt_file(key, in_filename, out_filename=None, chunksize=defaultsize):
    """
    解密文件

    Args:
        key (str): 16字节密钥
        in_filename (str): 待解密文件
        out_filename (str, optional): The decrypted output file
        chunksize (int, optional): 块大小,缺省64K
    """
    if not out_filename:
        out_filename = in_filename + '.dec'
    with open(in_filename, 'rb') as infile:
        filesize = struct.unpack('<Q', infile.read(8))[0]
        iv = infile.read(16)
        encryptor = AES.new(key, AES.MODE_CBC, iv)
        with open(out_filename, 'wb') as outfile:
            encrypted_filesize = os.path.getsize(in_filename)
            pos = 8 + 16  # the filesize and IV.
            while pos < encrypted_filesize:
                chunk = infile.read(chunksize)
                pos += len(chunk)
                chunk = encryptor.decrypt(chunk)
                if pos == encrypted_filesize:
                    chunk = unpad(chunk, AES.block_size)
                outfile.write(chunk)

   
# 密钥,随便写,Use only before use16字节
key = 'stayhungrystayfoolish'

def test_enc():
    sourcefilename=r'../resources/神龟虽寿.docx'
    encrypt_file(key[:16].encode('utf-8'), sourcefilename)

def test_dec():
    sourcefilename=r'../resources/神龟虽寿.docx.enc'
    targetfilename=r'../resources/decrypt.docx'
    decrypt_file(key[:16].encode('utf-8'), sourcefilename,out_filename=targetfilename)
    
if __name__ == '__main__':
    test_enc()
    test_dec()

我们这里使用128Bit key for encryption and decryption,The encrypted file is Microsoft'sWORD也打不开,The internal structure has been completely changed,The decrypted file is no different from the original document.从代码可以看出,The encryption and decryption of files provided in this article has nothing to do with the file type,It is completely possible to use this algorithm for music、Encrypt and decrypt video, etc,If used togetherQT等开发工具,Can be further upgraded to be easy to useGUIInterface file encryption and decryption.补充一点,The above encryption and decryption algorithm library needs to install the corresponding package,使用以下命令即可.

pip install PyCryptodome