So far I have researched timing attacks on RSA, We all know the ransomware named CryptoLocker uses RSA 2048 bit encryption. Now, is it possible to break the encryption using a timing attack. I have been gathering information about CryptoLocker, it’s a ransomware which encrypts files in the system with RSA 2048 bit encryption and asks for a ransom to release the private key stored in the server and decrypt the files infected. As it is a 2048 bit encryption it is not possible to break the key, however with a side-channel attack researchers have attacked even 4096 bit RSA encryption. Timing attack is a side channel attack.

So my question is, is it possible to attack the cyber criminal's server by performing a timing attack?

  • $\begingroup$ So if i deliberately repeatedly allow cryptolocker to encrypt my system with no important data and search for the servers, it is absolutely possible to attack the server with side channel attack. Thank you so much for the reply John. $\endgroup$ Feb 23, 2014 at 16:20
  • $\begingroup$ You can try an attack, but it's certainly not guaranteed to be successful. There are many possible types of attacks. You also don't have to let him repeatedly attack you, you can simply record which servers your system attempts to send the key requests to. Note that this is not a comment on the legality of attacking someone's server - even a criminal's server. $\endgroup$ Feb 23, 2014 at 16:24
  • $\begingroup$ Timing attack can recover the private key of rsa, the problem is that to perform a timing attack you have to have a predicted time path and delay. This can be a bit hard from the internet but easier in a LAN for instance or direct connection, there is a tool named Nanown you might give it a try $\endgroup$
    – Ibrahim
    Sep 29, 2015 at 5:30

1 Answer 1


No, it's not possible to recover the private RSA key; not with a timing attack, not with a debugger, not with any technical means. There isn't enough information on the victim's computer.

The timing attack you describe requires timing the decryption operation, which could reveal the decryption key. But the malware isn't ever decrypting anything, it's just encrypting the victim's data. The malware doesn't even have the decryption key until after you pay the ransom.

All a timing attack could tell you about RSA keys during encryption is the encryption key, but that's just the public key that your machine's virus retrieves from their server. The whole point of asymmetric encryption security is to separate encryption secrets from decryption secrets.


I reread your question more carefully, and I now understand that you're asking if it's possible to attack the criminal's server, not the client-side malware. Yes, servers can obviously be attacked. And yes, side-channel attacks are one of the many potential tools that could be used to attack it. But the thief doesn't operate just one server, he's operating a large farm of them; the client-side malware simply keeps testing for servers until it finds one that responds. In order to recover your own data, you would need to identify the correct server containing your key, hack into it, and exfiltrate all the data from it before he wipes all the stored private keys (either in response to the attack or because you didn't pay him in time.) Even if such an attack was successful, it will do little to help with future attacks as each private key is reportedly generated on request.


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