def readNewVMDK():
    '''
    read a new VMDK created from text file
    '''
    #read as binary instead of text as destination file has null bytes and to be edited as binary file
    with open("newVMDKdesc.txt", "rb") as vmdkDescFile:
        vmdkDescriptor = vmdkDescFile.read()
    print(len(vmdkDescriptor), "bytes read from the descriptor text file")
    print(vmdkDescriptor)
    return vmdkDescriptor

def replaceMetaDataDescriptor(newVmdkDescriptor):
    '''
    replace the encrypted VMDK descriptor with new unencrypted descriptor text read from file
    '''
    with open("Metadata.bin", "rb+") as metaDataFile:
        nullBytesToPad = 0x550 - 0x200 - len(newVmdkDescriptor)
        nullBytes = b'\x00' * nullBytesToPad
        metaDataFile.seek(0x200)
        metaDataFile.write(newVmdkDescriptor)
        print("VMDK descriptor replaced")
        metaDataFile.write(nullBytes)
        print("padded ", nullBytesToPad, "null bytes")


def main():
    newVmdkDescriptor = readNewVMDK()
    replaceMetaDataDescriptor(newVmdkDescriptor)

if __name__ == "__main__":
    main()