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diff --git a/doc-src/tutorials/gamecenter.html b/doc-src/tutorials/gamecenter.html new file mode 100644 index 00000000..d8209f5e --- /dev/null +++ b/doc-src/tutorials/gamecenter.html @@ -0,0 +1,122 @@ + +## The setup + +In this tutorial, I'm going to show you how simple it is to creatively +interfere with Apple Game Center traffic using mitmproxy. To set things up, I +registered my mitmproxy CA certificate with my iPhone - there's a [step by step +set of instructions](@!urlTo("certinstall/ios.html")!@) elsewhere in this manual. I then +started mitmproxy on my desktop, and configured the iPhone to use it as a +proxy. + + +## Taking a look at the Game Center traffic + +Lets take a first look at the Game Center traffic. The game I'll use in this +tutorial is [Super Mega +Worm](http://itunes.apple.com/us/app/super-mega-worm/id388541990?mt=8) - a +great little retro-apocalyptic sidescroller for the iPhone: + +<center> + <img src="@!urlTo('tutorials/supermega.png')!@"/> +</center> + +After finishing a game (take your time), watch the traffic flowing through +mitmproxy: + +<center> + <img src="@!urlTo('tutorials/one.png')!@"/> +</center> + +We see a bunch of things we might expect - initialisation, the retrieval of +leaderboards and so forth. Then, right at the end, there's a POST to this +tantalising URL: + +<pre> +https://service.gc.apple.com/WebObjects/GKGameStatsService.woa/wa/submitScore +</pre> + +The contents of the submission are particularly interesting: + +<!--(block|syntax("xml"))--> +<plist version="1.0"> + <dict> + <key>scores</key> + <array> + <dict> + <key>category</key> + <string>SMW_Adv_USA1</string> + <key>context</key> + <integer>0</integer> + <key>score-value</key> + <integer>0</integer> + <key>timestamp</key> + <integer>1363515361321</integer> + </dict> + </array> + </dict> +</plist> +<!--(end)--> + +This is a [property list](http://en.wikipedia.org/wiki/Property_list), +containing an identifier for the game, a score (55, in this case), and a +timestamp. Looks pretty simple to mess with. + + +## Modifying and replaying the score submission + +Lets edit the score submission. First, select it in mitmproxy, then press +__enter__ to view it. Make sure you're viewing the request, not the response - +you can use __tab__ to flick between the two. Now press __e__ for edit. You'll +be prompted for the part of the request you want to change - press __b__ for +body. Your preferred editor (taken from the EDITOR environment variable) will +now fire up. Lets bump the score up to something a bit more ambitious: + +<!--(block|syntax("xml"))--> +<plist version="1.0"> + <dict> + <key>scores</key> + <array> + <dict> + <key>category</key> + <string>SMW_Adv_USA1</string> + <key>context</key> + <integer>0</integer> + <key>score-value</key> + <integer>2200272667</integer> + <key>timestamp</key> + <integer>1363515361321</integer> + </dict> + </array> + </dict> +</plist> +<!--(end)--> + +Save the file and exit your editor. + +The final step is to replay this modified request. Simply press __r__ for +replay. + +## The glorious result and some intrigue + +<center> + <img src="@!urlTo('tutorials/leaderboard.png')!@"/> +</center> + +And that's it - according to the records, I am the greatest Super Mega Worm +player of all time. + +There's a curious addendum to this tale. When I first wrote this tutorial, all +the top competitors' scores were the same: 2,147,483,647 (this is no longer the +case, beacause there are now so many fellow cheaters using this tutorial). If +you think that number seems familiar, you're right: it's 2^31-1, the maximum +value you can fit into a signed 32-bit int. Now let me tell you another +peculiar thing about Super Mega Worm - at the end of every game, it submits +your highest previous score to the Game Center, not your current score. This +means that it stores your highscore somewhere, and I'm guessing that it reads +that stored score back into a signed integer. So, if you _were_ to cheat by the +relatively pedestrian means of modifying the saved score on your jailbroken +phone, then 2^31-1 might well be the maximum score you could get. Then again, +if the game itself stores its score in a signed 32-bit int, you could get the +same score through perfect play, effectively beating the game. So, which is it +in this case? I'll leave that for you to decide. + |