Find Decryption Key for Files Encrypted by Ransomware

fix-your-malware-problem-sensorstechforumCrypto-viruses are an increasing menace that aims to turn your day the other way around, making you pay to cyber-criminals for keys that were encrypted. And what is worse is that cyber-crooks constantly keep developing new and more sophisticated ways to increase the defense of their viruses, implementing combined encryption keys that travel safely to their servers. However, there still are those ransomware viruses that send unencrypted information, allowing you, the user to sniff out traffic from your computer and with luck to get the decryption key for your files. We have designed to make a tutorial which is as simple as possible to theoretically explain how could you detect your decryption key by sniffing out your web traffic using Wireshark.

Useful Advice: Before actually engaging in any network sniffing or other methods we have suggested below, it is urgently advisable to do it from a safe and secure computer system unaffected by any type of malware. If you want to make sure that your computer system is 100% safe while you are following these instructions, experts often advise to download an advanced anti-malware tool which is frequently updated and features next-gen active protection against viruses to see if your PC is safe:

Download

Malware Removal Tool


Spy Hunter scanner will only detect the threat. If you want the threat to be automatically removed, you need to purchase the full version of the anti-malware tool.Find Out More About SpyHunter Anti-Malware Tool / How to Uninstall SpyHunter

How It Works – Brief Explanation

Bear in mind that this solution is only theoretical since different ransomware viruses perform different activities on user PCs. To best clarify that, most ransomware viruses use encryption algorithm – a cryptic language replacing the original language code of the files, making them inaccessible. The two most widely used encryption algorithms are RSA and AES encryption algorithms. Both of them are extremely strong and impenetrable. In the past, most malware writers used only one encryption cipher in a special manner. The standard action for the ransomware virus was in the following consequence:

  • Drop it’s payload.
  • Modify the Windows Registry Editor to run on startup or after the specific action is done.
  • Delete backups and perform other activities.
  • Encrypt the files.
  • Send the decryption key in a file or as a communication directly to the command and control (C&C) center of the cyber-criminals.
  • Drop it’s ransom note and other support files that notify the user of this “complication”.

However, since malware researchers have united their resources and put a lot of effort to detect codes in the flaw or capture decryption keys and develop free decrypters, malware writers have also made quite the improvements themselves. One of those improvements is implementing a two-way encryption, using a combination of RSA and AES encryption algorithms.

In brief, they did not just encrypt your files with one of the ciphers, but now they also use a second encryption algorithm to encrypt the decryption key in a special file which is then sent to their servers. These files are impossible to decrypt, and users are hopelessly looking for alternative methods to decrypt them.

For more information on this encryption method, please visit:

Ransomware Encryption Explained – Why Is It So Effective?

Another tactic the cyber-crook “devs” started to use is a so-called cipher block chaining. This is a mode that briefly explained, breaks the file if you try to tamper with it, making any form of recovery completely impossible.

So, here is where we are. At this point, there are even new developments in the world of ransomware, which are yet to be revealed.

It is very difficult to stay ahead of ransomware, but despite all, we have decided to show you how to use Wireshark to your benefit and hopefully intercept HTTP traffic in the correct moment. However, bear in mind that these instructions are THEORETICAL, and there are a lot of factors that may prevent them from working in an actual situation. Still, it is better than not trying before paying the ransom, right?

Using Wireshark to Find Decryption Key

Before downloading and using Wireshark – one of the most widely used network sniffers out there, you should have the malware’s executable on standby and infect your computer once again. However, bear in mind that some ransomware viruses perform new encryption every time a computer is restarted as well, so you should also configure Wireshark to run automatically on startup. Let’s begin!

Step 1: Download Wireshark on your computer by clicking on the following buttons( for your version of Windows)

Download

Wireshark

Step 2: Run, configure and learn how to sniff packets with Wireshark. To learn how to start analyzing packets and check where your packets save the data, you should open Wireshark first and then choose your active network interface for analyzing packets. For most users, that would be the interface with traffic bouncing up and down on it’s right. You should choose it and click twice fast to start sniffing:

1-decrypt-files-wireshark-sensorstechforum

Step 3: Sniffing packets. Since ransomware viruses communicate via HTTP traffic, you should filter all the packets first. Here is how the packets look initially after you choose your interface and sniff traffic from it:

2-ransomware-decryption-keys-mixed-sensorstechforum

To intercept only HTTP traffic, you should type the following into the display filter bar:

http.request – to intercept the requested traffic

Once filtered it should look like this:

http-traffic-sensorstechforum-filtered

You can also filter the source and destination IP addresses by scrolling up and down and choosing one address, then right clicking on it and navigating to the following feature:

filter-host-dest-sensorstechforum

Step 4: Configure Wireshark to run automatically. To do this, first, you should go to the command prompt of your computer by typing cmd on your Windows search and running it. From there, type the following command with capital “-D” setting to get the unique key for your interface. The keys should look like the following:

wireshark-keys-sensorstechforum

Step 5: Copy the key for your active connection and create a New Text Document and in it write the following code:

→ wireshark -i 13MD2812-7212-3F21-4723-923F9G239F823(<= Your copied key) –k

You can additionally modify the command by adding the –w letter and creating a name for the file that will save it onto your computer, allowing you to analyze the packets. The result should look similarly to this one:

wireshark-sensorstechforum-text-file

Step 6: Save the newly created text document as a .bat file, by going to File>Save As… and choosing All Files after which typing .BAT as a file extension, like the picture below shows. Make sure the name of the file and the location where you save it are easy to find:

sensorstechforum-pic-wireshark-save-as-all-files

Step 7: Paste the .bat file in the Windows startup folder. The original location of the folder is:

