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2 Tor directory protocol, version 3
4 0. Scope and preliminaries
6 This directory protocol is used by Tor version 0.2.0.x-alpha and later.
7 See dir-spec-v1.txt for information on the protocol used up to the
8 0.1.0.x series, and dir-spec-v2.txt for information on the protocol
9 used by the 0.1.1.x and 0.1.2.x series.
11 Caches and authorities must still support older versions of the
12 directory protocols, until the versions of Tor that require them are
13 finally out of commission.
15 This document merges and supersedes the following proposals:
17 101 Voting on the Tor Directory System
18 103 Splitting identity key from regularly used signing key
19 104 Long and Short Router Descriptors
21 XXX when to download certificates.
22 XXX timeline
23 XXX fill in XXXXs
25 The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL
26 NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
27 "OPTIONAL" in this document are to be interpreted as described in
28 RFC 2119.
30 0.1. History
32 The earliest versions of Onion Routing shipped with a list of known
33 routers and their keys. When the set of routers changed, users needed to
34 fetch a new list.
36 The Version 1 Directory protocol
37 --------------------------------
39 Early versions of Tor (0.0.2) introduced "Directory authorities": servers
40 that served signed "directory" documents containing a list of signed
41 "router descriptors", along with short summary of the status of each
42 router. Thus, clients could get up-to-date information on the state of
43 the network automatically, and be certain that the list they were getting
44 was attested by a trusted directory authority.
46 Later versions (0.0.8) added directory caches, which download
47 directories from the authorities and serve them to clients. Non-caches
48 fetch from the caches in preference to fetching from the authorities, thus
49 distributing bandwidth requirements.
51 Also added during the version 1 directory protocol were "router status"
52 documents: short documents that listed only the up/down status of the
53 routers on the network, rather than a complete list of all the
54 descriptors. Clients and caches would fetch these documents far more
55 frequently than they would fetch full directories.
57 The Version 2 Directory Protocol
58 --------------------------------
60 During the Tor 0.1.1.x series, Tor revised its handling of directory
61 documents in order to address two major problems:
63 * Directories had grown quite large (over 1MB), and most directory
64 downloads consisted mainly of router descriptors that clients
65 already had.
67 * Every directory authority was a trust bottleneck: if a single
68 directory authority lied, it could make clients believe for a time
69 an arbitrarily distorted view of the Tor network. (Clients
70 trusted the most recent signed document they downloaded.) Thus,
71 adding more authorities would make the system less secure, not
72 more.
74 To address these, we extended the directory protocol so that
75 authorities now published signed "network status" documents. Each
76 network status listed, for every router in the network: a hash of its
77 identity key, a hash of its most recent descriptor, and a summary of
78 what the authority believed about its status. Clients would download
79 the authorities' network status documents in turn, and believe
80 statements about routers iff they were attested to by more than half of
81 the authorities.
83 Instead of downloading all router descriptors at once, clients
84 downloaded only the descriptors that they did not have. Descriptors
85 were indexed by their digests, in order to prevent malicious caches
86 from giving different versions of a router descriptor to different
87 clients.
89 Routers began working harder to upload new descriptors only when their
90 contents were substantially changed.
93 0.2. Goals of the version 3 protocol
95 Version 3 of the Tor directory protocol tries to solve the following
96 issues:
98 * A great deal of bandwidth used to transmit router descriptors was
99 used by two fields that are not actually used by Tor routers
100 (namely read-history and write-history). We save about 60% by
101 moving them into a separate document that most clients do not
102 fetch or use.
104 * It was possible under certain perverse circumstances for clients
105 to download an unusual set of network status documents, thus
106 partitioning themselves from clients who have a more recent and/or
107 typical set of documents. Even under the best of circumstances,
108 clients were sensitive to the ages of the network status documents
109 they downloaded. Therefore, instead of having the clients
110 correlate multiple network status documents, we have the
111 authorities collectively vote on a single consensus network status
112 document.
114 * The most sensitive data in the entire network (the identity keys
115 of the directory authorities) needed to be stored unencrypted so
116 that the authorities can sign network-status documents on the fly.
117 Now, the authorities' identity keys are stored offline, and used
118 to certify medium-term signing keys that can be rotated.
120 0.3. Some Remaining questions
122 Things we could solve on a v3 timeframe:
124 The SHA-1 hash is showing its age. We should do something about our
125 dependency on it. We could probably future-proof ourselves here in
126 this revision, at least so far as documents from the authorities are
127 concerned.
129 Too many things about the authorities are hardcoded by IP.
131 Perhaps we should start accepting longer identity keys for routers
132 too.
134 Things to solve eventually:
136 Requiring every client to know about every router won't scale forever.
138 Requiring every directory cache to know every router won't scale
139 forever.
142 1. Outline
144 There is a small set (say, around 5-10) of semi-trusted directory
145 authorities. A default list of authorities is shipped with the Tor
146 software. Users can change this list, but are encouraged not to do so,
147 in order to avoid partitioning attacks.
149 Every authority has a very-secret, long-term "Authority Identity Key".
150 This is stored encrypted and/or offline, and is used to sign "key
151 certificate" documents. Every key certificate contains a medium-term
152 (3-12 months) "authority signing key", that is used by the authority to
153 sign other directory information. (Note that the authority identity
154 key is distinct from the router identity key that the authority uses
155 in its role as an ordinary router.)
157 Routers periodically upload signed "routers descriptors" to the
158 directory authorities describing their keys, capabilities, and other
159 information. Routers may also upload signed "extra info documents"
160 containing information that is not required for the Tor protocol.
161 Directory authorities serve router descriptors indexed by router
162 identity, or by hash of the descriptor.
164 Routers may act as directory caches to reduce load on the directory
165 authorities. They announce this in their descriptors.
167 Periodically, each directory authority generates a view of
168 the current descriptors and status for known routers. They send a
169 signed summary of this view (a "status vote") to the other
170 authorities. The authorities compute the result of this vote, and sign
171 a "consensus status" document containing the result of the vote.
173 Directory caches download, cache, and re-serve consensus documents.
175 Clients, directory caches, and directory authorities all use consensus
176 documents to find out when their list of routers is out-of-date.
177 (Directory authorities also use vote statuses.) If it is, they download
178 any missing router descriptors. Clients download missing descriptors
179 from caches; caches and authorities download from authorities.
180 Descriptors are downloaded by the hash of the descriptor, not by the
181 relay's identity key: this prevents directory servers from attacking
182 clients by giving them descriptors nobody else uses.
184 All directory information is uploaded and downloaded with HTTP.
186 [Authorities also generate and caches also cache documents produced and
187 used by earlier versions of this protocol; see dir-spec-v1.txt and
188 dir-spec-v2.txt for notes on those versions.]
190 1.1. What's different from version 2?
192 Clients used to download multiple network status documents,
193 corresponding roughly to "status votes" above. They would compute the
194 result of the vote on the client side.
196 Authorities used to sign documents using the same private keys they used
197 for their roles as routers. This forced them to keep these extremely
198 sensitive keys in memory unencrypted.
200 All of the information in extra-info documents used to be kept in the
201 main descriptors.
203 1.2. Document meta-format
205 Router descriptors, directories, and running-routers documents all obey the
206 following lightweight extensible information format.
208 The highest level object is a Document, which consists of one or more
209 Items. Every Item begins with a KeywordLine, followed by zero or more
210 Objects. A KeywordLine begins with a Keyword, optionally followed by
211 whitespace and more non-newline characters, and ends with a newline. A
212 Keyword is a sequence of one or more characters in the set [A-Za-z0-9-].
213 An Object is a block of encoded data in pseudo-Open-PGP-style
214 armor. (cf. RFC 2440)
216 More formally:
218 NL = The ascii LF character (hex value 0x0a).
219 Document ::= (Item | NL)+
220 Item ::= KeywordLine Object*
221 KeywordLine ::= Keyword NL | Keyword WS ArgumentChar+ NL
222 Keyword = KeywordChar+
223 KeywordChar ::= 'A' ... 'Z' | 'a' ... 'z' | '0' ... '9' | '-'
224 ArgumentChar ::= any printing ASCII character except NL.
225 WS = (SP | TAB)+
226 Object ::= BeginLine Base-64-encoded-data EndLine
227 BeginLine ::= "-----BEGIN " Keyword "-----" NL
228 EndLine ::= "-----END " Keyword "-----" NL
230 The BeginLine and EndLine of an Object must use the same keyword.
232 When interpreting a Document, software MUST ignore any KeywordLine that
233 starts with a keyword it doesn't recognize; future implementations MUST NOT
234 require current clients to understand any KeywordLine not currently
235 described.
237 Other implementations that want to extend Tor's directory format MAY
238 introduce their own items. The keywords for extension items SHOULD start
239 with the characters "x-" or "X-", to guarantee that they will not conflict
240 with keywords used by future versions of Tor.
242 In our document descriptions below, we tag Items with a multiplicity in
243 brackets. Possible tags are:
245 "At start, exactly once": These items MUST occur in every instance of
246 the document type, and MUST appear exactly once, and MUST be the
247 first item in their documents.
249 "Exactly once": These items MUST occur exactly one time in every
250 instance of the document type.
252 "At end, exactly once": These items MUST occur in every instance of
253 the document type, and MUST appear exactly once, and MUST be the
254 last item in their documents.
256 "At most once": These items MAY occur zero or one times in any
257 instance of the document type, but MUST NOT occur more than once.
259 "Any number": These items MAY occur zero, one, or more times in any
260 instance of the document type.
262 "Once or more": These items MUST occur at least once in any instance
263 of the document type, and MAY occur more.
265 1.3. Signing documents
267 Every signable document below is signed in a similar manner, using a
268 given "Initial Item", a final "Signature Item", a digest algorithm, and
269 a signing key.
271 The Initial Item must be the first item in the document.
273 The Signature Item has the following format:
275 <signature item keyword> [arguments] NL SIGNATURE NL
277 The "SIGNATURE" Object contains a signature (using the signing key) of
278 the PKCS1-padded digest of the entire document, taken from the
279 beginning of the Initial item, through the newline after the Signature
280 Item's keyword and its arguments.
282 Unless otherwise, the digest algorithm is SHA-1.
284 All documents are invalid unless signed with the correct signing key.
286 The "Digest" of a document, unless stated otherwise, is its digest *as
287 signed by this signature scheme*.
289 1.4. Voting timeline
291 Every consensus document has a "valid-after" (VA) time, a "fresh-until"
292 (FU) time and a "valid-until" (VU) time. VA MUST precede FU, which MUST
293 in turn precede VU. Times are chosen so that every consensus will be
294 "fresh" until the next consensus becomes valid, and "valid" for a while
295 after. At least 3 consensuses should be valid at any given time.
297 The timeline for a given consensus is as follows:
299 VA-DistSeconds-VoteSeconds: The authorities exchange votes.
301 VA-DistSeconds-VoteSeconds/2: The authorities try to download any
302 votes they don't have.
304 VA-DistSeconds: The authorities calculate the consensus and exchange
305 signatures.
307 VA-DistSeconds/2: The authorities try to download any signatures
308 they don't have.
310 VA: All authorities have a multiply signed consensus.
312 VA ... FU: Caches download the consensus. (Note that since caches have
313 no way of telling what VA and FU are until they have downloaded
314 the consensus, they assume that the present consensus's VA is
315 equal to the previous one's FU, and that its FU is one interval after
316 that.)
318 FU: The consensus is no longer the freshest consensus.
320 FU ... (the current consensus's VU): Clients download the consensus.
321 (See note above: clients guess that the next consensus's FU will be
322 two intervals after the current VA.)
324 VU: The consensus is no longer valid.
326 VoteSeconds and DistSeconds MUST each be at least 20 seconds; FU-VA and
327 VU-FU MUST each be at least 5 minutes.
329 2. Router operation and formats
331 ORs SHOULD generate a new router descriptor and a new extra-info
332 document whenever any of the following events have occurred:
334 - A period of time (18 hrs by default) has passed since the last
335 time a descriptor was generated.
337 - A descriptor field other than bandwidth or uptime has changed.
339 - Bandwidth has changed by a factor of 2 from the last time a
340 descriptor was generated, and at least a given interval of time
341 (20 mins by default) has passed since then.
343 - Its uptime has been reset (by restarting).
345 [XXX this list is incomplete; see router_differences_are_cosmetic()
346 in routerlist.c for others]
348 ORs SHOULD NOT publish a new router descriptor or extra-info document
349 if none of the above events have occurred and not much time has passed
350 (12 hours by default).
352 After generating a descriptor, ORs upload them to every directory
353 authority they know, by posting them (in order) to the URL
355 http://<hostname:port>/tor/
357 2.1. Router descriptor format
359 Router descriptors consist of the following items. For backward
360 compatibility, there should be an extra NL at the end of each router
361 descriptor.
363 In lines that take multiple arguments, extra arguments SHOULD be
364 accepted and ignored. Many of the nonterminals below are defined in
365 section 2.3.
367 "router" nickname address ORPort SOCKSPort DirPort NL
369 [At start, exactly once.]
