Click here. Part of GameDev that actually IS working right now

This is something I've been thinking about myself; I'd like my animation editor to be able to encrypt files via a key so people can keep others from stealing their graphics Love to hear some good encryption techniques .....

I had this tremendously huge post over at a private forum describing in detail how I go about encrypting the save files for FB demo 2, but I don't feel like reproducing it for obvious reasons

But think about this: along with modification on the byte level, why not also cut the file data into 'chunks' of various sizes and rearrange them as well? Tie that into a simple algo with a random key (like maybe the time/date stamp on the file?) and you've got some really kooky possibilities.

It works quite well ^.^

As I understand it, nothing will help against such an individual All you can really do is just make it too much trouble to be worth the effort

This is, unfortunately, the truth of the matter. Even in the world of copy protection, where Star Control II reigned supreme, there were working TSR cracks -- albeit very few that actually worked consistently.

Seems the developers got the idea of grabbing up unused interrupts so would-be crackers couldn't find anything to latch their scopes on to. According to... damn... what was his name... of INC, they forgot about one interrupt that was at the time undocumented, and he latched onto it successfully and started doing his snooping around

The crack worked, but made the game so unstable I eventually bought a real copy just so I could play the game for more than ten minutes without it crashing So, I guess you could say the protection actually worked!

Save file encryption is not the key anymore... there're very elaborate tools available to get thegfx out of the running program, scan for changing values (like scores) or even scan for changing values and try to find out if there's a relation between these changing values and the one the user is searching for.
So, stuff like XORing or using a constant or changing modifier as an offset to the values in memory as well is not secure anymore.

There're also some "trainers" out there which try to automatically skip levels by checking the asm, and then trying to find the win scenario (the jump condition) and then faking it.

In other words: In a single player game, it's normally not worth the effort. if the player wants to cheat, let him. It's his experience which gets destroyed.

If somebody wants to rip the gfx, he will. There's still the screenshot and magic wand. Take a look at the many rips from comercial (and comercially protected) files, the amount of "p1r8 copies" etc. which floats around.

Most security schemes can be "killed" by turning a conditional jump to an unconditional one. No big deal here. Once this is done (and if there's interest in the game), the modified version will float the web...

While blizzard managed to get a good scheme working for starcraft, people simply started using Blizzard's own routines (stored in a dll) to load and save the encrypted values.

If they want to hack your game, they will. Then they'll make the modified version available on the web - and you've spend a lot of time with wasting your time

You shouldn't be worried about someone hacking on your games. Because it's not safe no matter what you do.

To get a fair amount of protection:

Use packfiles with a password attached. Just don't hardcode the password in your game like this.

char my_password[ 13 ] = "mikey doodle";

Thats' the first place I look when I want to look at someone's password protected datafiles. And I usually find it. Unless the exe has been shrunked with upx. Which is another good idea to do.

This will show up in the exe file where it keeps all it's strings. What I do and does about the same thing is this.

char my_password[ 13 ] = { 'm', 'i', 'k', 'e', 'y', ' ', 'd', 'o', 'o', 'd', 'l', 'e', '\0' };

Oops, I left out the last part..!:o

You could do something, like use the day of the month the file was created to choose what number to add, then you have 31 different ways to write the save files. Added on top of that, you could write two files, and compare them? You could make a file called "credits.bmp" or something no one would look at, and use it to store a second copy of all the save files in an array. Then if a save file was edited, you'd know because it wouldn't match the one in the fake bitmap file.

Dark, that would be a bad idea in my opinion. I'd hate it when the game would restrict me from copying savegames from one computer to another (yes, some people do play single-player games with their friends).

When choosing a password for an encrypted datafile, it's best to make it generated by some formula that uses rand() with a certain seed. A word of warning though - rand() isn't portable across platforms if you need the exact same series of numbers on the same seed, so you'll need to get some other random number generator implementation from the net. Or if you are really lazy, at least use a function name as the password, that wont show up as good as other strings in the game binary.

I encrypted the high score list for my previous incarnation of NukeWar with a method almost like that... I moved things around, stored a seed (based on the time the high score was calculated), multiplied different scores with different amounts, added random numbers, and had a few checksums and other nasty things to deter people from faking their high scores. Oh, and the game erased the high score list immediately if it found that it had been tampered with

That was when I was still a complete C/Allegro newbie... this time I'm going to do some research beforehand and implement something truly devious

One option is to set some-flag-or-another that blocks all messages from the keyboard to the system. There is one somewhere, but I'm not sure where.

Unfortunately, this also blocks vital stuff like the three finger salute. It could also be worked around with some kind of timer / other input activated snapshotters.

Not only that, but it's completely ineffective
Just because they can't use hotkeys doesn't mean they can't use timer programs..

Unless it's possible to deny other programs access to the system's resources, I don't think it's possible to stop screen captures...

i heard if you use this magical place called google, it will take you where you want too, and show you the dark secrets you wish.

but i also like to shoot off my mouth, so here goes some ways to do it (wordpad? bleach. most likely your porgram just uses ASCII output and that can be read in any text editor...)

here is a simple way, what's called XOR encryption. Just open that file, read it in byte by byte, and xor it by some silly number.

Hell, you can even do a random XOR seed and make it more fun for the small time weenie hackers.

A more complicated varation on this theme would be to take the number of bytes left in a file, multiple that by a random seed, and then xor that to the data.

that way, the key "mutates". here's a pretty nice algy that will warp some data for you:

but i wouldn't use that if I were you, since i just posted it on a message board where anyone can find it and use it against your program. It's just an example.

if you use Linux, (or a varaint of GCC) you can always just use the encrypt command.