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0x05c - Update Angr Example to Angr 9.2.2 #2103

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May 7, 2022
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0x05c - Update Angr Example to Angr 9.2.2 #2103

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bc0a83c
Update 0x05c-Reverse-Engineering-and-Tampering.md
kousha1999 Apr 25, 2022
58b7713
Update Document/0x05c-Reverse-Engineering-and-Tampering.md
cpholguera May 7, 2022
362cc0c
add angr version and details on solving
cpholguera May 7, 2022
938e453
Update Document/0x05c-Reverse-Engineering-and-Tampering.md
cpholguera May 7, 2022
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19 changes: 12 additions & 7 deletions Crackmes/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -130,13 +130,18 @@ A brand new Android app sparks your interest. Of course, you are planning to pur
Copy the binary to your Android device and run using the shell.

```shell
$ adb push validate /data/local/tmp
[100%] /data/local/tmp/validate
$ adb shell chmod 755 /data/local/tmp/validate
$ adb shell /data/local/tmp/validate
Usage: ./validate <serial>
$ adb shell /data/local/tmp/validate 1234
Incorrect serial (wrong format).
$ adb push validate /data/local/tmp
[100%] /data/local/tmp/validate
$ adb shell chmod 755 /data/local/tmp/validate
$ adb shell /data/local/tmp/validate
Usage: ./validate <serial>
$ adb shell /data/local/tmp/validate 1234
Incorrect serial (wrong format).
$ adb shell /data/local/tmp/validate JACE6ACIARNAAIIA
Entering base32_decode
Outlen = 10
Entering check_license
Product activation passed. Congratulations!
```

#### Solutions
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22 changes: 13 additions & 9 deletions Document/0x05c-Reverse-Engineering-and-Tampering.md
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Expand Up @@ -1216,18 +1216,21 @@ You need to perform several steps to initialize Angr's symbolic execution engine
The final solution script is presented below:

```python
import angr
import claripy
import angr # Version: 9.2.2
import base64

load_options = {}

b = angr.Project("./validate", load_options = load_options)

# The key validation function starts at 0x401760, so that's where we create the initial state.
# This speeds things up a lot because we're bypassing the Base32-encoder.

state = b.factory.blank_state(addr=0x401760)
options = {
angr.options.SYMBOL_FILL_UNCONSTRAINED_MEMORY,
angr.options.ZERO_FILL_UNCONSTRAINED_REGISTERS,
}

state = b.factory.blank_state(addr=0x401760, add_options=options)

simgr = b.factory.simulation_manager(state)
simgr.explore(find=0x401840, avoid=0x401854)
Expand All @@ -1238,7 +1241,7 @@ found = simgr.found[0]

# Get the solution string from *(R11 - 0x20).

addr = found.memory.load(found.regs.r11 - 0x20, endness='Iend_LE')
addr = found.memory.load(found.regs.r11 - 0x20, 1, endness="Iend_LE")
concrete_addr = found.solver.eval(addr)
solution = found.solver.eval(found.memory.load(concrete_addr,10), cast_to=bytes)
print(base64.b32encode(solution))
Expand All @@ -1257,13 +1260,14 @@ Also, it may appear as if the script is simply reading the solution string from
Running this script should return the following output:

```bash
(angr) $ python solve.py
WARNING | cle.loader | The main binary is a position-independent executable.
It is being loaded with a base address of 0x400000.
$ python3 solve.py
WARNING | ... | cle.loader | The main binary is a position-independent executable. It is being loaded with a base address of 0x400000.

b'ABGAATYAJQAFUABB'
b'JACE6ACIARNAAIIA'
```

Now you can run the validate binary in your Android device to verify the solution as indicated [here](../Crackmes/README.md#android-license-validatorandroidlicense01-"android-license-validator").
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> You may obtain different solutions using the script, as there are multiple valid license keys possible.

To conclude, learning symbolic execution might look a bit intimidating at first, as it requires deep understanding and extensive practice. However, the effort is justified considering the valuable time it can save in contrast to analyzing complex disassembled instructions manually. Typically you'd use hybrid techniques, as in the above example, where we performed manual analysis of the disassembled code to provide the correct criteria to the symbolic execution engine. Please to the iOS chapter for more examples on Angr usage.
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