371 Indicates the beginning of a router descriptor. "nickname" must be a
372 valid router nickname as specified in 2.3. "address" must be an IPv4
373 address in dotted-quad format. The last three numbers indicate the
374 TCP ports at which this OR exposes functionality. ORPort is a port at
375 which this OR accepts TLS connections for the main OR protocol;
376 SOCKSPort is deprecated and should always be 0; and DirPort is the
377 port at which this OR accepts directory-related HTTP connections. If
378 any port is not supported, the value 0 is given instead of a port
379 number. (At least one of DirPort and ORPort SHOULD be set;
380 authorities MAY reject any descriptor with both DirPort and ORPort of
381 0.)
383 "bandwidth" bandwidth-avg bandwidth-burst bandwidth-observed NL
385 [Exactly once]
387 Estimated bandwidth for this router, in bytes per second. The
388 "average" bandwidth is the volume per second that the OR is willing to
389 sustain over long periods; the "burst" bandwidth is the volume that
390 the OR is willing to sustain in very short intervals. The "observed"
391 value is an estimate of the capacity this relay can handle. The
392 relay remembers the max bandwidth sustained output over any ten
393 second period in the past day, and another sustained input. The
394 "observed" value is the lesser of these two numbers.
396 "platform" string NL
398 [At most once]
400 A human-readable string describing the system on which this OR is
401 running. This MAY include the operating system, and SHOULD include
402 the name and version of the software implementing the Tor protocol.
404 "published" YYYY-MM-DD HH:MM:SS NL
406 [Exactly once]
408 The time, in GMT, when this descriptor (and its corresponding
409 extra-info document if any) was generated.
411 "fingerprint" fingerprint NL
413 [At most once]
415 A fingerprint (a HASH_LEN-byte of asn1 encoded public key, encoded in
416 hex, with a single space after every 4 characters) for this router's
417 identity key. A descriptor is considered invalid (and MUST be
418 rejected) if the fingerprint line does not match the public key.
420 [We didn't start parsing this line until Tor 0.1.0.6-rc; it should
421 be marked with "opt" until earlier versions of Tor are obsolete.]
423 "hibernating" bool NL
425 [At most once]
427 If the value is 1, then the Tor relay was hibernating when the
428 descriptor was published, and shouldn't be used to build circuits.
430 [We didn't start parsing this line until Tor 0.1.0.6-rc; it should be
431 marked with "opt" until earlier versions of Tor are obsolete.]
433 "uptime" number NL
435 [At most once]
437 The number of seconds that this OR process has been running.
439 "onion-key" NL a public key in PEM format
441 [Exactly once]
443 This key is used to encrypt EXTEND cells for this OR. The key MUST be
444 accepted for at least 1 week after any new key is published in a
445 subsequent descriptor. It MUST be 1024 bits.
447 "signing-key" NL a public key in PEM format
449 [Exactly once]
451 The OR's long-term identity key. It MUST be 1024 bits.
453 "accept" exitpattern NL
454 "reject" exitpattern NL
456 [Any number]
458 These lines describe an "exit policy": the rules that an OR follows
459 when deciding whether to allow a new stream to a given address. The
460 'exitpattern' syntax is described below. There MUST be at least one
461 such entry. The rules are considered in order; if no rule matches,
462 the address will be accepted. For clarity, the last such entry SHOULD
463 be accept *:* or reject *:*.
465 "router-signature" NL Signature NL
467 [At end, exactly once]
469 The "SIGNATURE" object contains a signature of the PKCS1-padded
470 hash of the entire router descriptor, taken from the beginning of the
471 "router" line, through the newline after the "router-signature" line.
472 The router descriptor is invalid unless the signature is performed
473 with the router's identity key.
475 "contact" info NL
477 [At most once]
479 Describes a way to contact the relay's administrator, preferably
480 including an email address and a PGP key fingerprint.
482 "family" names NL
484 [At most once]
486 'Names' is a space-separated list of relay nicknames or
487 hexdigests. If two ORs list one another in their "family" entries,
488 then OPs should treat them as a single OR for the purpose of path
489 selection.
491 For example, if node A's descriptor contains "family B", and node B's
492 descriptor contains "family A", then node A and node B should never
493 be used on the same circuit.
495 "read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL
496 [At most once]
497 "write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL
498 [At most once]
500 Declare how much bandwidth the OR has used recently. Usage is divided
501 into intervals of NSEC seconds. The YYYY-MM-DD HH:MM:SS field
502 defines the end of the most recent interval. The numbers are the
503 number of bytes used in the most recent intervals, ordered from
504 oldest to newest.
506 [We didn't start parsing these lines until Tor 0.1.0.6-rc; they should
507 be marked with "opt" until earlier versions of Tor are obsolete.]
509 [See also migration notes in section 2.2.1.]
511 "eventdns" bool NL
513 [At most once]
515 Declare whether this version of Tor is using the newer enhanced
516 dns logic. Versions of Tor with this field set to false SHOULD NOT
517 be used for reverse hostname lookups.
519 [This option is obsolete. All Tor current relays should be presumed
520 to have the evdns backend.]
522 "caches-extra-info" NL
524 [At most once.]
526 Present only if this router is a directory cache that provides
527 extra-info documents.
529 [Versions before 0.2.0.1-alpha don't recognize this]
531 "extra-info-digest" digest NL
533 [At most once]
535 "Digest" is a hex-encoded digest (using upper-case characters) of the
536 router's extra-info document, as signed in the router's extra-info
537 (that is, not including the signature). (If this field is absent, the
538 router is not uploading a corresponding extra-info document.)
540 [Versions before 0.2.0.1-alpha don't recognize this]
542 "hidden-service-dir" *(SP VersionNum) NL
544 [At most once.]
546 Present only if this router stores and serves hidden service
547 descriptors. If any VersionNum(s) are specified, this router
548 supports those descriptor versions. If none are specified, it
549 defaults to version 2 descriptors.
551 "protocols" SP "Link" SP LINK-VERSION-LIST SP "Circuit" SP
552 CIRCUIT-VERSION-LIST NL
554 [At most once.]
556 Both lists are space-separated sequences of numbers, to indicate which
557 protocols the server supports. As of 30 Mar 2008, specified
558 protocols are "Link 1 2 Circuit 1". See section 4.1 of tor-spec.txt
559 for more information about link protocol versions.
561 "allow-single-hop-exits" NL
563 [At most once.]
565 Present only if the router allows single-hop circuits to make exit
566 connections. Most Tor relays do not support this: this is
567 included for specialized controllers designed to support perspective
568 access and such.
570 "or-address" SP ADDRESS ":" PORTLIST NL
572 [Any number]
574 ADDRESS = IP6ADDR | IP4ADDR
575 IPV6ADDR = an ipv6 address, surrounded by square brackets.
576 IPV4ADDR = an ipv4 address, represented as a dotted quad.
577 PORTLIST = PORTSPEC | PORTSPEC "," PORTLIST
578 PORTSPEC = PORT
579 PORT = a number between 1 and 65535 inclusive.
581 An alternative for the address and ORPort of the "router" line, but with
582 two added capabilities:
584 * or-address can be either an IPv4 or IPv6 address
585 * or-address allows for multiple ORPorts and addresses
587 A descriptor SHOULD NOT include an or-address line that does nothing but
588 duplicate the address:port pair from its "router" line.
590 The ordering of or-address lines and their PORT entries matter because
591 Tor MAY accept a limited number of addresses or ports. As of Tor 0.2.3.x
592 only the first address and the first port are used.
594 2.2. Extra-info documents
596 Extra-info documents consist of the following items:
598 "extra-info" Nickname Fingerprint NL
599 [At start, exactly once.]
601 Identifies what router this is an extra info descriptor for.
602 Fingerprint is encoded in hex (using upper-case letters), with
603 no spaces.
605 "published" YYYY-MM-DD HH:MM:SS NL
607 [Exactly once.]
609 The time, in GMT, when this document (and its corresponding router
610 descriptor if any) was generated. It MUST match the published time
611 in the corresponding router descriptor.
613 "read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL
614 [At most once.]
615 "write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL
616 [At most once.]
618 As documented in 2.1 above. See migration notes in section 2.2.1.
620 "geoip-db-digest" Digest NL
621 [At most once.]
623 SHA1 digest of the GeoIP database file that is used to resolve IP
624 addresses to country codes.
626 ("geoip-start-time" YYYY-MM-DD HH:MM:SS NL)
627 ("geoip-client-origins" CC=N,CC=N,... NL)
629 Only generated by bridge routers (see blocking.pdf), and only
630 when they have been configured with a geoip database.
631 Non-bridges SHOULD NOT generate these fields. Contains a list
632 of mappings from two-letter country codes (CC) to the number
633 of clients that have connected to that bridge from that
634 country (approximate, and rounded up to the nearest multiple of 8
635 in order to hamper traffic analysis). A country is included
636 only if it has at least one address. The time in
637 "geoip-start-time" is the time at which we began collecting geoip
638 statistics.
640 "geoip-start-time" and "geoip-client-origins" have been replaced by
641 "bridge-stats-end" and "bridge-stats-ips" in 0.2.2.4-alpha. The
642 reason is that the measurement interval with "geoip-stats" as
643 determined by subtracting "geoip-start-time" from "published" could
644 have had a variable length, whereas the measurement interval in
645 0.2.2.4-alpha and later is set to be exactly 24 hours long. In
646 order to clearly distinguish the new measurement intervals from
647 the old ones, the new keywords have been introduced.
649 "bridge-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
650 [At most once.]
652 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
653 interval of length NSEC seconds (86400 seconds by default).
655 A "bridge-stats-end" line, as well as any other "bridge-*" line,
656 is only added when the relay has been running as a bridge for at
657 least 24 hours.
659 "bridge-ips" CC=N,CC=N,... NL
660 [At most once.]
662 List of mappings from two-letter country codes to the number of
663 unique IP addresses that have connected from that country to the
664 bridge and which are no known relays, rounded up to the nearest
665 multiple of 8.
667 "dirreq-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
668 [At most once.]
670 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
671 interval of length NSEC seconds (86400 seconds by default).
673 A "dirreq-stats-end" line, as well as any other "dirreq-*" line,
674 is only added when the relay has opened its Dir port and after 24
675 hours of measuring directory requests.
677 "dirreq-v2-ips" CC=N,CC=N,... NL
678 [At most once.]
679 "dirreq-v3-ips" CC=N,CC=N,... NL
680 [At most once.]
682 List of mappings from two-letter country codes to the number of
683 unique IP addresses that have connected from that country to
684 request a v2/v3 network status, rounded up to the nearest multiple
685 of 8. Only those IP addresses are counted that the directory can
686 answer with a 200 OK status code.
688 "dirreq-v2-reqs" CC=N,CC=N,... NL
689 [At most once.]
690 "dirreq-v3-reqs" CC=N,CC=N,... NL
691 [At most once.]
693 List of mappings from two-letter country codes to the number of
694 requests for v2/v3 network statuses from that country, rounded up
695 to the nearest multiple of 8. Only those requests are counted that
696 the directory can answer with a 200 OK status code.
698 "dirreq-v2-share" num% NL
699 [At most once.]
700 "dirreq-v3-share" num% NL
701 [At most once.]
703 The share of v2/v3 network status requests that the directory
704 expects to receive from clients based on its advertised bandwidth
705 compared to the overall network bandwidth capacity. Shares are
706 formatted in percent with two decimal places. Shares are
707 calculated as means over the whole 24-hour interval.
709 "dirreq-v2-resp" status=num,... NL
710 [At most once.]
711 "dirreq-v3-resp" status=nul,... NL
712 [At most once.]
714 List of mappings from response statuses to the number of requests
715 for v2/v3 network statuses that were answered with that response
716 status, rounded up to the nearest multiple of 4. Only response
717 statuses with at least 1 response are reported. New response
718 statuses can be added at any time. The current list of response
719 statuses is as follows:
721 "ok": a network status request is answered; this number
722 corresponds to the sum of all requests as reported in
723 "dirreq-v2-reqs" or "dirreq-v3-reqs", respectively, before
724 rounding up.
725 "not-enough-sigs: a version 3 network status is not signed by a
726 sufficient number of requested authorities.
727 "unavailable": a requested network status object is unavailable.
728 "not-found": a requested network status is not found.
729 "not-modified": a network status has not been modified since the
730 If-Modified-Since time that is included in the request.
731 "busy": the directory is busy.
733 "dirreq-v2-direct-dl" key=val,... NL
734 [At most once.]
735 "dirreq-v3-direct-dl" key=val,... NL
736 [At most once.]
737 "dirreq-v2-tunneled-dl" key=val,... NL
738 [At most once.]
739 "dirreq-v3-tunneled-dl" key=val,... NL
740 [At most once.]
742 List of statistics about possible failures in the download process
743 of v2/v3 network statuses. Requests are either "direct"
744 HTTP-encoded requests over the relay's directory port, or
745 "tunneled" requests using a BEGIN_DIR cell over the relay's OR
746 port. The list of possible statistics can change, and statistics
747 can be left out from reporting. The current list of statistics is
748 as follows:
750 Successful downloads and failures:
752 "complete": a client has finished the download successfully.
753 "timeout": a download did not finish within 10 minutes after
754 starting to send the response.
