[tor-dev] Tor Proposal status updates: Feb 2015

Nick Mathewson nickm at torproject.org
Sun Feb 8 06:57:19 UTC 2015

This is an update to the Tor proposal status overview.  I last sent one
of these out almost a year ago; since 0.2.6 has entered feature freeze,
I really ought to do this regularly again.

Future versions of this document will be maintained in the torspec
repository as "proposals/proposal-status.txt".  I'll still send them
to tor-dev periodically.

If you're looking for something to review, think about, or comment

     Review 219 if you're a DNS geek, or you'd like Tor to work
     better with more DNS types.

     Review 220 (ed25519 identity keys) and 228
     (cross-certification) if you like designing signature things,
     if you have good ideas about future-proofing key type
     migration, or if you care about making Tor servers' identity
     keys stronger.

     Review 223 (ACE handshake) if you're a cryptographer, or a
     cryptography implementer, and you'd like an even faster
     replacement for the ntor handshake.

     Review 224 if you want to look through a big, complex protocol
     with a lot of pieces. Also review it if you care about hidden
     services and making them better.

     Review 226 if you're interested in bridgedb development.

     Review 241 for a big chance at making Tor clients and hidden services
     more secure.

     Review something else if you want to take a possibly good idea
     that needs more momentum and promote it, fix it up, or finally
     kill it off.

I note in passing that many of the proposals below seem stalled,
perhaps permanently: some because we don't know how to answer their
open questions, others because we're not sure if they're a good
idea, others because they don't seem implementable yet.  Is that the
best way to characterize it?  Should we have a new "stalled"
proposal status or something?  Should we have a
"rejected-pending-revision" status that we use effectively for
everything that doesn't seem likely to get revised or implemented
any time soon?  Other suggestions would be welcome.

Finally: if you've sent something to tor-dev or to me that should
have a proposal number, but doesn't have one yet, please ping me
again to remind me!

**NOTE**: The dates after each paragraph indicate when I last
          revised the paragraph.

127  Relaying dirport requests to Tor download site / website

     The idea here was to make it easier to fetch and learn about
     Tor by making it easy for relays to automatically act as
     proxies to the Tor website.  It needs more discussion, and
     there are some significant details to work out.  It's not at
     all clear whether this is actually a good idea or not.
     Probably, there are better choices when it comes to
     distributing software and updates. (11/2013)

131  Help users to verify they are using Tor [NEEDS-REVISION]

     This one is not a crazy idea, but I marked it as
     needs-revision since it doesn't seem to work so well with
     our current designs. It seems mostly superseded by proposal
     211. (11/2013)

132  A Tor Web Service For Verifying Correct Browser Configuration

     This proposal was meant to give users a way to see if their
     browser and privoxy (yes, it was a while ago) are correctly
     configured by running a local webserver on  I'm not
     sure the status here. Generally, I'm skeptical of designs
     that run webservers on localhost, since they become a target
     for cross-site attacks. (11/2013)

133  Incorporate Unreachable ORs into the Tor Network

     This proposal had an idea for letting ORs that can only make
     outgoing connections still relay data usefully in the network.
     It's something we should keep in mind, and it's a pretty neat
     idea, but it radically changes the network topology.  Anybody
     who wants to analyze new network topologies should definitely
     have a look. (5/2011)

140  Provide diffs between consensuses

     This proposal describes a way to transmit less directory
     traffic by sending only differences between consensuses, rather
     than the consensuses themselves.  Daniel Marti implemented this for his
     GSoC project last summer; it is still under revision and on target
     for merge into 0.2.7.  (See ticket #13339)  (2/2015)

141  Download server descriptors on demand

     The idea of this proposal was for clients to only download the
     consensus, and later ask nodes for their own server descriptors
     while building the circuit through them.  It would make each
     circuit more time-consuming to build, but make bootstrapping
     much cheaper.

     Microdescriptors obsolete a lot of this proposal, and present
     some difficulties in using in a way compatible with
     it. (6/2012)

143  Improvements of Distributed Storage for Tor Hidden Service

     Here's a proposal from Karsten about making the hidden
     service DHT more reliable and secure to use.  It could use
     more discussion and analysis. We should look into it as part
     of efforts to improve designs for the next generation of
     hidden services.

