A security researcher found a way to retrieve the encryption keys used by the WannaCrypt (AKA WannaCry) ransomware without paying the ransom of $300. This is big because WannaCry uses Microsoft’s built-in cryptographic tools to do what it needs to do. While Windows XP was not widely affected by the cyber-attack, the following technique may be applied in the case of other ransomware infections.
Wcry, now available on Windows XP
The tool is called Wcry and it plucks the key right out of the affected system’s memory. This solution is currently available for Windows XP and only when the PC in question hasn’t been rebooted or its memory overwritten.
Wcry was developed by Adrien Guinet, a French researcher, who posted the solution on GitHub for free.
How it works
According to Guinet, the software has only been tested under Windows XP and it runs perfectly. The note found next to the app also reads that “in order to work, your computer must not have been rebooted after being infected. Please also note that you need some luck for this to work (see below), and so it might not work in every case!”
In Windows XP, there is a flaw which prevents the erasure of the keys from the memory and this flaw is lacking from newer operating systems. It is important that the prime numbers are still in the memory.
Guinet says that:
This software allows to recover the prime numbers of the RSA private key that are used by Wanacry. It does so by searching for them in the wcry.exe process. This is the process that generates the RSA private key. The main issue is that the CryptDestroyKey and CryptReleaseContext does not erase the prime numbers from memory before freeing the associated memory.
As you can use the tool for more ransomware infections, it will prove to be very useful for providing tech support.
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