→ C:\Users\Username\AppData\Roaming\Microsoft\Windows\Start Menu\Programs\Startup,/p>

To easily access it, press Windows Button + R key combination and in the Window box type – shell:startup, like the picture below shows and click OK:

shell-startup-bat-file-sensorstechforum
wireshark-startup-sensorstechforum

After your computer is restarted, if the ransomware virus encrypts your files after which generates a key and sends it to the cyber-criminals’ servers, you should be able to intercept the communication packets and analyze them.

Step 8: How to analyze the traffic?

To analyze the traffic of a given packet, simply right-click it and then click on the following to intercept the traffic:

intercept-traffic-sensorstechforum-ransomware

After doing this, a Window will appear with the information. Make sure to inspect the information carefully and look for keywords that give away the encryption keys, like encrypted, RSA, AES, etc. Take your time and check the packets’ size, make sure that they are similar to the size of a key file.

intercept-stream-sensorstechforum-intercepted

Sniffing Ransomware Decryption Keys – Things You Need To Know

Like mentioned before, this tutorial is fully theoretical and in case you cannot cope with it and sniff out the keys, we strongly advise you to remove the ransomware that has infected you and attempt restoring your files using the step-by-step instructions below. Also, if you are going to attempt this method, we strongly advise you to test it out first on your computer and see the traffic. An example of how researchers have identified traffic by ransomware is the research, performed by PaloAlto network experts on Locky ransomware, which we also advise you to check.

Vencislav Krustev

A network administrator and malware researcher at SensorsTechForum with passion for discovery of new shifts and innovations in cyber security. Strong believer in basic education of every user towards online safety.

More Posts - Website

  • WATERCHILD

    I have tried to follow your recommendations about wireshark and somehow I get to find several lines that contain the following description in “info”:

    “Server Hello, Certificate, Certificate status, Server key exchange, Server Hello done”
    “Client key exchange, Change Cipher Spec, Encrypted Handshake message”
    Then Application Data……

    And this goes on and on all the time between one source and one destination (always the same).

    I can do a right click on the line, then “follow” and “TCP” : it opens a window with a dialogue but i don’t know if I could find in it a “key” and I don’t know either how to recognize it. It doesn’t look like a common text, but includes a mix between words, net adresses, symbols…

    Let’s assume it’s possible ang I find it, how then coul I use it? I wouldn’t know how to build my own working decryptor.

    Is there anyone here who knows more about all of this and tried the way of wireshark sniffing and would have some advice to help me use the software and get to discover my “key”?

    Thank you for your time

    • Hello, please see the following filters which you can use on the filter box on top of where the packets are of your Wireshark software:

      1. ip.addr ==10.0.0.1 [Sets a filter for any packet with 10.0.0.1, as either the
      source or dest]

      2. ip.addr==10.0.0.1 && ip.addr==10.0.0.2 [sets
      a conversation filter between the two defined IP addresses]

      3. http or dns [sets
      a filter to display all http and dns]

      4. tcp.port==4000
      [sets a filter for any TCP packet with 4000 as a source or dest port]

      5. tcp.flags.reset==1
      [displays all TCP resets]

      6. http.request
      [displays all HTTP GET requests]

      7. tcp contains
      traffic [displays all TCP packets that contain the word ‘traffic’.
      Excellent when searching on a specific string or user ID]

      8. !(arp or icmp or
      dns) [masks out arp, icmp, dns, or whatever other protocols may be
      background noise. Allowing you to focus on the traffic of interest]

      9. udp contains
      33:27:58 [sets a filter for the HEX values of 0x33 0x27 0x58 at any
      offset]

      10. tcp.analysis.retransmission
      [displays all retransmissions in the trace. Helps when tracking down slow
      application performance and packet loss]

      I have extracted those useful filters from:

      http://www.lovemytool.com/blog/2010/04/top-10-wireshark-filters-by-chris-greer.html

      You can also find other useful recommendations there. Also, bear in mind that you should focus on the POST traffic when an infection takes place. If you have the malware sample, try to reinfect a testing computer while monitoring the packets. This may help you gain a deeper understanding on how the malware communicates.

      In addition to this, when you “Follow TCP Stream” of a given packet, Wireshark has the so-called “SSL Dissector” which in some cases can be used to decipher some of the data in there and make sense of it. Ransomware is constantly evolving, however and may not also directly send the decryption key, but instead upload a .KEY file to the cyber-criminals’ command servers which is also encrypted with a strong algorithm. So if you are using WIreshark, first make sure the virus does not create such a file and directly sends the information via TCP or other form.

  • WATERCHILD
  • Ariel santos

    Is it work with Cerber ransomware?

  • Calin
Share on Facebook Share
Loading...
Share on Twitter Tweet
Loading...
Share on Google Plus Share
Loading...
Share on Linkedin Share
Loading...
Share on Digg Share
Share on Reddit Share
Loading...
Share on Stumbleupon Share
Loading...
Please wait...

Subscribe to our newsletter

Want to be notified when our article is published? Enter your email address and name below to be the first to know.