755 "running": a download is still running at the end of the
756 measurement period for less than 10 minutes after starting to
757 send the response.
759 Download times:
761 "min", "max": smallest and largest measured bandwidth in B/s.
762 "d[1-4,6-9]": 1st to 4th and 6th to 9th decile of measured
763 bandwidth in B/s. For a given decile i, i/10 of all downloads
764 had a smaller bandwidth than di, and (10-i)/10 of all downloads
765 had a larger bandwidth than di.
766 "q[1,3]": 1st and 3rd quartile of measured bandwidth in B/s. One
767 fourth of all downloads had a smaller bandwidth than q1, one
768 fourth of all downloads had a larger bandwidth than q3, and the
769 remaining half of all downloads had a bandwidth between q1 and
770 q3.
771 "md": median of measured bandwidth in B/s. Half of the downloads
772 had a smaller bandwidth than md, the other half had a larger
773 bandwidth than md.
775 "dirreq-read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM... NL
776 [At most once]
777 "dirreq-write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM... NL
778 [At most once]
780 Declare how much bandwidth the OR has spent on answering directory
781 requests. Usage is divided into intervals of NSEC seconds. The
782 YYYY-MM-DD HH:MM:SS field defines the end of the most recent
783 interval. The numbers are the number of bytes used in the most
784 recent intervals, ordered from oldest to newest.
786 "entry-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
787 [At most once.]
789 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
790 interval of length NSEC seconds (86400 seconds by default).
792 An "entry-stats-end" line, as well as any other "entry-*"
793 line, is first added after the relay has been running for at least
794 24 hours.
796 "entry-ips" CC=N,CC=N,... NL
797 [At most once.]
799 List of mappings from two-letter country codes to the number of
800 unique IP addresses that have connected from that country to the
801 relay and which are no known other relays, rounded up to the
802 nearest multiple of 8.
804 "cell-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
805 [At most once.]
807 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
808 interval of length NSEC seconds (86400 seconds by default).
810 A "cell-stats-end" line, as well as any other "cell-*" line,
811 is first added after the relay has been running for at least 24
812 hours.
814 "cell-processed-cells" num,...,num NL
815 [At most once.]
817 Mean number of processed cells per circuit, subdivided into
818 deciles of circuits by the number of cells they have processed in
819 descending order from loudest to quietest circuits.
821 "cell-queued-cells" num,...,num NL
822 [At most once.]
824 Mean number of cells contained in queues by circuit decile. These
825 means are calculated by 1) determining the mean number of cells in
826 a single circuit between its creation and its termination and 2)
827 calculating the mean for all circuits in a given decile as
828 determined in "cell-processed-cells". Numbers have a precision of
829 two decimal places.
831 "cell-time-in-queue" num,...,num NL
832 [At most once.]
834 Mean time cells spend in circuit queues in milliseconds. Times are
835 calculated by 1) determining the mean time cells spend in the
836 queue of a single circuit and 2) calculating the mean for all
837 circuits in a given decile as determined in
838 "cell-processed-cells".
840 "cell-circuits-per-decile" num NL
841 [At most once.]
843 Mean number of circuits that are included in any of the deciles,
844 rounded up to the next integer.
846 "conn-bi-direct" YYYY-MM-DD HH:MM:SS (NSEC s) BELOW,READ,WRITE,BOTH NL
847 [At most once]
849 Number of connections, split into 10-second intervals, that are
850 used uni-directionally or bi-directionally as observed in the NSEC
851 seconds (usually 86400 seconds) before YYYY-MM-DD HH:MM:SS. Every
852 10 seconds, we determine for every connection whether we read and
853 wrote less than a threshold of 20 KiB (BELOW), read at least 10
854 times more than we wrote (READ), wrote at least 10 times more than
855 we read (WRITE), or read and wrote more than the threshold, but
856 not 10 times more in either direction (BOTH). After classifying a
857 connection, read and write counters are reset for the next
858 10-second interval.
860 "exit-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
861 [At most once.]
863 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
864 interval of length NSEC seconds (86400 seconds by default).
866 An "exit-stats-end" line, as well as any other "exit-*" line, is
867 first added after the relay has been running for at least 24 hours
868 and only if the relay permits exiting (where exiting to a single
869 port and IP address is sufficient).
871 "exit-kibibytes-written" port=N,port=N,... NL
872 [At most once.]
873 "exit-kibibytes-read" port=N,port=N,... NL
874 [At most once.]
876 List of mappings from ports to the number of kibibytes that the
877 relay has written to or read from exit connections to that port,
878 rounded up to the next full kibibyte. Relays may limit the
879 number of listed ports and subsume any remaining kibibytes under
880 port "other".
882 "exit-streams-opened" port=N,port=N,... NL
883 [At most once.]
885 List of mappings from ports to the number of opened exit streams
886 to that port, rounded up to the nearest multiple of 4. Relays may
887 limit the number of listed ports and subsume any remaining opened
888 streams under port "other".
890 "transport" transportname address:port [arglist] NL
891 [Any number.]
893 Signals that the router supports the 'transportname' pluggable
894 transport in IP address 'address' and TCP port 'port'.
896 "router-signature" NL Signature NL
897 [At end, exactly once.]
899 A document signature as documented in section 1.3, using the
900 initial item "extra-info" and the final item "router-signature",
901 signed with the router's identity key.
903 2.2.1. Moving history fields to extra-info documents.
905 Tools that want to use the read-history and write-history values SHOULD
906 download extra-info documents as well as router descriptors. Such
907 tools SHOULD accept history values from both sources; if they appear in
908 both documents, the values in the extra-info documents are authoritative.
910 New versions of Tor no longer generate router descriptors
911 containing read-history or write-history. Tools should continue to
912 accept read-history and write-history values in router descriptors
913 produced by older versions of Tor until all Tor versions earlier
914 than 0.2.0.x are obsolete.
916 2.3. Nonterminals in router descriptors
918 nickname ::= between 1 and 19 alphanumeric characters ([A-Za-z0-9]),
919 case-insensitive.
920 hexdigest ::= a '$', followed by 40 hexadecimal characters
921 ([A-Fa-f0-9]). [Represents a relay by the digest of its identity
922 key.]
924 exitpattern ::= addrspec ":" portspec
925 portspec ::= "*" | port | port "-" port
926 port ::= an integer between 1 and 65535, inclusive.
928 [Some implementations incorrectly generate ports with value 0.
929 Implementations SHOULD accept this, and SHOULD NOT generate it.
930 Connections to port 0 are never permitted.]
932 addrspec ::= "*" | ip4spec | ip6spec
933 ipv4spec ::= ip4 | ip4 "/" num_ip4_bits | ip4 "/" ip4mask
934 ip4 ::= an IPv4 address in dotted-quad format
935 ip4mask ::= an IPv4 mask in dotted-quad format
936 num_ip4_bits ::= an integer between 0 and 32
937 ip6spec ::= ip6 | ip6 "/" num_ip6_bits
938 ip6 ::= an IPv6 address, surrounded by square brackets.
939 num_ip6_bits ::= an integer between 0 and 128
941 bool ::= "0" | "1"
943 3. Formats produced by directory authorities.
945 Every authority has two keys used in this protocol: a signing key, and
946 an authority identity key. (Authorities also have a router identity
947 key used in their role as a router and by earlier versions of the
948 directory protocol.) The identity key is used from time to time to
949 sign new key certificates using new signing keys; it is very sensitive.
950 The signing key is used to sign key certificates and status documents.
952 There are three kinds of documents generated by directory authorities:
954 Key certificates
955 Status votes
956 Status consensuses
958 Each is discussed below.
960 3.1. Key certificates
962 Key certificates consist of the following items:
964 "dir-key-certificate-version" version NL
966 [At start, exactly once.]
968 Determines the version of the key certificate. MUST be "3" for
969 the protocol described in this document. Implementations MUST
970 reject formats they don't understand.
972 "dir-address" IPPort NL
973 [At most once]
975 An IP:Port for this authority's directory port.
977 "fingerprint" fingerprint NL
979 [Exactly once.]
981 Hexadecimal encoding without spaces based on the authority's
982 identity key.
984 "dir-identity-key" NL a public key in PEM format
986 [Exactly once.]
988 The long-term authority identity key for this authority. This key
989 SHOULD be at least 2048 bits long; it MUST NOT be shorter than
990 1024 bits.
992 "dir-key-published" YYYY-MM-DD HH:MM:SS NL
994 [Exactly once.]
996 The time (in GMT) when this document and corresponding key were
997 last generated.
999 "dir-key-expires" YYYY-MM-DD HH:MM:SS NL
1001 [Exactly once.]
1003 A time (in GMT) after which this key is no longer valid.
1005 "dir-signing-key" NL a key in PEM format
1007 [Exactly once.]
1009 The directory server's public signing key. This key MUST be at
1010 least 1024 bits, and MAY be longer.
1012 "dir-key-crosscert" NL CrossSignature NL
1014 [At most once.]
1016 NOTE: Authorities MUST include this field in all newly generated
1017 certificates. A future version of this specification will make
1018 the field required.
1020 CrossSignature is a signature, made using the certificate's signing
1021 key, of the digest of the PKCS1-padded hash of the certificate's
1022 identity key. For backward compatibility with broken versions of the
1023 parser, we wrap the base64-encoded signature in -----BEGIN ID
1024 SIGNATURE---- and -----END ID SIGNATURE----- tags. Implementations
1025 MUST allow the "ID " portion to be omitted, however.
1027 When encountering a certificate with a dir-key-crosscert entry,
1028 implementations MUST verify that the signature is a correct signature
1029 of the hash of the identity key using the signing key.
1031 "dir-key-certification" NL Signature NL
1033 [At end, exactly once.]
1035 A document signature as documented in section 1.3, using the
1036 initial item "dir-key-certificate-version" and the final item
1037 "dir-key-certification", signed with the authority identity key.
1039 Authorities MUST generate a new signing key and corresponding
1040 certificate before the key expires.
1042 3.2. Microdescriptors
1044 Microdescriptors are a stripped-down version of router descriptors
1045 generated by the directory authorities which may additionally contain
1046 authority-generated information. Microdescriptors contain only the
1047 most relevant parts that clients care about. Microdescriptors are
1048 expected to be relatively static and only change about once per week.
1049 Microdescriptors do not contain any information that clients need to
1050 use to decide which servers to fetch information about, or which
1051 servers to fetch information from.
1053 Microdescriptors are a straight transform from the router descriptor
1054 and the consensus method. Microdescriptors have no header or footer.
1055 Microdescriptors are identified by the hash of its concatenated
1056 elements without a signature by the router. Microdescriptors do not
1057 contain any version information, because their version is determined
1058 by the consensus method.
1060 3.2.1. Microdescriptors in consensus method 8 or later
1062 Starting with consensus method 8, microdescriptors contain the
1063 following elements taken from or based on the router descriptor. Order
1064 matters here, because different directory authorities must be able to
1065 transform a given router descriptor and consensus method into the exact
1066 same microdescriptor.
1068 "onion-key" NL a public key in PEM format
1070 [Exactly once, at start]
1072 The "onion-key" element as specified in 2.1.
1074 "family" names NL
1076 [At most once]
1078 The "family" element as specified in 2.1.
1080 "p" SP ("accept" / "reject") SP PortList NL
1082 [At most once]
1084 The exit-policy summary as specified in 3.3 and 3.5.2. A missing
1085 "p" line is equivalent to "p reject 1-65535".
1087 [With microdescriptors, clients don't learn exact exit policies:
1088 clients can only guess whether a relay accepts their request, try the
1089 BEGIN request, and might get end-reason-exit-policy if they guessed
1090 wrong, in which case they'll have to try elsewhere.]
1092 (Note that with microdescriptors, clients do not learn the identity of
1093 their routers: they only learn a hash of the identity key. This is all
1094 they need to confirm the actual identity key when doing a TLS handshake,
1095 and all they need to put the identity key digest in their cREATE cells.)
1097 3.3. Vote and consensus status documents
1099 Votes and consensuses are more strictly formatted then other documents
1100 in this specification, since different authorities must be able to
1101 generate exactly the same consensus given the same set of votes.
1103 The procedure for deciding when to generate vote and consensus status
1104 documents are described in section 1.4 on the voting timeline.
1106 Status documents contain a preamble, an authority section, a list of
1107 router status entries, and one or more footer signature, in that order.
1109 Unlike other formats described above, a SP in these documents must be a
1110 single space character (hex 20).
1112 Some items appear only in votes, and some items appear only in
1113 consensuses. Unless specified, items occur in both.
1115 The preamble contains the following items. They MUST occur in the
1116 order given here:
1118 "network-status-version" SP version NL.
1120 [At start, exactly once.]
1122 A document format version. For this specification, the version is
1123 "3".
1125 "vote-status" SP type NL
1127 [Exactly once.]
1129 The status MUST be "vote" or "consensus", depending on the type of
1130 the document.
1132 "consensus-methods" SP IntegerList NL
1134 [At most once for votes; does not occur in consensuses.]
