Key safety vs Backup : History of a bad day (key-restoration problem)

[Sven Radde]

Hi!

Nicolas Pillot schrieb:

> Here comes the Sad-result-of-a-cursed-day :
> - i have lost the digital versions of my .gnupg, ascii pub/priv keys
> due to a failing usb stick which hadn't been used for 5+ years.
> - this means i have lost all my encrypted data (mainly accounting
> information, real-life & web password database, and some old
> work-related documents important enough to keep a personnal encrypted
> version at home).
> - i have a partial printed revocation certificate with 8 unreadable
> characters, which means i can't disable the published key.
> - this means, furthermore, that even if there are only few people who
> were using my public key, they could still use it to encrypt, even if
> it's quite useless.
> - It seems like i offered the world another confusing key which would
> never expire. Hurray !
> If i'm wrong on any of these 5 points, don't hesitate to say so !

You are quite right with all of the 5 points.

> Q1: I have the public key (0x26A2F0AE if it's of any use), i know the
> secret key passphrase perfectly. Is there any way i could re-compute /
> restore / whatever the secret part using this information ?

No. The passphrase is in no way connected to the actual private key
material. It is only used to encrypt that key material.
This would be an ideal compression scheme, if it was possible to do ;-)

> Q2: To try and make things straight, i would like to at least revoc
> the key. (...) My
> question is : can a revocation certificate be applied into the keyring
> if you only have the public key.

If you can get the revocation cert working again, then yes, you can
revoke the key. Just import your public key from a keyserver, import the
revocation cert ("gpg --import ...") and the re-submit the key to the
keyserver.
If you cannot recover the certificate, you are out of luck again.
Revocating a key is essentially a special kind of signature and you
would need the private key for that.

Maybe the developers can come up with some special hints that would save
you the hassle of brute-force-importing the revocation cert into GnuPG.
The ASCII-armored GnuPG outputs contain CRC information which could be
used to speed up the process using a suitably smart algorithm.

NB: This is an example where setting an expiration date on your key
would have helped (which is about the only thing you did 'wrong' in your
key safety preparations).

Regarding the secure long-term storage of key material and/or revocation
certs, you might want to search the archives for the subjects "Printing
Keys and using OCR." and "Proofreadable base64" which could be interesting.

HTH, Sven