6 ms·

If you restrict the machine code it makes it that much easier for me to write an emulator to execute your machine code and return the result. It might even be t

If you restrict the machine code it makes it that much easier for me to write an emulator to execute your machine code and return the result. It might even be trivial. It is a never ending Ouroboros. You build a more clever mouse trap, I will design a more clever mouse. If I have all your code and am running it on my computer it will be a matter of time before I can back out whatever obfuscation or technique you are doing and undo it. You may have some hope in network delivery of graphics only. If I am not running the game client code, and just streaming the game from one of your servers, you have a chance at keeping your client safe.

jonjojr 8y ago
"If I have all your code and am running it on my computer it will be a matter of time before I can back out whatever obfuscation or technique you are doing and undo it." sure try to undo a block-chain and see what happens. The code will be encrypted with a unique key that will need to be registered on the server with your account. Change that code and it invalidates your entire build along with your account. case closed.
- iancarroll 8y ago
  Blockchains are not a solution here. This comment doesn't make much sense; your proposed solution is missing a lot of details. If there was a simple solution to this problem there would not be insanely complicated packers that basically try to make their own instruction set.
- tangent128 8y ago
  If the player controls the CPU the code is running on, there is fundamentally no way to enforce they are actually running the code provided.
- throwaway2048 8y ago
  This is a very bad analogy, and you have misunderstood the problem to a huge degree.
- bitexploder 8y ago
  I think you are missing my point. This concept in client computing security basically chains back to the halting problem. You can't /know/ what I am doing with my computer. You can build a very elaborate trap / obfuscation and it might be hard, really hard, to defeat it or circumvent it, but it is a certainty that I can. The block-chain has absolutely nothing to do with client code security because it has a network enforced mechanism. What the grandparent was suggesting was running some nugget of code in a little VM (or actually on my machine), computing a result, and then returning the result to the server to make a security decision. The problem is I control that machine performing that computation and your security decision as the server is based solely on the computation performed on my computer. A skilled reverse engineer will just hook your code in the right place, intercept that security check and have it return the right bytes back to your server, while still doing whatever client side cheats they wanted to do. https://en.wikipedia.org/wiki/Rice%27s_theorem https://en.wikipedia.org/wiki/Rice%27s_theorem <--- this is all about program behavior and did the user actually run the code you sent them. Block chain is about "did I possess certain data" (such as a private key to sign a transaction) and not about "did I run certain code".
  - mikekchar 8y ago
    You are absolutely correct, but it occurs to me that CPU designers could actually implement a kind of RSA style memory fetch instruction. The CPU would generate a public/private key pair, where the private key is not accessible by any means. The client would send the public key to the server, which would in turn encrypt the memory location(s) that it wishes to inspect. There would then be an instruction on client's CPU which would accept that encrypted memory location and return the contents, without divulging location. The CPU could regenerate the public/private key values for each request. I can't imagine defeating that kind of scheme without hardware hacks. The more that I think about it, the more I wonder why no-one has done it before, because it seems useful. Probably there is something I'm missing...
    - unknownid 8y ago
      How do you prevent the cheat doing a MITM attack and changing keys?
- matheusmoreira 8y ago
  A server can't validate the integrity of the game remotely. A program on the user's computer must do that for you. You're trusting that the program will do what you expect it to do. All one needs to do is modify the program to make it always tell your server the build is valid. Problem solved.
infogulch 8y ago
> emulator to execute your machine code I think you missed a part. Namely that "It is allowed to read from anywhere". If it can't write anywhere but the sandbox, that just means it can't modify the game dynamically, just read its state. Which is plenty to verify whether the client has been hacked anywhere. You can read spans of .text to check whether code has been modified, you can read heap locations to check whether the state of the game is valid, and you can take all of that and hash it with a random seed included in the packet to set a high bar on the speed of any emulator. Your emulator would have to dynamically check every access to make sure it doesn't touch anything that has been tampered with, and change the reads to read from un-modified sections, while allowing it to view everything else accurately. Seems like a high level of effort for the cheater, for a low investment from the developer.
- drdaeman 8y ago
  A sandbox can be a virtual machine, for all practical purposes indistinguishable from any "normal" computers ordinary players use. Of course this will lead to the never ending Ouroboros of more sophisticated detectors and more sophisticated virtualization, ad infinitum. I've heard there are cheats that use hypervisors to stand above the operating systems and avoid kernel-level anti-cheats. I wouldn't be too surprised to learn about cheats that sit on a bus and use DMA to peek into anything they please (subject to the memory protections of IOMMU - again, this war doesn't seem to have an end) - they're probably impractical but not something that couldn't exist.
  - bitexploder 8y ago
    Hah. Are you me? That is what I always call the cat and mouse of cheat / anti cheat. (An Ouroboros) :-D
    - drdaeman 8y ago
      I've just read your comment above and then quoted you without the proper credit ;) Liked the naming.