     One problem with the analysis here, though, is that it
     assumes a fixed set of servers that doesn't change.  One
     reason that we upload to N servers at each chosen point in
     the ring is that the hidden service host and the hidden
     service client may have different views of which servers
     exist. We need to re-do the analysis with some fraction of
     recent consensuses.

     This is probably superseded by proposal 224; we should close it
     IMO. (2/2014)

144  Increase the diversity of circuits by detecting nodes
     belonging the same provider

     This is a version of the good idea, "Let's do routing in a way
     that tries to keep from routing traffic through the same
     provider too much!"  There are complex issues here that the
     proposal doesn't completely address, but I think it might be a
     fine idea for somebody to see how much more we know now than we
     did in 2008, particularly in light of the relevant paper(s) by
     Matt Edmann and Paul Syverson. (5/2011)

145  Separate "suitable as a guard" from "suitable as a new guard"

     Currently, the Guard flag means both "You can use this node as a
     guard if you need to pick a new guard" and "If this node is
     currently your guard, you can keep using it as a guard."  This
     proposal tries to separate these two concepts, so that clients can
     stop picking a router once it is full of existing clients using it
     as a guard, but the clients currently on it won't all drop it.

     It's not clear whether this has anonymity issues, and it's not
     clear whether the imagined performance gains are actually

     This is probably superseded by proposal 236, which has a better
     approach for weighting guard node selection probabilities; we
     should probably close this ticket. (2/2015)

156  Tracking blocked ports on the client side

     This proposal provides a way for clients to learn which ports
     they are (and aren't) able to connect to, and connect to the
     ones that work.  It comes with a patch, too.  It also lets
     routers track ports that _they_ can't connect to.

     I'm a little unconvinced that this will help a great deal: most
     clients that have some ports blocked will need bridges, not
     just restriction to a smaller set of ports.  This could be good
     behind restrictive firewalls, though.

     The router-side part is a little iffy: routers that can't
     connect to each other violate one of our network topology
     assumptions, and even if we do want to track failed
     router->router connections, the routers need to be sure that
     they aren't fooled into trying to connect repeatedly to a
     series of nonexistent addresses in an attempt to make them
     believe that (say) they can't reach port 443.

     This one is a paradigmatic "open" proposal: it needs more
     discussion.  The patch probably also needs to be ported to
     0.2.3.x; it touches some code that has changed.

     This is likely also to be relevant for the ideas of proposal 241,
     and maybe superseded by some version of that proposal. (2/2015)

159  Exit Scanning

     This is an overview of SoaT, with some ideas for how to integrate
     it into Tor. (5/2011)

164  Reporting the status of server votes

     This proposal explains a way for authorities to provide a
     slightly more verbose document that relay operators can use to
     diagnose reasons that their router was or was not listed in the
     consensus.  These documents would be like slightly more verbose
     versions of the authorities' votes, and would explain *why* the
     authority voted as it did.  It wouldn't be too hard to
     implement, and would be a fine project for somebody who wants
     to get to know the directory code. (5/2011)

165  Easy migration for voting authority sets

     This is a design for how to change the set of authorities without
     having a flag day where the authority operators all reconfigure
     their authorities at once.  It needs more discussion.  One
     difficulty here is that we aren't talking much about changing the
     set of authorities, but that may be a chicken-and-egg issue, since
     changing the set is so onerous.

     If anybody is interested, it would be great to move the discussion
     ahead here. (5/2011)

168  Reduce default circuit window

     This proposal reduces the default window for circuit sendme
     cells.  I think it's implemented (or mostly implemented) in  If so, we should make sure that tor-spec.txt is
     updated and close it. (11/2013)

172  GETINFO controller option for circuit information
173  GETINFO Option Expansion

     These would help controllers (particularly arm) provide more
     useful information about a running Tor process.  They're
     accepted and some parts of 173 are even implemented: somebody
     just needs to implement the rest. (5/2011)

175  Automatically promoting Tor clients to nodes

     Here's Steven's proposal for adding a mode between "client
     mode" and "relay mode" for "self-test to see if you would be a
     good relay, and if so become one."  It didn't get enough
     attention when it was posted to the list; more people should
     review it. (5/2011)

