## 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, install the [mitmproxy root certificate](@!urlTo("certinstall.html")!@). Then start mitmproxy on your desktop, and confige 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:

After finishing a game (take your time), watch the traffic flowing through mitmproxy:

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:

https://service.gc.apple.com/WebObjects/GKGameStatsService.woa/wa/submitScore

The contents of the submission are particularly interesting: scores category SMW_Adv_USA1 context 0 score-value 0 timestamp 1363515361321 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 __r__ for raw 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: scores category SMW_Adv_USA1 context 0 score-value 2200272667 timestamp 1363515361321 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

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. ='n26' href='#n26'>26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 216 217 218 219 220 221 222 223 224 225 226 227 228 229 230 231 232 233 234 235 236 237 238 239 240 241 242 243 244 245 246 247 248 249 250 251 252 253 254 255 256 257 258 259 260 261 262 263 264 265 266 267 268 269 270 271 272 273 274 275 276 277 278 279 280 281 282 283 284 285 286 287 288 289 290 291 292 293 294 295 296 297 298 299 300 301 302 303 304 305 306 307 308 309 310 311 312 313 314 315 316 317 318 319 320 321 322 323 324 325 326 327 328 329 330 331 332 333 334 335 336 337 338 339 340 341 342 343 344 345 346 347 348 349 350 351 352 353 354 355 356 357 358 359 360 361 362 363 364