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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 server's identity key: this prevents servers from attacking clients by
182 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 The "opt" keyword was used until Tor 0.1.2.5-alpha for non-critical future
238 extensions. All implementations MUST ignore any item of the form "opt
239 keyword ....." when they would not recognize "keyword ....."; and MUST
240 treat "opt keyword ....." as synonymous with "keyword ......" when keyword
241 is recognized.
243 Implementations before 0.1.2.5-alpha rejected any document with a
244 KeywordLine that started with a keyword that they didn't recognize.
245 When generating documents that need to be read by older versions of Tor,
246 implementations MUST prefix items not recognized by older versions of
247 Tor with an "opt" until those versions of Tor are obsolete. [Note that
248 key certificates, status vote documents, extra info documents, and
249 status consensus documents will never be read by older versions of Tor.]
251 Other implementations that want to extend Tor's directory format MAY
252 introduce their own items. The keywords for extension items SHOULD start
253 with the characters "x-" or "X-", to guarantee that they will not conflict
254 with keywords used by future versions of Tor.
256 In our document descriptions below, we tag Items with a multiplicity in
257 brackets. Possible tags are:
259 "At start, exactly once": These items MUST occur in every instance of
260 the document type, and MUST appear exactly once, and MUST be the
261 first item in their documents.
263 "Exactly once": These items MUST occur exactly one time in every
264 instance of the document type.
266 "At end, exactly once": These items MUST occur in every instance of
267 the document type, and MUST appear exactly once, and MUST be the
268 last item in their documents.
270 "At most once": These items MAY occur zero or one times in any
271 instance of the document type, but MUST NOT occur more than once.
273 "Any number": These items MAY occur zero, one, or more times in any
274 instance of the document type.
276 "Once or more": These items MUST occur at least once in any instance
277 of the document type, and MAY occur more.
279 1.3. Signing documents
281 Every signable document below is signed in a similar manner, using a
282 given "Initial Item", a final "Signature Item", a digest algorithm, and
283 a signing key.
285 The Initial Item must be the first item in the document.
287 The Signature Item has the following format:
289 <signature item keyword> [arguments] NL SIGNATURE NL
291 The "SIGNATURE" Object contains a signature (using the signing key) of
292 the PKCS1-padded digest of the entire document, taken from the
293 beginning of the Initial item, through the newline after the Signature
294 Item's keyword and its arguments.
296 Unless otherwise, the digest algorithm is SHA-1.
298 All documents are invalid unless signed with the correct signing key.
300 The "Digest" of a document, unless stated otherwise, is its digest *as
301 signed by this signature scheme*.
303 1.4. Voting timeline
305 Every consensus document has a "valid-after" (VA) time, a "fresh-until"
306 (FU) time and a "valid-until" (VU) time. VA MUST precede FU, which MUST
307 in turn precede VU. Times are chosen so that every consensus will be
308 "fresh" until the next consensus becomes valid, and "valid" for a while
309 after. At least 3 consensuses should be valid at any given time.
311 The timeline for a given consensus is as follows:
313 VA-DistSeconds-VoteSeconds: The authorities exchange votes.
315 VA-DistSeconds-VoteSeconds/2: The authorities try to download any
316 votes they don't have.
318 VA-DistSeconds: The authorities calculate the consensus and exchange
319 signatures.
321 VA-DistSeconds/2: The authorities try to download any signatures
322 they don't have.
324 VA: All authorities have a multiply signed consensus.
326 VA ... FU: Caches download the consensus. (Note that since caches have
327 no way of telling what VA and FU are until they have downloaded
328 the consensus, they assume that the present consensus's VA is
329 equal to the previous one's FU, and that its FU is one interval after
330 that.)
332 FU: The consensus is no longer the freshest consensus.
334 FU ... (the current consensus's VU): Clients download the consensus.
335 (See note above: clients guess that the next consensus's FU will be
336 two intervals after the current VA.)
338 VU: The consensus is no longer valid.
340 VoteSeconds and DistSeconds MUST each be at least 20 seconds; FU-VA and
341 VU-FU MUST each be at least 5 minutes.
343 2. Router operation and formats
345 ORs SHOULD generate a new router descriptor and a new extra-info
346 document whenever any of the following events have occurred:
348 - A period of time (18 hrs by default) has passed since the last
349 time a descriptor was generated.
351 - A descriptor field other than bandwidth or uptime has changed.
353 - Bandwidth has changed by a factor of 2 from the last time a
354 descriptor was generated, and at least a given interval of time
355 (20 mins by default) has passed since then.
357 - Its uptime has been reset (by restarting).
359 [XXX this list is incomplete; see router_differences_are_cosmetic()
360 in routerlist.c for others]
362 ORs SHOULD NOT publish a new router descriptor or extra-info document
363 if none of the above events have occurred and not much time has passed
364 (12 hours by default).
366 After generating a descriptor, ORs upload them to every directory
367 authority they know, by posting them (in order) to the URL
369 http://<hostname:port>/tor/
371 2.1. Router descriptor format
373 Router descriptors consist of the following items. For backward
374 compatibility, there should be an extra NL at the end of each router
375 descriptor.
377 In lines that take multiple arguments, extra arguments SHOULD be
378 accepted and ignored. Many of the nonterminals below are defined in
379 section 2.3.
381 "router" nickname address ORPort SOCKSPort DirPort NL
383 [At start, exactly once.]
385 Indicates the beginning of a router descriptor. "nickname" must be a
386 valid router nickname as specified in 2.3. "address" must be an IPv4
387 address in dotted-quad format. The last three numbers indicate the
388 TCP ports at which this OR exposes functionality. ORPort is a port at
389 which this OR accepts TLS connections for the main OR protocol;
390 SOCKSPort is deprecated and should always be 0; and DirPort is the
391 port at which this OR accepts directory-related HTTP connections. If
392 any port is not supported, the value 0 is given instead of a port
393 number. (At least one of DirPort and ORPort SHOULD be set;
394 authorities MAY reject any descriptor with both DirPort and ORPort of
395 0.)
397 "bandwidth" bandwidth-avg bandwidth-burst bandwidth-observed NL
399 [Exactly once]
401 Estimated bandwidth for this router, in bytes per second. The
402 "average" bandwidth is the volume per second that the OR is willing to
403 sustain over long periods; the "burst" bandwidth is the volume that
404 the OR is willing to sustain in very short intervals. The "observed"
405 value is an estimate of the capacity this server can handle. The
406 server remembers the max bandwidth sustained output over any ten
407 second period in the past day, and another sustained input. The
408 "observed" value is the lesser of these two numbers.
410 "platform" string NL
412 [At most once]
414 A human-readable string describing the system on which this OR is
415 running. This MAY include the operating system, and SHOULD include
416 the name and version of the software implementing the Tor protocol.
418 "published" YYYY-MM-DD HH:MM:SS NL
420 [Exactly once]
422 The time, in GMT, when this descriptor (and its corresponding
423 extra-info document if any) was generated.
425 "fingerprint" fingerprint NL
427 [At most once]
429 A fingerprint (a HASH_LEN-byte of asn1 encoded public key, encoded in
430 hex, with a single space after every 4 characters) for this router's
431 identity key. A descriptor is considered invalid (and MUST be
432 rejected) if the fingerprint line does not match the public key.
434 [We didn't start parsing this line until Tor 0.1.0.6-rc; it should
435 be marked with "opt" until earlier versions of Tor are obsolete.]
437 "hibernating" bool NL
439 [At most once]
441 If the value is 1, then the Tor server was hibernating when the
442 descriptor was published, and shouldn't be used to build circuits.
444 [We didn't start parsing this line until Tor 0.1.0.6-rc; it should be
445 marked with "opt" until earlier versions of Tor are obsolete.]
447 "uptime" number NL
449 [At most once]
451 The number of seconds that this OR process has been running.
453 "onion-key" NL a public key in PEM format
455 [Exactly once]
457 This key is used to encrypt EXTEND cells for this OR. The key MUST be
458 accepted for at least 1 week after any new key is published in a
459 subsequent descriptor. It MUST be 1024 bits.
461 "signing-key" NL a public key in PEM format
463 [Exactly once]
465 The OR's long-term identity key. It MUST be 1024 bits.
467 "accept" exitpattern NL
468 "reject" exitpattern NL
470 [Any number]
472 These lines describe an "exit policy": the rules that an OR follows
473 when deciding whether to allow a new stream to a given address. The
474 'exitpattern' syntax is described below. There MUST be at least one
475 such entry. The rules are considered in order; if no rule matches,
476 the address will be accepted. For clarity, the last such entry SHOULD
477 be accept *:* or reject *:*.
479 "router-signature" NL Signature NL
481 [At end, exactly once]
483 The "SIGNATURE" object contains a signature of the PKCS1-padded
484 hash of the entire router descriptor, taken from the beginning of the
485 "router" line, through the newline after the "router-signature" line.
486 The router descriptor is invalid unless the signature is performed
487 with the router's identity key.
489 "contact" info NL
491 [At most once]
493 Describes a way to contact the server's administrator, preferably
494 including an email address and a PGP key fingerprint.
496 "family" names NL
498 [At most once]
500 'Names' is a space-separated list of server nicknames or
501 hexdigests. If two ORs list one another in their "family" entries,
502 then OPs should treat them as a single OR for the purpose of path
503 selection.
505 For example, if node A's descriptor contains "family B", and node B's
506 descriptor contains "family A", then node A and node B should never
507 be used on the same circuit.
509 "read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL
510 [At most once]
511 "write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL
512 [At most once]
514 Declare how much bandwidth the OR has used recently. Usage is divided
515 into intervals of NSEC seconds. The YYYY-MM-DD HH:MM:SS field
516 defines the end of the most recent interval. The numbers are the
517 number of bytes used in the most recent intervals, ordered from
518 oldest to newest.
520 [We didn't start parsing these lines until Tor 0.1.0.6-rc; they should
521 be marked with "opt" until earlier versions of Tor are obsolete.]
523 [See also migration notes in section 2.2.1.]
525 "eventdns" bool NL
527 [At most once]
529 Declare whether this version of Tor is using the newer enhanced
530 dns logic. Versions of Tor with this field set to false SHOULD NOT
531 be used for reverse hostname lookups.
533 [This option is obsolete. All Tor current servers should be presumed
534 to have the evdns backend.]
536 "caches-extra-info" NL
538 [At most once.]
540 Present only if this router is a directory cache that provides
541 extra-info documents.
543 [Versions before 0.2.0.1-alpha don't recognize this, and versions
544 before 0.1.2.5-alpha will reject descriptors containing it unless
545 it is prefixed with "opt"; it should be so prefixed until these
546 versions are obsolete.]
