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Diffstat (limited to 'doc/spec')
| -rw-r--r-- | doc/spec/dir-spec-v2.txt | 888 | ||||
| -rw-r--r-- | doc/spec/dir-spec.txt | 828 |
2 files changed, 1530 insertions, 186 deletions
diff --git a/doc/spec/dir-spec-v2.txt b/doc/spec/dir-spec-v2.txt new file mode 100644 index 000000000..139c51162 --- /dev/null +++ b/doc/spec/dir-spec-v2.txt @@ -0,0 +1,888 @@ +$Id$ + + Tor directory protocol, version 2 + +0. Scope and preliminaries + + This directory protocol is used by Tor version 0.1.1.x and later. See + dir-spec-v1.txt for information on earlier versions. + +0.1. Goals and motivation + + There were several problems with the way Tor handles directory information + in version 0.1.0.x and earlier. Here are the problems we try to fix with + this new design, already implemented in 0.1.1.x: + 1. Directories were very large and use up a lot of bandwidth: clients + downloaded descriptors for all router several times an hour. + 2. Every directory authority was a trust bottleneck: if a single + directory authority lied, it could make clients believe for a time an + arbitrarily distorted view of the Tor network. + 3. Our current "verified server" system is kind of nonsensical. + + 4. Getting more directory authorities would add more points of failure + and worsen possible partitioning attacks. + + There are two problems that remain unaddressed by this design. + 5. Requiring every client to know about every router won't scale. + 6. Requiring every directory cache to know every router won't scale. + + We attempt to fix 1-4 here, and to build a solution that will work when we + figure out an answer for 5. We haven't thought at all about what to do + about 6. + +1. Outline + + There is a small set (say, around 10) of semi-trusted directory + authorities. A default list of authorities is shipped with the Tor + software. Users can change this list, but are encouraged not to do so, in + order to avoid partitioning attacks. + + Routers periodically upload signed "descriptors" to the directory + authorities describing their keys, capabilities, and other information. + Routers may act as directory mirrors (also called "caches"), to reduce + load on the directory authorities. They announce this in their + descriptors. + + Each directory authority periodically generates and signs a compact + "network status" document that lists that authority's view of the current + descriptors and status for known routers, but which does not include the + descriptors themselves. + + Directory mirrors download, cache, and re-serve network-status documents + to clients. + + Clients, directory mirrors, and directory authorities all use + network-status documents to find out when their list of routers is + out-of-date. If it is, they download any missing router descriptors. + Clients download missing descriptors from mirrors; mirrors and authorities + download from authorities. Descriptors are downloaded by the hash of the + descriptor, not by the server's identity key: this prevents servers from + attacking clients by giving them descriptors nobody else uses. + + All directory information is uploaded and downloaded with HTTP. + + Coordination among directory authorities is done client-side: clients + compute a vote-like algorithm among the network-status documents they + have, and base their decisions on the result. + +1.1. What's different from 0.1.0.x? + + Clients used to download a signed concatenated set of router descriptors + (called a "directory") from directory mirrors, regardless of which + descriptors had changed. + + Between downloading directories, clients would download "network-status" + documents that would list which servers were supposed to running. + + Clients would always believe the most recently published network-status + document they were served. + + Routers used to upload fresh descriptors all the time, whether their keys + and other information had changed or not. + +1.2. Document meta-format + + Router descriptors, directories, and running-routers documents all obey the + following lightweight extensible information format. + + The highest level object is a Document, which consists of one or more + Items. Every Item begins with a KeywordLine, followed by one or more + Objects. A KeywordLine begins with a Keyword, optionally followed by + whitespace and more non-newline characters, and ends with a newline. A + Keyword is a sequence of one or more characters in the set [A-Za-z0-9-]. + An Object is a block of encoded data in pseudo-Open-PGP-style + armor. (cf. RFC 2440) + + More formally: + + Document ::= (Item | NL)+ + Item ::= KeywordLine Object* + KeywordLine ::= Keyword NL | Keyword WS ArgumentsChar+ NL + Keyword = KeywordChar+ + KeywordChar ::= 'A' ... 'Z' | 'a' ... 