1136 A space-separated list of supported methods for generating
1137 consensuses from votes. See section 3.5.1 for details. Method "1"
1138 MUST be included.
1140 "consensus-method" SP Integer NL
1142 [At most once for consensuses; does not occur in votes.]
1144 See section 3.5.1 for details.
1146 (Only included when the vote is generated with consensus-method 2 or
1147 later.)
1149 "published" SP YYYY-MM-DD SP HH:MM:SS NL
1151 [Exactly once for votes; does not occur in consensuses.]
1153 The publication time for this status document (if a vote).
1155 "valid-after" SP YYYY-MM-DD SP HH:MM:SS NL
1157 [Exactly once.]
1159 The start of the Interval for this vote. Before this time, the
1160 consensus document produced from this vote should not be used.
1161 See 1.4 for voting timeline information.
1163 "fresh-until" SP YYYY-MM-DD SP HH:MM:SS NL
1165 [Exactly once.]
1167 The time at which the next consensus should be produced; before this
1168 time, there is no point in downloading another consensus, since there
1169 won't be a new one. See 1.4 for voting timeline information.
1171 "valid-until" SP YYYY-MM-DD SP HH:MM:SS NL
1173 [Exactly once.]
1175 The end of the Interval for this vote. After this time, the
1176 consensus produced by this vote should not be used. See 1.4 for
1177 voting timeline information.
1179 "voting-delay" SP VoteSeconds SP DistSeconds NL
1181 [Exactly once.]
1183 VoteSeconds is the number of seconds that we will allow to collect
1184 votes from all authorities; DistSeconds is the number of seconds
1185 we'll allow to collect signatures from all authorities. See 1.4 for
1186 voting timeline information.
1188 "client-versions" SP VersionList NL
1190 [At most once.]
1192 A comma-separated list of recommended Tor versions for client
1193 usage, in ascending order. The versions are given as defined by
1194 version-spec.txt. If absent, no opinion is held about client
1195 versions.
1197 "server-versions" SP VersionList NL
1199 [At most once.]
1201 A comma-separated list of recommended Tor versions for relay
1202 usage, in ascending order. The versions are given as defined by
1203 version-spec.txt. If absent, no opinion is held about server
1204 versions.
1206 "known-flags" SP FlagList NL
1208 [Exactly once.]
1210 A space-separated list of all of the flags that this document
1211 might contain. A flag is "known" either because the authority
1212 knows about them and might set them (if in a vote), or because
1213 enough votes were counted for the consensus for an authoritative
1214 opinion to have been formed about their status.
1216 "params" SP [Parameters] NL
1218 [At most once]
1220 Parameter ::= Keyword '=' Int32
1221 Int32 ::= A decimal integer between -2147483648 and 2147483647.
1222 Parameters ::= Parameter | Parameters SP Parameter
1224 The parameters list, if present, contains a space-separated list of
1225 case-sensitive key-value pairs, sorted in lexical order by their
1226 keyword (as ASCII byte strings). Each parameter has its own meaning.
1228 (Only included when the vote is generated with consensus-method 7 or
1229 later.)
1231 Commonly used "param" arguments at this point include:
1233 "circwindow" -- the default package window that circuits should
1234 be established with. It started out at 1000 cells, but some
1235 research indicates that a lower value would mean fewer cells in
1236 transit in the network at any given time. Obeyed by Tor 0.2.1.20
1237 and later.
1238 Min: 100, Max: 1000
1240 "CircuitPriorityHalflifeMsec" -- the halflife parameter used when
1241 weighting which circuit will send the next cell. Obeyed by Tor
1242 0.2.2.10-alpha and later. (Versions of Tor between 0.2.2.7-alpha
1243 and 0.2.2.10-alpha recognized a "CircPriorityHalflifeMsec" parameter,
1244 but mishandled it badly.)
1245 Min: -1, Max: 2147483647 (INT32_MAX)
1247 "perconnbwrate" and "perconnbwburst" -- if set, each relay sets
1248 up a separate token bucket for every client OR connection,
1249 and rate limits that connection indepedently. Typically left
1250 unset, except when used for performance experiments around trac
1251 entry 1750. Only honored by relays running Tor 0.2.2.16-alpha
1252 and later. (Note that relays running 0.2.2.7-alpha through
1253 0.2.2.14-alpha looked for bwconnrate and bwconnburst, but then
1254 did the wrong thing with them; see bug 1830 for details.)
1255 Min: 1, Max: 2147483647 (INT32_MAX)
1257 "refuseunknownexits" -- if set to one, exit relays look at
1258 the previous hop of circuits that ask to open an exit stream,
1259 and refuse to exit if they don't recognize it as a relay. The
1260 goal is to make it harder for people to use them as one-hop
1261 proxies. See trac entry 1751 for details.
1262 Min: 0, Max: 1
1264 "cbtdisabled", "cbtnummodes", "cbtrecentcount", "cbtmaxtimeouts",
1265 "cbtmincircs", "cbtquantile", "cbtclosequantile", "cbttestfreq",
1266 "cbtmintimeout", and "cbtinitialtimeout" -- see "2.4.5. Consensus
1267 parameters governing behavior" in path-spec.txt for a series of
1268 circuit build time related consensus params.
1270 "UseOptimisticData" -- If set to zero, clients by default
1271 shouldn't try to send optimistic data to servers until they have
1272 received a RELAY_CONNECTED cell.
1273 Min: 0, Max: 1
1275 The authority section of a vote contains the following items, followed
1276 in turn by the authority's current key certificate:
1278 "dir-source" SP nickname SP identity SP address SP IP SP dirport SP
1279 orport NL
1281 [Exactly once, at start]
1283 Describes this authority. The nickname is a convenient identifier
1284 for the authority. The identity is an uppercase hex fingerprint of
1285 the authority's current (v3 authority) identity key. The address is
1286 the server's hostname. The IP is the server's current IP address,
1287 and dirport is its current directory port. XXXXorport
1289 "contact" SP string NL
1291 [Exactly once.]
1293 An arbitrary string describing how to contact the directory
1294 server's administrator. Administrators should include at least an
1295 email address and a PGP fingerprint.
1297 "legacy-dir-key" SP FINGERPRINT NL
1299 [At most once]
1301 Lists a fingerprint for an obsolete _identity_ key still used
1302 by this authority to keep older clients working. This option
1303 is used to keep key around for a little while in case the
1304 authorities need to migrate many identity keys at once.
1305 (Generally, this would only happen because of a security
1306 vulnerability that affected multiple authorities, like the
1307 Debian OpenSSL RNG bug of May 2008.)
1309 The authority section of a consensus contains groups the following items,
1310 in the order given, with one group for each authority that contributed to
1311 the consensus, with groups sorted by authority identity digest:
1313 "dir-source" SP nickname SP identity SP address SP IP SP dirport SP
1314 orport NL
1316 [Exactly once, at start]
1318 As in the authority section of a vote.
1320 "contact" SP string NL
1322 [Exactly once.]
1324 As in the authority section of a vote.
1326 "vote-digest" SP digest NL
1328 [Exactly once.]
1330 A digest of the vote from the authority that contributed to this
1331 consensus, as signed (that is, not including the signature).
1332 (Hex, upper-case.)
1334 Each router status entry contains the following items. Router status
1335 entries are sorted in ascending order by identity digest.
1337 "r" SP nickname SP identity SP digest SP publication SP IP SP ORPort
1338 SP DirPort NL
1340 [At start, exactly once.]
1342 "Nickname" is the OR's nickname. "Identity" is a hash of its
1343 identity key, encoded in base64, with trailing equals sign(s)
1344 removed. "Digest" is a hash of its most recent descriptor as
1345 signed (that is, not including the signature), encoded in base64.
1346 "Publication" is the
1347 publication time of its most recent descriptor, in the form
1348 YYYY-MM-DD HH:MM:SS, in GMT. "IP" is its current IP address;
1349 ORPort is its current OR port, "DirPort" is its current directory
1350 port, or "0" for "none".
1352 "s" SP Flags NL
1354 [Exactly once.]
1356 A series of space-separated status flags, in lexical order (as ASCII
1357 byte strings). Currently documented flags are:
1359 "Authority" if the router is a directory authority.
1360 "BadExit" if the router is believed to be useless as an exit node
1361 (because its ISP censors it, because it is behind a restrictive
1362 proxy, or for some similar reason).
1363 "BadDirectory" if the router is believed to be useless as a
1364 directory cache (because its directory port isn't working,
1365 its bandwidth is always throttled, or for some similar
1366 reason).
1367 "Exit" if the router is more useful for building
1368 general-purpose exit circuits than for relay circuits. The
1369 path building algorithm uses this flag; see path-spec.txt.
1370 "Fast" if the router is suitable for high-bandwidth circuits.
1371 "Guard" if the router is suitable for use as an entry guard.
1372 "HSDir" if the router is considered a v2 hidden service directory.
1373 "Named" if the router's identity-nickname mapping is canonical,
1374 and this authority binds names.
1375 "Stable" if the router is suitable for long-lived circuits.
1376 "Running" if the router is currently usable.
1377 "Unnamed" if another router has bound the name used by this
1378 router, and this authority binds names.
1379 "Valid" if the router has been 'validated'.
1380 "V2Dir" if the router implements the v2 directory protocol.
1381 "V3Dir" if the router implements this protocol.
1383 "v" SP version NL
1385 [At most once.]
1387 The version of the Tor protocol that this relay is running. If
1388 the value begins with "Tor" SP, the rest of the string is a Tor
1389 version number, and the protocol is "The Tor protocol as supported
1390 by the given version of Tor." Otherwise, if the value begins with
1391 some other string, Tor has upgraded to a more sophisticated
1392 protocol versioning system, and the protocol is "a version of the
1393 Tor protocol more recent than any we recognize."
1395 Directory authorities SHOULD omit version strings they receive from
1396 descriptors if they would cause "v" lines to be over 128 characters
1397 long.
1399 "w" SP "Bandwidth=" INT [SP "Measured=" INT] NL
1401 [At most once.]
1403 An estimate of the bandwidth of this relay, in an arbitrary
1404 unit (currently kilobytes per second). Used to weight router
1405 selection.
1407 Additionally, the Measured= keyword is present in votes by
1408 participating bandwidth measurement authorities to indicate
1409 a measured bandwidth currently produced by measuring stream
1410 capacities.
1412 Other weighting keywords may be added later.
1413 Clients MUST ignore keywords they do not recognize.
1415 "p" SP ("accept" / "reject") SP PortList NL
1417 [At most once.]
1419 PortList = PortOrRange
1420 PortList = PortList "," PortOrRange
1421 PortOrRange = INT "-" INT / INT
1423 A list of those ports that this router supports (if 'accept')
1424 or does not support (if 'reject') for exit to "most
1425 addresses".
1427 "m" SP methods 1*(SP algorithm "=" digest) NL
1429 [Any number, only in votes.]
1431 Microdescriptor hashes for all consensus methods that an authority
1432 supports and that use the same microdescriptor format. "methods"
1433 is a comma-separated list of the consensus methods that the
1434 authority believes will produce "digest". "algorithm" is the name
1435 of the hash algorithm producing "digest", which can be "sha256" or
1436 something else, depending on the consensus "methods" supporting
1437 this algorithm. "digest" is the base64 encoding of the hash of
1438 the router's microdescriptor with trailing =s omitted.
1440 The footer section is delineated in all votes and consensuses supporting
1441 consensus method 9 and above with the following:
1443 "directory-footer" NL
1445 It contains two subsections, a bandwidths-weights line and a
1446 directory-signature.
1448 The bandwidths-weights line appears At Most Once for a consensus. It does
1449 not appear in votes.
1451 "bandwidth-weights" SP
1452 "Wbd=" INT SP "Wbe=" INT SP "Wbg=" INT SP "Wbm=" INT SP
1453 "Wdb=" INT SP
1454 "Web=" INT SP "Wed=" INT SP "Wee=" INT SP "Weg=" INT SP "Wem=" INT SP
1455 "Wgb=" INT SP "Wgd=" INT SP "Wgg=" INT SP "Wgm=" INT SP
1456 "Wmb=" INT SP "Wmd=" INT SP "Wme=" INT SP "Wmg=" INT SP "Wmm=" INT NL
1458 These values represent the weights to apply to router bandwidths
1459 during path selection. They are sorted in lexical order (as ASCII byte
1460 strings). The integer values are divided by BW_WEIGHT_SCALE=10000 or
1461 the consensus param "bwweightscale". They are:
1463 Wgg - Weight for Guard-flagged nodes in the guard position
1464 Wgm - Weight for non-flagged nodes in the guard Position
1465 Wgd - Weight for Guard+Exit-flagged nodes in the guard Position
1467 Wmg - Weight for Guard-flagged nodes in the middle Position
1468 Wmm - Weight for non-flagged nodes in the middle Position
1469 Wme - Weight for Exit-flagged nodes in the middle Position
1470 Wmd - Weight for Guard+Exit flagged nodes in the middle Position
1472 Weg - Weight for Guard flagged nodes in the exit Position
1473 Wem - Weight for non-flagged nodes in the exit Position
1474 Wee - Weight for Exit-flagged nodes in the exit Position
1475 Wed - Weight for Guard+Exit-flagged nodes in the exit Position
1477 Wgb - Weight for BEGIN_DIR-supporting Guard-flagged nodes
1478 Wmb - Weight for BEGIN_DIR-supporting non-flagged nodes
1479 Web - Weight for BEGIN_DIR-supporting Exit-flagged nodes
1480 Wdb - Weight for BEGIN_DIR-supporting Guard+Exit-flagged nodes
1482 Wbg - Weight for Guard flagged nodes for BEGIN_DIR requests
1483 Wbm - Weight for non-flagged nodes for BEGIN_DIR requests
1484 Wbe - Weight for Exit-flagged nodes for BEGIN_DIR requests
1485 Wbd - Weight for Guard+Exit-flagged nodes for BEGIN_DIR requests
1487 These values are calculated as specified in Section 3.5.3.
1489 The signature contains the following item, which appears Exactly Once
1490 for a vote, and At Least Once for a consensus.
