Re: [bitcoin-dev] Proposal: extend bip70 with OpenAlias

[Riccardo Spagni <ric@spagni.net>]

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> I appreciate the thought :)  I think where we differ is on where we
> believe the trade offs should be on perceived privacy versus censorship
> resistance and centralization.
>
>
> By having a limited number of proxies people need to go through to easily
> implement, be it the 4 you recommend, or 53, you actually have a very
> limited number of actors for an authority or hacker to go to in order to be
> able to install/force logging, or censorship.  This very centralization
> forces us back to a model where we need to trust a very small number of
> actors in order for the system to operate as designed.  This, to me,
> appears to be the opposite of the goals of the bitcoin ecosystem.  To
> ensure this point is clear, I strongly believe recommending people focus
> all lookups through 4 centralized "proxies" is a bad idea and counter to
> bitcoin's ideals.
>
>
> The fact that hackers or state actors need to corrupt only a small number
> of servers/services in order to gain global visibility into all queries, I
> believe, breaks any perceived privacy gains from using DNSCrypt.  A very
> small number of hacks or subpoenas and everyone's records are fair game in
> one place.
>

You're misstating (or not understanding) the attack surface.

State-level attackers won't compromise 50+ DNSCrypt servers, they can get
the information on lookups a lot more trivially. Censorship resistance and
protection from state-level attackers comes from the decentralised side of
OpenAlias (ie. Namecoin resolution, preferably done using a local copy of
the NMC blockchain). Since Netki supports Namecoin resolution too there is
no need to worry about protecting end users from that.

There is, however, a need to protect users from man-in-the-middle attacks
where the data is not modified en-route, but it is sniffed. Who you pay in
a financial transaction is, and should be, privileged information between
yourself and that person. By encouraging open DNS lookups you're
effectively hanging that information out for all to see.

It is true that there are only 4 DNSCrypt servers we are comfortable
recommending. It is also true that there were, at one stage, only 4
Electrum servers. There were also only 4 Bitcoin nodes. As something grows
and becomes more useful and usable the number of voluntary participants
becomes much greater, and we will provide the necessary tools to enable
these volunteers.

So in a world where tens of thousands of Bitcoiners are using an aliasing
standard (which, in and of itself, is a convenience service anyway), and
hundreds of individuals and companies are hosting DNSCrypt resolvers, is it
even a valid argument to harp on the number of "proxies"? Thus it is not
worth talking about today. It is definitely worth discussing in future if
the number of DNSCrypt resolvers doesn't increase, but that is a different
discussion for a different time.


> For the highly privacy conscious they can, today do their DNS lookups over
> a non logging VPN connection without forcing everyone else through a
> handful of centralized servers.  Or they can use DNSCrypt optionally
> themselves.  All of our tools have always been open source and folks can
> modify them for their own desired uses, or submit pull requests with their
> own ideas.
>

Everyone should be highly privacy conscious when it comes to financial
transactions, and it would be unconscionable of both you and I not to
defend end-user privacy.

We'd love to hear others thoughts on this.  While I believe that for now
> the centralization trade offs required to use DNSCrypt today (via a limited
> number of proxies) outweigh any perceived privacy benefits it provides, we
> are always open to what others in the community believe and have made
> modifications to how things work before as a result of feedback from
> industry participants.
>

It's important to remember that the "paranoid" won't use an aliasing
service, or at best will use a local Namecoin blockchain for that purpose.
This is a convenience service to provide general and broad appeal for the
non-technical, and those are the very people that need to be protected from
nosey neighbours / workmates / ISPs. Privacy is not only (or even at all)
about protecting people buying drugs on a darknet market, it is about
defending personal liberties.

I think DANE is a great idea.  We were just discussing that with Andreas
> S., and are currently looking at whether we want to add this as optional
> versus mandatory, based on how widely available DANE is for folks using
> services like Cloudflare, Akamai, etc for their DNS, which many providers
> in the space today are.
>
> Of course, the security conscious could setup DANE on the URL we use AS
> IS.  There is no need to create a special kv pair for this as is done in
> OpenAlias.  As you know, DNSSEC and HTTPS support this today out of the box.
>

Embedding the TLSA record in a KV pair just means that pinning takes one
less step.


> The CA validation, in our case, is an ADDITIONAL signature based
> validation to the DNSSEC chain, not a replacement for it.
>

Without DANE it's a weakness. It's trusting an additional CA (over and
above the domain owner), when we know that this is - and has been - an
issue in the past. Were it not an issue DANE (or certificate pinning in
general) would not have to exist.


