[tor-commits] [torspec/master] 264: Putting version numbers on the Tor subprotocols
nickm at torproject.org
nickm at torproject.org
Wed Jan 6 23:13:47 UTC 2016
commit 10771f66534d7db55001bcd43fde8fc7b9d033ca
Author: Nick Mathewson <nickm at torproject.org>
Date: Wed Jan 6 15:13:41 2016 -0800
264: Putting version numbers on the Tor subprotocols
---
proposals/000-index.txt | 2 +
proposals/264-subprotocol-versions.txt | 510 ++++++++++++++++++++++++++++++++
2 files changed, 512 insertions(+)
diff --git a/proposals/000-index.txt b/proposals/000-index.txt
index 8da27da..7979244 100644
--- a/proposals/000-index.txt
+++ b/proposals/000-index.txt
@@ -184,6 +184,7 @@ Proposals by number:
261 AEZ for relay cryptography [OPEN]
262 Re-keying live circuits with new cryptographic material [OPEN]
263 Request to change key exchange protocol for handshake [OPEN]
+264 Putting version numbers on the Tor subprotocols [OPEN]
Proposals by status:
@@ -240,6 +241,7 @@ Proposals by status:
261 AEZ for relay cryptography
262 Re-keying live circuits with new cryptographic material
263 Request to change key exchange protocol for handshake
+ 264 Putting version numbers on the Tor subprotocols
ACCEPTED:
140 Provide diffs between consensuses
172 GETINFO controller option for circuit information
diff --git a/proposals/264-subprotocol-versions.txt b/proposals/264-subprotocol-versions.txt
new file mode 100644
index 0000000..d0626f0
--- /dev/null
+++ b/proposals/264-subprotocol-versions.txt
@@ -0,0 +1,510 @@
+Filename: 264-subprotocol-versions.txt
+Title: Putting version numbers on the Tor subprotocols
+Author: Nick Mathewson
+Created: 6 Jan 2016
+Status: Open
+
+
+1. Introduction
+
+ At various points in Tor's history, we've needed to migrate from one
+ protocol to another. In the past, we've mostly done this by allowing
+ relays to advertise support for various features. We've done this in
+ an ad-hoc way, though. In some cases, we've done it entirely based on
+ the relays' advertised Tor version.
+
+ That's a pattern we shouldn't continue. We'd like to support more
+ live Tor relay implementations, and that means that tying "features"
+ to "tor version" won't work going forwards.
+
+ This proposal describes and alternative method that we can use to
+ simplify the advertisement and discovery of features, and the
+ transition from one set of features to another.
+
+1.1. History: "Protocols" vs version-based gating.
+
+ For ages, we've specified a "protocols" line in relay descriptors,
+ with a list of supported versions for "relay" and "link" protocols.
+ But we've never actually looked at it, and instead we've relied on
+ tor version numbers to determine which features we could rely upon.
+ We haven't kept the relay and link protocols listed there up-to-date
+ either.
+
+ Clients have used version checks for three purposes historically:
+ checking relays for bugs, checking relays for features, and
+ implementing bug-workarounds on their own state files.
+
+ In this design, feature checks are now performed directly with
+ subprotocol versions. We only need to keep using Tor versions
+ specifically for bug workarounds.
+
+2. Design: Advertising protocols.
+
+ We revive the "Protocols" design above, in a new form.
+
+ "proto" Entries NL
+
+ Entries =
+ Entries = Entry
+ Entries = Entry SP Entries
+
+ Entry = Keyword "=" Values
+
+ Values = Value
+ Values = Value "," Values
+
+ Value = Int
+ Value = Int "-" Int
+
+ Int = NON_ZERO_DIGIT
+ Int = Int DIGIT
+
+
+ Each 'Entry' in the "proto" line indicates that the Tor relay
+ supports one or more versions of the protocol in question. Entries
+ must be sorted by keyword. Values must be numerically ascending
+ within each entry. (This implies that there are no overlapping
+ ranges.) Ranges must be represented as compactly as possible. Ints
+ must be no more than 2^32 - 1.
+
+ The semantics for each keyword must be defined in a Tor
+ specification. Extension keywords are allowed if they begin with
+ "x-" or "X-". Keywords are case-sensitive.
+
+ During voting, authorities copy these lines immediately below the "v"
+ lines. When a descriptor does not contain a "proto" entry, the
+ authorities should reconstruct it using the approach described below
+ in section A.1. They are included in the consensus using the same
+ rules as currently used for "v" lines, if a sufficiently late
+ consensus method is in use.
