Make .txt file unreadable / uneditable

Question

I have a program which saves a little .txt file with a highscore in it:

 // Create a file to write to. 
string createHighscore = _higscore + Environment.NewL         


        

Answer 1

As you seem to look for relatively low security, I'd actually recommend going for a checksum. Some pseudo-code:

string toWrite = score + "|" + md5(score+"myKey") + Environment.NewLine

If the score would be 100, this would become

100|a6b6b0a8e56e42d8dac51a4812def434

To make sure the user didn't temper with the file, you can then use:

string[] split = readString().split("|");
if (split[1] != md5(split[0]+"myKey")){
     alert("No messing with the scores!");
}else{
     alert("Your score is "+split[0]);
}

Now of course as soon as someone gets to know your key they can mess with this whatever they want, but I'd consider that beyond the scope of this question. The same risk applies to any encryption/decryption mechanism.

One of the problems, as mentioned in the comments down below, is that once someone figures out your key (through brute-forcing), they could share it and everybody will be able to very easily change their files. A way to resolve this would be to add something computer-specific to the key. For instance, the name of the user who logged in, ran through md5.

string toWrite = score + "|" + md5(score+"myKey"+md5(System.username /**or so**/)) + Environment.NewLine

This will prevent the key from being "simply shared".