177  Abstaining from votes on individual flags

     Here's my proposal for letting authorities have opinions about some
     (flag,router) combinations without voting on whether _every_ router
     should have that flag.  It's simple, and I think it's basically
     right.  With more discussion and review, somebody could/should
     build it, I think. (11/2013)

182  Credit Bucket

     This proposal suggests an alternative approach to our current
     token-bucket based rate-limiting, that promises better
     performance, less buffering insanity, and a possible end to
     double-gating issues. (6/2012)

185  Directory caches without DirPort

     The old HTTP directory port feature is no longer used by
     clients and relays under most circumstances.  The proposal
     explains how we can get rid of the requirement that non-bridge
     directories have an open directory port. (6/2012)

188  Bridge Guards and other anti-enumeration defenses

     This proposal suggests some ways to make it harder for a relay
     on the Tor network to enumerate a list of Tor bridges. Worth
     investigating and possibly implementing. (6/2012)

190  Bridge Client Authorization Based on a Shared Secret [NEEDS-REVISION]
191  Bridge Detection Resistance against MITM-capable Adversaries

     Proposal 187 reserved the AUTHORIZE cell type; these
     proposals suggests how it could work to try to make it
     harder to probe for Tor bridges. They need more alternatives
     and attention, and possibly some revision and analysis.
     Number 190 needs revision, since its protocol isn't actually
     so great. (11/2013)

192  Automatically retrieve and store information about bridges

     This proposal gives an enhancement to the bridge information
     protocol, where clients remember more things about bridges, and
     are able to update what they know about them over time.  Could
     help a lot with bridge churn. (6/2012)

194  Mnemonic .onion URLs

     Here's one of several competing "let's make .onion URLs
     human-usable" proposals.  This one makes sentences using a
     fixed map.  This kind of approach is likely to obsoleted if
     we go ahead with current plans for hidden services that
     would make .onion addresses much longer, though. (11/2013)

195  TLS certificate normalization for Tor 0.2.4.x

     Here's the followup to proposal 179, containing all the parts
     of proposal 179 that didn't get built, and a couple of other
     tricks besides to try to make Tor's default protocol less
     detectable.  I'm pretty psyched about the part where we let
     relays drop in any any self-signed or CA-issued certificate
     that they like.  Some of this is done in ticket #7145;
     we should decide, however, how much we want to push towards
     normalizing the main Tor protocol. Some of the NSA documents
     published in Der Spiegel this past December imply that this kind of
     fingerprinting can be helpful for snoops; we should take another
     look at it. (2/2015)

196  Extended ORPort and TransportControlPort

     Here are some remaining pieces of the pluggable transport
     protocol that give Tor finer control over the behavior of
     its transports.  Much of this is implemented in 0.2.5
     now; we should figure out what's left, and whether we want
     to build that. (11/2013)

197  Message-based Inter-Controller IPC Channel

     This proposal is for an architectural enhancement in Tor
     deployments, where Tor coordinates communications between the
     various programs (Vidalia, TorBrowser, etc) that are using
     it. (6/2012)

199  Integration of BridgeFinder and BridgeFinderHelper

     Here's a proposal for how Tor can integrate with a client
     program that finds bridges for it. I've seen some work being
     done on things called "BridgeFinder"; I don't know what the
     status of the current proposal is, though. (11/2013)

201  Make bridges report statistics on daily v3 network status requests

     Here's a proposal for bridges to better estimate the number of
     bridge users. (6/2012)

202  Two improved relay encryption protocols for Tor cells

     Here's a sketch of the two broad classes of alternatives for
     improving how relay encryption works. Right now, progress on
     this proposal is stalled waiting for the ideal wide-block
     construction to come along the line. (11/2013)

203  Avoiding censorship by impersonating an HTTPS server

     This one is a design for making a bridge that acts like an
     HTTPS server (by *being* an HTTPS server) until the user
     proves they know it's a bridge. (11/2013)

209  Tuning the Parameters for the Path Bias Defense

     In this proposal, Mike discusses alternative parameters for
     getting better result out of the path-bias-attack detection
     code. (11/2013)

210  Faster Headless Consensus Bootstrapping

     This proposal suggests that we get our initial consensus by
     launching multiple connections in parallel, and fetching the
     consensus from whichever one completes. In my opinion, that
     would be a fine idea when we're fetching our initial
     consensus from non-Authority DirSources, but we shouldnt' do
     anything to increase the load on authorities.  (11/2013)