548 "extra-info-digest" digest NL
550 [At most once]
552 "Digest" is a hex-encoded digest (using upper-case characters) of the
553 router's extra-info document, as signed in the router's extra-info
554 (that is, not including the signature). (If this field is absent, the
555 router is not uploading a corresponding extra-info document.)
557 [Versions before 0.2.0.1-alpha don't recognize this, and versions
558 before 0.1.2.5-alpha will reject descriptors containing it unless
559 it is prefixed with "opt"; it should be so prefixed until these
560 versions are obsolete.]
562 "hidden-service-dir" *(SP VersionNum) NL
564 [At most once.]
566 Present only if this router stores and serves hidden service
567 descriptors. If any VersionNum(s) are specified, this router
568 supports those descriptor versions. If none are specified, it
569 defaults to version 2 descriptors.
571 [Versions of Tor before 0.1.2.5-alpha rejected router descriptors
572 with unrecognized items; the protocols line should be preceded with
573 an "opt" until these Tors are obsolete.]
575 "protocols" SP "Link" SP LINK-VERSION-LIST SP "Circuit" SP
576 CIRCUIT-VERSION-LIST NL
578 [At most once.]
580 Both lists are space-separated sequences of numbers, to indicate which
581 protocols the server supports. As of 30 Mar 2008, specified
582 protocols are "Link 1 2 Circuit 1". See section 4.1 of tor-spec.txt
583 for more information about link protocol versions.
585 [Versions of Tor before 0.1.2.5-alpha rejected router descriptors
586 with unrecognized items; the protocols line should be preceded with
587 an "opt" until these Tors are obsolete.]
589 "allow-single-hop-exits" NL
591 [At most once.]
593 Present only if the router allows single-hop circuits to make exit
594 connections. Most Tor servers do not support this: this is
595 included for specialized controllers designed to support perspective
596 access and such.
599 2.2. Extra-info documents
601 Extra-info documents consist of the following items:
603 "extra-info" Nickname Fingerprint NL
604 [At start, exactly once.]
606 Identifies what router this is an extra info descriptor for.
607 Fingerprint is encoded in hex (using upper-case letters), with
608 no spaces.
610 "published" YYYY-MM-DD HH:MM:SS NL
612 [Exactly once.]
614 The time, in GMT, when this document (and its corresponding router
615 descriptor if any) was generated. It MUST match the published time
616 in the corresponding router descriptor.
618 "read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL
619 [At most once.]
620 "write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL
621 [At most once.]
623 As documented in 2.1 above. See migration notes in section 2.2.1.
625 "geoip-db-digest" Digest NL
626 [At most once.]
628 SHA1 digest of the GeoIP database file that is used to resolve IP
629 addresses to country codes.
631 ("geoip-start" YYYY-MM-DD HH:MM:SS NL)
632 ("geoip-client-origins" CC=N,CC=N,... NL)
634 Only generated by bridge routers (see blocking.pdf), and only
635 when they have been configured with a geoip database.
636 Non-bridges SHOULD NOT generate these fields. Contains a list
637 of mappings from two-letter country codes (CC) to the number
638 of clients that have connected to that bridge from that
639 country (approximate, and rounded up to the nearest multiple of 8
640 in order to hamper traffic analysis). A country is included
641 only if it has at least one address. The time in
642 "geoip-start" is the time at which we began collecting geoip
643 statistics.
645 "geoip-start" and "geoip-client-origins" have been replaced by
646 "bridge-stats-end" and "bridge-stats-ips" in 0.2.2.4-alpha. The
647 reason is that the measurement interval with "geoip-stats" as
648 determined by subtracting "geoip-start" from "published" could
649 have had a variable length, whereas the measurement interval in
650 0.2.2.4-alpha and later is set to be exactly 24 hours long. In
651 order to clearly distinguish the new measurement intervals from
652 the old ones, the new keywords have been introduced.
654 "bridge-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
655 [At most once.]
657 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
658 interval of length NSEC seconds (86400 seconds by default).
660 A "bridge-stats-end" line, as well as any other "bridge-*" line,
661 is only added when the relay has been running as a bridge for at
662 least 24 hours.
664 "bridge-ips" CC=N,CC=N,... NL
665 [At most once.]
667 List of mappings from two-letter country codes to the number of
668 unique IP addresses that have connected from that country to the
669 bridge and which are no known relays, rounded up to the nearest
670 multiple of 8.
672 "dirreq-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
673 [At most once.]
675 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
676 interval of length NSEC seconds (86400 seconds by default).
678 A "dirreq-stats-end" line, as well as any other "dirreq-*" line,
679 is only added when the relay has opened its Dir port and after 24
680 hours of measuring directory requests.
682 "dirreq-v2-ips" CC=N,CC=N,... NL
683 [At most once.]
684 "dirreq-v3-ips" CC=N,CC=N,... NL
685 [At most once.]
687 List of mappings from two-letter country codes to the number of
688 unique IP addresses that have connected from that country to
689 request a v2/v3 network status, rounded up to the nearest multiple
690 of 8. Only those IP addresses are counted that the directory can
691 answer with a 200 OK status code.
693 "dirreq-v2-reqs" CC=N,CC=N,... NL
694 [At most once.]
695 "dirreq-v3-reqs" CC=N,CC=N,... NL
696 [At most once.]
698 List of mappings from two-letter country codes to the number of
699 requests for v2/v3 network statuses from that country, rounded up
700 to the nearest multiple of 8. Only those requests are counted that
701 the directory can answer with a 200 OK status code.
703 "dirreq-v2-share" num% NL
704 [At most once.]
705 "dirreq-v3-share" num% NL
706 [At most once.]
708 The share of v2/v3 network status requests that the directory
709 expects to receive from clients based on its advertised bandwidth
710 compared to the overall network bandwidth capacity. Shares are
711 formatted in percent with two decimal places. Shares are
712 calculated as means over the whole 24-hour interval.
714 "dirreq-v2-resp" status=num,... NL
715 [At most once.]
716 "dirreq-v3-resp" status=nul,... NL
717 [At most once.]
719 List of mappings from response statuses to the number of requests
720 for v2/v3 network statuses that were answered with that response
721 status, rounded up to the nearest multiple of 4. Only response
722 statuses with at least 1 response are reported. New response
723 statuses can be added at any time. The current list of response
724 statuses is as follows:
726 "ok": a network status request is answered; this number
727 corresponds to the sum of all requests as reported in
728 "dirreq-v2-reqs" or "dirreq-v3-reqs", respectively, before
729 rounding up.
730 "not-enough-sigs: a version 3 network status is not signed by a
731 sufficient number of requested authorities.
732 "unavailable": a requested network status object is unavailable.
733 "not-found": a requested network status is not found.
734 "not-modified": a network status has not been modified since the
735 If-Modified-Since time that is included in the request.
736 "busy": the directory is busy.
738 "dirreq-v2-direct-dl" key=val,... NL
739 [At most once.]
740 "dirreq-v3-direct-dl" key=val,... NL
741 [At most once.]
742 "dirreq-v2-tunneled-dl" key=val,... NL
743 [At most once.]
744 "dirreq-v3-tunneled-dl" key=val,... NL
745 [At most once.]
747 List of statistics about possible failures in the download process
748 of v2/v3 network statuses. Requests are either "direct"
749 HTTP-encoded requests over the relay's directory port, or
750 "tunneled" requests using a BEGIN_DIR cell over the relay's OR
751 port. The list of possible statistics can change, and statistics
752 can be left out from reporting. The current list of statistics is
753 as follows:
755 Successful downloads and failures:
757 "complete": a client has finished the download successfully.
758 "timeout": a download did not finish within 10 minutes after
759 starting to send the response.
760 "running": a download is still running at the end of the
761 measurement period for less than 10 minutes after starting to
762 send the response.
764 Download times:
766 "min", "max": smallest and largest measured bandwidth in B/s.
767 "d[1-4,6-9]": 1st to 4th and 6th to 9th decile of measured
768 bandwidth in B/s. For a given decile i, i/10 of all downloads
769 had a smaller bandwidth than di, and (10-i)/10 of all downloads
770 had a larger bandwidth than di.
771 "q[1,3]": 1st and 3rd quartile of measured bandwidth in B/s. One
772 fourth of all downloads had a smaller bandwidth than q1, one
773 fourth of all downloads had a larger bandwidth than q3, and the
774 remaining half of all downloads had a bandwidth between q1 and
775 q3.
776 "md": median of measured bandwidth in B/s. Half of the downloads
777 had a smaller bandwidth than md, the other half had a larger
778 bandwidth than md.
780 "dirreq-read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM... NL
781 [At most once]
782 "dirreq-write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM... NL
783 [At most once]
785 Declare how much bandwidth the OR has spent on answering directory
786 requests. Usage is divided into intervals of NSEC seconds. The
787 YYYY-MM-DD HH:MM:SS field defines the end of the most recent
788 interval. The numbers are the number of bytes used in the most
789 recent intervals, ordered from oldest to newest.
791 "entry-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
792 [At most once.]
794 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
795 interval of length NSEC seconds (86400 seconds by default).
797 An "entry-stats-end" line, as well as any other "entry-*"
798 line, is first added after the relay has been running for at least
799 24 hours.
801 "entry-ips" CC=N,CC=N,... NL
802 [At most once.]
804 List of mappings from two-letter country codes to the number of
805 unique IP addresses that have connected from that country to the
806 relay and which are no known other relays, rounded up to the
807 nearest multiple of 8.
809 "cell-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
810 [At most once.]
812 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
813 interval of length NSEC seconds (86400 seconds by default).
815 A "cell-stats-end" line, as well as any other "cell-*" line,
816 is first added after the relay has been running for at least 24
817 hours.
819 "cell-processed-cells" num,...,num NL
820 [At most once.]
822 Mean number of processed cells per circuit, subdivided into
823 deciles of circuits by the number of cells they have processed in
824 descending order from loudest to quietest circuits.
826 "cell-queued-cells" num,...,num NL
827 [At most once.]
829 Mean number of cells contained in queues by circuit decile. These
830 means are calculated by 1) determining the mean number of cells in
831 a single circuit between its creation and its termination and 2)
832 calculating the mean for all circuits in a given decile as
833 determined in "cell-processed-cells". Numbers have a precision of
834 two decimal places.
836 "cell-time-in-queue" num,...,num NL
837 [At most once.]
839 Mean time cells spend in circuit queues in milliseconds. Times are
840 calculated by 1) determining the mean time cells spend in the
841 queue of a single circuit and 2) calculating the mean for all
842 circuits in a given decile as determined in
843 "cell-processed-cells".
