[WeAreDevelopers World Conference] Reversing Android Apps

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Reversing Android Apps

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Marc Obrador Lead Architect @ Build38 Barcelona [email protected] @marcobrador /in/marc-obrador

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Source: https://en.wikipedia.org/wiki/Reverse_engineering It’s illegal (in the EU)!

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Josep Bernad iOS Albert Sunyer UI

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Artà is in Mallorca ABF takes place (usually) in June COVID-19 pushed it to … ?

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Get to know the app Step 0

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Get to know the app

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Get to know the app

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Get to know the app

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Get to know the app

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Static Analysis Step 1

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Static Analysis

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Getting the APK

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Decompiling the app https://ibotpeaches.github.io/Apktool/ $ brew install apktool

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Decompiling the app

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Let’s keep looking around

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Wait… “discount codes”?

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App users get a discount for events

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Let’s take a closer look…

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HTTP Basic Authorisation = Base64(“username:password”)

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HTTP Basic Authorisation = Base64(“username:password”) username = “string1” xor “string2” pasword = “string3” xor “string2”

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Protecting against static analysis ProGuard is a good start… for regular apps • It’s just method renaming and code shrinking • Tools for reversing ProGuard exist: http://apk-deguard.com/ Other (paid) alternatives exist for obfuscation Writing sensitve code in native (NDK) is a good idea

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Dynamic Analysis Step 2

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Dynamic Analysis

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Dynamic Analysis

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Network Sniffing a.k.a MITM

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Network Sniffing https://www.charlesproxy.com/

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Setting Up Charles Proxy

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Setting Up Charles Proxy

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Setting Up Charles Proxy

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First attempt…

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First attempt…

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Setting Up Charles Proxy

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Setting Up Charles Proxy

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Let’s try again…

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• Use certificate pinning • Implement Root/Debugger/Emulator/Hooking Framework detection • Try to detect app tampering Protecting against dynamic analysis

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Using Certificate Pinning Source: https://developer.android.com/training/articles/security-config

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Tampering with the App Step 3

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Assuming the app implemented Certificate Pinning…

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$ adb install “Downloads/Artà Beer Festival_v1.2.5_apkpure.com.apk” Performing Streamed Install Success $ adb shell am start com.marcobrador.android.artabeerfestival/.SplashActivity Starting: Intent { act=android.intent.action.MAIN cat=[android.intent.category .LAUNCHER] cmp=com.marcobrador.android.artabeerfestival/.SplashActivity }