'z' | '0' ... '9' | '-' + ArgumentChar ::= any printing ASCII character except NL. + WS = (SP | TAB)+ + Object ::= BeginLine Base-64-encoded-data EndLine + BeginLine ::= "-----BEGIN " Keyword "-----" NL + EndLine ::= "-----END " Keyword "-----" NL + + The BeginLine and EndLine of an Object must use the same keyword. + + When interpreting a Document, software MUST ignore any KeywordLine that + starts with a keyword it doesn't recognize; future implementations MUST NOT + require current clients to understand any KeywordLine not currently + described. + + The "opt" keyword was used until Tor 0.1.2.5-alpha for non-critical future + extensions. All implementations MUST ignore any item of the form "opt + keyword ....." when they would not recognize "keyword ....."; and MUST + treat "opt keyword ....." as synonymous with "keyword ......" when keyword + is recognized. + + Implementations before 0.1.2.5-alpha rejected any document with a + KeywordLine that started with a keyword that they didn't recognize. + Implementations MUST prefix items not recognized by older versions of Tor + with an "opt" until those versions of Tor are obsolete. + + Other implementations that want to extend Tor's directory format MAY + introduce their own items. The keywords for extension items SHOULD start + with the characters "x-" or "X-", to guarantee that they will not conflict + with keywords used by future versions of Tor. + +2. Router operation + + ORs SHOULD generate a new router descriptor whenever any of the + following events have occurred: + + - A period of time (18 hrs by default) has passed since the last + time a descriptor was generated. + + - A descriptor field other than bandwidth or uptime has changed. + + - Bandwidth has changed by more than +/- 50% from the last time a + descriptor was generated, and at least a given interval of time + (20 mins by default) has passed since then. + + - Its uptime has been reset (by restarting). + + After generating a descriptor, ORs upload it to every directory + authority they know, by posting it to the URL + + http://<hostname:port>/tor/ + +2.1. Router descriptor format + + Every router descriptor MUST start with a "router" Item; MUST end with a + "router-signature" Item and an extra NL; and MUST contain exactly one + instance of each of the following Items: "published" "onion-key" + "signing-key" "bandwidth". + + A router descriptor MAY have zero or one of each of the following Items, + but MUST NOT have more than one: "contact", "uptime", "fingerprint", + "hibernating", "read-history", "write-history", "eventdns", "platform", + "family". + + Additionally, a router descriptor MAY contain any number of "accept", + "reject", and "opt" Items. Other than "router" and "router-signature", + the items may appear in any order. + + The items' formats are as follows: + "router" nickname address ORPort SocksPort DirPort + + Indicates the beginning of a router descriptor. "address" must be an + IPv4 address in dotted-quad format. The last three numbers indicate + the TCP ports at which this OR exposes functionality. ORPort is a port + at which this OR accepts TLS connections for the main OR protocol; + SocksPort is deprecated and should always be 0; and DirPort is the + port at which this OR accepts directory-related HTTP connections. If + any port is not supported, the value 0 is given instead of a port + number. + + "bandwidth" bandwidth-avg bandwidth-burst bandwidth-observed + + Estimated bandwidth for this router, in bytes per second. The + "average" bandwidth is the volume per second that the OR is willing to + sustain over long periods; the "burst" bandwidth is the volume that + the OR is willing to sustain in very short intervals. The "observed" + value is an estimate of the capacity this server can handle. The + server remembers the max bandwidth sustained output over any ten + second period in the past day, and another sustained input. The + "observed" value is the lesser of these two numbers. + + "platform" string + + A human-readable string describing the system on which this OR is + running. This MAY include the operating system, and SHOULD include + the name and version of the software implementing the Tor protocol. + + "published" YYYY-MM-DD HH:MM:SS + + The time, in GMT, when this descriptor was generated. + + "fingerprint" + + A fingerprint (a HASH_LEN-byte of asn1 encoded public key, encoded in + hex, with a single space after every 4 characters) for this router's + identity key. A descriptor is considered invalid (and MUST be + rejected) if the fingerprint line does not match the public key. + + [We didn't start parsing this line until Tor 0.1.0.6-rc; it should + be marked with "opt" until earlier versions of Tor are obsolete.] + + "hibernating" 0|1 + + If the value is 1, then the Tor server was hibernating when the + descriptor was published, and shouldn't be used to build circuits. + + [We didn't start parsing this line until Tor 0.1.0.6-rc; it should be + marked with "opt" until earlier versions of Tor are obsolete.] + + "uptime" + + The number of seconds that this OR process has been running. + + "onion-key" NL a public key in PEM format + + This key is used to encrypt EXTEND cells for this OR. The key MUST be + accepted for at least 1 week after any new key is published in a + subsequent descriptor. + + "signing-key" NL a public key in PEM format + + The