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Reverse Engineering Snapchat: Obfuscation Techniques

hot3eed.github.io

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Re: Reverse Engineering Snapchat: Obfuscation Techniques

#4

Post by bri3d »

iampims wrote: post #2

Things were definitely much simpler a couple years ago.

I'm actually a bit surprised it's taken as long as it has for mobile obfuscation to catch up. Both on the Android bytecode and the iOS native code side there are obvious PC analogs in the form of .NET obfuscators for MSIL and packers and game DRM for native code. Of course, the Obj-C runtime throws a little wrench into things on iOS, making it a bit of a hybrid - but the approaches are still similar.

It's still an ultimately pointless cat and mouse game as long as an attacker can trace the hardware (and with full-platform emulation tools like Corellium, this capability is unlikely to go away soon), but still an amusing one to watch.

Re: Reverse Engineering Snapchat: Obfuscation Techniques

#6

Post by zelly »

Snapchat is notoriously difficult to automate/spam.

The goal is to get the X-Snapchat token. The most elegant solution is to find the secret in the binary and reverse the algorithm to generate tokens. Wouldn't it be easier to MITM the endpoint; set up a dummy server (which collects tokens) in front of a proxy that spoofs the DNS and TLS certs (may be easier on rooted Android than iOS).

In my last attempt I gave up and went for dumb UI automation, but it would be cool (and worth good money) to exploit the private API.

Re: Reverse Engineering Snapchat: Obfuscation Techniques

#7

Post by bri3d »

MintelIE wrote: post #5

Doesn't Snapchat mainly rely upon the iOS or Android platform having some software that prevents screen shots if a 'no screen shots' flag is set? I always thought this was their core defense.

Their "core defense" for an end user is to notify the sender of a message if their post was screenshotted by using native screenshot detection/notification libraries provided by the OS, combined with heuristics to try to prevent them from beeing hooked and bypassed.

However, the binary level protection is only tangentially anti-screenshot insofar as it also blocks third-party 'scraper' apps. Fundamentally, it's about requiring use of the Snapchat app to access the Snapchat APIs, and as we know from the ongoing saga with other social networks like Twitter, this is ultimately about business control over posts (preventing spam-bots, scheduled clients, and so on) and at the end of the day, ad revenue.

Re: Reverse Engineering Snapchat: Obfuscation Techniques

#8

Post by zelly »

programmarchy wrote: post #3

How many of these tricks are off the shelf techniques? Seems like a tremendous effort.

There are numerous commercial compilers (for C and C++) that specialize in obfuscation. I suspect they are using one because to do that level of obfuscation manually would make the source code unreadable.
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