How can I sign a digit and trust a message in a distributed program that I know can be programmed with feedback?

Question

The problem in short: I am developing an application (such as a game) that is distributed in binary form. The game calls home and sends the user a high score as a message to the online games server.

What I would like to do is digitally encrypt and sign the message so that I can trust that it has not been tampered with.

Public key cryptography is based on each end of the conversation that has a secret, but I cannot rely on the fact that my software is not reversed and the private key is discovered.

Is there a safe or secure way to digitally sign (in this case, part of the encryption is not required) message from my distributed binary application, when I know that it could be reverse engineering?

Answer 1

In short: no ... there is no perfect solution for this. The problem is that the application that sends you high scores works under the control of someone you don’t “trust” in this transaction. If they can reverse engineer the code, then they can modify the content of any message before signing it.

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