> We looked at doing this in a single lookup as you did.  With one or two
> currencies this can be potentially more efficient.  As the number of
> supported currencies and addresses under a single name grows, however, this
> solution becomes potentially more problematic.  Please follow the use cases
> below:
>

(snipped quote for brevity)

Many currencies and colored coin addresses are supported under the same
> name, lets say 100.  When you count different currencies and colored coin
> types, it could easily be hundreds, or over a thousand.
>

Coinmarketcap lists 643 currencies and assets, of which only 131 have had
more than $500 in trade volume in the last 24 hours (and only 8 have done
over $100 000 in volume). ShapeShift only lists 44 of those. I seriously
doubt that a convenience service such as aliasing will find great use
amongst every fly-by-night scamcoin that crops up, but that is an aside.

While you may end doing "less lookups" under Open Alias, as it scales, you
> end up causing a significant amount of extra, unnecessary traffic.
>

"Scale" is a misnomer. Someone trying to collect every single active
cryptocurrency and house them all under a single sub-domain is an outlier,
not a problem to be faced at scale. I do not think we will see a large
scale movement to "collect" all the various cryptocurrency tokens, no
matter how worthless they are, and then subsequently setup aliases for them.


> In addition to the obvious impact of being orders of magnitude more
> wasteful than necessary, it also creates privacy "leakage" by returning
> someone 100 different addresses when they only asked for one.
>

I'm not sure how this is any greater leakage than 100 individual requests
for the openly accessible data, especially since it would be encrypted if
made via DNSCrypt?


> Finally, because a single packet UDP transaction for a DNS lookup can
> create possibly hundreds of packets in response, the service can
> essentially become an amplifier for DDoS attacks.  (If I spoof the source
> address of my target with a query to a lookup that issues hundreds of
> packets in response to one packet, and I can have a real impact :( )
>

Naughty naughty, you're doing that thing again where you're using a
smattering of expertise to appear knowledgeable about a subject.

So let's hypothetically say that an individual was crazy enough to have all
643 of the Coinmarketcap currencies/assets aliased on a single sub-domain.
The OpenAlias example of a Monero address (with a recipient name) is 157
bytes long, due to there being two public keys serialised in the address,
plus the ~12 bytes of overhead per RR (the DNS wire format uses label
compression, so the FQDN wouldn't be repeated for each returned record).
Let's call it 170 bytes. That makes the returned data just over 100kb.

Now let's first address a couple of things, assuming that someone would be
nuts enough to do this:

1. This is way larger than the UDP packet maximum, and this would never
come back as a "regular" ol' DNS request (512 bytes max). This may seem
bad, until you consider that DNSSEC responses are almost assured to exceed
512 bytes (eg. an NXDOMAIN with NSEC3). The size of the response is big,
but that's hardly something to write home about.

2. If the DNS server supports RFC2671 (EDNS) then it would try and send it
via UDP, and as long as the client says it can receive such a huge response
over UDP it'll come over the wire.

3. However, because RFC2671 can result in a DNS amplification attack, it's
been obsoleted by RFC6891 (EDNS0), which is pretty much ubiquitous for all
resolvers that support DNSSEC (because of the very large DNSSEC responses,
and the fact that DNSSEC resolvers want to avoid participation in an
amplification attack). EDNS0 mitigates amplification attacks.

4. In the event that an EDNS0 response fails (eg. the client says it can't
accept anything over, say, 4kb, which is quite common) then there's an
automatic and silent switch to DNS-over-TCP (RFC5966). DNS-over-TCP uses
TFO (TCP Fast Open) to do an extremely fast handshake and passing a cookie
to the client in the SYN-ACK, which can then be used for subsequent
requests, but data is still carried in the SYN. TFO mitigates amplification
attacks.

You can't both be overly concerned about amplification attacks *and* use
DNSSEC, which necessitates large records. And, at any rate, the issue with
amplification attacks *isn't* the size of the records (there are tons of
records just under 4kb, like an ANY request against isc.org, that are far
better suited to amplification attacks), it is the number of recursive open
resolvers. There is improvement in this space, though, and many open
recursive resolvers have been fixed in recent years.

It is important to note, that ICANN has "required" for some years that
> registrars and registries support DNSSEC on the domains they register.  I
> personally believe we shouldn't delay use of DNSSEC until their registries
> had come up to current required Internet standards.  (Here are ICANN's
> registrar requirements showing the DNSSEC requirement, btw:
> https://www.icann.org/resources/pages/approved-with-specs-2013-09-17-en#operation
> )
>

Doesn't really matter what they require as long as there are zones that
remain unsigned. Plus it's not like new .za / .sg / .to registrations
magically get DNSSEC, they're also out of luck.


