Windows crypto-ransomware POC

Windows crypto-ransomware POC

Credits: mauri870

Note: This project is purely academic, use at your own risk. I do not encourage in any way the use of this software illegally or to attack targets without their previous authorization

The intent here is to disseminate and teach more about security in the actual world. Remember, security is always a double-edged sword.

What is Ransomware?

Ransomware is a type of malware that prevents or limits users from accessing their system, either by locking the system’s screen or by locking the users’ files unless a ransom is paid. More modern ransomware families, collectively categorized as crypto-ransomware, encrypt certain file types on infected systems and forces users to pay the ransom through certain online payment methods to get a decrypt key.

Project Summary

This project aims to build an almost functional crypto-ransomware for educational purposes, written in Go. Basically, it will encrypt your files in background using AES-256-CTR, a strong encryption algorithm, using RSA-4096 to secure the key exchange with server. Yeah, a Cryptolocker like malware.

It is composed of two main parts, the server and the malware itself.

The server is responsible for store the Id and the respective encryption key and possibly act as a Command and Control server in the near future.

The malware encrypt with your RSA-4096 public key any payload before send then to the server. This approach with the https transport together make the security and authentication almost unbreakable (in theory)

Project tasks

  • Run in Background (or not)
  • Encrypt files using AES-256-CTR(Counter Mode) with random IV for each file
  • Without virus signature (at the moment)
  • Use RSA-4096 to secure the authenticity
  • HTTPS and HTTP\2 Transport by default
  • Stream encryption to avoid load an entire file into memory
  • Walk all drives by default, including usb’s and network locations
  • Lock registry entry with hash digest(maybe SHA-256) to identify an infected victim
  • Tor or other approach to hide the connection with the C&C see issue 3
  • Docker image for compilation

Building the binaries


go get -v


# You can compile the server for windows using env GOOS=windows make instead of make

./ make

Done! The binaries live on the bin folder


You need Go at least 1.8 with the $GOPATH/bin in your $PATH and $GOROOT pointing to your Go installation folder

Build the project require a lot of steps, like the RSA key generation, build three binaries, embed manifest files, so, let’s leave make do your job:

make deps

If you like build the server for windows from a unix machine, run env GOOS=windows make.


Usage and How it Works

The malware will run in background. You can see what is going on commenting the HIDDEN line on Makefile before build

By default, the server will listen on https://localhost:8080. The client will use this host as the default url too.

You can put the server on any domain and start it. Simply overwrite the SERVER_HOST and SERVER_PORT on Makefile before build and the malware will try to connect with this url instead

After build, a binary called ransomware.exe, server/server.exe and unlocker.exe will be generated on the bin folder. The execution of ransomware.exe and unlocker.exe (even if it is compiled for linux/darwin) is locked to windows machines only.

Feel free to edit the parameters across the files for testing. The most important parameters are defined in cmd/common.go and Makefile.

Put the binaries on a correct windows test environment and start the server. It will wait for the malware contact and persist the id/encryption keys

When double click on ransomware.exe it will run in background by default, walking interesting directories and encrypting all files that match the interesting file extensions using AES-256-CTR and a random IV for each file, recreating then with encrypted content and a custom extension(.encrypted by default) and create a READ_TO_DECRYPT.html and FILES_ENCRYPTED.html files on desktop.

In theory, to decrypt your files you need to send an amount of BTC to the attacker’s wallet, followed by a contact sending your ID(located on the file created on desktop). If your payment was confirmed, the attacker possibly(or maybe not) will return your encryption key and the unlocker.exe and you can use then to recover your files. This exchange can be accomplished in several ways and WILL NOT be implemented in this project for obvious reasons.

Let’s suppose you get your encryption key back, you can retrieve it pointing to the following url:

curl -k https://localhost:8080/api/keys/:id

Where :id is your identification stored in the file on desktop. After, run the unlocker.exe by double click and follow the instructions.

That’s it, got your files back

Server endpoints

The server has only two endpoints at the moment

POST api/keys/add – Used by the malware to persist new keys. Some verifications are made, like the verification of the RSA autenticity. Returns 204 (empty content) in case of success or a json error.

GET api/keys/:id – Id is a 32 characters parameter, representing an Id already persisted. Returns a json containing the encryption key or a json error

The end

As you can see, building a functional ransomware, with some of the best existing algorithms is not dificult, anyone with some programming skills can buit that in any programming language.


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