OR's long-term identity key. + + "accept" exitpattern + "reject" exitpattern + + These lines describe the rules that an OR follows when + deciding whether to allow a new stream to a given address. The + 'exitpattern' syntax is described below. The rules are considered in + order; if no rule matches, the address will be accepted. For clarity, + the last such entry SHOULD be accept *:* or reject *:*. + + "router-signature" NL Signature NL + + The "SIGNATURE" object contains a signature of the PKCS1-padded + hash of the entire router descriptor, taken from the beginning of the + "router" line, through the newline after the "router-signature" line. + The router descriptor is invalid unless the signature is performed + with the router's identity key. + + "contact" info NL + + Describes a way to contact the server's administrator, preferably + including an email address and a PGP key fingerprint. + + "family" names NL + + 'Names' is a space-separated list of server nicknames or + hexdigests. If two ORs list one another in their "family" entries, + then OPs should treat them as a single OR for the purpose of path + selection. + + For example, if node A's descriptor contains "family B", and node B's + descriptor contains "family A", then node A and node B should never + be used on the same circuit. + + "read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL + "write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL + + Declare how much bandwidth the OR has used recently. Usage is divided + into intervals of NSEC seconds. The YYYY-MM-DD HH:MM:SS field + defines the end of the most recent interval. The numbers are the + number of bytes used in the most recent intervals, ordered from + oldest to newest. + + [We didn't start parsing these lines until Tor 0.1.0.6-rc; they should + be marked with "opt" until earlier versions of Tor are obsolete.] + + "eventdns" bool NL + + Declare whether this version of Tor is using the newer enhanced + dns logic. Versions of Tor without eventdns SHOULD NOT be used for + reverse hostname lookups. + + [All versions of Tor before 0.1.2.2-alpha should be assumed to have + this option set to 0 if it is not present. All Tor versions at + 0.1.2.2-alpha or later should be assumed to have this option set to + 1 if it is not present. Until 0.1.2.1-alpha-dev, this option was + not generated, even when eventdns was in use. Versions of Tor + before 0.1.2.1-alpha-dev did not parse this option, so it should be + marked "opt". With some future version, the old 'dnsworker' logic + will be removed, rendering this option of historical interest only.] + +2.2. Nonterminals in router descriptors + + nickname ::= between 1 and 19 alphanumeric characters, case-insensitive. + hexdigest ::= a '$', followed by 20 hexadecimal characters. + [Represents a server by the digest of its identity key.] + + exitpattern ::= addrspec ":" portspec + portspec ::= "*" | port | port "-" port + port ::= an integer between 1 and 65535, inclusive. + [Some implementations incorrectly generate ports with value 0. + Implementations SHOULD accept this, and SHOULD NOT generate it.] + + addrspec ::= "*" | ip4spec | ip6spec + ipv4spec ::= ip4 | ip4 "/" num_ip4_bits | ip4 "/" ip4mask + ip4 ::= an IPv4 address in dotted-quad format + ip4mask ::= an IPv4 mask in dotted-quad format + num_ip4_bits ::= an integer between 0 and 32 + ip6spec ::= ip6 | ip6 "/" num_ip6_bits + ip6 ::= an IPv6 address, surrounded by square brackets. + num_ip6_bits ::= an integer between 0 and 128 + + bool ::= "0" | "1" + + Ports are required; if they are not included in the router + line, they must appear in the "ports" lines. + +3. Network status format + + Directory authorities generate, sign, and compress network-status + documents. Directory servers SHOULD generate a fresh network-status + document when the contents of such a document would be different from the + last one generated, and some time (at least one second, possibly longer) + has passed since the last one was generated. + + The network status document contains a preamble, a set of router status + entries, and a signature, in that order. + + We use the same meta-format as used for directories and router descriptors + in "tor-spec.txt". Implementations MAY insert blank lines + for clarity between sections; these blank lines are ignored. + Implementations MUST NOT depend on blank lines in any particular location. + + As used here, "whitespace" is a sequence of 1 or more tab or space + characters. + + The preamble contains: + + "network-status-version" -- A document format version. For this + specification, the version is "2". + "dir-source" -- The authority's hostname, current IP address, and + directory port, all separated by whitespace. + "fingerprint" -- A base16-encoded hash of the signing key's + fingerprint, with no additional spaces added. + "contact" -- An arbitrary string describing how to contact the + directory server's administrator. Administrators should include at + least an email address and a PGP fingerprint. + "dir-signing-key" -- The directory server's public signing