> That said, what do others in the industry think?  We are basing our
> current standard on our believed best practices, and defaulted to "first,
> lose no money", given the irreversibility of bitcoin.
>

Oh, ok. "First, lose no money, but it's ok if your ISP / neighbour /
colleague reports you to the cops because you sent a donation somewhere you
shouldn't."


> I think "DNSSEC is hard" is a bit of a boogey man that's not really true.
> We are working on developing registrar by registrar instructions of how to
> do this, and we have typically found that if you are setting up DNS by
> yourself, adding DNSSEC doesn't take a lot of additional time, maybe an
> hour or so depending on your registrar.
>

Adding the DS record to a domain is trivial, but to use DNSSEC with Gandi
or GoDaddy (if you don't have their PremiumDNS product) you have to host
your own DNS server. Sorry, but that is a non-trivial task. Even worse: you
need to secure your private KSK and not keep it on the server, and if
Bitcoiners are anything to go by this won't happen.

Oh, and incidentally, ENOM/Namecheap doesn't have DNSSEC support yet.

You're literally layering complexity on top of a convenience service, and
to what end?

This known concern, however, is why when we launched our product (based on
> our standard record formats) that we wanted to launch it with a variety of
> options for people.
>

That's completely, 100% centralised. You're creating decentralisation
theatre by providing "options" that no ordinary person will use.

That's some interesting data, and runs counter to the research of the IETF
> DNS working group.  If you are willing to share your data, I can put you in
> touch with the appropriate folks there to share your research.  I'd also
> love to see it!
>

I doubt that very much. See:
http://stats.labs.apnic.net/dnssec/XA?c=XA&x=1&g=1&r=1&w=30

As can be seen, only ~14% of all DNS queries request DNSSEC validation.
That's very far from ubiquitous, and completely matches what Thomas and I
found in Berlin. Unsurprisingly, this stat is particularly bad given that
it also shows that ~15% of all queries are being handled by Google's Public
DNS, without which the stat would be much lower.

I'd argue that we aren't locking "huge portions" of the Internet.  You are
> correct that about 15% of TLD's are not yet signed, even though they were
> required to be by ICANN.
>

Fine, so we're just cutting Africa out, then?
http://www.internetsociety.org/deploy360/wp-content/uploads/2015/06/cctlddnssec-2015-06-19.pdf

Even beyond that, ICANN's page listing DNSSEC-capable registrars (last
updated December 2014) only lists only a handful:
https://www.icann.org/resources/pages/deployment-2012-02-25-en

As I said above, I believe the requirement to not lose money and the fact
> that other options are available for those running on TLD's that are out of
> compliance, is worth the trade off that some existing names won't work
> until their TLD's come into compliance with current Internet standards.
>

A soft fail doesn't magically let the money go. It warns users of the risk
and asks them to verify the address by site. This could even be built out
so that higher value transactions (say, anything over $1000) hard fails in
the absence of DNSSEC, and anything particularly high value (say, anything
over $50 000) refuses to use an alias at all and requires an actual
cryptocurrency address.

I'm a little confused by these closing statements.  Our system has, from
> the beginning been open in terms of the fact that anyone could both serve
> names or do lookups without ever touching our servers, talking to us, or us
> even knowing that they did it or that they even exist.  Our system has
> NEVER been one where folks were required to use us for any portion of the
> service, and from our first beta product launch our open source tools did
> all lookups against DNS records and the blockchain, never any proprietary
> servers or interfaces on our side.
>

Now you're just trolling.

https://github.com/bitpay/copay/pull/2431/files

Which has this lovely line in it:
https://github.com/wdawg33/copay/blob/be6c3e80ab7601d245b186f7802d7050992eb1f0/config.js#L98

So you provide an open standard that uses DNS...but then you wanted to
force CoPay users to use your centralised API?

I'd love to know where you got information that we were in some way a
> closed and centralized system so that we can have an opportunity to clarify
> that misconception.
>

In December 2014 your website had no "developer" section (curl -s
https://web.archive.org/web/20141221141023/https://netki.com/ | grep
"Developers")

The first time that section got scraped was the end of April:
https://web.archive.org/web/20150428231016/https://www.netki.com/partials/developers.html

Even in its current form your website makes no mention of alternatives or
options for those wishing to secure an alias. End users are undoubtedly
left with the distinct impression that they can only get one by paying you.

Riccardo

PS. your mail won't go to the list if you CC the list address, you may want
to resend it

>

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