Nick:
> Quoth Mike Perry:
> > > > Hidden service circuits require ~4X as many Tor router traversals
> > > > as normal Tor exit circuits to set up, and unlike normal Tor exit
> > > > circuits, they are often *not* prebuilt. Once they are set up, they
> > > > still require 2X as many Tor router traversals end-to-end as normal
> > > > circuits. You could easily circle the globe several times to issue
> > > > a single search query.
> > > > 
> > > > And all this is to use the Tor hidden service's 80bit-secure hash 
> > > > instead of an https cert, along with all of the other issues with
> > > > Tor Hidden Services that have accumulated over the past decade due
> > > > to the lack of time for maintenance on Tor's part? I am not
> > > > convinced.
> > > 
> > > This is good to know -- don't promote hidden service versions of
> > > websites (including DDG) when they have an https version, as hidden
> > > services are broken as of now.
> > 
> > Right. However, hidden services are still useful in narrow
> > circumstances, even as janky as they are. I think their most compelling
> > usecase is as fully internal TCP-style application endpoints, not as
> > authentication mechanisms for services that already exist on the
> > surveilled Internet, and use it for their communications.
> 
> But don't hidden services have the advantage that as there is no 
> exit node, the adversary controlling the entry and exit node problem 
> goes away? Or am I misunderstanding. I see that in this case the tor 
> connection to the website is not likely to be the weak point anyway, 
> but I'd be keen to know if I've got this wrong.

If you're talking about attacks as strong as end-to-end correlation,
then it turns out hidden services have similar weaknesses on that order.
There are a number of points where the adversary can inject themselves
either to observe or manipulate hidden service circuit construction.

For some recent examples of that, see
http://www.ieee-security.org/TC/SP2013/papers/4977a080.pdf.

Some of those attacks are quite powerful indeed (and many of them allow
the adversary to choose their own nodes for observation!) and it will
take Tor at least a full stable release cycle or more to fix them...


In terms of data confidentiality and integrity though, I think it is
probably true that the Tor hidden service trust root is much stronger
than the browser CA trust root, even given the 80bit name hash and
RSA-1024 sized keys (which probably are roughly equivalent to each other
in strength for most purposes).

However, Mozilla is working on supporting cert pinning for https, which
we should pick up in Tor Browser in the next few months. Basically, all
we have to do after that is pin our search provider's actual leaf
certificate in Tor Browser itself, and the https usecase becomes both
stronger than the hidden service case in terms of data confidentiality
and integrity to the actual search engine (who knows what happens after
that, of course), and roughly 4X faster...


Still, despite all of this, I still think hidden services have an
important roll to play in Tor. The search engines of today just aren't
the proper use case for them right now.


-- 
Mike Perry
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