key. + "client-versions" -- A comma-separated list of recommended client + versions. + "server-versions" -- A comma-separated list of recommended server + versions. + "published" -- The publication time for this network-status object. + "dir-options" -- A set of flags, in any order, separated by whitespace: + "Names" if this directory authority performs name bindings. + "Versions" if this directory authority recommends software versions. + "BadExits" if the directory authority flags nodes that it believes + are performing incorrectly as exit nodes. + "BadDirectories" if the directory authority flags nodes that it + believes are performing incorrectly as directory caches. + + The dir-options entry is optional. The "-versions" entries are required if + the "Versions" flag is present. The other entries are required and must + appear exactly once. The "network-status-version" entry must appear first; + the others may appear in any order. Implementations MUST ignore + additional arguments to the items above, and MUST ignore unrecognized + flags. + + For each router, the router entry contains: (This format is designed for + conciseness.) + + "r" -- followed by the following elements, in order, separated by + whitespace: + - The OR's nickname, + - A hash of its identity key, encoded in base64, with trailing = + signs removed. + - A hash of its most recent descriptor, encoded in base64, with + trailing = signs removed. (The hash is calculated as for + computing the signature of a descriptor.) + - The publication time of its most recent descriptor, in the form + YYYY-MM-DD HH:MM:SS, in GMT. + - An IP address + - An OR port + - A directory port (or "0" for none") + "s" -- A series of whitespace-separated status flags, in any order: + "Authority" if the router is a directory authority. + "BadExit" if the router is believed to be useless as an exit node + (because its ISP censors it, because it is behind a restrictive + proxy, or for some similar reason). + "BadDirectory" if the router is believed to be useless as a + directory cache (because its directory port isn't working, + its bandwidth is always throttled, or for some similar + reason). + "Exit" if the router is useful for building general-purpose exit + circuits. + "Fast" if the router is suitable for high-bandwidth circuits. + "Guard" if the router is suitable for use as an entry guard. + "Named" if the router's identity-nickname mapping is canonical, + and this authority binds names. + "Stable" if the router is suitable for long-lived circuits. + "Running" if the router is currently usable. + "Valid" if the router has been 'validated'. + "V2Dir" if the router implements this protocol. + "v" -- The version of the Tor protocol that this server is running. If + the value begins with "Tor" SP, the rest of the string is a Tor + version number, and the protocol is "The Tor protocol as supported + by the given version of Tor." Otherwise, if the value begins with + some other string, Tor has upgraded to a more sophisticated + protocol versioning system, and the protocol is "a version of the + Tor protocol more recent than any we recognize." + + The "r" entry for each router must appear first and is required. The + "s" entry is optional (see Section 3.1 below for how the flags are + decided). Unrecognized flags on the "s" line and extra elements + on the "r" line must be ignored. The "v" line is optional; it was not + supported until 0.1.2.5-alpha, and it must be preceded with an "opt" + until all earlier versions of Tor are obsolete. + + The signature section contains: + + "directory-signature" nickname-of-dirserver NL Signature + + Signature is a signature of this network-status document + (the document up until the signature, including the line + "directory-signature <nick>\n"), using the directory authority's + signing key. + + We compress the network status list with zlib before transmitting it. + +3.1. Establishing server status + + (This section describes how directory authorities choose which status + flags to apply to routers, as of Tor 0.1.1.18-rc. Later directory + authorities MAY do things differently, so long as clients keep working + well. Clients MUST NOT depend on the exact behaviors in this section.) + + In the below definitions, a router is considered "active" if it is + running, valid, and not hibernating. + + "Valid" -- a router is 'Valid' if it is running a version of Tor not + known to be broken, and the directory authority has not blacklisted + it as suspicious. + + "Named" -- Directory authority administrators may decide to support name + binding. If they do, then they must maintain a file of + nickname-to-identity-key mappings, and try to keep this file consistent + with other directory authorities. If they don't, they act as clients, and + report bindings made by other directory authorities (name X is bound to + identity Y if at least one binding directory lists it, and no directory + binds X to some other Y'.) A router is called 'Named' if the router + believes the given name should be bound to the given key. + + "Running" -- A