1492 "directory-signature" SP identity SP signing-key-digest NL Signature
1494 This is a signature of the status document, with the initial item
1495 "network-status-version", and the signature item
1496 "directory-signature", using the signing key. (In this case, we take
1497 the hash through the _space_ after directory-signature, not the
1498 newline: this ensures that all authorities sign the same thing.)
1499 "identity" is the hex-encoded digest of the authority identity key of
1500 the signing authority, and "signing-key-digest" is the hex-encoded
1501 digest of the current authority signing key of the signing authority.
1503 3.4. Assigning flags in a vote
1505 (This section describes how directory authorities choose which status
1506 flags to apply to routers, as of Tor 0.2.0.0-alpha-dev. Later directory
1507 authorities MAY do things differently, so long as clients keep working
1508 well. Clients MUST NOT depend on the exact behaviors in this section.)
1510 In the below definitions, a router is considered "active" if it is
1511 running, valid, and not hibernating.
1513 "Valid" -- a router is 'Valid' if it is running a version of Tor not
1514 known to be broken, and the directory authority has not blacklisted
1515 it as suspicious.
1517 "Named" -- Directory authority administrators may decide to support name
1518 binding. If they do, then they must maintain a file of
1519 nickname-to-identity-key mappings, and try to keep this file consistent
1520 with other directory authorities. If they don't, they act as clients, and
1521 report bindings made by other directory authorities (name X is bound to
1522 identity Y if at least one binding directory lists it, and no directory
1523 binds X to some other Y'.) A router is called 'Named' if the router
1524 believes the given name should be bound to the given key.
1526 Two strategies exist on the current network for deciding on
1527 values for the Named flag. In the original version, relay
1528 operators were asked to send nickname-identity pairs to a
1529 mailing list of Naming directory authorities' operators. The
1530 operators were then supposed to add the pairs to their
1531 mapping files; in practice, they didn't get to this often.
1533 Newer Naming authorities run a script that registers routers
1534 in their mapping files once the routers have been online at
1535 least two weeks, no other router has that nickname, and no
1536 other router has wanted the nickname for a month. If a router
1537 has not been online for six months, the router is removed.
1539 "Unnamed" -- Directory authorities that support naming should vote for a
1540 router to be 'Unnamed' if its given nickname is mapped to a different
1541 identity.
1543 "Running" -- A router is 'Running' if the authority managed to connect to
1544 it successfully within the last 45 minutes.
1546 "Stable" -- A router is 'Stable' if it is active, and either its Weighted
1547 MTBF is at least the median for known active routers or its Weighted MTBF
1548 corresponds to at least 7 days. Routers are never called Stable if they are
1549 running a version of Tor known to drop circuits stupidly. (0.1.1.10-alpha
1550 through 0.1.1.16-rc are stupid this way.)
1552 To calculate weighted MTBF, compute the weighted mean of the lengths
1553 of all intervals when the router was observed to be up, weighting
1554 intervals by $\alpha^n$, where $n$ is the amount of time that has
1555 passed since the interval ended, and $\alpha$ is chosen so that
1556 measurements over approximately one month old no longer influence the
1557 weighted MTBF much.
1559 [XXXX what happens when we have less than 4 days of MTBF info.]
1561 "Exit" -- A router is called an 'Exit' iff it allows exits to at
1562 least two of the ports 80, 443, and 6667 and allows exits to at
1563 least one /8 address space.
1565 "Fast" -- A router is 'Fast' if it is active, and its bandwidth is
1566 either in the top 7/8ths for known active routers or at least some
1567 minimum (20KB/s until 0.2.3.7-alpha, and 100KB/s after that).
1569 "Guard" -- A router is a possible 'Guard' if its Weighted Fractional
1570 Uptime is at least the median for "familiar" active routers, and if
1571 its bandwidth is at least median or at least 250KB/s.
1573 To calculate weighted fractional uptime, compute the fraction
1574 of time that the router is up in any given day, weighting so that
1575 downtime and uptime in the past counts less.
1577 A node is 'familiar' if 1/8 of all active nodes have appeared more
1578 recently than it, OR it has been around for a few weeks.
1580 "Authority" -- A router is called an 'Authority' if the authority
1581 generating the network-status document believes it is an authority.
1583 "V2Dir" -- A router supports the v2 directory protocol if it has an open
1584 directory port, and it is running a version of the directory protocol that
1585 supports the functionality clients need. (Currently, this is
1586 0.1.1.9-alpha or later.)
1588 "V3Dir" -- A router supports the v3 directory protocol if it has an open
1589 directory port, and it is running a version of the directory protocol that
1590 supports the functionality clients need. (Currently, this is
1591 0.2.0.?????-alpha or later.)
1593 "HSDir" -- A router is a v2 hidden service directory if it stores and
1594 serves v2 hidden service descriptors and the authority managed to connect
1595 to it successfully within the last 24 hours.
1597 Directory server administrators may label some relays or IPs as
1598 blacklisted, and elect not to include them in their network-status lists.
1600 Authorities SHOULD 'disable' any relays in excess of 3 on any single IP.
1601 When there are more than 3 to choose from, authorities should first prefer
1602 authorities to non-authorities, then prefer Running to non-Running, and
1603 then prefer high-bandwidth to low-bandwidth. To 'disable' a relay, the
1604 authority *should* advertise it without the Running or Valid flag.
1606 Thus, the network-status vote includes all non-blacklisted,
1607 non-expired, non-superseded descriptors.
1609 The bandwidth in a "w" line should be taken as the best estimate
1610 of the router's actual capacity that the authority has. For now,
1611 this should be the lesser of the observed bandwidth and bandwidth
1612 rate limit from the router descriptor. It is given in kilobytes
1613 per second, and capped at some arbitrary value (currently 10 MB/s).
1615 The Measured= keyword on a "w" line vote is currently computed
1616 by multiplying the previous published consensus bandwidth by the
1617 ratio of the measured average node stream capacity to the network
1618 average. If 3 or more authorities provide a Measured= keyword for
1619 a router, the authorities produce a consensus containing a "w"
1620 Bandwidth= keyword equal to the median of the Measured= votes.
1622 The ports listed in a "p" line should be taken as those ports for
1623 which the router's exit policy permits 'most' addresses, ignoring any
1624 accept not for all addresses, ignoring all rejects for private
1625 netblocks. "Most" addresses are permitted if no more than 2^25
1626 IPv4 addresses (two /8 networks) were blocked. The list is encoded
1627 as described in 3.5.2.
1629 3.5. Computing a consensus from a set of votes
1631 Given a set of votes, authorities compute the contents of the consensus
1632 document as follows:
1634 The "valid-after", "valid-until", and "fresh-until" times are taken as
1635 the median of the respective values from all the votes.
1637 The times in the "voting-delay" line are taken as the median of the
1638 VoteSeconds and DistSeconds times in the votes.
1640 Known-flags is the union of all flags known by any voter.
1642 Entries are given on the "params" line for every keyword on which a
1643 majority of authorities (total authorities, not just those
1644 participating in this vote) voted on, or if at least three
1645 authorities voted for that parameter. The values given are the
1646 low-median of all votes on that keyword.
1648 Consensus methods 11 and before, entries are given on the "params"
1649 line for every keyword on which any authority voted, the value given
1650 being the low-median of all votes on that keyword.
1652 "client-versions" and "server-versions" are sorted in ascending
1653 order; A version is recommended in the consensus if it is recommended
1654 by more than half of the voting authorities that included a
1655 client-versions or server-versions lines in their votes.
1657 The authority item groups (dir-source, contact, fingerprint,
1658 vote-digest) are taken from the votes of the voting
1659 authorities. These groups are sorted by the digests of the
1660 authorities identity keys, in ascending order. If the consensus
1661 method is 3 or later, a dir-source line must be included for
1662 every vote with legacy-key entry, using the legacy-key's
1663 fingerprint, the voter's ordinary nickname with the string
1664 "-legacy" appended, and all other fields as from the original
1665 vote's dir-source line.
1667 A router status entry:
1668 * is included in the result if some router status entry with the same
1669 identity is included by more than half of the authorities (total
1670 authorities, not just those whose votes we have).
1672 * For any given identity, we include at most one router status entry.
1674 * A router entry has a flag set if that is included by more than half
1675 of the authorities who care about that flag.
1677 * Two router entries are "the same" if they have the same
1678 <descriptor digest, published time, nickname, IP, ports> tuple.
1679 We choose the tuple for a given router as whichever tuple appears
1680 for that router in the most votes. We break ties first in favor of
1681 the more recently published, then in favor of smaller server
1682 descriptor digest.
1684 * The Named flag appears if it is included for this routerstatus by
1685 _any_ authority, and if all authorities that list it list the same
1686 nickname. However, if consensus-method 2 or later is in use, and
1687 any authority calls this identity/nickname pair Unnamed, then
1688 this routerstatus does not get the Named flag.
1690 * If consensus-method 2 or later is in use, the Unnamed flag is
1691 set for a routerstatus if any authorities have voted for a different
1692 identities to be Named with that nickname, or if any authority
1693 lists that nickname/ID pair as Unnamed.
1695 (With consensus-method 1, Unnamed is set like any other flag.)
1697 * The version is given as whichever version is listed by the most
1698 voters, with ties decided in favor of more recent versions.
1700 * If consensus-method 4 or later is in use, then routers that
1701 do not have the Running flag are not listed at all.
1703 * If consensus-method 5 or later is in use, then the "w" line
1704 is generated using a low-median of the bandwidth values from
1705 the votes that included "w" lines for this router.
1707 * If consensus-method 5 or later is in use, then the "p" line
1708 is taken from the votes that have the same policy summary
1709 for the descriptor we are listing. (They should all be the
1710 same. If they are not, we pick the most commonly listed
1711 one, breaking ties in favor of the lexicographically larger
1712 vote.) The port list is encoded as specified in 3.5.2.
1714 * If consensus-method 6 or later is in use and if 3 or more
1715 authorities provide a Measured= keyword in their votes for
1716 a router, the authorities produce a consensus containing a
1717 Bandwidth= keyword equal to the median of the Measured= votes.
1719 * If consensus-method 7 or later is in use, the params line is
1720 included in the output.
1722 * If the consensus method is under 11, bad exits are considered as
1723 possible exits when computing bandwidth weights. Otherwise, if
1724 method 11 or later is in use, any router that is determined to get
1725 the BadExit flag doesn't count when we're calculating weights.
1727 * If consensus method 12 or later is used, only consensus
1728 parameters that more than half of the total number of
1729 authorities voted for are included in the consensus.
1731 The signatures at the end of a consensus document are sorted in
1732 ascending order by identity digest.
1734 All ties in computing medians are broken in favor of the smaller or
1735 earlier item.
1737 3.5.1. Forward compatibility
1739 Future versions of Tor will need to include new information in the
1740 consensus documents, but it is important that all authorities (or at least
1741 half) generate and sign the same signed consensus.
1743 To achieve this, authorities list in their votes their supported methods
1744 for generating consensuses from votes. Later methods will be assigned
1745 higher numbers. Currently recognized methods:
1746 "1" -- The first implemented version.
1747 "2" -- Added support for the Unnamed flag.
1748 "3" -- Added legacy ID key support to aid in authority ID key rollovers
1749 "4" -- No longer list routers that are not running in the consensus
1750 "5" -- adds support for "w" and "p" lines.
1751 "6" -- Prefers measured bandwidth values rather than advertised
1752 "7" -- Provides keyword=integer pairs of consensus parameters
1753 "8" -- Provides microdescriptor summaries
1754 "9" -- Provides weights for selecting flagged routers in paths
1755 "10" -- Fixes edge case bugs in router flag selection weights
1756 "11" -- Don't consider BadExits when calculating bandwidth weights
1757 "12" -- Params are only included if enough auths voted for them
1760 Before generating a consensus, an authority must decide which consensus
1761 method to use. To do this, it looks for the highest version number
1762 supported by more than 2/3 of the authorities voting. If it supports this
1763 method, then it uses it. Otherwise, it falls back to method 1.
1765 (The consensuses generated by new methods must be parsable by
1766 implementations that only understand the old methods, and must not cause
1767 those implementations to compromise their anonymity. This is a means for
1768 making changes in the contents of consensus; not for making
1769 backward-incompatible changes in their format.)
