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I got a ransomware called StopDjvu. On my PC, I have found the public key that is used by the malware (maybe RSA hardcoded).

Is it possible to extract the private key from the public key?

2 Answers 2

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No. If it were possible to derive the private key from the public key, then this would break asymmetric encryption. This would make it possible to break the encryption for https, VPNs, SSH, Signal, cryptocurrencies, and much more.

As a thought experiment, take a look at this bitcoin address: https://www.blockchain.com/btc/address/12tkqA9xSoowkzoERHMWNKsTey55YEBqkv

As you can see, this address has ~28,000 bitcoins associated with it. At today's exchange rate, that's almost half a billion USD. The public key is in the clear. If it were possible to derive the private key from the public key, someone would have done it by now and used the private key to steal all the bitcoins from this address. But, to date, this has never happened. So, think of bitcoin as a massive bug bounty on exactly what you are trying to do.

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  • So, things like this video youtube.com/watch?v=sYCzu04ftaY or this article 0day.work/… are useless for my case?
    – ransomhate
    Commented Nov 10, 2022 at 11:03
  • No, for the reasons stated by Spyros. See what I added to my answer above.
    – mti2935
    Commented Nov 10, 2022 at 12:03
  • Actually a bitcoin address is a hash of (a defined representation of) the public key; to reverse an address you must both reverse the hash and the (resulting) public key, both of which are impossible. If there had been a payment from this address (more exactly a spend of any TXO(s) for the address) that txn's script would have exposed the public key (but not the private key). Commented Nov 11, 2022 at 2:18
  • @dave_thompson_085 Thanks for pointing this out. I meant to choose an address that had a payment from the address for the purpose of this example, but inexplicably chose this one that doesn't.
    – mti2935
    Commented Nov 11, 2022 at 2:25
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Public key cryptography uses mathematical constructs that makes it really difficult (practically impossible) to find a private key once you know the public key.

So, the answer is no.

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  • So, things like this video youtube.com/watch?v=sYCzu04ftaY or this article 0day.work/… are useless for my case?
    – ransomhate
    Commented Nov 10, 2022 at 11:03
  • Yes. Both are specially crafted examples for demonstration purposes only. The prerequisites of the examples do not apply in the real world.
    – user284677
    Commented Nov 10, 2022 at 11:28

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