+
+2.1. An alternative: Moving 'v' lines into microdescriptors.
+
+ [[[[[
+ Here's an alternative: we could put "v" and "proto" lines into
+ microdescriptors.
+
+ When building microdescriptors, authorities could copy all valid
+ "proto" entries verbatim if a sufficiently late consensus method is
+ in use. When a descriptor does not contain a "proto" entry, the
+ authorities should reconstruct it using the approach described below
+ in section A.1.
+
+ Tor clients that want to use "v" lines should prefer those in
+ microdescriptors if present, and ignore those in the consensus.
+
+ (Existing maintined client versions can be adapted to never look at
+ "v" lines at all; the only versions that they still check for are
+ ones not allowed on the network. The "v" line can be dropped
+ from the consensus entirely when current clients have upgraded.)
+ ]]]]]
+
+ [I am rejecting this alternative for now, since proto lines should
+ compress very well, given that the proto line is completely
+ inferrable from the v line. Removing all the v lines from the
+ current consensus would save only 1.7% after gzip compression.]
+
+3. Using "protos" and "v" lines
+
+ Whenever possible, clients and relays should use the list of
+ advertised protocols instead of version numbers. Version numbers
+ should only be used when implementing bug-workarounds for specific
+ Tor versions.
+
+ Every new feature in tor-spec.txt, dir-spec.txt, and rend-spec.txt
+ should be gated on a particular protocol version.
+
+4. Required protocols
+
+ The consensus may contain three lines: RequiredRelayProtocols,
+ RecommendedClientProtocols, and RequiredClientProtocols. Each has
+ the same format as the "protos" line. To vote on these entries, a
+ protocol/version combination is included only if it is listed by a
+ majority of the voters.
+
+ When a relay lacks a protocol listed in RequiredRelayProtocols, it
+ must not attempt to join the network.
+
+ When a client lacks a protocol listed in RecommendedClientProtocols,
+ it should warn the user that the client is obsolete.
+
+ When a client lacks a protocol listed in RequiredClientProtocols, it
+ must not use the corresponding feature. If the corresponding feature
+ is required to operate a Tor client, the client must must log an
+ error message and shut down without connecting to the network, even
+ if the cached consensus is out-of-date. This implements a "safe
+ forward shutdown" mechanism for zombie clients.
+
+ The above features should be backported to 0.2.4 and later.
+
+5. Current protocols
+
+ (See "6. Maintaining the protocol list" below for information about
+ how I got these, and why version 0.2.4.19 comes up so often.)
+
+5.1. "Link"
+
+ The "link" protocols are those used by clients and relays to initiate
+ and receive OR connections and to handle cells on OR connections.
+ The "link" protocol versions correspond 1:1 to those versions.
+
+ Two Tor instances can make a connection to each other only if they
+ have at least one link protocol in common.
+
+ The current "link" versions are: "1" through "4"; see tor-spec.txt
+ for more information. All current Tor versions support "1-3";
+ version from 0.2.4.11-alpha and on support "1-4". Eventually we
+ will drop "1" and "2".
+
+5.2. "LinkAuth"
+
+ LinkAuth protocols correspond to varieties of Authenticate cells used
+ for the v3+ link protocools.
+
+ The currrent version is "1".
+
+5.3. "Relay"
+
+ The "relay" protocols are those used to handle CREATE cells, and
+ those that that handle the various RELAY cell types received after a
+ CREATE cell. (Except, relay cells used to manage introduction and
+ rendezvous points are managed with the "HSMid" protocols.)
+
+ "1" -- supports the TAP key exchange, with all features in Tor
+ 0.2.3. Support for CREATE and CREATED and CREATE_FAST and
+ CREATED_FAST and EXTEND and EXTENDED.
+
+ "2" -- supports the ntor key exchange, and all features in Tor
+ 0.2.4.19. Includes support for CREATE2 and CREATED2 and
+ EXTEND2 and EXTENDED2.
+
+5.3. "HSMid"
+
+ The "HSMid" protocols are those that handle introduction points and
+ rendezvous points.
+
+ "1" -- supports all features in Tor 0.2.4.19
+
+5.4. "DirCache"
+
+ The "DirCache" protocols are the set of documents available for
+ download from a directory cache via BEGIN_DIR, and the set of URLs
+ available to fetch them. (This excludes URLs for hidden service
+ objects.)
+
+ "1" -- supports all features in Tor 0.2.4.19.
+
+5.5. "HSDir"
+
+ The HSDir protocols are the set of hidden service document types
+ that can be uploaded to, understood by, and downloaded from a tor
+ relay, and the set of URLs available to fetch them.