1771 3.5.2. Encoding port lists
1773 Whether the summary shows the list of accepted ports or the list of
1774 rejected ports depends on which list is shorter (has a shorter string
1775 representation). In case of ties we choose the list of accepted
1776 ports. As an exception to this rule an allow-all policy is
1777 represented as "accept 1-65535" instead of "reject " and a reject-all
1778 policy is similarly given as "reject 1-65535".
1780 Summary items are compressed, that is instead of "80-88,89-100" there
1781 only is a single item of "80-100", similarly instead of "20,21" a
1782 summary will say "20-21".
1784 Port lists are sorted in ascending order.
1786 The maximum allowed length of a policy summary (including the "accept "
1787 or "reject ") is 1000 characters. If a summary exceeds that length we
1788 use an accept-style summary and list as much of the port list as is
1789 possible within these 1000 bytes. [XXXX be more specific.]
1791 3.5.3. Computing Bandwidth Weights
1793 Let weight_scale = 10000
1795 Let G be the total bandwidth for Guard-flagged nodes.
1796 Let M be the total bandwidth for non-flagged nodes.
1797 Let E be the total bandwidth for Exit-flagged nodes.
1798 Let D be the total bandwidth for Guard+Exit-flagged nodes.
1799 Let T = G+M+E+D
1801 Let Wgd be the weight for choosing a Guard+Exit for the guard position.
1802 Let Wmd be the weight for choosing a Guard+Exit for the middle position.
1803 Let Wed be the weight for choosing a Guard+Exit for the exit position.
1805 Let Wme be the weight for choosing an Exit for the middle position.
1806 Let Wmg be the weight for choosing a Guard for the middle position.
1808 Let Wgg be the weight for choosing a Guard for the guard position.
1809 Let Wee be the weight for choosing an Exit for the exit position.
1811 Balanced network conditions then arise from solutions to the following
1812 system of equations:
1814 Wgg*G + Wgd*D == M + Wmd*D + Wme*E + Wmg*G (guard bw = middle bw)
1815 Wgg*G + Wgd*D == Wee*E + Wed*D (guard bw = exit bw)
1816 Wed*D + Wmd*D + Wgd*D == D (aka: Wed+Wmd+Wdg = 1)
1817 Wmg*G + Wgg*G == G (aka: Wgg = 1-Wmg)
1818 Wme*E + Wee*E == E (aka: Wee = 1-Wme)
1820 We are short 2 constraints with the above set. The remaining constraints
1821 come from examining different cases of network load. The following
1822 constraints are used in consensus method 10 and above. There are another
1823 incorrect and obsolete set of constraints used for these same cases in
1824 consensus method 9. For those, see dir-spec.txt in Tor 0.2.2.10-alpha
1825 to 0.2.2.16-alpha.
1827 Case 1: E >= T/3 && G >= T/3 (Neither Exit nor Guard Scarce)
1829 In this case, the additional two constraints are: Wmg == Wmd,
1830 Wed == 1/3.
1832 This leads to the solution:
1833 Wgd = weight_scale/3
1834 Wed = weight_scale/3
1835 Wmd = weight_scale/3
1836 Wee = (weight_scale*(E+G+M))/(3*E)
1837 Wme = weight_scale - Wee
1838 Wmg = (weight_scale*(2*G-E-M))/(3*G)
1839 Wgg = weight_scale - Wmg
1841 Case 2: E < T/3 && G < T/3 (Both are scarce)
1843 Let R denote the more scarce class (Rare) between Guard vs Exit.
1844 Let S denote the less scarce class.
1846 Subcase a: R+D < S
1848 In this subcase, we simply devote all of D bandwidth to the
1849 scarce class.
1851 Wgg = Wee = weight_scale
1852 Wmg = Wme = Wmd = 0;
1853 if E < G:
1854 Wed = weight_scale
1855 Wgd = 0
1856 else:
1857 Wed = 0
1858 Wgd = weight_scale
1860 Subcase b: R+D >= S
1862 In this case, if M <= T/3, we have enough bandwidth to try to achieve
1863 a balancing condition.
1865 Add constraints Wgg = 1, Wmd == Wgd to maximize bandwidth in the guard
1866 position while still allowing exits to be used as middle nodes:
1868 Wee = (weight_scale*(E - G + M))/E
1869 Wed = (weight_scale*(D - 2*E + 4*G - 2*M))/(3*D)
1870 Wme = (weight_scale*(G-M))/E
1871 Wmg = 0
1872 Wgg = weight_scale
1873 Wmd = (weight_scale - Wed)/2
1874 Wgd = (weight_scale - Wed)/2
1876 If this system ends up with any values out of range (ie negative, or
1877 above weight_scale), use the constraints Wgg == 1 and Wee == 1, since
1878 both those positions are scarce:
1880 Wgg = weight_scale
1881 Wee = weight_scale
1882 Wed = (weight_scale*(D - 2*E + G + M))/(3*D)
1883 Wmd = (weight_Scale*(D - 2*M + G + E))/(3*D)
1884 Wme = 0
1885 Wmg = 0
1886 Wgd = weight_scale - Wed - Wmd
1888 If M > T/3, then the Wmd weight above will become negative. Set it to 0
1889 in this case:
1890 Wmd = 0
1891 Wgd = weight_scale - Wed
1893 Case 3: One of E < T/3 or G < T/3
1895 Let S be the scarce class (of E or G).
1897 Subcase a: (S+D) < T/3:
1898 if G=S:
1899 Wgg = Wgd = weight_scale;
1900 Wmd = Wed = Wmg = 0;
1901 // Minor subcase, if E is more scarce than M,
1902 // keep its bandwidth in place.
1903 if (E < M) Wme = 0;
1904 else Wme = (weight_scale*(E-M))/(2*E);
1905 Wee = weight_scale-Wme;
1906 if E=S:
1907 Wee = Wed = weight_scale;
1908 Wmd = Wgd = Wme = 0;
1909 // Minor subcase, if G is more scarce than M,
1910 // keep its bandwidth in place.
1911 if (G < M) Wmg = 0;
1912 else Wmg = (weight_scale*(G-M))/(2*G);
1913 Wgg = weight_scale-Wmg;
1915 Subcase b: (S+D) >= T/3
1916 if G=S:
1917 Add constraints Wgg = 1, Wmd == Wed to maximize bandwidth
1918 in the guard position, while still allowing exits to be
1919 used as middle nodes:
1920 Wgg = weight_scale
1921 Wgd = (weight_scale*(D - 2*G + E + M))/(3*D)
1922 Wmg = 0
1923 Wee = (weight_scale*(E+M))/(2*E)
1924 Wme = weight_scale - Wee
1925 Wmd = (weight_scale - Wgd)/2
1926 Wed = (weight_scale - Wgd)/2
1927 if E=S:
1928 Add constraints Wee == 1, Wmd == Wgd to maximize bandwidth
1929 in the exit position:
1930 Wee = weight_scale;
1931 Wed = (weight_scale*(D - 2*E + G + M))/(3*D);
1932 Wme = 0;
1933 Wgg = (weight_scale*(G+M))/(2*G);
1934 Wmg = weight_scale - Wgg;
1935 Wmd = (weight_scale - Wed)/2;
1936 Wgd = (weight_scale - Wed)/2;
1938 To ensure consensus, all calculations are performed using integer math
1939 with a fixed precision determined by the bwweightscale consensus
1940 parameter (defaults at 10000, Min: 1, Max: INT32_MAX).
1942 For future balancing improvements, Tor clients support 11 additional weights
1943 for directory requests and middle weighting. These weights are currently
1944 set at weight_scale, with the exception of the following groups of
1945 assignments:
1947 Directory requests use middle weights:
1948 Wbd=Wmd, Wbg=Wmg, Wbe=Wme, Wbm=Wmm
1950 Handle bridges and strange exit policies:
1951 Wgm=Wgg, Wem=Wee, Weg=Wed
1953 3.6. Consensus flavors
1955 Consensus flavors are variants of the consensus that clients can choose
1956 to download and use instead of the unflavored consensus. The purpose
1957 of a consensus flavor is to remove or replace information in the
1958 unflavored consensus without forcing clients to download information
1959 they would not use anyway.
1961 Directory authorities can produce and serve an arbitrary number of
1962 flavors of the same consensus. A downside of creating too many new
1963 flavors is that clients will be distinguishable based on which flavor
1964 they download. A new flavor should not be created when adding a field
1965 instead wouldn't be too onerous.
1967 Examples for consensus flavors include:
1968 - Publishing hashes of microdescriptors instead of hashes of
1969 full descriptors (see 3.6.2).
1970 - Including different digests of descriptors, instead of the
1971 perhaps-soon-to-be-totally-broken SHA1.
1973 Consensus flavors are derived from the unflavored consensus once the
1974 voting process is complete. This is to avoid consensus synchronization
1975 problems.
1977 Every consensus flavor has a name consisting of a sequence of one
1978 or more alphanumeric characters and dashes. For compatibility,
1979 current descriptor flavor is called "ns".
1981 The supported consensus flavors are defined as part of the
1982 authorities' consensus method.
1984 All consensus flavors have in common that their first line is
1985 "network-status-version" where version is 3 or higher, and the flavor
1986 is a string consisting of alphanumeric characters and dashes:
1988 "network-status-version" SP version SP flavor NL
1990 3.6.1. ns consensus
1992 The ns consensus flavor is equivalent to the unflavored consensus
1993 except for its first line which states its consensus flavor name:
1995 "network-status-version" SP version SP "ns" NL
1997 [At start, exactly once.]
1999 3.6.2. Microdescriptor consensus
2001 The microdescriptor consensus is a consensus flavor that contains
2002 microdescriptor hashes instead of descriptor hashes and that omits
2003 exit-policy summaries which are contained in microdescriptors. The
2004 microdescriptor consensus was designed to contain elements that are
2005 small and frequently changing. Clients use the information in the
2006 microdescriptor consensus to decide which servers to fetch information
2007 about and which servers to fetch information from.
2009 The microdescriptor consensus is based on the unflavored consensus with
2010 the exceptions as follows:
2012 "network-status-version" SP version SP "microdesc" NL
2014 [At start, exactly once.]
2016 The flavor name of a microdescriptor consensus is "microdesc".
2018 Changes to router status entries are as follows:
2020 "r" SP nickname SP identity SP publication SP IP SP ORPort
2021 SP DirPort NL
2023 [At start, exactly once.]
2025 Similar to "r" lines in 3.3, but without the digest element.
2027 "p" ... NL
2029 [Zero times.]
2031 Exit policy summaries are contained in microdescriptors and
2032 therefore omitted in the microdescriptor consensus.
2034 "m" SP digest NL
2036 [Exactly once.]
2038 "digest" is the base64 of the SHA256 hash of the router's
2039 microdescriptor with trailing =s omitted. For a given router
2040 descriptor digest and consensus method there should only be a
2041 single microdescriptor digest in the "m" lines of all votes.
2042 If different votes have different microdescriptor digests for
2043 the same descriptor digest and consensus method, at least one
2044 of the authorities is broken. If this happens, the microdesc
2045 consensus should contain whichever microdescriptor digest is
2046 most common. If there is no winner, we break ties in the favor
2047 of the lexically earliest.
2049 3.7. Detached signatures
2051 Assuming full connectivity, every authority should compute and sign the
2052 same consensus including any flavors in each period. Therefore, it
2053 isn't necessary to download the consensus or any flavors of it computed
2054 by each authority; instead, the authorities only push/fetch each
2055 others' signatures. A "detached signature" document contains items as
2056 follows:
2058 "consensus-digest" SP Digest NL
2060 [At start, at most once.]
2062 The digest of the consensus being signed.
2064 "valid-after" SP YYYY-MM-DD SP HH:MM:SS NL
2065 "fresh-until" SP YYYY-MM-DD SP HH:MM:SS NL
2066 "valid-until" SP YYYY-MM-DD SP HH:MM:SS NL
2068 [As in the consensus]
2070 "additional-digest" SP flavor SP algname SP digest NL
2072 [Any number.]
2074 For each supported consensus flavor, every directory authority
2075 adds one or more "additional-digest" lines. "flavor" is the name
2076 of the consensus flavor, "algname" is the name of the hash
2077 algorithm that is used to generate the digest, and "digest" is the
2078 hex-encoded digest.
2080 The hash algorithm for the microdescriptor consensus flavor is
2081 defined as SHA256 with algname "sha256".
2083 "additional-signature" SP flavor SP algname SP identity SP
2084 signing-key-digest NL signature.
2086 [Any number.]
2088 For each supported consensus flavor and defined digest algorithm,
2089 every directory authority adds an "additional-signature" line.
2090 "flavor" is the name of the consensus flavor. "algname" is the
2091 name of the algorithm that was used to hash the identity and
2092 signing keys, and to compute the signature. "identity" is the
2093 hex-encoded digest of the authority identity key of the signing
2094 authority, and "signing-key-digest" is the hex-encoded digest of
2095 the current authority signing key of the signing authority.
2097 The "sha256" signature format is defined as the RSA signature of
2098 the OAEP+-padded SHA256 digest of the item to be signed. When
2099 checking signatures, the signature MUST be treated as valid if the
2100 signature material begins with SHA256(document), so that other
2101 data can get added later.