jonjojr 8y ago

"If I have all your code and am running it on my computer it will be a matter of time before I can back out whatever obfuscation or technique you are doing and undo it." sure try to undo a block-chain and see what happens. The code will be encrypted with a unique key that will need to be registered on the server with your account. Change that code and it invalidates your entire build along with your account. case closed.

iancarroll 8y ago
Blockchains are not a solution here. This comment doesn't make much sense; your proposed solution is missing a lot of details. If there was a simple solution to this problem there would not be insanely complicated packers that basically try to make their own instruction set.
tangent128 8y ago
If the player controls the CPU the code is running on, there is fundamentally no way to enforce they are actually running the code provided.
throwaway2048 8y ago
This is a very bad analogy, and you have misunderstood the problem to a huge degree.
bitexploder 8y ago
I think you are missing my point. This concept in client computing security basically chains back to the halting problem. You can't /know/ what I am doing with my computer. You can build a very elaborate trap / obfuscation and it might be hard, really hard, to defeat it or circumvent it, but it is a certainty that I can. The block-chain has absolutely nothing to do with client code security because it has a network enforced mechanism. What the grandparent was suggesting was running some nugget of code in a little VM (or actually on my machine), computing a result, and then returning the result to the server to make a security decision. The problem is I control that machine performing that computation and your security decision as the server is based solely on the computation performed on my computer. A skilled reverse engineer will just hook your code in the right place, intercept that security check and have it return the right bytes back to your server, while still doing whatever client side cheats they wanted to do. https://en.wikipedia.org/wiki/Rice%27s_theorem https://en.wikipedia.org/wiki/Rice%27s_theorem <--- this is all about program behavior and did the user actually run the code you sent them. Block chain is about "did I possess certain data" (such as a private key to sign a transaction) and not about "did I run certain code".
- mikekchar 8y ago
  You are absolutely correct, but it occurs to me that CPU designers could actually implement a kind of RSA style memory fetch instruction. The CPU would generate a public/private key pair, where the private key is not accessible by any means. The client would send the public key to the server, which would in turn encrypt the memory location(s) that it wishes to inspect. There would then be an instruction on client's CPU which would accept that encrypted memory location and return the contents, without divulging location. The CPU could regenerate the public/private key values for each request. I can't imagine defeating that kind of scheme without hardware hacks. The more that I think about it, the more I wonder why no-one has done it before, because it seems useful. Probably there is something I'm missing...
  - unknownid 8y ago
    How do you prevent the cheat doing a MITM attack and changing keys?
matheusmoreira 8y ago
A server can't validate the integrity of the game remotely. A program on the user's computer must do that for you. You're trusting that the program will do what you expect it to do. All one needs to do is modify the program to make it always tell your server the build is valid. Problem solved.

infogulch 8y ago

> emulator to execute your machine code I think you missed a part. Namely that "It is allowed to read from anywhere". If it can't write anywhere but the sandbox, that just means it can't modify the game dynamically, just read its state. Which is plenty to verify whether the client has been hacked anywhere. You can read spans of .text to check whether code has been modified, you can read heap locations to check whether the state of the game is valid, and you can take all of that and hash it with a random seed included in the packet to set a high bar on the speed of any emulator. Your emulator would have to dynamically check every access to make sure it doesn't touch anything that has been tampered with, and change the reads to read from un-modified sections, while allowing it to view everything else accurately. Seems like a high level of effort for the cheater, for a low investment from the developer.

drdaeman 8y ago
A sandbox can be a virtual machine, for all practical purposes indistinguishable from any "normal" computers ordinary players use. Of course this will lead to the never ending Ouroboros of more sophisticated detectors and more sophisticated virtualization, ad infinitum. I've heard there are cheats that use hypervisors to stand above the operating systems and avoid kernel-level anti-cheats. I wouldn't be too surprised to learn about cheats that sit on a bus and use DMA to peek into anything they please (subject to the memory protections of IOMMU - again, this war doesn't seem to have an end) - they're probably impractical but not something that couldn't exist.
- bitexploder 8y ago
  Hah. Are you me? That is what I always call the cat and mouse of cheat / anti cheat. (An Ouroboros) :-D
  - drdaeman 8y ago
    I've just read your comment above and then quoted you without the proper credit ;) Liked the naming.