router is 'Running' if the authority managed to connect to + it successfully within the last 30 minutes. + + "Stable" -- A router is 'Stable' if it is active, and either its + uptime is at least the median uptime for known active routers, or + its uptime is at least 30 days. Routers are never called stable if + they are running a version of Tor known to drop circuits stupidly. + (0.1.1.10-alpha through 0.1.1.16-rc are stupid this way.) + + "Fast" -- A router is 'Fast' if it is active, and its bandwidth is + in the top 7/8ths for known active routers. + + "Guard" -- A router is a possible 'Guard' if it is 'Stable' and its + bandwidth is above median for known active routers. If the total + bandwidth of active non-BadExit Exit servers is less than one third + of the total bandwidth of all active servers, no Exit is listed as + a Guard. + + "Authority" -- A router is called an 'Authority' if the authority + generating the network-status document believes it is an authority. + + "V2Dir" -- A router supports the v2 directory protocol if it has an open + directory port, and it is running a version of the directory protocol that + supports the functionality clients need. (Currently, this is + 0.1.1.9-alpha or later.) + + Directory server administrators may label some servers or IPs as + blacklisted, and elect not to include them in their network-status lists. + + Thus, the network-status list includes all non-blacklisted, + non-expired, non-superseded descriptors. + +4. Directory server operation + + All directory authorities and directory mirrors ("directory servers") + implement this section, except as noted. + +4.1. Accepting uploads (authorities only) + + When a router posts a signed descriptor to a directory authority, the + authority first checks whether it is well-formed and correctly + self-signed. If it is, the authority next verifies that the nickname + question is already assigned to a router with a different public key. + Finally, the authority MAY check that the router is not blacklisted + because of its key, IP, or another reason. + + If the descriptor passes these tests, and the authority does not already + have a descriptor for a router with this public key, it accepts the + descriptor and remembers it. + + If the authority _does_ have a descriptor with the same public key, the + newly uploaded descriptor is remembered if its publication time is more + recent than the most recent old descriptor for that router, and either: + - There are non-cosmetic differences between the old descriptor and the + new one. + - Enough time has passed between the descriptors' publication times. + (Currently, 12 hours.) + + Differences between router descriptors are "non-cosmetic" if they would be + sufficient to force an upload as described in section 2 above. + + Note that the "cosmetic difference" test only applies to uploaded + descriptors, not to descriptors that the authority downloads from other + authorities. + +4.2. Downloading network-status documents (authorities and caches) + + All directory servers (authorities and mirrors) try to keep a fresh + set of network-status documents from every authority. To do so, + every 5 minutes, each authority asks every other authority for its + most recent network-status document. Every 15 minutes, each mirror + picks a random authority and asks it for the most recent network-status + documents for all the authorities the authority knows about (including + the chosen authority itself). + + Directory servers and mirrors remember and serve the most recent + network-status document they have from each authority. Other + network-status documents don't need to be stored. If the most recent + network-status document is over 10 days old, it is discarded anyway. + Mirrors SHOULD store and serve network-status documents from authorities + they don't recognize, but SHOULD NOT use such documents for any other + purpose. Mirrors SHOULD discard network-status documents older than 48 + hours. + +4.3. Downloading and storing router descriptors (authorities and caches) + + Periodically (currently, every 10 seconds), directory servers check + whether there are any specific descriptors (as identified by descriptor + hash in a network-status document) that they do not have and that they + are not currently trying to download. + + If so, the directory server launches requests to the authorities for these + descriptors, such that each authority is only asked for descriptors listed + in its most recent network-status. When more than one authority lists the + descriptor, we choose which to ask at random. + + If one of these downloads fails, we do not try to download that descriptor + from the authority that failed to serve it again unless we receive a newer + network-status from that authority that lists the same descriptor. + + Directory servers must potentially cache multiple descriptors for each + router. Servers must not discard any descriptor listed by any current + network-status document from any authority. If there is enough space to + store additional descriptors, servers SHOULD