# Frida Tutorial 2

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**Ovo je sažetak posta**: [https://11x256.github.io/Frida-hooking-android-part-2/](https://11x256.github.io/Frida-hooking-android-part-2/) (Delovi 2, 3 i 4)\
**APKs i izvorni kod**: [https://github.com/11x256/frida-android-examples](https://github.com/11x256/frida-android-examples)

Deo 1 je veoma lak.

**Neki delovi originalnog koda ne rade i ovde su modifikovani.**

## Deo 2

Ovde možete videti primer kako da **hook-ujete 2 funkcije sa istim imenom** ali različitim parametrima.\
Takođe, naučićete kako da **pozovete funkciju sa svojim parametrima**.\
I na kraju, postoji primer kako da **pronađete instancu klase i naterate je da pozove funkciju**.
```javascript
//s2.js
console.log("Script loaded successfully ");
Java.perform(function x() {
console.log("Inside java perform function");
var my_class = Java.use("com.example.a11x256.frida_test.my_activity");
//Hook "fun" with parameters (int, int)
my_class.fun.overload("int", "int").implementation = function (x, y) { //hooking the old function
console.log("original call: fun(" + x + ", " + y + ")");
var ret_value = this.fun(2, 5);
return ret_value;
};
//Hook "fun" with paramater(String)
var string_class = Java.use("java.lang.String");
my_class.fun.overload("java.lang.String").implementation = function (x) { //hooking the new function
console.log("*")
//Create a new String and call the function with your input.
var my_string = string_class.$new("My TeSt String#####");
console.log("Original arg: " + x);
var ret = this.fun(my_string);
console.log("Return value: " + ret);
console.log("*")
return ret;
};
//Find an instance of the class and call "secret" function.
Java.choose("com.example.a11x256.frida_test.my_activity", {
onMatch: function (instance) {
console.log(tring, and the it has"Found instance: " + instance);
console.log("Result of secret func: " + instance.secret());
},
onComplete: function () { }
});
});
```
Možete videti da je za kreiranje String-a prvo referencirana klasa _java.lang.String_, a zatim je kreiran _$new_ objekat te klase sa String-om kao sadržajem. Ovo je ispravan način za kreiranje novog objekta klase. Ali, u ovom slučaju, mogli biste jednostavno proslediti `this.fun()` bilo koji String kao: `this.fun("hey there!")`

### Python
```python
//loader.py
import frida
import time

device = frida.get_usb_device()
pid = device.spawn(["com.example.a11x256.frida_test"])
device.resume(pid)
time.sleep(1) #Without it Java.perform silently fails
session = device.attach(pid)
script = session.create_script(open("s2.js").read())
script.load()

#prevent the python script from terminating
raw_input()
```

```
python loader.py
```
## Deo 3

### Python

Sada ćete videti kako da šaljete komande aplikaciji koja je uhvaćena putem Pythona da pozovete funkciju:
```python
//loader.py
import time
import frida

def my_message_handler(message, payload):
print message
print payload


device = frida.get_usb_device()
pid = device.spawn(["com.example.a11x256.frida_test"])
device.resume(pid)
time.sleep(1)  # Without it Java.perform silently fails
session = device.attach(pid)
with open("s3.js") as f:
script = session.create_script(f.read())
script.on("message", my_message_handler)
script.load()

command = ""
while 1 == 1:
command = raw_input("Enter command:\n1: Exit\n2: Call secret function\n3: Hook Secret\nchoice:")
if command == "1":
break
elif command == "2":
script.exports.callsecretfunction()
elif command == "3":
script.exports.hooksecretfunction()
```
Komanda "**1**" će **izaći**, komanda "**2**" će pronaći i **instancirati klasu i pozvati privatnu funkciju** _**secret()**_, a komanda "**3**" će **hook-ovati** funkciju _**secret()**_ tako da **vrati** **drugi string**.

Dakle, ako pozovete "**2**", dobićete **pravi tajni podatak**, ali ako pozovete "**3**" i zatim "**2**", dobićete **lažni tajni podatak**.

### JS
```javascript
console.log("Script loaded successfully ")
var instances_array = []
function callSecretFun() {
Java.perform(function () {
if (instances_array.length == 0) {
// if array is empty
Java.choose("com.example.a11x256.frida_test.my_activity", {
onMatch: function (instance) {
console.log("Found instance: " + instance)
instances_array.push(instance)
console.log("Result of secret func: " + instance.secret())
},
onComplete: function () {},
})
} else {
//else if the array has some values
console.log("Result of secret func: " + instances_array[0].secret())
}
})
}

function hookSecret() {
Java.perform(function () {
var my_class = Java.use("com.example.a11x256.frida_test.my_activity")
var string_class = Java.use("java.lang.String")
my_class.secret.overload().implementation = function () {
var my_string = string_class.$new("TE ENGANNNNEEE")
return my_string
}
})
}
rpc.exports = {
callsecretfunction: callSecretFun,
hooksecretfunction: hookSecret,
}
```
## Deo 4

Ovde ćete videti kako da **Python i JS interaguju** koristeći JSON objekte. JS koristi `send()` funkciju da pošalje podatke klijentu u Pythonu, a Python koristi `post()` funkcije da pošalje podatke JS skripti. **JS će blokirati izvršenje** dok ne primi odgovor od Pythona.

### Python
```python
//loader.py
import time
import frida

def my_message_handler(message, payload):
print message
print payload
if message["type"] == "send":
print message["payload"]
data = message["payload"].split(":")[1].strip()
print 'message:', message
data = data.decode("base64")
user, pw = data.split(":")
data = ("admin" + ":" + pw).encode("base64")
print "encoded data:", data
script.post({"my_data": data})  # send JSON object
print "Modified data sent"


device = frida.get_usb_device()
pid = device.spawn(["com.example.a11x256.frida_test"])
device.resume(pid)
time.sleep(1)
session = device.attach(pid)
with open("s4.js") as f:
script = session.create_script(f.read())
script.on("message", my_message_handler)  # register the message handler
script.load()
raw_input()
```
### JS
```javascript
console.log("Script loaded successfully ")
Java.perform(function () {
var tv_class = Java.use("android.widget.TextView")
tv_class.setText.overload("java.lang.CharSequence").implementation =
function (x) {
var string_to_send = x.toString()
var string_to_recv = ""
send(string_to_send) // send data to python code
recv(function (received_json_object) {
string_to_recv = received_json_object.my_data
}).wait() //block execution till the message is received
console.log("Final string_to_recv: " + string_to_recv)
return this.setText(string_to_recv)
}
})
```
Postoji deo 5 koji neću objašnjavati jer nema ništa novo. Ali ako želite da pročitate, ovde je: [https://11x256.github.io/Frida-hooking-android-part-5/](https://11x256.github.io/Frida-hooking-android-part-5/)

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