+
+ "1" -- supports all features in Tor 0.2.4.19.
+
+5.6. "Desc"
+
+ Describes features present or absent in descriptors.
+
+ Most features in descriptors don't require a "Desc" update -- only
+ those that need to someday be required. For example, someday clients
+ will need to understand ed25519 identities.
+
+ "1" -- supports all features in Tor 0.2.4.19.
+
+ "2" -- cross-signing with onion-keys, signing with ed25519
+ identities.
+
+5.7. "Microdesc"
+
+ Describes features present or absent in microdescriptors.
+
+ Most features in descriptors don't require a "MircoDesc" update --
+ only those that need to someday be required.
+ These correspond more or less with consensus methods.
+
+ "1" -- consensus methods 9 through 20.
+
+ "2" -- consensus method 21 (adds ed25519 keys to microdescs).
+
+5.8. "Cons"
+
+ Describes features present or absent in consensus documents.
+
+ Most features in consensus documents don't require a "Cons" update --
+ only those that need to someday be required.
+
+ These correspond more or less with consensus methods.
+
+ "1" -- consensus methods 9 through 20.
+
+ "2" -- consensus method 21 (adds ed25519 keys to microdescs).
+
+
+6. Maintaining the protocol lists
+
+ What makes a good fit for a "protocol" type? Generally, it's a set
+ of communications functionality that tends to upgrade in tandem, and
+ in isolation from other parts of the Tor protocols. It tends to be
+ functionality where it doesn't make sense to implement only part of
+ it -- though omitting the whole thing might make sense.
+
+ (Looking through our suite of protocols, you might make a case for
+ splitting DirCache into sub-protocols.)
+
+ We shouldn't add protocols for features where others can remain
+ oblivious to their presence or absence. For example, if some
+ directory caches start supporting a new header, and clients can
+ safely send that header without knowing whether the directory cache
+ will understand it, then a new protocol version is not required.
+
+ Because all relays currently on the network are 0.2.4.19 or later, we
+ can require 0.2.4.19, and use 0.2.4.19 as the minimal version so we
+ we don't need to do code archeology to determine which number
+
+ Adding new protocol types is pretty cheap, given compression.
+
+A.1. Inferring missing protos lines.
+
+ The directory authorities no longer allow versions of Tor before
+ 0.2.4.8-alpha. But right now, there is no version of Tor in the
+ consensus before 0.2.4.19. Therefore, we should disallow versions of
+ Tor earlier than 0.2.4.19, so that we can have the protocol list for
+ all current Tor versions include:
+
+ DirCache=1 HSDir=1 HSMid=1 Link=1-4 LinkAuth=1 Relay=1-2
+
+ For Desc, Tor versions before 0.2.7.stable should be taken to have
+ Desc=1 and versions 0.2.7.stable or later should have Desc=1-2.
+
+ For Microdesc and Cons, Tor versions before 0.2.7.stable should be
+ taken to support version 1; 0.2.7.stable and later should have
+ 1-2.
+
+A.2. Initial required protocols
+
+ For clients we will Recommend and Require:
+
+ DirCache=1 HSDir=1 Desc=1 Cons=ANYOF(9-20) Microdesc=ANYOF(9-20)
+ HSMid=1 Link=4 LinkAuth=1 Relay=2
+
+ For relays we will Require:
+
+ DirCache=1 HSDir=1 Desc=1 Cons=ANYOF(9-20) Microdesc=ANYOF(9-20)
+ HSMid=1 Link=3-4 LinkAuth=1 Relay=1-2
+
+A.3. Example integration with other open proposals
+
+ In this appendix, I try to show that this proposal is viable by
+ showing how it can integrate with other open proposals to avoid
+ version-gating. I'm looking at open/draft/accepted proposals only.
+
+ 140 Provide diffs between consensuses
+
+ This proposal doesn't affect interoperability, though we could
+ add a DirCache protocol version for it if we think we might
+ want to require it someday.
+
+ 164 Reporting the status of server votes
+
+ Interoperability not affected; no new protocol.
+
+ 165 Easy migration for voting authority sets
+
+ Authority-only; no new protocol.
+
+ 168 Reduce default circuit window
+
+ Interoperability slightly affected; could be a new Relay
+ protocol.
+
+ 172 GETINFO controller option for circuit information
+ 173 GETINFO Option Expansion
+
+ Client/Relay interop not affected; no new protocol.
+
+ 177 Abstaining from votes on individual flags
+
+ Authority-only; no new protocol.