845 "cell-circuits-per-decile" num NL
846 [At most once.]
848 Mean number of circuits that are included in any of the deciles,
849 rounded up to the next integer.
851 "conn-bi-direct" YYYY-MM-DD HH:MM:SS (NSEC s) BELOW,READ,WRITE,BOTH NL
852 [At most once]
854 Number of connections, split into 10-second intervals, that are
855 used uni-directionally or bi-directionally as observed in the NSEC
856 seconds (usually 86400 seconds) before YYYY-MM-DD HH:MM:SS. Every
857 10 seconds, we determine for every connection whether we read and
858 wrote less than a threshold of 20 KiB (BELOW), read at least 10
859 times more than we wrote (READ), wrote at least 10 times more than
860 we read (WRITE), or read and wrote more than the threshold, but
861 not 10 times more in either direction (BOTH). After classifying a
862 connection, read and write counters are reset for the next
863 10-second interval.
865 "exit-stats-end" YYYY-MM-DD HH:MM:SS (NSEC s) NL
866 [At most once.]
868 YYYY-MM-DD HH:MM:SS defines the end of the included measurement
869 interval of length NSEC seconds (86400 seconds by default).
871 An "exit-stats-end" line, as well as any other "exit-*" line, is
872 first added after the relay has been running for at least 24 hours
873 and only if the relay permits exiting (where exiting to a single
874 port and IP address is sufficient).
876 "exit-kibibytes-written" port=N,port=N,... NL
877 [At most once.]
878 "exit-kibibytes-read" port=N,port=N,... NL
879 [At most once.]
881 List of mappings from ports to the number of kibibytes that the
882 relay has written to or read from exit connections to that port,
883 rounded up to the next full kibibyte.
885 "exit-streams-opened" port=N,port=N,... NL
886 [At most once.]
888 List of mappings from ports to the number of opened exit streams
889 to that port, rounded up to the nearest multiple of 4.
891 "router-signature" NL Signature NL
892 [At end, exactly once.]
894 A document signature as documented in section 1.3, using the
895 initial item "extra-info" and the final item "router-signature",
896 signed with the router's identity key.
898 2.2.1. Moving history fields to extra-info documents.
900 Tools that want to use the read-history and write-history values SHOULD
901 download extra-info documents as well as router descriptors. Such
902 tools SHOULD accept history values from both sources; if they appear in
903 both documents, the values in the extra-info documents are authoritative.
905 New versions of Tor no longer generate router descriptors
906 containing read-history or write-history. Tools should continue to
907 accept read-history and write-history values in router descriptors
908 produced by older versions of Tor until all Tor versions earlier
909 than 0.2.0.x are obsolete.
911 2.3. Nonterminals in router descriptors
913 nickname ::= between 1 and 19 alphanumeric characters ([A-Za-z0-9]),
914 case-insensitive.
915 hexdigest ::= a '$', followed by 40 hexadecimal characters
916 ([A-Fa-f0-9]). [Represents a server by the digest of its identity
917 key.]
919 exitpattern ::= addrspec ":" portspec
920 portspec ::= "*" | port | port "-" port
921 port ::= an integer between 1 and 65535, inclusive.
923 [Some implementations incorrectly generate ports with value 0.
924 Implementations SHOULD accept this, and SHOULD NOT generate it.
925 Connections to port 0 are never permitted.]
927 addrspec ::= "*" | ip4spec | ip6spec
928 ipv4spec ::= ip4 | ip4 "/" num_ip4_bits | ip4 "/" ip4mask
929 ip4 ::= an IPv4 address in dotted-quad format
930 ip4mask ::= an IPv4 mask in dotted-quad format
931 num_ip4_bits ::= an integer between 0 and 32
932 ip6spec ::= ip6 | ip6 "/" num_ip6_bits
933 ip6 ::= an IPv6 address, surrounded by square brackets.
934 num_ip6_bits ::= an integer between 0 and 128
936 bool ::= "0" | "1"
938 3. Formats produced by directory authorities.
940 Every authority has two keys used in this protocol: a signing key, and
941 an authority identity key. (Authorities also have a router identity
942 key used in their role as a router and by earlier versions of the
943 directory protocol.) The identity key is used from time to time to
944 sign new key certificates using new signing keys; it is very sensitive.
945 The signing key is used to sign key certificates and status documents.
947 There are three kinds of documents generated by directory authorities:
949 Key certificates
950 Status votes
951 Status consensuses
953 Each is discussed below.
955 3.1. Key certificates
957 Key certificates consist of the following items:
959 "dir-key-certificate-version" version NL
961 [At start, exactly once.]
963 Determines the version of the key certificate. MUST be "3" for
964 the protocol described in this document. Implementations MUST
965 reject formats they don't understand.
967 "dir-address" IPPort NL
968 [At most once]
970 An IP:Port for this authority's directory port.
972 "fingerprint" fingerprint NL
974 [Exactly once.]
976 Hexadecimal encoding without spaces based on the authority's
977 identity key.
979 "dir-identity-key" NL a public key in PEM format
981 [Exactly once.]
983 The long-term authority identity key for this authority. This key
984 SHOULD be at least 2048 bits long; it MUST NOT be shorter than
985 1024 bits.
987 "dir-key-published" YYYY-MM-DD HH:MM:SS NL
989 [Exactly once.]
991 The time (in GMT) when this document and corresponding key were
992 last generated.
994 "dir-key-expires" YYYY-MM-DD HH:MM:SS NL
996 [Exactly once.]
998 A time (in GMT) after which this key is no longer valid.
1000 "dir-signing-key" NL a key in PEM format
1002 [Exactly once.]
1004 The directory server's public signing key. This key MUST be at
1005 least 1024 bits, and MAY be longer.
1007 "dir-key-crosscert" NL CrossSignature NL
1009 [At most once.]
1011 NOTE: Authorities MUST include this field in all newly generated
1012 certificates. A future version of this specification will make
1013 the field required.
1015 CrossSignature is a signature, made using the certificate's signing
1016 key, of the digest of the PKCS1-padded hash of the certificate's
1017 identity key. For backward compatibility with broken versions of the
1018 parser, we wrap the base64-encoded signature in -----BEGIN ID
1019 SIGNATURE---- and -----END ID SIGNATURE----- tags. Implementations
1020 MUST allow the "ID " portion to be omitted, however.
1022 When encountering a certificate with a dir-key-crosscert entry,
1023 implementations MUST verify that the signature is a correct signature
1024 of the hash of the identity key using the signing key.
1026 "dir-key-certification" NL Signature NL
1028 [At end, exactly once.]
1030 A document signature as documented in section 1.3, using the
1031 initial item "dir-key-certificate-version" and the final item
1032 "dir-key-certification", signed with the authority identity key.
1034 Authorities MUST generate a new signing key and corresponding
1035 certificate before the key expires.
1037 3.2. Vote and consensus status documents
1039 Votes and consensuses are more strictly formatted then other documents
1040 in this specification, since different authorities must be able to
1041 generate exactly the same consensus given the same set of votes.
1043 The procedure for deciding when to generate vote and consensus status
1044 documents are described in section 1.4 on the voting timeline.
1046 Status documents contain a preamble, an authority section, a list of
1047 router status entries, and one or more footer signature, in that order.
1049 Unlike other formats described above, a SP in these documents must be a
1050 single space character (hex 20).
1052 Some items appear only in votes, and some items appear only in
1053 consensuses. Unless specified, items occur in both.
1055 The preamble contains the following items. They MUST occur in the
1056 order given here:
1058 "network-status-version" SP version NL.
1060 [At start, exactly once.]
1062 A document format version. For this specification, the version is
1063 "3".
1065 "vote-status" SP type NL
1067 [Exactly once.]
1069 The status MUST be "vote" or "consensus", depending on the type of
1070 the document.
1072 "consensus-methods" SP IntegerList NL
1074 [Exactly once for votes; does not occur in consensuses.]
1076 A space-separated list of supported methods for generating
1077 consensuses from votes. See section 3.4.1 for details. Method "1"
1078 MUST be included.
1080 "consensus-method" SP Integer NL
1082 [Exactly once for consensuses; does not occur in votes.]
1084 See section 3.4.1 for details.
1086 (Only included when the vote is generated with consensus-method 2 or
1087 later.)
1089 "published" SP YYYY-MM-DD SP HH:MM:SS NL
1091 [Exactly once for votes; does not occur in consensuses.]
1093 The publication time for this status document (if a vote).
1095 "valid-after" SP YYYY-MM-DD SP HH:MM:SS NL
1097 [Exactly once.]
1099 The start of the Interval for this vote. Before this time, the
1100 consensus document produced from this vote should not be used.
1101 See 1.4 for voting timeline information.
1103 "fresh-until" SP YYYY-MM-DD SP HH:MM:SS NL
1105 [Exactly once.]
1107 The time at which the next consensus should be produced; before this
1108 time, there is no point in downloading another consensus, since there
1109 won't be a new one. See 1.4 for voting timeline information.
1111 "valid-until" SP YYYY-MM-DD SP HH:MM:SS NL
1113 [Exactly once.]
1115 The end of the Interval for this vote. After this time, the
1116 consensus produced by this vote should not be used. See 1.4 for
1117 voting timeline information.
1119 "voting-delay" SP VoteSeconds SP DistSeconds NL
1121 [Exactly once.]
1123 VoteSeconds is the number of seconds that we will allow to collect
1124 votes from all authorities; DistSeconds is the number of seconds
1125 we'll allow to collect signatures from all authorities. See 1.4 for
1126 voting timeline information.
1128 "client-versions" SP VersionList NL
1130 [At most once.]
1132 A comma-separated list of recommended client versions, in
1133 ascending order. If absent, no opinion is held about client
1134 versions.
1136 "server-versions" SP VersionList NL
1138 [At most once.]
1140 A comma-separated list of recommended server versions, in
1141 ascending order. If absent, no opinion is held about server
1142 versions.
1144 "known-flags" SP FlagList NL
1146 [Exactly once.]
1148 A space-separated list of all of the flags that this document
1149 might contain. A flag is "known" either because the authority
1150 knows about them and might set them (if in a vote), or because
1151 enough votes were counted for the consensus for an authoritative
1152 opinion to have been formed about their status.
1154 "params" SP [Parameters] NL
1156 [At most once]
1158 Parameter ::= Keyword '=' Int32
1159 Int32 ::= A decimal integer between -2147483648 and 2147483647.
1160 Parameters ::= Parameter | Parameters SP Parameter
1162 The parameters list, if present, contains a space-separated list of
1163 case-sensitive key-value pairs, sorted in lexical order by
1164 their keyword. Each parameter has its own meaning.
