This code is used to brute force the pin on an android device.

Copyright 2013 Brett Brotherton http://www.bbrotherton.com

Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License. You may obtain a copy of the License at

   http://www.apache.org/licenses/LICENSE-2.0

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This code in conjunction with STM32F4DISCOVERY board firmware package implements a simple HID keyboard device designed for brute force attacks against an Android phone.

Simply stated, this quickly tries to brute force unlock an Android phone by acting as a USB keyboard and sending keystrokes to the phone. As of November 2013, Android does not lock out after a certain number of incorrect guesses, it only delays 30 seconds after 5 incorrect guesses and then allows you to try again. The basic break down of the guessing algorithm is:

1. Make 5 guesses
2. Send the following sequence

[Windows Key+g] cyouremail@yourdomain.com\t[last guess]\t[last guess]\t\t\n".

This complicated string attempts to launch gmail and send you an email with the last guess that was made. 3. Wait 30 seconds and then repeat

In theory you will get an email with a guess and you can work back narrowing it down to the correct one.
It was decided to only try to send the email every 5 guess in order to speed things up. Sending an email is my attempt to automate this whereas other brute force attacks i've seen did not do this and therefore you would need to watch the device and see the screen unlock.

This was a quick prototype designed to solve a problem for my lovely girlfriend who is so concerned about security that now even she cannot access her phone. It is not a polished cracking tool. It is designed for fun and for benign use, I am not responsible if you use this software to break any laws! It does have the caveat that it doesn't detect if USB is unplugged, so if the phone battery dies it will keep on guessing and you will have to start over. Also, the email sending sequence does not work 100% reliably. In these cases it was saved in the drafts folder. Since I was trying to unlock a phone with a forgotten PIN code that was still a sufficient success in my case so I did not spend time perfecting it.

This is really designed to hone down your choices if you know some information about the PIN. For example, with my girlfriends forgotten PIN we started with the following information:

1. The pin was 6 digits
2. The pin does not have the numbers 1, 2, or 3 in it
3. The pin did not repeat any digits
4. The pin likely did not start with 0.

Tweaking based on this information can all be done in main.c

First we set a start guess of 4 followed by five zeros (since it is believed the pin does not start with 0) and it is a 6 digit pin.

strcpy(guess, "400000");

Now that we have our initial guess we simply call nextPermutation after each guess. The first argument is our guess string we will modify this to obtain our next guess. The second argument is a string with exclusion characters (next perumation is designed only for pins with digits 0-9), any permutation that has a character in the exclusion list will not be tried. The next argument is an integer that sets a maximum number of repeats for any one digit (in this case 1 meaning no each digit can only appear once). The last argument is a flag to allow only permutations where there are repeats in this case we set it to zero since we are not allowing repeated digits.

nextPermutation(guess, "123", 1, 0);

Using this we have narrowed down our guesses from approx 45,000 to around 5,000 at just under 10 guesses per minute due to 30 second blockout after 5 wrong attmempts that is a run time of under 9 hours...not too bad! (Note actual rate in real life use seemd to be about 510 guesses per hour).

If you want to modify to brute force any 4 digit pin 10,000 different permutations and about 19 hours of time worst case you would modify the above lines to be:

strcpy(guess, "0000");
nextPermutation(guess, NULL, 0, 0);

Requirements:

• Linux system with arm toolchain and stlink installed and running see http://liviube.wordpress.com/2013/04/22/blink-for-stm32f4-discovery-board-on-linux-with-makefile/ for setup information
• ST32F4 Discovery Board
• [STM32F4DISCOVERY board firmware package] [5]

1. Download and extract the STM32F4DISCOVERY board firmware package
2. in the same directory where you extracted the firmware package pull this git repo
3. cd to the git repo
4. vi Makefile and if necessary modify TOOLS_DIR and STM_ROOTs
5. run: make to build and then make flash to push it to the board via stlink (Note stlink executables must be in your path or you need to modify the Makefile).

1. Power the STM board via a mini-usb cable LED 3 should light up
2. Connect the micro usb side of the board to the phone via USB OTG adapter and micro usb cable.
3. LED 3 should turn off indicating the micro is connected to your phone
4. press the user button to start the guessing! LED4 will light up to indicate guessing is active and LED6 will toggle as guesses are made
5. If you wish to pause you can hold the user button till the green (LED 4) turns off.
6. press the user button again to continue guessing.

The big problem with performing this "attack" in real life is the phone's battery life! You cannot charge and have a USB OTG device plugged in at the same time. To circumvent this problem, I used an adjustable voltage power supply. I set the supply to 4.0 V and clipped the leads the spring loaded battery contacts. This allowed me to run for several days without worrying about battery. The other problem I ran into was for some reason I never quite figured out, when running off of a power supply the phone (Galaxy Nexus) would drop the USB connection after a few minutes. A friend suggested connecting the STM board to the phone through a USB hub and that solved the problem.

They Modifier keys and conversion from ascii to keycodes came from the Arduino library.

Liveiu Beraru had an excellent blog entry on setting up the toolchain to a great example makefile in his Github Project.

ST Micro had a great software kit that provided all the low level drivers and was pretty easy to modify their demo project to get this working.