Secure Honey

SSH honeypot written in C

Creating An Antidote For Android Simplelocker Ransomware

Tuesday 17th June 2014 10:09

In yesterday's blog post (How To Dissect Android Simplelocker Ransomware) we dissected the new Android Simplelocker ransomware.

In this blog post we'll be creating an antidote for the ransomware to decrypt any files it encrypts.

The process of creating the antidote is actually very simple because the ransomware comes with a built-in decrypt method and cipher password. This means we're able to create our own Java class and copy the decryption code from the ransomware into our antidote class.

So let's jump right in and start creating our antidote for Simplelocker!

NB: if you haven't already read the previous post (How To Dissect Android Simplelocker Ransomware) it might be worth having a quick read through that now, since I'll be referencing Java classes that were analysed in that post.

First, we want to examine the AesCrypt class, which is shown in full below:

package org.simplelocker;

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.MessageDigest;
import java.security.spec.AlgorithmParameterSpec;
import javax.crypto.Cipher;
import javax.crypto.CipherInputStream;
import javax.crypto.CipherOutputStream;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class AesCrypt
{
  private final Cipher cipher;
  private final SecretKeySpec key;
  private AlgorithmParameterSpec spec;

  public AesCrypt(String paramString)
    throws Exception
  {
    MessageDigest localMessageDigest = MessageDigest.getInstance("SHA-256");
    localMessageDigest.update(paramString.getBytes("UTF-8"));
    byte[] arrayOfByte = new byte[32];
    System.arraycopy(localMessageDigest.digest(), 0, arrayOfByte, 0, arrayOfByte.length);
    this.cipher = Cipher.getInstance("AES/CBC/PKCS7Padding");
    this.key = new SecretKeySpec(arrayOfByte, "AES");
    this.spec = getIV();
  }

  public void decrypt(String paramString1, String paramString2)
    throws Exception
  {
    FileInputStream localFileInputStream = new FileInputStream(paramString1);
    FileOutputStream localFileOutputStream = new FileOutputStream(paramString2);
    this.cipher.init(2, this.key, this.spec);
    CipherInputStream localCipherInputStream = new CipherInputStream(localFileInputStream, this.cipher);
    byte[] arrayOfByte = new byte[8];
    while (true)
    {
      int i = localCipherInputStream.read(arrayOfByte);
      if (i == -1)
      {
        localFileOutputStream.flush();
        localFileOutputStream.close();
        localCipherInputStream.close();
        return;
      }
      localFileOutputStream.write(arrayOfByte, 0, i);
    }
  }

  public void encrypt(String paramString1, String paramString2)
    throws Exception
  {
    FileInputStream localFileInputStream = new FileInputStream(paramString1);
    FileOutputStream localFileOutputStream = new FileOutputStream(paramString2);
    this.cipher.init(1, this.key, this.spec);
    CipherOutputStream localCipherOutputStream = new CipherOutputStream(localFileOutputStream, this.cipher);
    byte[] arrayOfByte = new byte[8];
    while (true)
    {
      int i = localFileInputStream.read(arrayOfByte);
      if (i == -1)
      {
        localCipherOutputStream.flush();
        localCipherOutputStream.close();
        localFileInputStream.close();
        return;
      }
      localCipherOutputStream.write(arrayOfByte, 0, i);
    }
  }

  public AlgorithmParameterSpec getIV()
  {
    return new IvParameterSpec(new byte[16]);
  }
}

We can see that the decrypt() method is clearly provided within this class. We also already know the decryption password (as set in the Constants class), so all we need to is call this method on any files ending in .enc.

Let's create a new Java class called SimplelockerAntidote with a method called getEncryptedFiles() which will scan the current directory for all files ending with .enc:

public static String[] getEncryptedFiles() {

		File dir = new File(System.getProperty("user.dir"));

		Collection<String> files  =new ArrayList<String>();

		if(dir.isDirectory()){
			File[] listFiles = dir.listFiles();

			for(File file : listFiles){
				String filename = file.getName();
				if(
					file.isFile() 
					&& (filename.lastIndexOf(".") >= 0)
					&& (filename.substring(filename.lastIndexOf(".")).toLowerCase().equals(".enc"))
				) {
					files.add(file.getName());
				}
			}
		}
		
		return files.toArray(new String[]{});
	}

This method returns an array of String files names (of all files ending in .enc in the current directory) which we can then feed into the decrypt() method. Line 3 sets the current directory (where the Java program is running). Line 10 iterates over all files in the directory. Finally, line 15 checks if the current file ends in .enc where line 17 adds it to the return array if it matches.

