bug#47634: Accompany .asc and .DIGESTS keys for the ISO

[Carlo Zancanaro <carlo@zancanaro.id.au>]

Hi bo0od!

On Sat, Apr 10 2021, bo0od wrote:
>> Which implies that the signatures are sufficient, right?
>
> Well this is simple question but the answer is sorta deeper, So 
> i will answer with yes and no:
>
> yes signatures are sufficient but signatures with PGP has 
> problems...

I grant that this might be true, but whether or not to use PGP is 
a different issue to whether cryptographic signatures are 
sufficient to verify downloads. If we compare the projects you've 
shown as examples:

 - Qubes provides hashes, PGP signatures, and a release signing 
 key

 - Whonix provides hashes, PGP signatures, and a release signing 
 key

For verification purposes the hashes only provide transport 
integrity - they don't provide any mechanism to verify where the 
content came from, and because they're stored next to the images 
it's likely that any attacker who could manipulate the images 
could also manipulate the hashes. The signature provides a better 
guarantee that the image contains what the project intends to 
distribute (i.e. that nobody has compromised image itself). In 
this instance, the hash provides no significant additional value 
over the signature.

If we look at the Tor project (who, I hope you will agree, care 
about security), their download page[1] only provides links to PGP 
signatures as their sole method of verification.

I'm not convinced there's much value to add anything beyond the 
signatures, and I think there is some cost. Having multiple 
verification options makes the download page more confusing (by 
providing more choices to do the same thing), and may make it less 
likely that people do any verification.

I think there may be a larger conversation to have around using 
something like Signify rather than PGP/GPG, but I'm not familiar 
enough with Signify to have an opinion about that at the moment.

Carlo

[1]: https://www.torproject.org/download/