QARJ Ransomware (.qarj File Extension)

What is Qarj?

Qarj ransomware is a formidable adversary, encrypting your files and demanding a ransom, while also compromising several critical system functions. You may find yourself struggling to access certain websites or perform basic tasks. Yet, understanding your opponent is half the battle won.

Employing the Salsa20 encryption algorithm, this ransomware presents a near-impossible challenge to overcome. With an extensive key length and an astronomical number of potential keys, brute-force attacks are impractical without extraordinarily powerful computing resources. While utilizing already compromised decryption keys is one approach, the success rate of such decryption tools is generally low.

The intrusion of ransomware into your PC is no mysterious affair. Qarj ransomware predominantly spreads through dubious means, including "free" versions of well-known software, cheat engines, Windows activators, and keygens. These methods are common across all STOP/Djvu ransomware family members, with Qarj being no exception. Investing in legitimate software licenses is not only simpler but also significantly cheaper than the hefty sum demanded for file decryption.

Qarj Encryption process

The Qarj uses the Salsa20 encryption algorithm. That is not the strongest method, but it still provides an overwhelming amount of possible decryption keys. To brute force the 78-digit number of keys, you need 3.5 unvigintillion years (1*10^65), even if you use the most powerful regular PC. Quantum computers can show a bit better results, but it is still too slow to get your files back while you are alive.

The exact algorithm of encryption is next: malware scans each folder for the files it is able to encrypt. Then, when it finds the target, it makes a copy of your file, removes the original one, encrypts the copy and leaves it instead of the removed original. Such a procedure is done to prevent the situation when you have already opened the file, so ransomware is not able to read it because of the Windows restrictions. To each encrypted copy, the virus adds the specific extension - ".qarj". Then, ransomware creates a _readme.txt file in the folder where the encrypted file is located, and goes to the next folder.

Such an encryption method can be exploited for file recovery. Since the original file is deleted, you may try to recover it using the file recovery tools. The less time is passed - the bigger the chance to get your files back, so hurry up!

Another specific moment that can help you to use the files even after the encryption is the fact that Qarj ransomware encrypts only the first 150KB of each file. Hence, you can try to run a big file, such as video or music, without the encryption. Similar feature also works with other ransomware families - Dharma, Conti and Makop encrypt the same 150KB.

Qarj note:

Ransom note is the same for the whole STOP/DJVU family. In fact, it is one of the main signs of to which family the certain ransomware belongs. Here is the typical note for STOP/Djvu family:

External Links:

Indicators of Compromise(IOC)