Next, create a main method which calls getEncryptedFiles() and sets the decryption password:

	public static void main(String[] args) throws Exception{

		// set default cipher password
		String cipher_password = "jndlasf074hr";

		// overwrite cipher password if set by first argument
		if(args.length == 1)
		{
			cipher_password = args[0];
		}

		// create new SimplelockerAntidote object
		SimplelockerAntidote sa = new SimplelockerAntidote(cipher_password);

		// get array of filenames to decrypt from current directory
		String[] files = sa.getEncryptedFiles();

		// iterate through files in the array
		for (int i = 0; i < files.length; i++) {

			// set input and output filenames
			// and remove the .enc file extension
			String inputFilename = files[i];			
			String outputFilename = inputFilename.substring(0,inputFilename.length()-4);

			System.out.println("Decrypting "+outputFilename);

			// call decrypt on the current file
			sa.decrypt(inputFilename,outputFilename);
		}

		System.out.println("Decryption complete.");

	}

Now all we need to do is copy-and-paste the constructor method from AesCrypt along with AlgorithmParameterSpec getIV(), encrypt() and decrypt().

This completes the antidote. The full Java class file is shown below:

// Simplelocker antidote, written by Simon Bell, SecureHoney.net

import javax.crypto.*;
import javax.crypto.interfaces.*;
import javax.crypto.spec.*;
import java.io.*;
import java.security.*;
import java.security.cert.*;
import java.security.interfaces.*;
import java.security.spec.*;
import javax.xml.bind.DatatypeConverter;
import java.util.ArrayList;
import java.util.Collection;

public class SimplelockerAntidote {

	private final Cipher cipher;
	private final SecretKeySpec key;
	private AlgorithmParameterSpec spec;

	public SimplelockerAntidote(String password) throws Exception {

		MessageDigest digest = MessageDigest.getInstance("SHA-256");
		digest.update(password.getBytes("UTF-8"));
		byte[] keyBytes = new byte[32];
		System.arraycopy(digest.digest(), 0, keyBytes, 0, keyBytes.length);

		cipher = Cipher.getInstance("AES/CBC/PKCS5Padding");
		key = new SecretKeySpec(keyBytes, "AES");
		spec = getIV();
	}

	public AlgorithmParameterSpec getIV() {
		return new IvParameterSpec(new byte[16]);
	}

	public void encrypt(String paramString1, String paramString2) throws Exception {
		FileInputStream localFileInputStream = new FileInputStream(paramString1);
		FileOutputStream localFileOutputStream = new FileOutputStream(paramString2);
		this.cipher.init(1, this.key, this.spec);
		CipherOutputStream localCipherOutputStream = new CipherOutputStream(localFileOutputStream, this.cipher);
		byte[] arrayOfByte = new byte[8];
		while (true) {
			int i = localFileInputStream.read(arrayOfByte);
			if (i == -1) {
				localCipherOutputStream.flush();
				localCipherOutputStream.close();
				localFileInputStream.close();
				return;
			}
			localCipherOutputStream.write(arrayOfByte, 0, i);
		}
	}

	public void decrypt(String paramString1, String paramString2) throws Exception {
		FileInputStream localFileInputStream = new FileInputStream(paramString1);
		FileOutputStream localFileOutputStream = new FileOutputStream(paramString2);
		this.cipher.init(2, this.key, this.spec);
		CipherInputStream localCipherInputStream = new CipherInputStream(localFileInputStream, this.cipher);
		byte[] arrayOfByte = new byte[8];
		while (true) {
			int i = localCipherInputStream.read(arrayOfByte);
			if (i == -1) {
				localFileOutputStream.flush();
				localFileOutputStream.close();
				localCipherInputStream.close();
				return;
			}
			localFileOutputStream.write(arrayOfByte, 0, i);
		}
	} 

	public static String[] getEncryptedFiles() {

		File dir = new File(System.getProperty("user.dir"));

		Collection<String> files  =new ArrayList<String>();

		if(dir.isDirectory()){
			File[] listFiles = dir.listFiles();

			for(File file : listFiles){
				String filename = file.getName();
				if(
					file.isFile() 
					&& (filename.lastIndexOf(".") >= 0)
					&& (filename.substring(filename.lastIndexOf(".")).toLowerCase().equals(".enc"))
				) {
					files.add(file.getName());
				}
			}
		}
		
		return files.toArray(new String[]{});
	}

	public static void main(String[] args) throws Exception{

		// set default cipher password
		String cipher_password = "jndlasf074hr";

		// overwrite cipher password if set by first argument
		if(args.length == 1)
		{
			cipher_password = args[0];
		}

		// create new SimplelockerAntidote object
		SimplelockerAntidote sa = new SimplelockerAntidote(cipher_password);

		// get array of filenames to decrypt from current directory
		String[] files = sa.getEncryptedFiles();

		// iterate through files in the array
		for (int i = 0; i < files.length; i++) {

			// set input and output filenames
			// and remove the .enc file extension
			String inputFilename = files[i];			
			String outputFilename = inputFilename.substring(0,inputFilename.length()-4);

			System.out.println("Decrypting "+outputFilename);

			// call decrypt on the current file
			sa.decrypt(inputFilename,outputFilename);
		}

		System.out.println("Decryption complete.");

	}
}

Once compiled, this Java program will scan the current directory for all files ending in .enc and attempt to decrypt them using the pre-set password.