try to hold those which + clients are likely to download the most. (Currently, this is judged + based on the interval for which each descriptor seemed newest.) + + Authorities SHOULD NOT download descriptors for routers that they would + immediately reject for reasons listed in 3.1. + +4.4. HTTP URLs + + "Fingerprints" in these URLs are base-16-encoded SHA1 hashes. + + The authoritative network-status published by a host should be available at: + http://<hostname>/tor/status/authority.z + + The network-status published by a host with fingerprint + <F> should be available at: + http://<hostname>/tor/status/fp/<F>.z + + The network-status documents published by hosts with fingerprints + <F1>,<F2>,<F3> should be available at: + http://<hostname>/tor/status/fp/<F1>+<F2>+<F3>.z + + The most recent network-status documents from all known authorities, + concatenated, should be available at: + http://<hostname>/tor/status/all.z + + The most recent descriptor for a server whose identity key has a + fingerprint of <F> should be available at: + http://<hostname>/tor/server/fp/<F>.z + + The most recent descriptors for servers with identity fingerprints + <F1>,<F2>,<F3> should be available at: + http://<hostname>/tor/server/fp/<F1>+<F2>+<F3>.z + + (NOTE: Implementations SHOULD NOT download descriptors by identity key + fingerprint. This allows a corrupted server (in collusion with a cache) to + provide a unique descriptor to a client, and thereby partition that client + from the rest of the network.) + + The server descriptor with (descriptor) digest <D> (in hex) should be + available at: + http://<hostname>/tor/server/d/<D>.z + + The most recent descriptors with digests <D1>,<D2>,<D3> should be + available at: + http://<hostname>/tor/server/d/<D1>+<D2>+<D3>.z + + The most recent descriptor for this server should be at: + http://<hostname>/tor/server/authority.z + [Nothing in the Tor protocol uses this resource yet, but it is useful + for debugging purposes. Also, the official Tor implementations + (starting at 0.1.1.x) use this resource to test whether a server's + own DirPort is reachable.] + + A concatenated set of the most recent descriptors for all known servers + should be available at: + http://<hostname>/tor/server/all.z + + For debugging, directories SHOULD expose non-compressed objects at URLs like + the above, but without the final ".z". + Clients MUST handle compressed concatenated information in two forms: + - A concatenated list of zlib-compressed objects. + - A zlib-compressed concatenated list of objects. + Directory servers MAY generate either format: the former requires less + CPU, but the latter requires less bandwidth. + + Clients SHOULD use upper case letters (A-F) when base16-encoding + fingerprints. Servers MUST accept both upper and lower case fingerprints + in requests. + +5. Client operation: downloading information + + Every Tor that is not a directory server (that is, those that do + not have a DirPort set) implements this section. + +5.1. Downloading network-status documents + + Each client maintains an ordered list of directory authorities. + Insofar as possible, clients SHOULD all use the same ordered list. + + For each network-status document a client has, it keeps track of its + publication time *and* the time when the client retrieved it. Clients + consider a network-status document "live" if it was published within the + last 24 hours. + + Clients try to have a live network-status document hours from *every* + authority, and try to periodically get new network-status documents from + each authority in rotation as follows: + + If a client is missing a live network-status document for any + authority, it tries to fetch it from a directory cache. On failure, + the client waits briefly, then tries that network-status document + again from another cache. The client does not build circuits until it + has live network-status documents from more than half the authorities + it trusts, and it has descriptors for more than 1/4 of the routers + that it believes are running. + + If the most recently _retrieved_ network-status document is over 30 + minutes old, the client attempts to download a network-status document. + When choosing which documents to download, clients treat their list of + directory authorities as a circular ring, and begin with the authority + appearing immediately after the authority for their most recently + retrieved network-status document. If this attempt fails, the client + retries at other caches several times, before moving on to the next + network-status document in sequence. + + Clients discard all network-status documents over 24 hours old. + + If enough mirrors (currently 4) claim not to have a given network status, + we stop trying to download that authority's network-status, until we + download a new network-status that makes us believe that the authority in + question is running. Clients should wait a little longer after each + failure. + + Clients SHOULD try to batch as many network-status requests as possible + into each HTTP GET. + + (Note: clients