Well, in short I would deem nothing 'unhackable'. Most people would have considered OpenSSL to be safe, and the Heartbleed-bug showed that in certain cases this was unsafe as well. A cynical answer would therefore be: nothing is unhackable.
The other part of this is that everything that will be decrypted on your user's client side will be accessible to him/her. So, by asking for something unhackable, who is not allowed to have the information? Is it your user that cannot see the information? Or is it just the data as it is in transit?
In the encryption debate, I think it is important to strike a balance between 'unhackability' and 'impact if hacked'. If the consequences of an intercepted message would be that one player would know the location of another, and would be cheating, it would probably be more efficient to implement a good banning system, instead of trying to create a really secure system.