how to brute force the key stored in `.encfs6.xml`

[mrVanDalo]

This might be a strange issue, but I lost my .encfs6.xml file and I tried everything to get it back. (I did not properly backup that file). I created the a new .encfs6.xml by accident, because syncthing was not started, once syncthing started the .encfs6.xml was overwritten on all my other servers. So kids always backup the .encfs6.xml!

Now to my question, I have a lot of encrypted data now, which I would love to see decrypted at some point in time (maybe in 20 years). How would you try to recover the key needed to decrypt the data?

I guess it makes no sense to randomly generate the .encfs6.xml and try to decrypt the folder, and verify if a file looks like it should look.

[benrubson]

Unfortunately, due to how the encryption key is randomly generated, I think you're stuck 😕

[mrVanDalo]

@benrubson yes, but my question was more in the direction on how would I verify very quickly if the key is wrong or correct? So I can brute force it in a few years maybe.

[rfjakob]

The SSL_Cipher::readKey() function seems to be what decrypts the key using the password.

Interesting here is:

// First N bytes are checksum bytes

However, that checksum is quite weak and only 4 bytes long (MAC32).

So this checksum can be used to quickly check if a key could be correct or is definitely incorrect. You will still have lots of possible keys that give the right MAC32, though. For those you need a second validation step, possilby trying to decrypt a file or a filename and looking at the content.

[mrVanDalo]

thanks, that sounds like a useful start.

[benrubson]

Closing this for now, feel free to re-open if needed.