211  Internal Mapaddress for Tor Configuration Testing

     Here, the idea is to serve an XML document over HTTP that
     would let the know when it's using Tor.  The XML document
     would be returned when you make a request over Tor for a
     magic address in  I think we need to do
     _something_to solve this problem, but I'm not thrilled with
     the idea of having any more magical addresses like this; we
     got rid of .noconnect for a reason, after all. (11/2013)

212  Increase Acceptable Consensus Age

     This proposal suggests that we increase the maximum age of a
     consensus that clients are willing to use when they can't
     find a new one, in order to make the network robust for
     longer against a failure to reach consensus.  In my
     opinion, we should do that.  If I recall correctly, there
     was some tor-dev discussion on this one that should get
     incorporated into a final, implementable version. (11/2013)

219  Support for full DNS and DNSSEC resolution in Tor

     Here's a design to allow Tor to support a full range of DNS
     request types. It probably isn't adequate on its to make
     DNSSEC work realistically, since naive DNSSEC requires many
     round trips that wouldn't be practical over Tor.  It has a
     ton of inline discussion that needs to get resolved before
     this is buildable.

     One thing to consider here is whether we can get the server-side
     done with reasonable confidence, and figure out the client side
     once more servers have upgraded.  (12/2013)

220  Migrate server identity keys to Ed25519
     This one is a design to migrate server identity keys to
     Ed25519 for improved security margin.  It needs more analysis of
     long-term migration to other signing key types -- what do we do
     if we want to add support for EdDSA over Curve3617 or something?
     Can we make it easier than this?  And it also needs analysis to
     make sure it enables us to eventually drop RSA1024 keys

     I've started building this in #12498, though, so we'd better figure
     out out fairly soon.  Other proposals, like 224, depend on this
     one.  (2/2015)

223  Ace: Improved circuit-creation key exchange

     Here's an interesting one. It proposes a replacement for the
     ntor handshake, using the multi-exponentiation optimization, to
     run a bit faster at an equivalent security level.

     Assuming that more cryptographers like the security proof, and
     that the ntor handshake winds up being critical-path in profiles
     as more clients upgrade to 0.2.4 or 0.2.5, this is something we
     should consider. (12/2013)

224  Next-Generation Hidden Services in Tor

     This proposal outlines a more or less completely revised version
     of the Tor hidden services protocol, improved to accomodate
     better cryptography, better scalability, and defenses for
     several attacks we'd never considered when we did the original

     Some parts of this one are clearly right; some (like
     scalability) are entirely unwritten. This proposal needs a lot
     of attention and improvements to get it done right. I hope to
     implement this over the course of 2015-2016. (2/2015)

225  Strawman proposal: commit-and-reveal shared rng

     Proposal 224's solutions for bug #8244 require that authorities
     regularly agree upon a shared random value which none of them
     could have influenced or predicted in advance.  This proposal
     outlines a simple one that isn't perfect (it's vulnerable to DOS
     and to limited influence by one or more collaborating hostile
     authorities), but it's quite simple, and it's meant to start

     I hope that we never build this, but instead replace it with
     something better. Some alternatives have already been discussed
     on tor-dev; more work is needed, though. (12/2013)

226  Scalability and Stability Improvements to BridgeDB:
     Switching to a Distributed Database System and RDBMS

     This one outlines design and behavior changes for a seriously
     refactored bridgedb.  (2/2014)

228  Cross-certifying identity keys with onion keys

     This proposal signs each server's identity key with its onion
     keys, to prove onion key ownership in the router descriptor.
     It's not clear that this actually improves security, but it
     fixes an annoying gap in our key authentication.  I have it coded
     up in my #12498 branch, targetting 0.2.7. (2/2015)

229  Further SOCKS5 extensions

     Here's a nice idea for how we can support a new SOCKS5 protocol
     extension to relay information between clients and Tor, and
     between Tor and pluggable transports, more effectively.  It
     also adds some additional SOCKS5 error codes. There are some
     open questions to answer. "Trunnel" has an implementation of
     the protocol extension formats in its examples directory. (2/2015)