1166 (Only included when the vote is generated with consensus-method 7 or
1167 later.)
1169 Commonly used "param" arguments at this point include:
1171 "circwindow" -- the default package window that circuits should
1172 be established with. It started out at 1000 cells, but some
1173 research indicates that a lower value would mean fewer cells in
1174 transit in the network at any given time. Obeyed by Tor 0.2.1.20
1175 and later.
1177 "CircuitPriorityHalflifeMsec" -- the halflife parameter used when
1178 weighting which circuit will send the next cell. Obeyed by Tor
1179 0.2.2.10-alpha and later. (Versions of Tor between 0.2.2.7-alpha
1180 and 0.2.2.10-alpha recognized a "CircPriorityHalflifeMsec" parameter,
1181 but mishandled it badly.)
1183 "perconnbwrate" and "perconnbwburst" -- if set, each relay sets
1184 up a separate token bucket for every client OR connection,
1185 and rate limits that connection indepedently. Typically left
1186 unset, except when used for performance experiments around trac
1187 entry 1750. Only honored by relays running Tor 0.2.2.16-alpha
1188 and later. (Note that relays running 0.2.2.7-alpha through
1189 0.2.2.14-alpha looked for bwconnrate and bwconnburst, but then
1190 did the wrong thing with them; see bug 1830 for details.)
1192 "refuseunknownexits" -- if set and non-zero, exit relays look at
1193 the previous hop of circuits that ask to open an exit stream,
1194 and refuse to exit if they don't recognize it as a relay. The
1195 goal is to make it harder for people to use them as one-hop
1196 proxies. See trac entry 1751 for details.
1198 See also "2.4.5. Consensus parameters governing behavior"
1199 in path-spec.txt for a series of circuit build time related
1200 consensus params.
1202 The authority section of a vote contains the following items, followed
1203 in turn by the authority's current key certificate:
1205 "dir-source" SP nickname SP identity SP address SP IP SP dirport SP
1206 orport NL
1208 [Exactly once, at start]
1210 Describes this authority. The nickname is a convenient identifier
1211 for the authority. The identity is an uppercase hex fingerprint of
1212 the authority's current (v3 authority) identity key. The address is
1213 the server's hostname. The IP is the server's current IP address,
1214 and dirport is its current directory port. XXXXorport
1216 "contact" SP string NL
1218 [At most once.]
1220 An arbitrary string describing how to contact the directory
1221 server's administrator. Administrators should include at least an
1222 email address and a PGP fingerprint.
1224 "legacy-key" SP FINGERPRINT NL
1226 [At most once]
1228 Lists a fingerprint for an obsolete _identity_ key still used
1229 by this authority to keep older clients working. This option
1230 is used to keep key around for a little while in case the
1231 authorities need to migrate many identity keys at once.
1232 (Generally, this would only happen because of a security
1233 vulnerability that affected multiple authorities, like the
1234 Debian OpenSSL RNG bug of May 2008.)
1236 The authority section of a consensus contains groups the following items,
1237 in the order given, with one group for each authority that contributed to
1238 the consensus, with groups sorted by authority identity digest:
1240 "dir-source" SP nickname SP identity SP address SP IP SP dirport SP
1241 orport NL
1243 [Exactly once, at start]
1245 As in the authority section of a vote.
1247 "contact" SP string NL
1249 [At most once.]
1251 As in the authority section of a vote.
1253 "vote-digest" SP digest NL
1255 [Exactly once.]
1257 A digest of the vote from the authority that contributed to this
1258 consensus, as signed (that is, not including the signature).
1259 (Hex, upper-case.)
1261 Each router status entry contains the following items. Router status
1262 entries are sorted in ascending order by identity digest.
1264 "r" SP nickname SP identity SP digest SP publication SP IP SP ORPort
1265 SP DirPort NL
1267 [At start, exactly once.]
1269 "Nickname" is the OR's nickname. "Identity" is a hash of its
1270 identity key, encoded in base64, with trailing equals sign(s)
1271 removed. "Digest" is a hash of its most recent descriptor as
1272 signed (that is, not including the signature), encoded in base64.
1273 "Publication" is the
1274 publication time of its most recent descriptor, in the form
1275 YYYY-MM-DD HH:MM:SS, in GMT. "IP" is its current IP address;
1276 ORPort is its current OR port, "DirPort" is it's current directory
1277 port, or "0" for "none".
1279 "s" SP Flags NL
1281 [At most once.]
1283 A series of space-separated status flags, in alphabetical order.
1284 Currently documented flags are:
1286 "Authority" if the router is a directory authority.
1287 "BadExit" if the router is believed to be useless as an exit node
1288 (because its ISP censors it, because it is behind a restrictive
1289 proxy, or for some similar reason).
1290 "BadDirectory" if the router is believed to be useless as a
1291 directory cache (because its directory port isn't working,
1292 its bandwidth is always throttled, or for some similar
1293 reason).
1294 "Exit" if the router is more useful for building
1295 general-purpose exit circuits than for relay circuits. The
1296 path building algorithm uses this flag; see path-spec.txt.
1297 "Fast" if the router is suitable for high-bandwidth circuits.
1298 "Guard" if the router is suitable for use as an entry guard.
1299 "HSDir" if the router is considered a v2 hidden service directory.
1300 "Named" if the router's identity-nickname mapping is canonical,
1301 and this authority binds names.
1302 "Stable" if the router is suitable for long-lived circuits.
1303 "Running" if the router is currently usable.
1304 "Unnamed" if another router has bound the name used by this
1305 router, and this authority binds names.
1306 "Valid" if the router has been 'validated'.
1307 "V2Dir" if the router implements the v2 directory protocol.
1308 "V3Dir" if the router implements this protocol.
1310 "v" SP version NL
1312 [At most once.]
1314 The version of the Tor protocol that this server is running. If
1315 the value begins with "Tor" SP, the rest of the string is a Tor
1316 version number, and the protocol is "The Tor protocol as supported
1317 by the given version of Tor." Otherwise, if the value begins with
1318 some other string, Tor has upgraded to a more sophisticated
1319 protocol versioning system, and the protocol is "a version of the
1320 Tor protocol more recent than any we recognize."
1322 Directory authorities SHOULD omit version strings they receive from
1323 descriptors if they would cause "v" lines to be over 128 characters
1324 long.
1326 "w" SP "Bandwidth=" INT [SP "Measured=" INT] NL
1328 [At most once.]
1330 An estimate of the bandwidth of this server, in an arbitrary
1331 unit (currently kilobytes per second). Used to weight router
1332 selection.
1334 Additionally, the Measured= keyword is present in votes by
1335 participating bandwidth measurement authorities to indicate
1336 a measured bandwidth currently produced by measuring stream
1337 capacities.
1339 Other weighting keywords may be added later.
1340 Clients MUST ignore keywords they do not recognize.
1342 "p" SP ("accept" / "reject") SP PortList NL
1344 [At most once.]
1346 PortList = PortOrRange
1347 PortList = PortList "," PortOrRange
1348 PortOrRange = INT "-" INT / INT
1350 A list of those ports that this router supports (if 'accept')
1351 or does not support (if 'reject') for exit to "most
1352 addresses".
1354 The footer section is delineated in all votes and consensuses supporting
1355 consensus method 9 and above with the following:
1357 "directory-footer" NL
1359 It contains two subsections, a bandwidths-weights line and a
1360 directory-signature.
1362 The bandwidths-weights line appears At Most Once for a consensus. It does
1363 not appear in votes.
1365 "bandwidth-weights" SP
1366 "Wbd=" INT SP "Wbe=" INT SP "Wbg=" INT SP "Wbm=" INT SP
1367 "Wdb=" INT SP
1368 "Web=" INT SP "Wed=" INT SP "Wee=" INT SP "Weg=" INT SP "Wem=" INT SP
1369 "Wgb=" INT SP "Wgd=" INT SP "Wgg=" INT SP "Wgm=" INT SP
1370 "Wmb=" INT SP "Wmd=" INT SP "Wme=" INT SP "Wmg=" INT SP "Wmm=" INT NL
1372 These values represent the weights to apply to router bandwidths during
1373 path selection. They are sorted in alphabetical order in the list. The
1374 integer values are divided by BW_WEIGHT_SCALE=10000 or the consensus
1375 param "bwweightscale". They are:
1377 Wgg - Weight for Guard-flagged nodes in the guard position
1378 Wgm - Weight for non-flagged nodes in the guard Position
1379 Wgd - Weight for Guard+Exit-flagged nodes in the guard Position
1381 Wmg - Weight for Guard-flagged nodes in the middle Position
1382 Wmm - Weight for non-flagged nodes in the middle Position
1383 Wme - Weight for Exit-flagged nodes in the middle Position
1384 Wmd - Weight for Guard+Exit flagged nodes in the middle Position
1386 Weg - Weight for Guard flagged nodes in the exit Position
1387 Wem - Weight for non-flagged nodes in the exit Position
1388 Wee - Weight for Exit-flagged nodes in the exit Position
1389 Wed - Weight for Guard+Exit-flagged nodes in the exit Position
1391 Wgb - Weight for BEGIN_DIR-supporting Guard-flagged nodes
1392 Wmb - Weight for BEGIN_DIR-supporting non-flagged nodes
1393 Web - Weight for BEGIN_DIR-supporting Exit-flagged nodes
1394 Wdb - Weight for BEGIN_DIR-supporting Guard+Exit-flagged nodes
1396 Wbg - Weight for Guard flagged nodes for BEGIN_DIR requests
1397 Wbm - Weight for non-flagged nodes for BEGIN_DIR requests
1398 Wbe - Weight for Exit-flagged nodes for BEGIN_DIR requests
1399 Wbd - Weight for Guard+Exit-flagged nodes for BEGIN_DIR requests
1401 These values are calculated as specified in Section 3.4.3.
1403 The signature contains the following item, which appears Exactly Once
1404 for a vote, and At Least Once for a consensus.
1406 "directory-signature" SP identity SP signing-key-digest NL Signature
1408 This is a signature of the status document, with the initial item
1409 "network-status-version", and the signature item
1410 "directory-signature", using the signing key. (In this case, we take
1411 the hash through the _space_ after directory-signature, not the
1412 newline: this ensures that all authorities sign the same thing.)
1413 "identity" is the hex-encoded digest of the authority identity key of
1414 the signing authority, and "signing-key-digest" is the hex-encoded
1415 digest of the current authority signing key of the signing authority.
1417 3.3. Assigning flags in a vote
1419 (This section describes how directory authorities choose which status
1420 flags to apply to routers, as of Tor 0.2.0.0-alpha-dev. Later directory
1421 authorities MAY do things differently, so long as clients keep working
1422 well. Clients MUST NOT depend on the exact behaviors in this section.)