It's also possible to override the default cipher password by calling the program as follows:

java SimplelockerAntidote <cipher-password>

The complete Java program can be downloaded here: SimplelockerAntidote.java.

It would be fairly straightforward from here to convert this Java program into an Android app. This app could then search for all .enc files on the SD card and attempt to decrypt them - thus providing a direct Android antidote app.

The antidote for this ransomware was incredibly easy to create because the ransomware came with both the decryption method and the decryption password. Therefore producing an antidote was more of a copy-and-paste job than anything.

It's also worth noting that while this antidote doesn't detect the decryption password automatically, it could be possible to do so. However, future versions of the ransomware will probably not reveal the decryption password so easily and will likely receive it from the C&C server.

Since the Simplelocker ransomware is a proof-of-concept, the antidote provided here is simply a solution to this proof-of-concept. Future versions of advanced smartphone ransomware will likely prove significantly harder to reverse engineer.

Image credit: "Chemistry" by Paul, flickr.com/photos/howzey/4955405374.

Comments

Roshin

Tue, 17 Jun 2014 12:45:00 +0100

you're awesome!

GK

Tue, 17 Jun 2014 12:49:35 +0100

Small type: \"with both the decryption method and the decryption password.\", should be encryption method I assume. Awesome write-up, thanks alot! :)

Hello

Tue, 17 Jun 2014 18:20:52 +0100

I guess it should be Android Simplocker Ransomware.

Cii3er

Wed, 18 Jun 2014 21:45:13 +0100

Very good Job. (Y)

Alex

Fri, 20 Jun 2014 13:37:53 +0100

Ctrl+C, Ctrl+V from source decompiled code.

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Live Stats (see full stats)

Attempted logins

date range # attempts
today1,815
yesterday1,331
past 7 days21,727
past 30 days182,527
all time3,038,805

Top 5 passwords

password # attempts
-5,901
1234565,848
6666663,231
admin3,016
zxcvbnm2,510

Top 5 usernames

username # attempts
root2,978,327
admin18,428
bin1,903
oracle1,705
test1,452

Stats represent data collected from SSH login attempts on multiple honeypots. Parts of some stats may be filtered to maintain anonymity.

Updated: Mon, 20 Oct 2014 12:01:49 +0100

Live Password Cloud

qazqaz 123456qwerty 123456 administrator abcdefg qazxsw 11111111 a guest woaini oracle !@#$%^ admin qwert password1 654321 username 121212 qwe passwd 123445 5201314 123qweasdzxc aaaaaa 7758521 1q2w3e4r5t6y p0o9i8u7 power 1234qwer q1w2e3r4t5 _ asdfghjkl sql manager a123456 zxcv zaqwsx qwertyu redhat topidc server hacker 123654 258258 shanghai asdfgh root windows P@ssw0rd 1q2w3e4r 225588 system zzzzzz abcd1234 pass access 1234 edong q1w2e3 1qaz2wsx3edc 123123 987654 secret 336699 Passw0rd qazwsx123 12345 adminpp 1234567890 welcome password123 963852741 a1s2d3f4 qwertyui 147258 !QAZ2wsx 666666 qwerty 0000 456789 123321 abc123 asdfg zaq1xsw2 qq123456 12345678 idc2654321 789456 sa890pp qweasdzxc idcidc 12p30495867 110110 123789 idc2008 - 23456 2008 qwe123 zxcvbnm qwerasdf qazwsxedc china password qq 112233 admin123 qwer idc cisco mnbvcxz wang qazwsx 1111 12344321 qwer1234 sqlpp 778899 webserver master 1qazxsw2 159753 1234567 1QA2WS3ED 54321 user 1q2w3e 987654321 1p203948576 147258369 123 sapp 123qwe 888888 sasa 888999 111111 qwertyuiop zaq12wsx qwaszx asdf 12qwaszx 123abc changeme admin1 123456789 zitian Aa123456 iloveyou zxcvbn sa caonima zaqxswcde 1314520 zxcvb zhang backup 111222 server2000 qqpp test f**kyou 7890pp 11223344 1qaz@WSX test123 zaqxsw 1q2w3e4r5t 1qaz2wsx 000000 chinaidc q1w2e3r4 123123123 qweasd