Re: [Tails-dev] Filling remaining space on DVDR from /dev/ra…

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Author: Daniel Kahn Gillmor
Date:  
To: Anonymous, tails-dev
Subject: Re: [Tails-dev] Filling remaining space on DVDR from /dev/random
On Wed 2016-06-08 18:03:21 -0400, Anonymous wrote:

> I would like to fill remaining space on DVDR from /dev/random
> after I have burned the Tails 2.4 ISO.


This is a strange request, and i don't think it accomplishes the goals
you're setting out to accomplish. I'm not even sure the goals you're
aiming for make a lot of sense on their own. More explanation below...

> "When creating the CD-R image, also remember to use /dev/random to
> fill the remaining CD-R space so that any malware trying to hide
> inside the CD-R (assuming you create the CD-R image from a more secure
> environment without being infected in the first place) when mounting
> the CD-R on a public computer."


If the goal is to remove potentially-malicious data that someone else
may have written onto a disk, /dev/zero is at least as good for
replacement purposes (and much faster to produce than /dev/random).

> After writing the ISO to the CD-R, query the CD-R for the amount of
> disk space and then make a file with the same size as the remaining
> disk space and then pipe /dev/random output into that file.
>
> To find out CD-R space after copying Tails onto CD-R:
> fdisk -l /dev/cdrom
>
> Fill up the CD-R with random stuff:
> dd if=/dev/random of=/dev/cdrom/ bs=2048 count=


I don't think that optical media burners work this way with dd. I
haven't played with optical media burners in a long time, so it's
possible something changed, but even if it did, the above steps make no
sense in terms of how to write only to unallocated space.

FWIW, even if the rest of the space on the CD-R is full of malware, once
you've burned a proper Tails disk and booted from Tails, that malware
should be no more of a risk to you than would any malware sitting on the
computer's hard drive (or on any other computer's hard drive, for that
matter. Tails doesn't try to read or execute any of the data in these
sectors.

I think someone is either pulling your leg with these instructions, or
is actively confused.

Regards,

        --dkg