+
+ 182 Credit Bucket
+
+ No new protocol.
+
+ 188 Bridge Guards and other anti-enumeration defenses
+
+ No new protocol.
+
+ 189 AUTHORIZE and AUTHORIZED cells
+
+ This would be a new protocol, either a Link protocol or a new
+ LinkAuthz protocol.
+
+ 191 Bridge Detection Resistance against MITM-capable Adversaries
+
+ No new protocol.
+
+ 192 Automatically retrieve and store information about bridges
+
+ No new protocol.
+
+ 195 TLS certificate normalization for Tor 0.2.4.x
+
+ Interop not affected; no new protocol.
+
+ 201 Make bridges report statistics on daily v3 network status
+ requests
+
+ No new protocol.
+
+ 202 Two improved relay encryption protocols for Tor cells
+
+ This would be a new Relay protocol.
+
+ 203 Avoiding censorship by impersonating an HTTPS server
+
+ Bridge/PT only; no new protocol.
+
+ 209 Tuning the Parameters for the Path Bias Defense
+
+ Client behavior only; no new protocol.
+
+ 210 Faster Headless Consensus Bootstrapping
+
+ Client behavior only; no new protocol.
+
+ 212 Increase Acceptable Consensus Age
+
+ Possibly add a new DirCache protocol version to describe the
+ "will hold older descriptors" property.
+
+ 219 Support for full DNS and DNSSEC resolution in Tor
+
+ New relay protocol, or new protocol class (DNS=2?)
+
+ 220 Migrate server identity keys to Ed25519
+
+ Once link authentication is supported, that's a new LinkAuth
+ protocol version.
+
+ No new protocol version is required for circuit extension,
+ since it's a backward-compatible change.
+
+ 224 Next-Generation Hidden Services in Tor
+
+ Adds new HSDir and HSMid protocols.
+
+ 226 "Scalability and Stability Improvements to BridgeDB: Switching
+ to a Distributed Database System and RDBMS"
+
+ No new protocol.
+
+ 229 Further SOCKS5 extensions
+
+ Client-only; no new protocol.
+
+ 233 Making Tor2Web mode faster
+
+ No new protocol.
+
+ 234 Adding remittance field to directory specification
+
+ Could be a new protocol; or not.
+
+ 237 All relays are directory servers
+
+ No new protocol.
+
+ 239 Consensus Hash Chaining
+
+ No new protocol.
+
+ 242 Better performance and usability for the MyFamily option
+
+ New Desc protocol.
+
+ 244 Use RFC5705 Key Exporting in our AUTHENTICATE calls
+
+ Part of prop220. Also adds another LinkAuth protocol version.
+
+ 245 Deprecating and removing the TAP circuit extension protocol
+
+ Removes Linkauth protocol 1.
+
+ Removes a Desc protocol.
+
+ 246 Merging Hidden Service Directories and Introduction Points
+
+ Possibly adds a new HSMid protocol.
+
+ 247 Defending Against Guard Discovery Attacks using Vanguards
+
+ No new protocol.
+
+ 248 Remove all RSA identity keys
+
+ Adds a new Desc protocol version and a new Cons protocol
+ version; eventually removes a version of each.
+
+ 249 Allow CREATE cells with >505 bytes of handshake data
+
+ Adds a new Link protocol version for CREATE2V.
+
+ Adds a new Relay protocol version for new EXTEND2 semantics.
+
+ 250 Random Number Generation During Tor Voting
+
+ No new protocol.
+
+ 251 Padding for netflow record resolution reduction
+
+ No new protocol.
+
+ 252 Single Onion Services
+
+ No new protocol.
+
+ 253 Out of Band Circuit HMACs
+
+ New Relay protocol.
+
+ 254 Padding Negotiation
+
+ New Link protocol, new Relay protocol.
+
+ 255 Controller features to allow for load-balancing hidden services
+
+ No new protocol.
+
+ 256 Key revocation for relays and authorities
+
+ New Desc protocol.
+
+ 257 Refactoring authorities and taking parts offline
+
+ No new protocol.
+
+ 258 Denial-of-service resistance for directory authorities
+
+ No new protocol.
+
+ 259 New Guard Selection Behaviour
+
+ No new protocol
+
+ 260 Rendezvous Single Onion Services
+
+ No new protocol
+
+ 261 AEZ for relay cryptography
+
+ New Relay protocol version.
+
+ 262 Re-keying live circuits with new cryptographic material
+
+ New Relay protocol version
+
+ 263 Request to change key exchange protocol for handshake
+
+ New Relay protocol version.
+
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