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Bad news: I forgot a GnuPG secret key passphrase.

Good news: I do know the words it is constructed of. So, I can easily use john or similar to recover (too many combinations to do it manually, though).

Problem: The secret key is not in the secring.gpg format that john understands, but in some new format, apparently distributed across 2 files, in 

~/.gnupg/private-keys-v1.d/0123456789ABCDEF0123456789ABCDEF01234567.key

and

~/.gnupg/private-keys-v1.d/123456789ABCDEF0123456789ABCDEF012345678.key

(files renamed for this question, obviously) created within the timespan of a few seconds - could be pubkey and seckey, if so which one is which?

Could someone please help, maybe by telling me how to extract the (still locked) seckey from these files without a passphrase? An ASCII armor format would be ideal.

Alternatively, maybe someone knows how to feed these files to john directly?

On a related note: Can I enforce the secring.gpg format in GnuPG? I share /home between systems with different versions of GnuPG and don't want to duplicate key files.

Thanks.

PS: Since I already have files encrypted with the key a revocation and replacement would not be a viable solution.

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7
  • Did you try gpg --list-packets 123.key to see what's inside?
    – Arminius
    Commented Mar 30, 2017 at 16:59
  • @Arminius: gpg: no valid OpenPGP data found.
    – Ned64
    Commented Mar 30, 2017 at 17:16
  • Apparently, gpg cannot understand these files, only gpg-agent (a daemon) can. Passphrases are read by a third, separate program pinentry. Could it be more complicated?
    – Ned64
    Commented Mar 30, 2017 at 22:22
  • The gpg command doesn't understand the new private key database format, you need to use gpg2 command instead.
    – Lie Ryan
    Commented Mar 30, 2017 at 23:25
  • 2
    This wasn't the wrong forum to ask. I think your question has a limited number of people that can answer this with any authority*. (e.g. Needs to know internals of gpg-agent, how to use john in a not yet supported way, and how to crack an encryption that wasn't designed to be) Cryptography would be the only other SE site better qualified to answer this. *I don't consider myself an authority, I'm just wildly speculating a possible solution.
    – Core.B
    Commented May 16, 2017 at 18:32

2 Answers 2

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I'm taking a guess at these, but I have no easy way to test if these are actually possible.

Easiest: Nasty and crackgpg have been designed for this purpose. If one of them has been updated to support this new format, try it.

Harder: The file format is documented in gnupg/agent/keyformat.txt. Can you get something like john to try your wordlist until it gets a ( as the first character?

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3
  • Thanks. I tried nasty before but it is just too old for the "new" format. I am assuming the same for crackgpg. Will have a look, though. The format documentation you have linked to is from the future - apparently another change is planned already. I am unsure what you mean by using john - which encryption algorithm (I suppose john knows many?) would I tell john to use?
    – Ned64
    Commented May 17, 2017 at 22:18
  • For keyformat.txt, look at an earlier version in the repository, or the source of your currently installed version on your machine. (With an RPM based distro, you'd get tgr SRPM)
    – Core.B
    Commented May 17, 2017 at 22:24
  • I missed some words on the john answer. It appears to have a DYNAMIC mode that would let you customize what its trying to crack. I'll try to work out if thats practical and edit links into the answer.
    – Core.B
    Commented May 17, 2017 at 22:28
1

A developer of John the Ripper has posted a program that can be used with the mask mode of JtR to crack this format. It has to be linked against libgcrypt from GnuPG.

It is available here.

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