1424 In the below definitions, a router is considered "active" if it is
1425 running, valid, and not hibernating.
1427 "Valid" -- a router is 'Valid' if it is running a version of Tor not
1428 known to be broken, and the directory authority has not blacklisted
1429 it as suspicious.
1431 "Named" -- Directory authority administrators may decide to support name
1432 binding. If they do, then they must maintain a file of
1433 nickname-to-identity-key mappings, and try to keep this file consistent
1434 with other directory authorities. If they don't, they act as clients, and
1435 report bindings made by other directory authorities (name X is bound to
1436 identity Y if at least one binding directory lists it, and no directory
1437 binds X to some other Y'.) A router is called 'Named' if the router
1438 believes the given name should be bound to the given key.
1440 Two strategies exist on the current network for deciding on
1441 values for the Named flag. In the original version, server
1442 operators were asked to send nickname-identity pairs to a
1443 mailing list of Naming directory authorities operators. The
1444 operators were then supposed to add the pairs to their
1445 mapping files; in practice, they didn't get to this often.
1447 Newer Naming authorities run a script that registers routers
1448 in their mapping files once the routers have been online at
1449 least two weeks, no other router has that nickname, and no
1450 other router has wanted the nickname for a month. If a router
1451 has not been online for six months, the router is removed.
1453 "Unnamed" -- Directory authorities that support naming should vote for a
1454 router to be 'Unnamed' if its given nickname is mapped to a different
1455 identity.
1457 "Running" -- A router is 'Running' if the authority managed to connect to
1458 it successfully within the last 30 minutes.
1460 "Stable" -- A router is 'Stable' if it is active, and either its Weighted
1461 MTBF is at least the median for known active routers or its Weighted MTBF
1462 corresponds to at least 7 days. Routers are never called Stable if they are
1463 running a version of Tor known to drop circuits stupidly. (0.1.1.10-alpha
1464 through 0.1.1.16-rc are stupid this way.)
1466 To calculate weighted MTBF, compute the weighted mean of the lengths
1467 of all intervals when the router was observed to be up, weighting
1468 intervals by $\alpha^n$, where $n$ is the amount of time that has
1469 passed since the interval ended, and $\alpha$ is chosen so that
1470 measurements over approximately one month old no longer influence the
1471 weighted MTBF much.
1473 [XXXX what happens when we have less than 4 days of MTBF info.]
1475 "Exit" -- A router is called an 'Exit' iff it allows exits to at
1476 least two of the ports 80, 443, and 6667 and allows exits to at
1477 least one /8 address space.
1479 "Fast" -- A router is 'Fast' if it is active, and its bandwidth is
1480 either in the top 7/8ths for known active routers or at least 20KB/s.
1482 "Guard" -- A router is a possible 'Guard' if its Weighted Fractional
1483 Uptime is at least the median for "familiar" active routers, and if
1484 its bandwidth is at least median or at least 250KB/s.
1486 To calculate weighted fractional uptime, compute the fraction
1487 of time that the router is up in any given day, weighting so that
1488 downtime and uptime in the past counts less.
1490 A node is 'familiar' if 1/8 of all active nodes have appeared more
1491 recently than it, OR it has been around for a few weeks.
1493 "Authority" -- A router is called an 'Authority' if the authority
1494 generating the network-status document believes it is an authority.
1496 "V2Dir" -- A router supports the v2 directory protocol if it has an open
1497 directory port, and it is running a version of the directory protocol that
1498 supports the functionality clients need. (Currently, this is
1499 0.1.1.9-alpha or later.)
1501 "V3Dir" -- A router supports the v3 directory protocol if it has an open
1502 directory port, and it is running a version of the directory protocol that
1503 supports the functionality clients need. (Currently, this is
1504 0.2.0.?????-alpha or later.)
1506 "HSDir" -- A router is a v2 hidden service directory if it stores and
1507 serves v2 hidden service descriptors and the authority managed to connect
1508 to it successfully within the last 24 hours.
1510 Directory server administrators may label some servers or IPs as
1511 blacklisted, and elect not to include them in their network-status lists.
1513 Authorities SHOULD 'disable' any servers in excess of 3 on any single IP.
1514 When there are more than 3 to choose from, authorities should first prefer
1515 authorities to non-authorities, then prefer Running to non-Running, and
1516 then prefer high-bandwidth to low-bandwidth. To 'disable' a server, the
1517 authority *should* advertise it without the Running or Valid flag.
1519 Thus, the network-status vote includes all non-blacklisted,
1520 non-expired, non-superseded descriptors.
1522 The bandwidth in a "w" line should be taken as the best estimate
1523 of the router's actual capacity that the authority has. For now,
1524 this should be the lesser of the observed bandwidth and bandwidth
1525 rate limit from the router descriptor. It is given in kilobytes
1526 per second, and capped at some arbitrary value (currently 10 MB/s).
1528 The Measured= keyword on a "w" line vote is currently computed
1529 by multiplying the previous published consensus bandwidth by the
1530 ratio of the measured average node stream capacity to the network
1531 average. If 3 or more authorities provide a Measured= keyword for
1532 a router, the authorities produce a consensus containing a "w"
1533 Bandwidth= keyword equal to the median of the Measured= votes.
1535 The ports listed in a "p" line should be taken as those ports for
1536 which the router's exit policy permits 'most' addresses, ignoring any
1537 accept not for all addresses, ignoring all rejects for private
1538 netblocks. "Most" addresses are permitted if no more than 2^25
1539 IPv4 addresses (two /8 networks) were blocked. The list is encoded
1540 as described in 3.4.2.
1542 3.4. Computing a consensus from a set of votes
1544 Given a set of votes, authorities compute the contents of the consensus
1545 document as follows:
1547 The "valid-after", "valid-until", and "fresh-until" times are taken as
1548 the median of the respective values from all the votes.
1550 The times in the "voting-delay" line are taken as the median of the
1551 VoteSeconds and DistSeconds times in the votes.
1553 Known-flags is the union of all flags known by any voter.
1555 Entries are given on the "params" line for every keyword on which any
1556 authority voted. The values given are the low-median of all votes on
1557 that keyword.
1559 "client-versions" and "server-versions" are sorted in ascending
1560 order; A version is recommended in the consensus if it is recommended
1561 by more than half of the voting authorities that included a
1562 client-versions or server-versions lines in their votes.
1564 The authority item groups (dir-source, contact, fingerprint,
1565 vote-digest) are taken from the votes of the voting
1566 authorities. These groups are sorted by the digests of the
1567 authorities identity keys, in ascending order. If the consensus
1568 method is 3 or later, a dir-source line must be included for
1569 every vote with legacy-key entry, using the legacy-key's
1570 fingerprint, the voter's ordinary nickname with the string
1571 "-legacy" appended, and all other fields as from the original
1572 vote's dir-source line.
1574 A router status entry:
1575 * is included in the result if some router status entry with the same
1576 identity is included by more than half of the authorities (total
1577 authorities, not just those whose votes we have).
1579 * For any given identity, we include at most one router status entry.
1581 * A router entry has a flag set if that is included by more than half
1582 of the authorities who care about that flag.
1584 * Two router entries are "the same" if they have the same
1585 <descriptor digest, published time, nickname, IP, ports> tuple.
1586 We choose the tuple for a given router as whichever tuple appears
1587 for that router in the most votes. We break ties first in favor of
1588 the more recently published, then in favor of smaller server
1589 descriptor digest.
1591 * The Named flag appears if it is included for this routerstatus by
1592 _any_ authority, and if all authorities that list it list the same
1593 nickname. However, if consensus-method 2 or later is in use, and
1594 any authority calls this identity/nickname pair Unnamed, then
1595 this routerstatus does not get the Named flag.
1597 * If consensus-method 2 or later is in use, the Unnamed flag is
1598 set for a routerstatus if any authorities have voted for a different
1599 identities to be Named with that nickname, or if any authority
1600 lists that nickname/ID pair as Unnamed.
1602 (With consensus-method 1, Unnamed is set like any other flag.)
1604 * The version is given as whichever version is listed by the most
1605 voters, with ties decided in favor of more recent versions.
1607 * If consensus-method 4 or later is in use, then routers that
1608 do not have the Running flag are not listed at all.
1610 * If consensus-method 5 or later is in use, then the "w" line
1611 is generated using a low-median of the bandwidth values from
1612 the votes that included "w" lines for this router.
1614 * If consensus-method 5 or later is in use, then the "p" line
1615 is taken from the votes that have the same policy summary
1616 for the descriptor we are listing. (They should all be the
1617 same. If they are not, we pick the most commonly listed
1618 one, breaking ties in favor of the lexicographically larger
1619 vote.) The port list is encoded as specified in 3.4.2.
1621 * If consensus-method 6 or later is in use and if 3 or more
1622 authorities provide a Measured= keyword in their votes for
1623 a router, the authorities produce a consensus containing a
1624 Bandwidth= keyword equal to the median of the Measured= votes.
1626 * If consensus-method 7 or later is in use, the params line is
1627 included in the output.
1629 The signatures at the end of a consensus document are sorted in
1630 ascending order by identity digest.
1632 All ties in computing medians are broken in favor of the smaller or
1633 earlier item.
1635 3.4.1. Forward compatibility
1637 Future versions of Tor will need to include new information in the
1638 consensus documents, but it is important that all authorities (or at least
1639 half) generate and sign the same signed consensus.
1641 To achieve this, authorities list in their votes their supported methods
1642 for generating consensuses from votes. Later methods will be assigned
1643 higher numbers. Currently recognized methods:
1644 "1" -- The first implemented version.
1645 "2" -- Added support for the Unnamed flag.
1646 "3" -- Added legacy ID key support to aid in authority ID key rollovers
1647 "4" -- No longer list routers that are not running in the consensus
1648 "5" -- adds support for "w" and "p" lines.
1649 "6" -- Prefers measured bandwidth values rather than advertised
1650 "7" -- Provides keyword=integer pairs of consensus parameters
1651 "8" -- Provides microdescriptor summaries
1652 "9" -- Provides weights for selecting flagged routers in paths
1653 "10" -- Fixes edge case bugs in router flag selection weights
1655 Before generating a consensus, an authority must decide which consensus
1656 method to use. To do this, it looks for the highest version number
1657 supported by more than 2/3 of the authorities voting. If it supports this
1658 method, then it uses it. Otherwise, it falls back to method 1.
1660 (The consensuses generated by new methods must be parsable by
1661 implementations that only understand the old methods, and must not cause
1662 those implementations to compromise their anonymity. This is a means for
1663 making changes in the contents of consensus; not for making
1664 backward-incompatible changes in their format.)
