How does Apple know you are using private API?

Question

I submitted a binary file to Apple without any source code.

Apart from manually checking the source code how does Apple know what was used and what APIs you have called?

Answer 1

A executable isn't exactly a black box. If you call out to a library, it's an easy thing to find. This is why I lament the loss of the assembly languages in modern CS educations. =] Tools like ldd will tell you what you have linked in, though I don't remember what incarnation of ldd made it to the mac iPhone dev kit.

Answer 2

I imagine they look at all symbols your binary's trying to import (info no doubt easily available to them in the symbol table thereof) and ding you if any of those symbols are found in their "private API list". Pretty easy to automate, in fact.

Answer 3

This desktop application, App Scanner, can scan .app files for private api usage by pulling apart the Mach-O Binary file. If it can, then Apple can too!

Answer 4

You can list the selectors in a Mach-O program using the following one-liner in Terminal:

otool -s __TEXT __objc_methname "$1" |expand -8 | cut -c17- | sed -n '3,$p' | perl -n -e 'print join("\n",split(/\x00/,scalar reverse (reverse unpack("(a4)*",pack("(H8)*",split(/\s/,$_))))))'

Answer 5

aside from symbol investigation...

apple could very easily have a version of the sdk that checks each of the private methods stacks when called to make sure it is entered from one of the designated methods.

Answer 6

Let's say you want to use some private API; objective C allows you to construct any SEL from a string:

   SEL my_sel = NSSelectorFromString([NSString stringWithFormat:\
@"%@%@%@", "se","tOr","ientation:"]);
    [UIDevice performSelector:my_sel ...];

How could a robot or library scan catch this? They would have to catch this using some tool that monitors private accesses at runtime. Even if they constructed such a runtime tool, it is hard to catch because this call may be hidden in some rarely exercised path.