Date: Fri, 26 Apr 2013 07:41:47 +0200 From: Alistair Crooks <agc@...src.org> To: oss-security@...ts.openwall.com Subject: Re: upstream source code authenticity checking On Thu, Apr 25, 2013 at 03:40:46PM +0200, nicolas vigier wrote: > On Thu, 25 Apr 2013, Alistair Crooks wrote: > > > > > Q4. where's the public key for this? > > > > A4. could be anywhere. If it's on one of the HKP servers, then cool. > > Not, however, that it can be verified - I know of at least one person > > who has had pubkey information uploaded to the key servers for a key > > he had no knowledge about. Anyone can put whatever email address into > > the userid that they want. If it came with the tarball, ho hum. > > Even if the key comes with the tarball, if the tarball is always signed > with the same key for all releases, then it's useful. You download the > key the first time, keep it somewhere (for instance in the package > source) and use it again to check next releases. And if a new release is > signed with a different key you know you need to be more careful and > can check if the key change is legitimate. Possibly. You actually know very little about the key before and after the signing took place; so you have no way of ascertaining whether the key has been used to sign other things fraudulently. Where a role account is used to sign packages, this is more worrying. But, yes, I'm being alarmist here again. I do agree that signing things is way better than not; but I am also well aware that just because something is signed does not mean that it should be treated as being without need of security. > > Q5. what was signed? > > > > A5. if it comes out as a text document, according to RFC 4880, it has > > some weird properties; hopefully all tar files will be binary. > > Whatever, what was signed was something with the same digest as the > > tarball. Default algorithm is SHA1. Second pre-image attacks on SHA1 > > are getting closer to being possible, and there are means to modify > > entries in the tarball so that an attack is much easier. > > > > Q6. Is this a DSA key? (DSA keys rely on good entropy at signing > > time) If so, how good was the entropy on the machine used to generate > > the signature? > > > > A6. Again, unknown. > > > > Q7. Has someone found the k value for Q6/A6 previously? > > > > A7. They might have done. We'd only know if they told us. > > > > Same could be said about ssh, tls or almost anything using cryptography ... Absolutely, they share the same building blocks - see the Karlsruhe 2010 proceedings for how to interchange ssh and pgp keys for signing and verification. And the only difference between SSL and PGP is the assurance model - whether a trusted third party should be used (FSVO "trusted"), or whether that should be crowdsourced to the web of trust model. Regards, Alistair
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