1666 3.4.2. Encoding port lists
1668 Whether the summary shows the list of accepted ports or the list of
1669 rejected ports depends on which list is shorter (has a shorter string
1670 representation). In case of ties we choose the list of accepted
1671 ports. As an exception to this rule an allow-all policy is
1672 represented as "accept 1-65535" instead of "reject " and a reject-all
1673 policy is similarly given as "reject 1-65535".
1675 Summary items are compressed, that is instead of "80-88,89-100" there
1676 only is a single item of "80-100", similarly instead of "20,21" a
1677 summary will say "20-21".
1679 Port lists are sorted in ascending order.
1681 The maximum allowed length of a policy summary (including the "accept "
1682 or "reject ") is 1000 characters. If a summary exceeds that length we
1683 use an accept-style summary and list as much of the port list as is
1684 possible within these 1000 bytes. [XXXX be more specific.]
1686 3.4.3. Computing Bandwidth Weights
1688 Let weight_scale = 10000
1690 Let G be the total bandwidth for Guard-flagged nodes.
1691 Let M be the total bandwidth for non-flagged nodes.
1692 Let E be the total bandwidth for Exit-flagged nodes.
1693 Let D be the total bandwidth for Guard+Exit-flagged nodes.
1694 Let T = G+M+E+D
1696 Let Wgd be the weight for choosing a Guard+Exit for the guard position.
1697 Let Wmd be the weight for choosing a Guard+Exit for the middle position.
1698 Let Wed be the weight for choosing a Guard+Exit for the exit position.
1700 Let Wme be the weight for choosing an Exit for the middle position.
1701 Let Wmg be the weight for choosing a Guard for the middle position.
1703 Let Wgg be the weight for choosing a Guard for the guard position.
1704 Let Wee be the weight for choosing an Exit for the exit position.
1706 Balanced network conditions then arise from solutions to the following
1707 system of equations:
1709 Wgg*G + Wgd*D == M + Wmd*D + Wme*E + Wmg*G (guard bw = middle bw)
1710 Wgg*G + Wgd*D == Wee*E + Wed*D (guard bw = exit bw)
1711 Wed*D + Wmd*D + Wgd*D == D (aka: Wed+Wmd+Wdg = 1)
1712 Wmg*G + Wgg*G == G (aka: Wgg = 1-Wmg)
1713 Wme*E + Wee*E == E (aka: Wee = 1-Wme)
1715 We are short 2 constraints with the above set. The remaining constraints
1716 come from examining different cases of network load. The following
1717 constraints are used in consensus method 10 and above. There are another
1718 incorrect and obsolete set of constraints used for these same cases in
1719 consensus method 9. For those, see dir-spec.txt in Tor 0.2.2.10-alpha
1720 to 0.2.2.16-alpha.
1722 Case 1: E >= T/3 && G >= T/3 (Neither Exit nor Guard Scarce)
1724 In this case, the additional two constraints are: Wmg == Wmd,
1725 Wed == 1/3.
1727 This leads to the solution:
1728 Wgd = weight_scale/3
1729 Wed = weight_scale/3
1730 Wmd = weight_scale/3
1731 Wee = (weight_scale*(E+G+M))/(3*E)
1732 Wme = weight_scale - Wee
1733 Wmg = (weight_scale*(2*G-E-M))/(3*G)
1734 Wgg = weight_scale - Wmg
1736 Case 2: E < T/3 && G < T/3 (Both are scarce)
1738 Let R denote the more scarce class (Rare) between Guard vs Exit.
1739 Let S denote the less scarce class.
1741 Subcase a: R+D < S
1743 In this subcase, we simply devote all of D bandwidth to the
1744 scarce class.
1746 Wgg = Wee = weight_scale
1747 Wmg = Wme = Wmd = 0;
1748 if E < G:
1749 Wed = weight_scale
1750 Wgd = 0
1751 else:
1752 Wed = 0
1753 Wgd = weight_scale
1755 Subcase b: R+D >= S
1757 In this case, if M <= T/3, we have enough bandwidth to try to achieve
1758 a balancing condition.
1760 Add constraints Wgg = 1, Wmd == Wgd to maximize bandwidth in the guard
1761 position while still allowing exits to be used as middle nodes:
1763 Wee = (weight_scale*(E - G + M))/E
1764 Wed = (weight_scale*(D - 2*E + 4*G - 2*M))/(3*D)
1765 Wme = (weight_scale*(G-M))/E
1766 Wmg = 0
1767 Wgg = weight_scale
1768 Wmd = (weight_scale - Wed)/2
1769 Wgd = (weight_scale - Wed)/2
1771 If this system ends up with any values out of range (ie negative, or
1772 above weight_scale), use the constraints Wgg == 1 and Wee == 1, since
1773 both those positions are scarce:
1775 Wgg = weight_scale
1776 Wee = weight_scale
1777 Wed = (weight_scale*(D - 2*E + G + M))/(3*D)
1778 Wmd = (weight_Scale*(D - 2*M + G + E))/(3*D)
1779 Wme = 0
1780 Wmg = 0
1781 Wgd = weight_scale - Wed - Wmd
1783 If M > T/3, then the Wmd weight above will become negative. Set it to 0
1784 in this case:
1785 Wmd = 0
1786 Wgd = weight_scale - Wed
1788 Case 3: One of E < T/3 or G < T/3
1790 Let S be the scarce class (of E or G).
1792 Subcase a: (S+D) < T/3:
1793 if G=S:
1794 Wgg = Wgd = weight_scale;
1795 Wmd = Wed = Wmg = 0;
1796 // Minor subcase, if E is more scarce than M,
1797 // keep its bandwidth in place.
1798 if (E < M) Wme = 0;
1799 else Wme = (weight_scale*(E-M))/(2*E);
1800 Wee = weight_scale-Wme;
1801 if E=S:
1802 Wee = Wed = weight_scale;
1803 Wmd = Wgd = Wme = 0;
1804 // Minor subcase, if G is more scarce than M,
1805 // keep its bandwidth in place.
1806 if (G < M) Wmg = 0;
1807 else Wmg = (weight_scale*(G-M))/(2*G);
1808 Wgg = weight_scale-Wmg;
1810 Subcase b: (S+D) >= T/3
1811 if G=S:
1812 Add constraints Wgg = 1, Wmd == Wed to maximize bandwidth
1813 in the guard position, while still allowing exits to be
1814 used as middle nodes:
1815 Wgg = weight_scale
1816 Wgd = (weight_scale*(D - 2*G + E + M))/(3*D)
1817 Wmg = 0
1818 Wee = (weight_scale*(E+M))/(2*E)
1819 Wme = weight_scale - Wee
1820 Wmd = (weight_scale - Wgd)/2
1821 Wed = (weight_scale - Wgd)/2
1822 if E=S:
1823 Add constraints Wee == 1, Wmd == Wgd to maximize bandwidth
1824 in the exit position:
1825 Wee = weight_scale;
1826 Wed = (weight_scale*(D - 2*E + G + M))/(3*D);
1827 Wme = 0;
1828 Wgg = (weight_scale*(G+M))/(2*G);
1829 Wmg = weight_scale - Wgg;
1830 Wmd = (weight_scale - Wed)/2;
1831 Wgd = (weight_scale - Wed)/2;
1833 To ensure consensus, all calculations are performed using integer math
1834 with a fixed precision determined by the bwweightscale consensus
1835 parameter (defaults at 10000).
1837 For future balancing improvements, Tor clients support 11 additional weights
1838 for directory requests and middle weighting. These weights are currently
1839 set at weight_scale, with the exception of the following groups of
1840 assignments:
1842 Directory requests use middle weights:
1843 Wbd=Wmd, Wbg=Wmg, Wbe=Wme, Wbm=Wmm
1845 Handle bridges and strange exit policies:
1846 Wgm=Wgg, Wem=Wee, Weg=Wed
1848 3.5. Detached signatures
1850 Assuming full connectivity, every authority should compute and sign the
1851 same consensus directory in each period. Therefore, it isn't necessary to
1852 download the consensus computed by each authority; instead, the
1853 authorities only push/fetch each others' signatures. A "detached
1854 signature" document contains items as follows:
1856 "consensus-digest" SP Digest NL
1858 [At start, at most once.]
1860 The digest of the consensus being signed.
1862 "valid-after" SP YYYY-MM-DD SP HH:MM:SS NL
1863 "fresh-until" SP YYYY-MM-DD SP HH:MM:SS NL
1864 "valid-until" SP YYYY-MM-DD SP HH:MM:SS NL
1866 [As in the consensus]
1868 "directory-signature"
1870 [As in the consensus; the signature object is the same as in the
1871 consensus document.]
1874 4. Directory server operation
1876 All directory authorities and directory caches ("directory servers")
1877 implement this section, except as noted.
1879 4.1. Accepting uploads (authorities only)
1881 When a router posts a signed descriptor to a directory authority, the
1882 authority first checks whether it is well-formed and correctly
1883 self-signed. If it is, the authority next verifies that the nickname
1884 in question is not already assigned to a router with a different
1885 public key.
1886 Finally, the authority MAY check that the router is not blacklisted
1887 because of its key, IP, or another reason.
1889 If the descriptor passes these tests, and the authority does not already
1890 have a descriptor for a router with this public key, it accepts the
1891 descriptor and remembers it.
1893 If the authority _does_ have a descriptor with the same public key, the
1894 newly uploaded descriptor is remembered if its publication time is more
1895 recent than the most recent old descriptor for that router, and either:
1896 - There are non-cosmetic differences between the old descriptor and the
1897 new one.
1898 - Enough time has passed between the descriptors' publication times.
1899 (Currently, 12 hours.)
1901 Differences between router descriptors are "non-cosmetic" if they would be
1902 sufficient to force an upload as described in section 2 above.
1904 Note that the "cosmetic difference" test only applies to uploaded
1905 descriptors, not to descriptors that the authority downloads from other
1906 authorities.
1908 When a router posts a signed extra-info document to a directory authority,
1909 the authority again checks it for well-formedness and correct signature,
1910 and checks that its matches the extra-info-digest in some router
1911 descriptor that it believes is currently useful. If so, it accepts it and
1912 stores it and serves it as requested. If not, it drops it.
1914 4.2. Voting (authorities only)
1916 Authorities divide time into Intervals. Authority administrators SHOULD
1917 try to all pick the same interval length, and SHOULD pick intervals that
1918 are commonly used divisions of time (e.g., 5 minutes, 15 minutes, 30
1919 minutes, 60 minutes, 90 minutes). Voting intervals SHOULD be chosen to
1920 divide evenly into a 24-hour day.