230  How to change RSA1024 relay identity keys [DRAFT]
231  Migrating authority RSA1024 identity keys [DRAFT]

     Who remembers the OpenSSL "Heartbleed" vulnerability?
     These proposals I wrote try to explain safer mechanisms for a bunch
     of servers to migrate their RSA1024 identity keys at once.  I'm not
     sure we'll be able to build thee, though: implementating proposal
     220 above seems cleverer to me. (2/2015)

232  Pluggable Transport through SOCKS proxy [OPEN]

     Arturo Filastò wrote this proposal for chaining pluggable
     transports which themselves need to go through proxies. Seems
     potentially useful! (2/2015)

233  Making Tor2Web mode faster [OPEN]

     This one by Virgil, Fabio, and Giovanni describes a couple of ways
     that Tor2Web builds of Tor can save some circuit hops that they use
     today.  Potentially useful for Tor2Web; any implementation needs to
     be sure that it never changes the behavior of non-tor2web clients.

234  Adding remittance field to directory specification [OPEN]

     Virgil, Leif, and Rob added this proposal for relays to specify
     payment addresses for schemes that want to compensate relay
     operators for their use of bandwidth.  (2/2015)

235  Stop assigning (and eventually supporting) the Named flag [DRAFT]

     This proposal is about removing the Named flag.  (Thanks to
     Sebastian Hahn for writing it!)  The rationale is that the naming
     system for relays never worked particularly well, and it had
     strange and hard-to-explain security properties.  We've implemented
     the key part of this already: directory authorities don't assign
     the Named flag any longer.  Next up will be removing client support
     for parsing and understanding it. (2/2015)

236  The move to a single guard node [OPEN]

     This proposal suggests that to limit client fingerprinting, and to
     limit opportunities for attacks, clients should use a single guard
     node, rotated infrequently.  This transition is in progress; we use
     a single guard node for circuit traffic now, but in order to make
     guards more long-lived, we need to adjust how they are chosen.
     George has a patch for that as #9321, targetting inclusion into
     0.2.6.  (Thanks to George Kadianakis and Nicholas Hopper for
     writing this one.) (2/2015)

237  All relays are directory servers [OPEN]

     Matthew Finkel wrote this proposal to describe a transition to a
     world where Tor relays can be directory servers without having an
     open DirPort -- and eventually, where every relay can be a
     DirServer.  He has an implementation, possibly for 0.2.6 or 0.2.7,
     in ticket #12538.  (2/2015)

238  Better hidden service stats from Tor relays [DRAFT]

     Here's an important one that needs many eyes.  George Kadianakis,
     David Goulet, Karsten Loesing, and Aaron Johnson wrote this to
     describe a mechanism for the tor network to securely produce
     aggregate hidden service usage statistics without exposing
     sensitive intermediate results.  This has an implementation in
     0.2.6 and should probably be marked closed.  (2/2015)

239  Consensus Hash Chaining [DRAFT]

     Here's the start of a good idea that Andrea Shepard wrote up (with
     some help from Nick).  The idea is to make it hard even for a set
     of corrupt authorities (or authority-key-thieves) to make a
     personalized false consensus for a target user, by authenticating
     the whole sequence as a hash chain.  Others on tor-dev suggested
     improvements and had good questions (thanks, Leif and Sebastian G!)

240  Early signing key revocation for directory authorities [DRAFT]

     This one is another Andrea+Nick collaboration about certificate
     revocation for our most sensitive keys.  If an authority key needs
     to be replaced, it would be great to take the old one out of
     circulation as fast as possible.  Peter Palfrader on tor-dev had
     some ideas for making this better. (2/2015)

241  Resisting guard-turnover attacks [DRAFT]

     I wrote this one with good ideas from Aaron Johnson and Rob
     Jansen.  It describes a way to respond to an important class of
     attacks where an adversary kills off a targeted user's guards until
     the user has chosen a guard the attacker controls.  (See the
     "Sniper Attack") paper.  The defense is tricky, and if not done
     right, might lead clients to kick themselves off the network out of
     paranoia. So, this proposal could use more analysis.  (2/2015)

Since last time:

     Proposal 140 and 227 have been implemented and closed.

     Proposal 215 was implemented and closed

     Proposals 230 through 241 are new.

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