KOOL Ransomware (.kool File Extension)

What is Kool?

Kool ransomware exemplifies a "classic" ransomware infection. This virus infiltrates your PC, encrypts your files, and then demands payment for decryption. The average ransom amount is $980, accompanied by threats of permanent file deletion or non-decryption if payment isn't made. Crucially, it also modifies numerous system settings.

The malware changes your system's configurations to weaken defenses and hinder early virus detection efforts. It specifically deactivates Microsoft Defender and obstructs the installation of antivirus software. These alterations not only compromise your security but also affect your ability to install other software and must be promptly reversed.

Kool ransomware employs the Salsa20 encryption algorithm, a common choice among the STOP/Djvu ransomware family. The strength of this cipher, with 1.158x10^77 (a 78-digit number) possible decryption keys, makes conventional hacking attempts futile. Brute-forcing this encryption would take over two unvigintillion years, highlighting the impracticality of such an approach for recovery.

Kool Encryption process

The Kool 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 - ".kool". 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 Kool 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.

Kool 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)