1922 Authorities SHOULD act according to interval and delays in the
1923 latest consensus. Lacking a latest consensus, they SHOULD default to a
1924 30-minute Interval, a 5 minute VotingDelay, and a 5 minute DistDelay.
1926 Authorities MUST take pains to ensure that their clocks remain accurate
1927 within a few seconds. (Running NTP is usually sufficient.)
1929 The first voting period of each day begins at 00:00 (midnight) GMT. If
1930 the last period of the day would be truncated by one-half or more, it is
1931 merged with the second-to-last period.
1933 An authority SHOULD publish its vote immediately at the start of each voting
1934 period (minus VoteSeconds+DistSeconds). It does this by making it
1935 available at
1936 http://<hostname>/tor/status-vote/next/authority.z
1937 and sending it in an HTTP POST request to each other authority at the URL
1938 http://<hostname>/tor/post/vote
1940 If, at the start of the voting period, minus DistSeconds, an authority
1941 does not have a current statement from another authority, the first
1942 authority downloads the other's statement.
1944 Once an authority has a vote from another authority, it makes it available
1945 at
1946 http://<hostname>/tor/status-vote/next/<fp>.z
1947 where <fp> is the fingerprint of the other authority's identity key.
1948 And at
1949 http://<hostname>/tor/status-vote/next/d/<d>.z
1950 where <d> is the digest of the vote document.
1952 The consensus status, along with as many signatures as the server
1953 currently knows, should be available at
1954 http://<hostname>/tor/status-vote/next/consensus.z
1955 All of the detached signatures it knows for consensus status should be
1956 available at:
1957 http://<hostname>/tor/status-vote/next/consensus-signatures.z
1959 Once there are enough signatures, or once the voting period starts,
1960 these documents are available at
1961 http://<hostname>/tor/status-vote/current/consensus.z
1962 and
1963 http://<hostname>/tor/status-vote/current/consensus-signatures.z
1964 [XXX current/consensus-signatures is not currently implemented, as it
1965 is not used in the voting protocol.]
1967 The other vote documents are analogously made available under
1968 http://<hostname>/tor/status-vote/current/authority.z
1969 http://<hostname>/tor/status-vote/current/<fp>.z
1970 http://<hostname>/tor/status-vote/current/d/<d>.z
1971 once the consensus is complete.
1973 Once an authority has computed and signed a consensus network status, it
1974 should send its detached signature to each other authority in an HTTP POST
1975 request to the URL:
1976 http://<hostname>/tor/post/consensus-signature
1978 [XXX Note why we support push-and-then-pull.]
1980 [XXX possible future features include support for downloading old
1981 consensuses.]
1983 4.3. Downloading consensus status documents (caches only)
1985 All directory servers (authorities and caches) try to keep a recent
1986 network-status consensus document to serve to clients. A cache ALWAYS
1987 downloads a network-status consensus if any of the following are true:
1988 - The cache has no consensus document.
1989 - The cache's consensus document is no longer valid.
1990 Otherwise, the cache downloads a new consensus document at a randomly
1991 chosen time in the first half-interval after its current consensus
1992 stops being fresh. (This time is chosen at random to avoid swarming
1993 the authorities at the start of each period. The interval size is
1994 inferred from the difference between the valid-after time and the
1995 fresh-until time on the consensus.)
1997 [For example, if a cache has a consensus that became valid at 1:00,
1998 and is fresh until 2:00, that cache will fetch a new consensus at
1999 a random time between 2:00 and 2:30.]
2001 4.4. Downloading and storing router descriptors (authorities and caches)
2003 Periodically (currently, every 10 seconds), directory servers check
2004 whether there are any specific descriptors that they do not have and that
2005 they are not currently trying to download. Caches identify these
2006 descriptors by hash in the recent network-status consensus documents;
2007 authorities identify them by hash in vote (if publication date is more
2008 recent than the descriptor we currently have).
2010 [XXXX need a way to fetch descriptors ahead of the vote? v2 status docs can
2011 do that for now.]
2013 If so, the directory server launches requests to the authorities for these
2014 descriptors, such that each authority is only asked for descriptors listed
2015 in its most recent vote (if the requester is an authority) or in the
2016 consensus (if the requester is a cache). If we're an authority, and more
2017 than one authority lists the descriptor, we choose which to ask at random.
2019 If one of these downloads fails, we do not try to download that descriptor
2020 from the authority that failed to serve it again unless we receive a newer
2021 network-status (consensus or vote) from that authority that lists the same
2022 descriptor.
2024 Directory servers must potentially cache multiple descriptors for each
2025 router. Servers must not discard any descriptor listed by any recent
2026 consensus. If there is enough space to store additional descriptors,
2027 servers SHOULD try to hold those which clients are likely to download the
2028 most. (Currently, this is judged based on the interval for which each
2029 descriptor seemed newest.)
2030 [XXXX define recent]
2032 Authorities SHOULD NOT download descriptors for routers that they would
2033 immediately reject for reasons listed in 3.1.
2035 4.5. Downloading and storing extra-info documents
2037 All authorities, and any cache that chooses to cache extra-info documents,
2038 and any client that uses extra-info documents, should implement this
2039 section.
2041 Note that generally, clients don't need extra-info documents.
2043 Periodically, the Tor instance checks whether it is missing any extra-info
2044 documents: in other words, if it has any router descriptors with an
2045 extra-info-digest field that does not match any of the extra-info
2046 documents currently held. If so, it downloads whatever extra-info
2047 documents are missing. Caches download from authorities; non-caches try
2048 to download from caches. We follow the same splitting and back-off rules
2049 as in 4.4 (if a cache) or 5.3 (if a client).
2051 4.6. General-use HTTP URLs
2053 "Fingerprints" in these URLs are base-16-encoded SHA1 hashes.
2055 The most recent v3 consensus should be available at:
2056 http://<hostname>/tor/status-vote/current/consensus.z
2058 Starting with Tor version 0.2.1.1-alpha is also available at:
2059 http://<hostname>/tor/status-vote/current/consensus/<F1>+<F2>+<F3>.z
2061 Where F1, F2, etc. are authority identity fingerprints the client trusts.
2062 Servers will only return a consensus if more than half of the requested
2063 authorities have signed the document, otherwise a 404 error will be sent
2064 back. The fingerprints can be shortened to a length of any multiple of
2065 two, using only the leftmost part of the encoded fingerprint. Tor uses
2066 3 bytes (6 hex characters) of the fingerprint.
2068 Clients SHOULD sort the fingerprints in ascending order. Server MUST
2069 accept any order.
2071 Clients SHOULD use this format when requesting consensus documents from
2072 directory authority servers and from caches running a version of Tor
2073 that is known to support this URL format.
2075 A concatenated set of all the current key certificates should be available
2076 at:
2077 http://<hostname>/tor/keys/all.z
2079 The key certificate for this server (if it is an authority) should be
2080 available at:
2081 http://<hostname>/tor/keys/authority.z
2083 The key certificate for an authority whose authority identity fingerprint
2084 is <F> should be available at:
2085 http://<hostname>/tor/keys/fp/<F>.z
2087 The key certificate whose signing key fingerprint is <F> should be
2088 available at:
2089 http://<hostname>/tor/keys/sk/<F>.z
2091 The key certificate whose identity key fingerprint is <F> and whose signing
2092 key fingerprint is <S> should be available at:
2094 http://<hostname>/tor/keys/fp-sk/<F>-<S>.z
2096 (As usual, clients may request multiple certificates using:
2097 http://<hostname>/tor/keys/fp-sk/<F1>-<S1>+<F2>-<S2>.z )
2098 [The above fp-sk format was not supported before Tor 0.2.1.9-alpha.]
2100 The most recent descriptor for a server whose identity key has a
2101 fingerprint of <F> should be available at:
2102 http://<hostname>/tor/server/fp/<F>.z
2104 The most recent descriptors for servers with identity fingerprints
2105 <F1>,<F2>,<F3> should be available at:
2106 http://<hostname>/tor/server/fp/<F1>+<F2>+<F3>.z
2108 (NOTE: Implementations SHOULD NOT download descriptors by identity key
2109 fingerprint. This allows a corrupted server (in collusion with a cache) to
2110 provide a unique descriptor to a client, and thereby partition that client
2111 from the rest of the network.)
2113 The server descriptor with (descriptor) digest <D> (in hex) should be
2114 available at:
2115 http://<hostname>/tor/server/d/<D>.z
2117 The most recent descriptors with digests <D1>,<D2>,<D3> should be
2118 available at:
2119 http://<hostname>/tor/server/d/<D1>+<D2>+<D3>.z
2121 The most recent descriptor for this server should be at:
2122 http://<hostname>/tor/server/authority.z
2123 [Nothing in the Tor protocol uses this resource yet, but it is useful
2124 for debugging purposes. Also, the official Tor implementations
2125 (starting at 0.1.1.x) use this resource to test whether a server's
2126 own DirPort is reachable.]
2128 A concatenated set of the most recent descriptors for all known servers
2129 should be available at:
2130 http://<hostname>/tor/server/all.z
2132 Extra-info documents are available at the URLS
2133 http://<hostname>/tor/extra/d/...
2134 http://<hostname>/tor/extra/fp/...
2135 http://<hostname>/tor/extra/all[.z]
2136 http://<hostname>/tor/extra/authority[.z]
2137 (As for /tor/server/ URLs: supports fetching extra-info
2138 documents by their digest, by the fingerprint of their servers,
2139 or all at once. When serving by fingerprint, we serve the
2140 extra-info that corresponds to the descriptor we would serve by
2141 that fingerprint. Only directory authorities of version
2142 0.2.0.1-alpha or later are guaranteed to support the first
2143 three classes of URLs. Caches may support them, and MUST
2144 support them if they have advertised "caches-extra-info".)
2146 For debugging, directories SHOULD expose non-compressed objects at URLs like
2147 the above, but without the final ".z".
2148 Clients MUST handle compressed concatenated information in two forms:
2149 - A concatenated list of zlib-compressed objects.
2150 - A zlib-compressed concatenated list of objects.
2151 Directory servers MAY generate either format: the former requires less
2152 CPU, but the latter requires less bandwidth.
2154 Clients SHOULD use upper case letters (A-F) when base16-encoding
2155 fingerprints. Servers MUST accept both upper and lower case fingerprints
2156 in requests.
2158 5. Client operation: downloading information
2160 Every Tor that is not a directory server (that is, those that do
2161 not have a DirPort set) implements this section.
2163 5.1. Downloading network-status documents
2165 Each client maintains a list of directory authorities. Insofar as
2166 possible, clients SHOULD all use the same list.
