It uses a key that you can set, so it is tied to your application in a way.
It's not too difficult to crack but I doubt anyone would go to the trouble if it's just a game save.
If you really feel like the data file needs extra protection you could also use blowfish to encrypt it.
However your app will still need to decrypt it before it could be loaded into memory, so with the right tools all one has to do is grab the file after it has been decrypted. I did that before with an online game that was uploaded to this site, set my character's level to 9999
Prolly the biggest concern is memory hacking, once the file is decrypted and loaded then it's stored in memory as plain text. It can then be edited with a memory viewer and then your program will then save the edited data back to the file.
Like I said though, most won't go to the trouble, so just use the encryption since it'll keep most people from tampering and it's easy to use.
All encryptions are breakable, it all depends on what skills the person trying to break it has. But I really doubt that anyone will go to such lengths to open a savefile or what-not. As long as there isn't money involved it's just not that important.
Also don't use something stupid for a key like 123456.
You could try a defense-in-depth approach.
1. Calculate your own checksum of values. For example checksum = (time mod 555) + (level * 3) + (lives * 7)
Extend it to as many items you're gonna use of course. Also add some random unused items just to confuse.
2. Encrypt with blowfish or RC4 or encryption of your choice.
3. Store a hash of the encrypted file in a second file.
- Ok, you must admit that was the most creative cussing this site have ever seen -