你以后是专门的工具这是能够做字符串混淆

这个免费的工具做得很好
http://www.ntcore.com/phoenix.php

The problem is that my dll deals with encryption and the key is stored in constant variable. I want the key to be difficult to get. I understand that there's no way to hide it completely, but I hope there's a way to make it difficult to get the key. What could you suggest?
Thank you for your help!

What you are after is specifically tool that is capable of doing "String Obfuscation"

This free tool does it well http://www.ntcore.com/phoenix.php