2102 [To be honest, I didn't fully understand the previous paragraph
2103 and only copied it from the proposals. Review carefully. -KL]
2105 "directory-signature"
2107 [As in the consensus; the signature object is the same as in the
2108 consensus document.]
2110 4. Directory server operation
2112 All directory authorities and directory caches ("directory servers")
2113 implement this section, except as noted.
2115 4.1. Accepting uploads (authorities only)
2117 When a router posts a signed descriptor to a directory authority, the
2118 authority first checks whether it is well-formed and correctly
2119 self-signed. If it is, the authority next verifies that the nickname
2120 in question is not already assigned to a router with a different
2121 public key.
2122 Finally, the authority MAY check that the router is not blacklisted
2123 because of its key, IP, or another reason.
2125 If the descriptor passes these tests, and the authority does not already
2126 have a descriptor for a router with this public key, it accepts the
2127 descriptor and remembers it.
2129 If the authority _does_ have a descriptor with the same public key, the
2130 newly uploaded descriptor is remembered if its publication time is more
2131 recent than the most recent old descriptor for that router, and either:
2132 - There are non-cosmetic differences between the old descriptor and the
2133 new one.
2134 - Enough time has passed between the descriptors' publication times.
2135 (Currently, 12 hours.)
2137 Differences between router descriptors are "non-cosmetic" if they would be
2138 sufficient to force an upload as described in section 2 above.
2140 Note that the "cosmetic difference" test only applies to uploaded
2141 descriptors, not to descriptors that the authority downloads from other
2142 authorities.
2144 When a router posts a signed extra-info document to a directory authority,
2145 the authority again checks it for well-formedness and correct signature,
2146 and checks that its matches the extra-info-digest in some router
2147 descriptor that it believes is currently useful. If so, it accepts it and
2148 stores it and serves it as requested. If not, it drops it.
2150 4.2. Voting (authorities only)
2152 Authorities divide time into Intervals. Authority administrators SHOULD
2153 try to all pick the same interval length, and SHOULD pick intervals that
2154 are commonly used divisions of time (e.g., 5 minutes, 15 minutes, 30
2155 minutes, 60 minutes, 90 minutes). Voting intervals SHOULD be chosen to
2156 divide evenly into a 24-hour day.
2158 Authorities SHOULD act according to interval and delays in the
2159 latest consensus. Lacking a latest consensus, they SHOULD default to a
2160 30-minute Interval, a 5 minute VotingDelay, and a 5 minute DistDelay.
2162 Authorities MUST take pains to ensure that their clocks remain accurate
2163 within a few seconds. (Running NTP is usually sufficient.)
2165 The first voting period of each day begins at 00:00 (midnight) GMT. If
2166 the last period of the day would be truncated by one-half or more, it is
2167 merged with the second-to-last period.
2169 An authority SHOULD publish its vote immediately at the start of each voting
2170 period (minus VoteSeconds+DistSeconds). It does this by making it
2171 available at
2172 http://<hostname>/tor/status-vote/next/authority.z
2173 and sending it in an HTTP POST request to each other authority at the URL
2174 http://<hostname>/tor/post/vote
2176 If, at the start of the voting period, minus DistSeconds, an authority
2177 does not have a current statement from another authority, the first
2178 authority downloads the other's statement.
2180 Once an authority has a vote from another authority, it makes it available
2181 at
2182 http://<hostname>/tor/status-vote/next/<fp>.z
2183 where <fp> is the fingerprint of the other authority's identity key.
2184 And at
2185 http://<hostname>/tor/status-vote/next/d/<d>.z
2186 where <d> is the digest of the vote document.
2188 The consensus status, along with as many signatures as the server
2189 currently knows, should be available at
2190 http://<hostname>/tor/status-vote/next/consensus.z
2191 All of the detached signatures it knows for consensus status should be
2192 available at:
2193 http://<hostname>/tor/status-vote/next/consensus-signatures.z
2195 Once there are enough signatures, or once the voting period starts,
2196 these documents are available at
2197 http://<hostname>/tor/status-vote/current/consensus.z
2198 and
2199 http://<hostname>/tor/status-vote/current/consensus-signatures.z
2200 [XXX current/consensus-signatures is not currently implemented, as it
2201 is not used in the voting protocol.]
2203 The other vote documents are analogously made available under
2204 http://<hostname>/tor/status-vote/current/authority.z
2205 http://<hostname>/tor/status-vote/current/<fp>.z
2206 http://<hostname>/tor/status-vote/current/d/<d>.z
2207 once the consensus is complete.
2209 Once an authority has computed and signed a consensus network status, it
2210 should send its detached signature to each other authority in an HTTP POST
2211 request to the URL:
2212 http://<hostname>/tor/post/consensus-signature
2214 [XXX Note why we support push-and-then-pull.]
2216 [XXX possible future features include support for downloading old
2217 consensuses.]
2219 The authorities serve another consensus of each flavor "F" from the
2220 locations
2221 /tor/status-vote/(current|next)/consensus-F.z. and
2222 /tor/status-vote/(current|next)/consensus-F/<FP1>+....z.
2224 4.3. Downloading consensus status documents (caches only)
2226 All directory servers (authorities and caches) try to keep a recent
2227 network-status consensus document to serve to clients. A cache ALWAYS
2228 downloads a network-status consensus if any of the following are true:
2229 - The cache has no consensus document.
2230 - The cache's consensus document is no longer valid.
2231 Otherwise, the cache downloads a new consensus document at a randomly
2232 chosen time in the first half-interval after its current consensus
2233 stops being fresh. (This time is chosen at random to avoid swarming
2234 the authorities at the start of each period. The interval size is
2235 inferred from the difference between the valid-after time and the
2236 fresh-until time on the consensus.)
2238 [For example, if a cache has a consensus that became valid at 1:00,
2239 and is fresh until 2:00, that cache will fetch a new consensus at
2240 a random time between 2:00 and 2:30.]
2242 Directory caches also fetch consensus flavors from the authorities.
2243 Caches check the correctness of consensus flavors, but do not check
2244 anything about an unrecognized consensus document beyond its digest and
2245 length. Caches serve all consensus flavors from the same locations as
2246 the directory authorities.
2248 4.4. Downloading and storing router descriptors (authorities and caches)
2250 Periodically (currently, every 10 seconds), directory servers check
2251 whether there are any specific descriptors that they do not have and that
2252 they are not currently trying to download. Caches identify these
2253 descriptors by hash in the recent network-status consensus documents;
2254 authorities identify them by hash in vote (if publication date is more
2255 recent than the descriptor we currently have).
2257 [XXXX need a way to fetch descriptors ahead of the vote? v2 status docs can
2258 do that for now.]
2260 If so, the directory server launches requests to the authorities for these
2261 descriptors, such that each authority is only asked for descriptors listed
2262 in its most recent vote (if the requester is an authority) or in the
2263 consensus (if the requester is a cache). If we're an authority, and more
2264 than one authority lists the descriptor, we choose which to ask at random.
2266 If one of these downloads fails, we do not try to download that descriptor
2267 from the authority that failed to serve it again unless we receive a newer
2268 network-status (consensus or vote) from that authority that lists the same
2269 descriptor.
2271 Directory servers must potentially cache multiple descriptors for each
2272 router. Servers must not discard any descriptor listed by any recent
2273 consensus. If there is enough space to store additional descriptors,
2274 servers SHOULD try to hold those which clients are likely to download the
2275 most. (Currently, this is judged based on the interval for which each
2276 descriptor seemed newest.)
2277 [XXXX define recent]
2279 Authorities SHOULD NOT download descriptors for routers that they would
2280 immediately reject for reasons listed in 3.1.
2282 4.5. Downloading and storing microdescriptors (caches only)
2284 Directory mirrors should fetch, cache, and serve each microdescriptor
2285 from the authorities.
2287 The microdescriptors with base64 hashes <D1>,<D2>,<D3> are available
2288 at:
2289 http://<hostname>/tor/micro/d/<D1>-<D2>-<D3>[.z]
2291 <Dn> are base-64 encoded with trailing =s omitted for size and for
2292 consistency with the microdescriptor consensus format. -s are used
2293 instead of +s to separate items, since the + character is used in
2294 base64 encoding.
2296 All the microdescriptors from the current consensus should also be
2297 available at:
2298 http://<hostname>/tor/micro/all[.z]
2299 so a client that's bootstrapping doesn't need to send a 70KB URL just
2300 to name every microdescriptor it's looking for.
2301 [Note that /tor/micro/all[.z] is not implemented as of February 21,
2302 2012. -KL]
2304 Directory mirrors should check to make sure that the microdescriptors
2305 they're about to serve match the right hashes (either the hashes from
2306 the fetch URL or the hashes from the consensus, respectively).
2308 4.6. Downloading and storing extra-info documents
2310 All authorities, and any cache that chooses to cache extra-info documents,
2311 and any client that uses extra-info documents, should implement this
2312 section.
2314 Note that generally, clients don't need extra-info documents.
2316 Periodically, the Tor instance checks whether it is missing any extra-info
2317 documents: in other words, if it has any router descriptors with an
2318 extra-info-digest field that does not match any of the extra-info
2319 documents currently held. If so, it downloads whatever extra-info
2320 documents are missing. Caches download from authorities; non-caches try
2321 to download from caches. We follow the same splitting and back-off rules
2322 as in 4.4 (if a cache) or 5.3 (if a client).
2324 4.7. General-use HTTP URLs
2326 "Fingerprints" in these URLs are base-16-encoded SHA1 hashes.
2328 The most recent v3 consensus should be available at:
2329 http://<hostname>/tor/status-vote/current/consensus.z
2331 Starting with Tor version 0.2.1.1-alpha is also available at:
2332 http://<hostname>/tor/status-vote/current/consensus/<F1>+<F2>+<F3>.z
2334 Where F1, F2, etc. are authority identity fingerprints the client trusts.
2335 Servers will only return a consensus if more than half of the requested
2336 authorities have signed the document, otherwise a 404 error will be sent
2337 back. The fingerprints can be shortened to a length of any multiple of
2338 two, using only the leftmost part of the encoded fingerprint. Tor uses
2339 3 bytes (6 hex characters) of the fingerprint.
2341 Clients SHOULD sort the fingerprints in ascending order. Server MUST
2342 accept any order.
2344 Clients SHOULD use this format when requesting consensus documents from
2345 directory authority servers and from caches running a version of Tor
2346 that is known to support this URL format.
2348 A concatenated set of all the current key certificates should be available
2349 at:
2350 http://<hostname>/tor/keys/all.z
2352 The key certificate for this server (if it is an authority) should be
2353 available at:
2354 http://<hostname>/tor/keys/authority.z
2356 The key certificate for an authority whose authority identity fingerprint
2357 is <F> should be available at:
2358 http://<hostname>/tor/keys/fp/<F>.z
2360 The key certificate whose signing key fingerprint is <F> should be
2361 available at:
2362 http://<hostname>/tor/keys/sk/<F>.z
2364 The key certificate whose identity key fingerprint is <F> and whose signing
2365 key fingerprint is <S> should be available at:
2367 http://<hostname>/tor/keys/fp-sk/<F>-<S>.z
2369 (As usual, clients may request multiple certificates using:
2370 http://<hostname>/tor/keys/fp-sk/<F1>-<S1>+<F2>-<S2>.z )
2371 [The above fp-sk format was not supported before Tor 0.2.1.9-alpha.]
2373 The most recent descriptor for a server whose identity key has a
2374 fingerprint of <F> should be available at:
2375 http://<hostname>/tor/server/fp/<F>.z
2377 The most recent descriptors for servers with identity fingerprints
2378 <F1>,<F2>,<F3> should be available at:
2379 http://<hostname>/tor/server/fp/<F1>+<F2>+<F3>.z
2381 (NOTE: Implementations SHOULD NOT download descriptors by identity key
2382 fingerprint. This allows a corrupted server (in collusion with a cache) to
2383 provide a unique descriptor to a client, and thereby partition that client
2384 from the rest of the network.)
2386 The server descriptor with (descriptor) digest <D> (in hex) should be
2387 available at:
2388 http://<hostname>/tor/server/d/<D>.z
2390 The most recent descriptors with digests <D1>,<D2>,<D3> should be
2391 available at:
2392 http://<hostname>/tor/server/d/<D1>+<D2>+<D3>.z
2394 The most recent descriptor for this server should be at:
2395 http://<hostname>/tor/server/authority.z
2396 [Nothing in the Tor protocol uses this resource yet, but it is useful
2397 for debugging purposes. Also, the official Tor implementations
2398 (starting at 0.1.1.x) use this resource to test whether a server's
2399 own DirPort is reachable.]
2401 A concatenated set of the most recent descriptors for all known servers
2402 should be available at:
2403 http://<hostname>/tor/server/all.z
2405 Extra-info documents are available at the URLS
2406 http://<hostname>/tor/extra/d/...
2407 http://<hostname>/tor/extra/fp/...
