Use aes to encrypt game resource files

Original article, reprinted Please note:Reprinted from All-iPad.netLink:Use aes to encrypt game resource files

During the study of Angry Birds, I learned that some Lua script files are encrypted. For details about how to decrypt and how to find the decryption key, see the previous blog. File encryption of game resources is a must for games on PCs. Although no encryption method can prevent other people from cracking, encryption can at least increase the threshold for application cracking, to put it bluntly, no one can see everything in it.

Andgry birds uses the AES encryption algorithm to encrypt Lua files. The CBC mode is used. In addition, the original file content is compressed by 7z. In order to be able to decrypt, the key encrypted by AES will inevitably be stored somewhere in the application, so others can still find a method to crack and restore the original resource file, the specific method used is described in the previous blog.

In the course of learning how to decrypt, I found a good article to introduce how to use Python's pycrypto module to encrypt files with AES and provide Python-compiled encryption and decryption source code, in the comments that follow, someone transformed it to support streamio mode encryption and decryption, that is, the memory data can be operated.

Code has high practical value. If you need to add an encryption module to your application, this is a good start, although it may not necessarily be implemented using python.

The Code is as follows:

 

 

#!/usr/bin/env python## Code adapted from: http://eli.thegreenplace.net/2010/06/25/aes-encryption-of-files-in-python-with-pycrypto/##import os, random, structfrom Crypto.Cipher import AESfrom StringIO import StringIOimport hashlibimport base64## def encrypt_file(key, in_filename, out_filename=None, chunksize=64*1024):## ( This is an adaptation from using filenames in order that StringIO can be used to encrypt a string. )## Note: If in_file / out_file is provided, open with +b!def encrypt_file(key, in_file, out_file=None, chunksize=64*1024):    """ Encrypts a file using AES (CBC mode) with the        given key.        key:            The encryption key - a string that must be            either 16, 24 or 32 bytes long. Longer keys            are more secure.        in_file:            Input file        out_file:            If None, a StringIO will be returned.        chunksize:            Sets the size of the chunk which the function            uses to read and encrypt the file. Larger chunk            sizes can be faster for some files and machines.            chunksize must be divisible by 16.    """    if not out_file:        out_file = StringIO()    iv = ''.join(chr(random.randint(0, 0xFF)) for i in range(16))    encryptor = AES.new(key, AES.MODE_CBC, iv)    in_file.seek(0,2)    filesize=in_file.tell()    in_file.seek(0)    # filesize = os.path.getsize(in_file)    infile=in_file    outfile=out_file    outfile.seek(0)    outfile.write(struct.pack('<Q', filesize))    outfile.write(iv)    while True:        chunk = infile.read(chunksize)        if len(chunk) == 0:            break        elif len(chunk) % 16 != 0:            chunk += ' ' * (16 - len(chunk) % 16)        outfile.write(encryptor.encrypt(chunk))    outfile.seek(0)    return outfile## def decrypt_file(key, in_filename, out_filename=None, chunksize=24*1024):## ( This is an adaptation from using filenames in order that StringIO can be used to encrypt a string. )## Note: If in_file / out_file is provided, open with +b!def decrypt_file(key, in_file, out_file=None, chunksize=24*1024):    """ Decrypts a file using AES (CBC mode) with the        given key. Parameters are similar to encrypt_file.    """    if not out_file:        out_file = StringIO()    infile=in_file    infile.seek(0)    outfile=out_file    outfile.seek(0)    origsize = struct.unpack('<Q', infile.read(struct.calcsize('Q')))[0]    iv = infile.read(16)    decryptor = AES.new(key, AES.MODE_CBC, iv)    while True:        chunk = infile.read(chunksize)        if len(chunk) == 0:            break        outfile.write(decryptor.decrypt(chunk))    outfile.truncate(origsize)    outfile.seek(0)    return outfile# Method suggested by Eli by turn mnemonic password into 32 byte key.def getHashKey(aKey):    return hashlib.sha256(aKey).digest()# My ( J. Norment's ) Additionsdef getInFile(aFileName=None):    if not aFileName:        return StringIO()    else:        return open(aFileName,'rb')def getOutFile(aFileName=None):    if not aFileName:        return StringIO()    else:        return open(aFileName,'wb')def getB64encoded(aString):    return base64.b64encode(aString)def getB64decoded(aString):    return base64.b64decode(aString)

Original article, reprinted Please note:Reprinted from All-iPad.net

Link:Use aes to encrypt game resource files