can and should pick caches based on the network-status + information they have: once they have first fetched network-status info + from an authority, they should not need to go to the authority directly + again.) + +5.2. Downloading and storing router descriptors + + Clients try to have the best descriptor for each router. A descriptor is + "best" if: + * It is the most recently published descriptor listed for that router + by at least two network-status documents. + OR, + * No descriptor for that router is listed by two or more + network-status documents, and it is the most recently published + descriptor listed by any network-status document. + + Periodically (currently every 10 seconds) clients check whether there are + any "downloadable" descriptors. A descriptor is downloadable if: + - It is the "best" descriptor for some router. + - The descriptor was published at least 10 minutes in the past. + (This prevents clients from trying to fetch descriptors that the + mirrors have probably not yet retrieved and cached.) + - The client does not currently have it. + - The client is not currently trying to download it. + - The client would not discard it immediately upon receiving it. + - The client thinks it is running and valid (see 6.1 below). + + If at least 16 known routers have downloadable descriptors, or if + enough time (currently 10 minutes) has passed since the last time the + client tried to download descriptors, it launches requests for all + downloadable descriptors, as described in 5.3 below. + + When a descriptor download fails, the client notes it, and does not + consider the descriptor downloadable again until a certain amount of time + has passed. (Currently 0 seconds for the first failure, 60 seconds for the + second, 5 minutes for the third, 10 minutes for the fourth, and 1 day + thereafter.) Periodically (currently once an hour) clients reset the + failure count. + + No descriptors are downloaded until the client has downloaded more than + half of the network-status documents. + + Clients retain the most recent descriptor they have downloaded for each + router so long as it is not too old (currently, 48 hours), OR so long as + it is recommended by at least one networkstatus AND no "better" + descriptor has been downloaded. [Versions of Tor before 0.1.2.3-alpha + would discard descriptors simply for being published too far in the past.] + [The code seems to discard descriptors in all cases after they're 5 + days old. True? -RD] + +5.3. Managing downloads + + When a client has no live network-status documents, it downloads + network-status documents from a randomly chosen authority. In all other + cases, the client downloads from mirrors randomly chosen from among those + believed to be V2 directory servers. (This information comes from the + network-status documents; see 6 below.) + + When downloading multiple router descriptors, the client chooses multiple + mirrors so that: + - At least 3 different mirrors are used, except when this would result + in more than one request for under 4 descriptors. + - No more than 128 descriptors are requested from a single mirror. + - Otherwise, as few mirrors as possible are used. + After choosing mirrors, the client divides the descriptors among them + randomly. + + After receiving any response client MUST discard any network-status + documents and descriptors that it did not request. + +6. Using directory information + + Everyone besides directory authorities uses the approaches in this section + to decide which servers to use and what their keys are likely to be. + (Directory authorities just believe their own opinions, as in 3.1 above.) + +6.1. Choosing routers for circuits. + + Tor implementations only pay attention to "live" network-status documents. + A network status is "live" if it is the most recently downloaded network + status document for a given directory server, and the server is a + directory server trusted by the client, and the network-status document is + no more than 1 day old. + + For time-sensitive information, Tor implementations focus on "recent" + network-status documents. A network status is "recent" if it is live, and + if it was published in the last 60 minutes. If there are fewer + than 3 such documents, the most recently published 3 are "recent." If + there are fewer than 3 in all, all are "recent.") + + Circuits SHOULD NOT be built until the client has enough directory + information: network-statuses (or failed attempts to download + network-statuses) for all authorities, network-statuses for at more than + half of the authorites, and descriptors for at least 1/4 of the servers + believed to be running. + + A server is "listed" if it is included by more than half of the live + network status documents. Clients SHOULD NOT use unlisted servers. + + Clients believe the flags "Valid", "Exit", "Fast", "Guard", "Stable", and + "V2Dir" about a given router when they are asserted by more than half of + the live network-status documents. Clients believe the flag "Running" if + it is listed by more than half of the recent