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Re: [tor-talk] Problems? Verifying signatures in Tor 4.0.4




On Sat, Feb 28, 2015, at 06:23 PM, Simon Nicolussi wrote:
> andre76@fastmail.fm wrote:
> > I have no idea what all of this means but when I see something that says
> > "BAD signature" that tells me something is wrong.
> 
> Yes, the .asc file that Nicolas was talking about is the one an attacker
> would distribute alongside a manipulated .tar.xz file. Your .asc file is
> fine, so GnuPG sounds the alarm if someone messed with the archive.
> 
> An attacker, however, could easily fool GnuPG with a file inline-signed
> by the Tor Browser Developers. Using, e.g., sha256sums.incrementals.txt
> and the respective detached signature sha256sums.incrementals.txt.asc
> (both available at https://dist.torproject.org/torbrowser/4.0.4/), an
> attacker first creates a signed file with an arbitrary key:
> > $ gpg2 --digest-algo SHA1 --compress-algo uncompressed       \
> > >      --set-filename tor-browser-linux32-4.0.4_en-US.tar.xz \
> > >      --output fake.asc --sign sha256sums.incrementals.txt
> 
> The newly created signature packet gets thrown away:
> > $ eval $(gpg2 --list-packets fake.asc | grep ^# | grep " tag=2 " \
> > >                                     | grep -o " off=[[:digit:]]* ")
> > $ dd if=fake.asc of=tor-browser-linux32-4.0.4_en-US.tar.xz.asc \
> > > bs=1 count=$off
> 
> And the signature of the Tor Browser Developers takes its place:
> > $ gpg2 --output - --dearmor sha256sums.incrementals.txt.asc \
> >        >> tor-browser-linux32-4.0.4_en-US.tar.xz.asc
> 
> GnuPG now won't even take a look at the .tar.xz archive when called with
> that .asc file as its only argument, but still reports a good signature.
> I've attached the file for you to try it out.
> 
> > What must be done to fix this?
> 
> Specify both the detached signature and the archive you want to verify.
> 
> -- 
> Simon Nicolussi <sinic@sinic.name>
> http{s,}://{www.,}sinic.name/
> Email had 2 attachments:
> + tor-browser-linux32-4.0.4_en-US.tar.xz.asc
>   8k (text/plain)
> + Attachment2
>   1k (application/pgp-signature)

Thanks for the help but I have no idea if the Tor files I have a good or
bad.

Here's the output from terminal;

$ gpg --verify tor-browser-linux32-4.0.4_en-US.tar.xz.asc
tor-browser-linux32-4.0.4_en-US.tar.xz
gpg: Signature made Wed 25 Feb 2015 02:54:55 AM EST using RSA key ID
F65C2036
gpg: BAD signature from "Tor Browser Developers (signing key)
<torbrowser@torproject.org>"

Are these files good or bad and not to be trusted? If not to be trusted
which aren't to be trusted?

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