Continued maintenance of the UbuntuHashes wiki page

[Neal McBurnett]

Hashes are useful for identifying file corruption, and most any hash scheme would help with that.

But the practice of using hashes to improve security is especially relevant to ISO downloads.

For many other forms of file download, package upgrade, etc, the system that is pulling the new bits has an existing knowledge of your security policies, trust paths, etc, and a variety of ways to check the bits against your own truly trusted signatures etc.

But when booting a system from a BIOS, that is generally much harder to achieve.  So thats why we have the VerifyIsoHowto:

 https://help.ubuntu.com/community/VerifyIsoHowto

  (by the way, why is that marked as a "Duplicate Article", with no hint as to what it might be a duplicate of?)

  (and it has some issues too, like the sentence "The file SHA256SUMS contains MD5 hashes of the ISO images."
  But sticking to the hashes page for now....)

We can't assume that Alice gets an ISO via download directly from cdimages.  There are other attacks also, e.g. someone provides them in another "more convenient" form and points people to a modified UbuntuHashes page.

The harm in keeping a less secure page which also lists the hashes is simply that it expands the attack surface.  We should instead try to limit any proliferation of pages that may be seen to give folks all they need to verify an iso, and help them not only get the hashes from a very secure spot, but also get them complete with signatures.

E.g. rather than having separate SHA256SUMS and SHA256SUMS.gpg files, would it make sense to provide that as a single ASCII-armored file (via gpg --clearsign), keeping the signature right there with the hashes?  After an appropriate transition, we might drop or stop producing the separate files.

Cheers,

Neal McBurnett                 http://neal.mcburnett.org/

On Thu, Jul 09, 2015 at 09:22:34PM -0500, Ian Nicholson wrote:
> On 07/09/2015 04:26 PM, Alberto Salvia Novella wrote:
> > Why do you think having those hashes there is important?
> 
> I think that an argument can be made(I'm not necessarily saying that
> this is a *valid* argument) that if Eve was running a MITM attack on
> Alice's iso download, Eve would have to then compromise both
> cdimages.ubuntu.com and wiki.ubuntu.com(or Alice's connections to those
> hosts) in order to ensure that Alice(who always checks both SHA256 and
> MD5 signatures) isn't alerted to malicious activity.
> Of course that's all hypothetical and dependent on way that the trusted
> hashes are generated, I won't be offended if you aren't as paranoid as I
> am. ;)
> 
> I don't really feel like I contribute enough to say that I'm "voting",
> but my general feeling is that if there's someone who's committed to
> ensuring that the wiki page up to date, what's the harm in keeping it?
> 
> -- 
> Ian Nicholson
> 
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