Aperi’CTF 2019 - F*ck It

Challenge details

Event	Challenge	Category	Points	Solves
Aperi’CTF 2019	F*ck it	Mobile	175	4

Oula ! Ça risque de prendre du temps … (oui, il faut retrouver le mot de passe ;) )

Fichier: app-debug.s.apk - md5sum : a2ab0db5735b36dc51165de1b1d4d0d4

Frida

This application is obfuscated. The easiest way to solve this task is to use frida:

// frida -U -l script.js -f com.example.challenge --no-pause
Java.perform(function(){
    const CryptoUtil = Java.use("com.example.challenge.CryptoUtil")

    CryptoUtil.af7bd616b.implementation = function(x){
        var out = this.af7bd616b(x)
        
        
        var buffer = Java.array('byte', out);
        console.log(buffer.length);
        var result = "";
        for(var i = 0; i < buffer.length; ++i){
            result+= (String.fromCharCode(buffer[i]));
        }
        console.log(result);

        return out
    }
})

Flag

APRK{ObfuscationIsCancer}

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