Posts

Analyzing ATM Malwares

This post will explain how to analyze ATM malwares developed using middle ware CEN/XFS (extension for financial services). ATM (Automated Teller machine). The three leading ATM vendors are - 1.NCR 2.Diebold 3.Wincor The main services (peripherals) of an ATM are - 1.Card Reader 2.PinPad 3.Cash Dispenser Applications developed to interact with ATM services (peripherals) uses CEN/XFS (extension for financial services). XFS provides the API to access and manipulate the ATM peripherals from different vendors as shown in below image. CEN/XFS Application Programming interface and SDK can be downloaded from below website under Published CWA's. https://www.cen.eu/work/areas/ICT/eBusiness/Pages/WS-XFS.aspx Apart from CEN/XFS Application Programming interface and SDK other important guides as mentioned below and can be download from above mentioned website. 1.Service Class Definition - Programmer's Reference 2.Identification Card Device Class Interface - Programmer...
150 comments
Read more

FireEye FLARE CTF 2017 : APK Challenge 8

Image
The challenge required decrypting passwords in order to form AES key to decrypt the flag bytes. On decompiling flair.apk file we can see four classes for which we need to decrypt passwords. 1.Michael Class  It was pretty simple password comparison.The password is  MYPRSHE__FTW . 2. Brian Class Password is formed as shown below. String.format("%s_%s%x_%s!", new Object[]{t, y, Integer.valueOf(p), c}); t = (ImageView) findViewById(R.id.pfdu).getTag().toString() y = getApplicationContext().getPackageManager().getApplicationInfo(getApplicationContext().getPackageName(), 128).metaData.getString("vdf") p = (TextView) findViewById(R.id.vcxv).getCurrentTextColor() & SupportMenu.USER_MASK; c = (TextView) findViewById(R.id.vcxv).getText().toString().split(" ")[4]; The Password is  hashtag_covfefe_Fajitas! . 3.Milton Class The password is formed by decrypting a string and taking SHA1 of the decrypted string. Decryption algorithm...
17 comments
Read more

FireEye FLARE CTF 2017 : PEWPEWBOAT Challenge 5

Image
The challenge is about selecting correct coordinates on to the map and advancing to the next stage to get flag. As we advance to next stage, the game print some metadata. After debugging the binary, the logic to calculate co-ordinate can be rewritten. Below is the python implementation of calculating co-ordinate and decrypting metadata for each stage. import binascii key = 0x3B1EE5F6B3D99FF7                #initial key to decrypt metadata. offset = 0x50E0                         #offset of metadata in binary f = open('pewpewboat.exe','rb') for i in range(0,11):     stage = i     v = ((i << 3) + i) << 6     f.seek(offset + v)     mask = '0x'     temp = '0x'     res = []     metadata = []     for i in range(0,0x240):         key = ((key * 0x41c64e6d) +...
18 comments
Read more

Samsung CTF : Chicken or Egg Reversing Challenge

Image
 The CTF is over but i really enjoyed solving the challenge (https://sctf.codeground.org/ctf/prob).The challenge is to decrypt flag.enc. This is another APK + JNI (Java Native Interface) kind of challenge similar to the one in Google CTF 2017 (http://shasaurabh.blogspot.com/2017/07/google-ctf-2017-android-re-challenge.html). Challenge can be divided into three parts. 1.Android application (application) loading Native Library 2.Native Library decrypts DEX file in memory. 3.Using Reflection to call methods of decrypted DEX file in step 2. 1. Android application loading Native Library OnClick() method of MainActivity class calls constructor of Crypt class. Calling constructor of Crypt class results in loading of Native library ( libegg.so ) which is ELF for ARM. Constructor of Crypt class calls crackEgg method implemented in native library. 2.Native Library decrypts DEX file in memory. The native library reads the encrypted DEX file stor...
22 comments
Read more