security issue with signing files
Sun Nov 25 01:12:01 2001
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On Sat, Nov 24, 2001 at 08:54:57PM +0100, Florian Weimer wrote:
> David Shaw <firstname.lastname@example.org> writes:
> > All that said, a possible solution to your problem is to make a local
> > copy of the file to be signed in a place that only you can write to,
> > and verify that local copy is the one you want to sign before signing
> > it. Is that perfectly secure? No. It just changes the threat
> > model. Only you can decide if it changes it enough to make your
> > application safe enough.
> > Another way to approach the problem is a program that reads the file
> > into memory, shows it to you for approval, then pipes it directly from
> > memory to GnuPG for signing. This has the advantage of raising the
> > bar fairly high for an attacker - it is harder (but again, not
> > impossible) to modify the memory of a running process.
> I don't think both scenarios (local copy vs. in-memory copy) make much
> of a difference. If an attacker is able to fiddle with my files, in
> almost all but a few constructed cases, he can also take over my
> account, grab the secret key, and eavesdrop the passphrase.
I don't think either. However, I'm not the signer. It is not up to
me to determine what is secure enough - I don't know which OS is being
used, the physical security situation, signing policy of the site,
etc. Only the signer can make that call. That is why I didn't answer
"You should do this". I answered "Here are the issues. Make your own
David Shaw | email@example.com | WWW http://www.jabberwocky.com/
"There are two major products that come out of Berkeley: LSD and UNIX.
We don't believe this to be a coincidence." - Jeremy S. Anderson
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