2168 Clients try to have a live consensus network-status document at all times.
2169 A network-status document is "live" if the time in its valid-until field
2170 has not passed.
2172 If a client is missing a live network-status document, it tries to fetch
2173 it from a directory cache (or from an authority if it knows no caches).
2174 On failure, the client waits briefly, then tries that network-status
2175 document again from another cache. The client does not build circuits
2176 until it has a live network-status consensus document, and it has
2177 descriptors for more than 1/4 of the routers that it believes are running.
2179 (Note: clients can and should pick caches based on the network-status
2180 information they have: once they have first fetched network-status info
2181 from an authority, they should not need to go to the authority directly
2182 again.)
2184 To avoid swarming the caches whenever a consensus expires, the
2185 clients download new consensuses at a randomly chosen time after the
2186 caches are expected to have a fresh consensus, but before their
2187 consensus will expire. (This time is chosen uniformly at random from
2188 the interval between the time 3/4 into the first interval after the
2189 consensus is no longer fresh, and 7/8 of the time remaining after
2190 that before the consensus is invalid.)
2192 [For example, if a cache has a consensus that became valid at 1:00,
2193 and is fresh until 2:00, and expires at 4:00, that cache will fetch
2194 a new consensus at a random time between 2:45 and 3:50, since 3/4
2195 of the one-hour interval is 45 minutes, and 7/8 of the remaining 75
2196 minutes is 65 minutes.]
2198 5.2. Downloading and storing router descriptors
2200 Clients try to have the best descriptor for each router. A descriptor is
2201 "best" if:
2202 * It is listed in the consensus network-status document.
2204 Periodically (currently every 10 seconds) clients check whether there are
2205 any "downloadable" descriptors. A descriptor is downloadable if:
2206 - It is the "best" descriptor for some router.
2207 - The descriptor was published at least 10 minutes in the past.
2208 (This prevents clients from trying to fetch descriptors that the
2209 mirrors have probably not yet retrieved and cached.)
2210 - The client does not currently have it.
2211 - The client is not currently trying to download it.
2212 - The client would not discard it immediately upon receiving it.
2213 - The client thinks it is running and valid (see 6.1 below).
2215 If at least 16 known routers have downloadable descriptors, or if
2216 enough time (currently 10 minutes) has passed since the last time the
2217 client tried to download descriptors, it launches requests for all
2218 downloadable descriptors, as described in 5.3 below.
2220 When a descriptor download fails, the client notes it, and does not
2221 consider the descriptor downloadable again until a certain amount of time
2222 has passed. (Currently 0 seconds for the first failure, 60 seconds for the
2223 second, 5 minutes for the third, 10 minutes for the fourth, and 1 day
2224 thereafter.) Periodically (currently once an hour) clients reset the
2225 failure count.
2227 Clients retain the most recent descriptor they have downloaded for each
2228 router so long as it is not too old (currently, 48 hours), OR so long as
2229 no better descriptor has been downloaded for the same router.
2231 [Versions of Tor before 0.1.2.3-alpha would discard descriptors simply for
2232 being published too far in the past.] [The code seems to discard
2233 descriptors in all cases after they're 5 days old. True? -RD]
2235 5.3. Managing downloads
2237 When a client has no consensus network-status document, it downloads it
2238 from a randomly chosen authority. In all other cases, the client
2239 downloads from caches randomly chosen from among those believed to be V2
2240 directory servers. (This information comes from the network-status
2241 documents; see 6 below.)
2243 When downloading multiple router descriptors, the client chooses multiple
2244 mirrors so that:
2245 - At least 3 different mirrors are used, except when this would result
2246 in more than one request for under 4 descriptors.
2247 - No more than 128 descriptors are requested from a single mirror.
2248 - Otherwise, as few mirrors as possible are used.
2249 After choosing mirrors, the client divides the descriptors among them
2250 randomly.
2252 After receiving any response client MUST discard any network-status
2253 documents and descriptors that it did not request.
2255 6. Using directory information
2257 Everyone besides directory authorities uses the approaches in this section
2258 to decide which servers to use and what their keys are likely to be.
2259 (Directory authorities just believe their own opinions, as in 3.1 above.)
2261 6.1. Choosing routers for circuits.
2263 Circuits SHOULD NOT be built until the client has enough directory
2264 information: a live consensus network status [XXXX fallback?] and
2265 descriptors for at least 1/4 of the servers believed to be running.
2267 A server is "listed" if it is included by the consensus network-status
2268 document. Clients SHOULD NOT use unlisted servers.
2270 These flags are used as follows:
2272 - Clients SHOULD NOT use non-'Valid' or non-'Running' routers unless
2273 requested to do so.
2275 - Clients SHOULD NOT use non-'Fast' routers for any purpose other than
2276 very-low-bandwidth circuits (such as introduction circuits).
2278 - Clients SHOULD NOT use non-'Stable' routers for circuits that are
2279 likely to need to be open for a very long time (such as those used for
2280 IRC or SSH connections).
2282 - Clients SHOULD NOT choose non-'Guard' nodes when picking entry guard
2283 nodes.
2285 - Clients SHOULD NOT download directory information from non-'V2Dir'
2286 caches.
2288 See the "path-spec.txt" document for more details.
2290 6.2. Managing naming
2292 In order to provide human-memorable names for individual server
2293 identities, some directory servers bind names to IDs. Clients handle
2294 names in two ways:
2296 When a client encounters a name it has not mapped before:
2298 If the consensus lists any router with that name as "Named", or if
2299 consensus-method 2 or later is in use and the consensus lists any
2300 router with that name as having the "Unnamed" flag, then the name is
2301 bound. (It's bound to the ID listed in the entry with the Named,
2302 or to an unknown ID if no name is found.)
2304 When the user refers to a bound name, the implementation SHOULD provide
2305 only the router with ID bound to that name, and no other router, even
2306 if the router with the right ID can't be found.
2308 When a user tries to refer to a non-bound name, the implementation SHOULD
2309 warn the user. After warning the user, the implementation MAY use any
2310 router that advertises the name.
2312 Not every router needs a nickname. When a router doesn't configure a
2313 nickname, it publishes with the default nickname "Unnamed". Authorities
2314 SHOULD NOT ever mark a router with this nickname as Named; client software
2315 SHOULD NOT ever use a router in response to a user request for a router
2316 called "Unnamed".
2318 6.3. Software versions
2320 An implementation of Tor SHOULD warn when it has fetched a consensus
2321 network-status, and it is running a software version not listed.
2323 6.4. Warning about a router's status.
2325 If a router tries to publish its descriptor to a Naming authority
2326 that has its nickname mapped to another key, the router SHOULD
2327 warn the operator that it is either using the wrong key or is using
2328 an already claimed nickname.
2330 If a router has fetched a consensus document,, and the
2331 authorities do not publish a binding for the router's nickname, the
2332 router MAY remind the operator that the chosen nickname is not
2333 bound to this key at the authorities, and suggest contacting the
2334 authority operators.
2336 ...
2338 6.5. Router protocol versions
2340 A client should believe that a router supports a given feature if that
2341 feature is supported by the router or protocol versions in more than half
2342 of the live networkstatuses' "v" entries for that router. In other words,
2343 if the "v" entries for some router are:
2344 v Tor 0.0.8pre1 (from authority 1)
2345 v Tor 0.1.2.11 (from authority 2)
2346 v FutureProtocolDescription 99 (from authority 3)
2347 then the client should believe that the router supports any feature
2348 supported by 0.1.2.11.
2350 This is currently equivalent to believing the median declared version for
2351 a router in all live networkstatuses.
2353 7. Standards compliance
2355 All clients and servers MUST support HTTP 1.0. Clients and servers MAY
2356 support later versions of HTTP as well.
2358 7.1. HTTP headers
2360 Servers MAY set the Content-Length: header. Servers SHOULD set
2361 Content-Encoding to "deflate" or "identity".
2363 Servers MAY include an X-Your-Address-Is: header, whose value is the
2364 apparent IP address of the client connecting to them (as a dotted quad).
2365 For directory connections tunneled over a BEGIN_DIR stream, servers SHOULD
2366 report the IP from which the circuit carrying the BEGIN_DIR stream reached
2367 them. [Servers before version 0.1.2.5-alpha reported 127.0.0.1 for all
2368 BEGIN_DIR-tunneled connections.]
2370 Servers SHOULD disable caching of multiple network statuses or multiple
2371 router descriptors. Servers MAY enable caching of single descriptors,
2372 single network statuses, the list of all router descriptors, a v1
2373 directory, or a v1 running routers document. XXX mention times.
2375 7.2. HTTP status codes
2377 Tor delivers the following status codes. Some were chosen without much
2378 thought; other code SHOULD NOT rely on specific status codes yet.
2380 200 -- the operation completed successfully
2381 -- the user requested statuses or serverdescs, and none of the ones we
2382 requested were found (0.2.0.4-alpha and earlier).
2384 304 -- the client specified an if-modified-since time, and none of the
2385 requested resources have changed since that time.
2387 400 -- the request is malformed, or
2388 -- the URL is for a malformed variation of one of the URLs we support,
2389 or
2390 -- the client tried to post to a non-authority, or
2391 -- the authority rejected a malformed posted document, or
2393 404 -- the requested document was not found.
2394 -- the user requested statuses or serverdescs, and none of the ones
2395 requested were found (0.2.0.5-alpha and later).
2397 503 -- we are declining the request in order to save bandwidth
2398 -- user requested some items that we ordinarily generate or store,
2399 but we do not have any available.
2401 9. Backward compatibility and migration plans
2403 Until Tor versions before 0.1.1.x are completely obsolete, directory
2404 authorities should generate, and mirrors should download and cache, v1
2405 directories and running-routers lists, and allow old clients to download
2406 them. These documents and the rules for retrieving, serving, and caching
2407 them are described in dir-spec-v1.txt.
2409 Until Tor versions before 0.2.0.x are completely obsolete, directory
2410 authorities should generate, mirrors should download and cache, v2
2411 network-status documents, and allow old clients to download them.
2412 Additionally, all directory servers and caches should download, store, and
2413 serve any router descriptor that is required because of v2 network-status
2414 documents. These documents and the rules for retrieving, serving, and
2415 caching them are described in dir-spec-v1.txt.
2417 A. Consensus-negotiation timeline.
2419 Period begins: this is the Published time.
2420 Everybody sends votes
2421 Reconciliation: everybody tries to fetch missing votes.
2422 consensus may exist at this point.
2423 End of voting period:
2424 everyone swaps signatures.
2425 Now it's okay for caches to download
2426 Now it's okay for clients to download.
2428 Valid-after/valid-until switchover