2408 http://<hostname>/tor/extra/all[.z]
2409 http://<hostname>/tor/extra/authority[.z]
2410 (As for /tor/server/ URLs: supports fetching extra-info
2411 documents by their digest, by the fingerprint of their servers,
2412 or all at once. When serving by fingerprint, we serve the
2413 extra-info that corresponds to the descriptor we would serve by
2414 that fingerprint. Only directory authorities of version
2415 0.2.0.1-alpha or later are guaranteed to support the first
2416 three classes of URLs. Caches may support them, and MUST
2417 support them if they have advertised "caches-extra-info".)
2419 For debugging, directories SHOULD expose non-compressed objects at URLs like
2420 the above, but without the final ".z".
2421 Clients MUST handle compressed concatenated information in two forms:
2422 - A concatenated list of zlib-compressed objects.
2423 - A zlib-compressed concatenated list of objects.
2424 Directory servers MAY generate either format: the former requires less
2425 CPU, but the latter requires less bandwidth.
2427 Clients SHOULD use upper case letters (A-F) when base16-encoding
2428 fingerprints. Servers MUST accept both upper and lower case fingerprints
2429 in requests.
2431 [XXX Add new URLs for microdescriptors, consensus flavors, and
2432 microdescriptor consensus. -KL]
2434 5. Client operation: downloading information
2436 Every Tor that is not a directory server (that is, those that do
2437 not have a DirPort set) implements this section.
2439 5.1. Downloading network-status documents
2441 Each client maintains a list of directory authorities. Insofar as
2442 possible, clients SHOULD all use the same list.
2444 Clients try to have a live consensus network-status document at all times.
2445 A network-status document is "live" if the time in its valid-until field
2446 has not passed.
2448 If a client is missing a live network-status document, it tries to fetch
2449 it from a directory cache (or from an authority if it knows no caches).
2450 On failure, the client waits briefly, then tries that network-status
2451 document again from another cache. The client does not build circuits
2452 until it has a live network-status consensus document, and it has
2453 descriptors for more than 1/4 of the routers that it believes are running.
2455 (Note: clients can and should pick caches based on the network-status
2456 information they have: once they have first fetched network-status info
2457 from an authority, they should not need to go to the authority directly
2458 again.)
2460 To avoid swarming the caches whenever a consensus expires, the
2461 clients download new consensuses at a randomly chosen time after the
2462 caches are expected to have a fresh consensus, but before their
2463 consensus will expire. (This time is chosen uniformly at random from
2464 the interval between the time 3/4 into the first interval after the
2465 consensus is no longer fresh, and 7/8 of the time remaining after
2466 that before the consensus is invalid.)
2468 [For example, if a cache has a consensus that became valid at 1:00,
2469 and is fresh until 2:00, and expires at 4:00, that cache will fetch
2470 a new consensus at a random time between 2:45 and 3:50, since 3/4
2471 of the one-hour interval is 45 minutes, and 7/8 of the remaining 75
2472 minutes is 65 minutes.]
2474 Clients may choose to download the microdescriptor consensus instead
2475 of the general network status consensus. In that case they should use
2476 the same update strategy as for the normal consensus. They should not
2477 download more than one consensus flavor.
2479 5.2. Downloading and storing router descriptors or microdescriptors
2481 Clients try to have the best descriptor for each router. A descriptor is
2482 "best" if:
2483 * It is listed in the consensus network-status document.
2485 Periodically (currently every 10 seconds) clients check whether there are
2486 any "downloadable" descriptors. A descriptor is downloadable if:
2487 - It is the "best" descriptor for some router.
2488 - The descriptor was published at least 10 minutes in the past.
2489 (This prevents clients from trying to fetch descriptors that the
2490 mirrors have probably not yet retrieved and cached.)
2491 - The client does not currently have it.
2492 - The client is not currently trying to download it.
2493 - The client would not discard it immediately upon receiving it.
2494 - The client thinks it is running and valid (see 6.1 below).
2496 If at least 16 known routers have downloadable descriptors, or if
2497 enough time (currently 10 minutes) has passed since the last time the
2498 client tried to download descriptors, it launches requests for all
2499 downloadable descriptors, as described in 5.3 below.
2501 When a descriptor download fails, the client notes it, and does not
2502 consider the descriptor downloadable again until a certain amount of time
2503 has passed. (Currently 0 seconds for the first failure, 60 seconds for the
2504 second, 5 minutes for the third, 10 minutes for the fourth, and 1 day
2505 thereafter.) Periodically (currently once an hour) clients reset the
2506 failure count.
2508 Clients retain the most recent descriptor they have downloaded for each
2509 router so long as it is not too old (currently, 48 hours), OR so long as
2510 no better descriptor has been downloaded for the same router.
2512 [Versions of Tor before 0.1.2.3-alpha would discard descriptors simply for
2513 being published too far in the past.] [The code seems to discard
2514 descriptors in all cases after they're 5 days old. True? -RD]
2516 Clients which chose to download the microdescriptor consensus instead
2517 of the general consensus must download the referenced microdescriptors
2518 instead of router descriptors. Clients fetch and cache
2519 microdescriptors preemptively from dir mirrors when starting up, like
2520 they currently fetch descriptors. After bootstrapping, clients only
2521 need to fetch the microdescriptors that have changed.
2523 Clients maintain a cache of microdescriptors along with metadata like
2524 when it was last referenced by a consensus, and which identity key
2525 it corresponds to. They keep a microdescriptor until it hasn't been
2526 mentioned in any consensus for a week. Future clients might cache them
2527 for longer or shorter times.
2529 5.3. Managing downloads
2531 When a client has no consensus network-status document, it downloads it
2532 from a randomly chosen authority. In all other cases, the client
2533 downloads from caches randomly chosen from among those believed to be V2
2534 directory servers. (This information comes from the network-status
2535 documents; see 6 below.)
2537 When downloading multiple router descriptors, the client chooses multiple
2538 mirrors so that:
2539 - At least 3 different mirrors are used, except when this would result
2540 in more than one request for under 4 descriptors.
2541 - No more than 128 descriptors are requested from a single mirror.
2542 - Otherwise, as few mirrors as possible are used.
2543 After choosing mirrors, the client divides the descriptors among them
2544 randomly.
2546 After receiving any response client MUST discard any network-status
2547 documents and descriptors that it did not request.
2549 When a client gets a new microdescriptor consensus, it looks to see if
2550 there are any microdescriptors it needs to learn. If it needs to learn
2551 more than half of the microdescriptors, it requests 'all', else it
2552 requests only the missing ones. Clients MAY try to determine whether
2553 the upload bandwidth for listing the microdescriptors they want is more
2554 or less than the download bandwidth for the microdescriptors they do
2555 not want.
2557 6. Using directory information
2559 Everyone besides directory authorities uses the approaches in this section
2560 to decide which relays to use and what their keys are likely to be.
2561 (Directory authorities just believe their own opinions, as in 3.1 above.)
2563 6.1. Choosing routers for circuits.
2565 Circuits SHOULD NOT be built until the client has enough directory
2566 information: a live consensus network status [XXXX fallback?] and
2567 descriptors for at least 1/4 of the relays believed to be running.
2569 A relay is "listed" if it is included by the consensus network-status
2570 document. Clients SHOULD NOT use unlisted relays.
2572 These flags are used as follows:
2574 - Clients SHOULD NOT use non-'Valid' or non-'Running' routers unless
2575 requested to do so.
2577 - Clients SHOULD NOT use non-'Fast' routers for any purpose other than
2578 very-low-bandwidth circuits (such as introduction circuits).
2580 - Clients SHOULD NOT use non-'Stable' routers for circuits that are
2581 likely to need to be open for a very long time (such as those used for
2582 IRC or SSH connections).
2584 - Clients SHOULD NOT choose non-'Guard' nodes when picking entry guard
2585 nodes.
2587 - Clients SHOULD NOT download directory information from non-'V2Dir'
2588 caches.
2590 See the "path-spec.txt" document for more details.
2592 6.2. Managing naming
2594 In order to provide human-memorable names for individual router
2595 identities, some directory servers bind names to IDs. Clients handle
2596 names in two ways:
2598 When a client encounters a name it has not mapped before:
2600 If the consensus lists any router with that name as "Named", or if
2601 consensus-method 2 or later is in use and the consensus lists any
2602 router with that name as having the "Unnamed" flag, then the name is
2603 bound. (It's bound to the ID listed in the entry with the Named,
2604 or to an unknown ID if no name is found.)
2606 When the user refers to a bound name, the implementation SHOULD provide
2607 only the router with ID bound to that name, and no other router, even
2608 if the router with the right ID can't be found.
2610 When a user tries to refer to a non-bound name, the implementation SHOULD
2611 warn the user. After warning the user, the implementation MAY use any
2612 router that advertises the name.
2614 Not every router needs a nickname. When a router doesn't configure a
2615 nickname, it publishes with the default nickname "Unnamed". Authorities
2616 SHOULD NOT ever mark a router with this nickname as Named; client software
2617 SHOULD NOT ever use a router in response to a user request for a router
2618 called "Unnamed".
2620 6.3. Software versions
2622 An implementation of Tor SHOULD warn when it has fetched a consensus
2623 network-status, and it is running a software version not listed.
2625 6.4. Warning about a router's status.
2627 If a router tries to publish its descriptor to a Naming authority
2628 that has its nickname mapped to another key, the router SHOULD
2629 warn the operator that it is either using the wrong key or is using
2630 an already claimed nickname.
2632 If a router has fetched a consensus document,, and the
2633 authorities do not publish a binding for the router's nickname, the
2634 router MAY remind the operator that the chosen nickname is not
2635 bound to this key at the authorities, and suggest contacting the
2636 authority operators.
2638 ...
2640 6.5. Router protocol versions
2642 A client should believe that a router supports a given feature if that
2643 feature is supported by the router or protocol versions in more than half
2644 of the live networkstatuses' "v" entries for that router. In other words,
2645 if the "v" entries for some router are:
2646 v Tor 0.0.8pre1 (from authority 1)
2647 v Tor 0.1.2.11 (from authority 2)
2648 v FutureProtocolDescription 99 (from authority 3)
2649 then the client should believe that the router supports any feature
2650 supported by 0.1.2.11.
2652 This is currently equivalent to believing the median declared version for
2653 a router in all live networkstatuses.
2655 7. Standards compliance
2657 All clients and servers MUST support HTTP 1.0. Clients and servers MAY
2658 support later versions of HTTP as well.
2660 7.1. HTTP headers
2662 Servers MAY set the Content-Length: header. Servers SHOULD set
2663 Content-Encoding to "deflate" or "identity".
2665 Servers MAY include an X-Your-Address-Is: header, whose value is the
2666 apparent IP address of the client connecting to them (as a dotted quad).
2667 For directory connections tunneled over a BEGIN_DIR stream, servers SHOULD
2668 report the IP from which the circuit carrying the BEGIN_DIR stream reached
2669 them.
2671 Servers SHOULD disable caching of multiple network statuses or multiple
2672 router descriptors. Servers MAY enable caching of single descriptors,
2673 single network statuses, the list of all router descriptors, a v1
2674 directory, or a v1 running routers document. XXX mention times.
2676 7.2. HTTP status codes
2678 Tor delivers the following status codes. Some were chosen without much
2679 thought; other code SHOULD NOT rely on specific status codes yet.
2681 200 -- the operation completed successfully
2682 -- the user requested statuses or serverdescs, and none of the ones we
2683 requested were found (0.2.0.4-alpha and earlier).
2685 304 -- the client specified an if-modified-since time, and none of the
2686 requested resources have changed since that time.
2688 400 -- the request is malformed, or
2689 -- the URL is for a malformed variation of one of the URLs we support,
2690 or
2691 -- the client tried to post to a non-authority, or
2692 -- the authority rejected a malformed posted document, or
2694 404 -- the requested document was not found.
2695 -- the user requested statuses or serverdescs, and none of the ones
2696 requested were found (0.2.0.5-alpha and later).
2698 503 -- we are declining the request in order to save bandwidth
2699 -- user requested some items that we ordinarily generate or store,
2700 but we do not have any available.
2702 9. Backward compatibility and migration plans
2704 Until Tor versions before 0.1.1.x are completely obsolete, directory
2705 authorities should generate, and mirrors should download and cache, v1
2706 directories and running-routers lists, and allow old clients to download
2707 them. These documents and the rules for retrieving, serving, and caching
2708 them are described in dir-spec-v1.txt.
2710 Until Tor versions before 0.2.0.x are completely obsolete, directory
2711 authorities should generate, mirrors should download and cache, v2
2712 network-status documents, and allow old clients to download them.
2713 Additionally, all directory servers and caches should download, store, and
2714 serve any router descriptor that is required because of v2 network-status
2715 documents. These documents and the rules for retrieving, serving, and
2716 caching them are described in dir-spec-v1.txt.
2718 A. Consensus-negotiation timeline.
2720 Period begins: this is the Published time.
2721 Everybody sends votes
2722 Reconciliation: everybody tries to fetch missing votes.
2723 consensus may exist at this point.
2724 End of voting period:
2725 everyone swaps signatures.
2726 Now it's okay for caches to download
2727 Now it's okay for clients to download.
2729 Valid-after/valid-until switchover