how ro recover encrypted slice

[Poul-Henning Kamp]

In message <c3421fc3355c.c3355cc3421f at nyroc.rr.com>, mmarkows at twcny.rr.com writ
es:
>Hi,
>
>I mounted a GEOM-encrypted slice to /home2 and stored all my data there. Two days ago, I decided to update my FreeBSD from 5.2 to 5.2.1. I have done it several times before, so I felt self-assured. I backed up my config files, forgetting unfortunately about /etc/gbde/ad1s2.
>
>During the update procedure my system was messed up to the extent that it seemed reasonable to do a clean install of 5.2.1. I did it without saving /etc/gbde/ad1s2, and without touching the encrypted slice.
>
>Now, I am in a predicament because I cannot access my files that I need for my work tomorrow. I know that I messed up, but my last backup is 3 weeks old, and essentially it is no good any more.
>
>Is there any way to recover the data? I have 13 hours to do it.

The data stored in the file you lost is only the encrypted location of
the master key, so in theory you could do a brute force search for the
master key.

Unless your encrypted partition is of rather trivial size, this will take
a lot of time.

You will need to adapt the code from gbde(8) to do this, but that should
be rather straight forward: simply try every single byte offset on the
disk.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.