I need help decrypting a game save.

[INeedHelp1]

I'm trying to decrypt the files in a 360 save, I have no Idea what I'm doing and understand none of this.

The only think I know is that the game uses a XOR key, saved in ~~xenon~filemap~~ file, and the code to decrypt it is:

for (int i = 0, n = 0; i < buffer.Length; i++, n++) {
if (n % filemap.Length == 0)
n = 0;

buffer[i] ^= filemap[n];
}

here's a link to the files:
http://www.mediafire.com/file/e7r878kep1l658q/Im+So+Lost.rar

I have the program Dev-C++ if anyone would be kind enough to figure this out, or at least hold my hand in attempting this myself because I have literally 0 experience with this.

Also absolute worst case scenario this information is old and I'd need to figure this out some other way. Maybe there's a way to bruteforce the correct key so I could re-encrypt it, or maybe they get decrypted but are compressed... Then I'd need even more help.

[jonnin]

if you have the keys it should be simple. but you need the datatypes as well, is this byte-wise?

the key to simple encryption with xor is that
a ^ b = c
then
c ^ b = a

so the process is 100% reversible.
so what you need is how many bytes are being encrypted per xor, then just apply the value from the key table to the data, and its done.

I used to encrypt this way in college because our code was reachable by other students who would steal your homework if you did not... I just used this..

cin numeric password
srand(password)
for(all the bytes)
byte ^= rand()

and as rand gives the same values for the same seed, it was just 5 or 10 lines (including file handling etc) to do a file but unbreakable enough without the password to deter lazy students.

the only way I know to crack this is to either have the keys, the algorithm for the keys, or if the algorithm is repeatable, you can have it encrypt known data, and you can do the same thing as above, known data xord with the encrypted version will give the keys same as encrypted data xored with the keys gives the data... so you can hack it easily if the keys are the same for every file... but they probably are not... depends on how serious they were about keeping you out of it. I don't mind sharing this 'hack' because its so simple.. anything that can be cracked this way can't have been critical to protect...

if the file is compressed, the first 100 bytes or so of almost all compressed files will tell you that, eg a zip file will have a dozen "this is a zip file" clues in plain text that you can see in a hex editor.