network-status documents. + + These flags are used as follows: + + - Clients SHOULD NOT use non-'Valid' or non-'Running' routers unless + requested to do so. + + - Clients SHOULD NOT use non-'Fast' routers for any purpose other than + very-low-bandwidth circuits (such as introduction circuits). + + - Clients SHOULD NOT use non-'Stable' routers for circuits that are + likely to need to be open for a very long time (such as those used for + IRC or SSH connections). + + - Clients SHOULD NOT choose non-'Guard' nodes when picking entry guard + nodes. + + - Clients SHOULD NOT download directory information from non-'V2Dir' + caches. + +6.2. Managing naming + + In order to provide human-memorable names for individual server + identities, some directory servers bind names to IDs. Clients handle + names in two ways: + + When a client encounters a name it has not mapped before: + + If all the live "Naming" network-status documents the client has + claim that the name binds to some identity ID, and the client has at + least three live network-status documents, the client maps the name to + ID. + + When a user tries to refer to a router with a name that does not have a + mapping under the above rules, the implementation SHOULD warn the user. + After giving the warning, the implementation MAY use a router that at + least one Naming authority maps the name to, so long as no other naming + authority maps that name to a different router. If no Naming authority + maps the name to a router, the implementation MAY use any router that + advertises the name. + + Not every router needs a nickname. When a router doesn't configure a + nickname, it publishes with the default nickname "Unnamed". Authorities + SHOULD NOT ever mark a router with this nickname as Named; client software + SHOULD NOT ever use a router in response to a user request for a router + called "Unnamed". + +6.3. Software versions + + An implementation of Tor SHOULD warn when it has fetched (or has + attempted to fetch and failed four consecutive times) a network-status + for each authority, and it is running a software version + not listed on more than half of the live "Versioning" network-status + documents. + +6.4. Warning about a router's status. + + If a router tries to publish its descriptor to a Naming authority + that has its nickname mapped to another key, the router SHOULD + warn the operator that it is either using the wrong key or is using + an already claimed nickname. + + If a router has fetched (or attempted to fetch and failed four + consecutive times) a network-status for every authority, and at + least one of the authorities is "Naming", and no live "Naming" + authorities publish a binding for the router's nickname, the + router MAY remind the operator that the chosen nickname is not + bound to this key at the authorities, and suggest contacting the + authority operators. + + ... + +6.5. Router protocol versions + + A client should believe that a router supports a given feature if that + feature is supported by the router or protocol versions in more than half + of the live networkstatus's "v" entries for that router. In other words, + if the "v" entries for some router are: + v Tor 0.0.8pre1 (from authority 1) + v Tor 0.1.2.11 (from authority 2) + v FutureProtocolDescription 99 (from authority 3) + then the client should believe that the router supports any feature + supported by 0.1.2.11. + + This is currently equivalent to believing the median declared version for + a router in all live networkstatuses. + +7. Standards compliance + + All clients and servers MUST support HTTP 1.0. + +7.1. HTTP headers + + Servers MAY set the Content-Length: header. Servers SHOULD set + Content-Encoding to "deflate" or "identity". + + Servers MAY include an X-Your-Address-Is: header, whose value is the + apparent IP address of the client connecting to them (as a dotted quad). + For directory connections tunneled over a BEGIN_DIR stream, servers SHOULD + report the IP from which the circuit carrying the BEGIN_DIR stream reached + them. [Servers before version 0.1.2.5-alpha reported 127.0.0.1 for all + BEGIN_DIR-tunneled connections.] + + Servers SHOULD disable caching of multiple network statuses or multiple + router descriptors. Servers MAY enable caching of single descriptors, + single network statuses, the list of all router descriptors, a v1 + directory, or a v1 running routers document. XXX mention times. + +7.2. HTTP status codes + + XXX We should write down what return codes dirservers send in what situations. + diff --git a/doc/spec/dir-spec.txt b/doc/spec/dir-spec.txt index 139c51162..690064641 100644 --- a/doc/spec/dir-spec.txt +++ b/doc/spec/dir-spec.txt @@ -1,84 +1,200 @@ $Id$ - Tor directory protocol, version 2 + Tor directory protocol, version 3 0. Scope and preliminaries - This directory protocol is used by Tor version 0.1.1.x and later. See - dir-spec-v1.txt for information on earlier versions. + This directory protocol is used by Tor version 0.2.0.x-alpha and later. + See dir-spec-v1.txt for information on the protocol used up to the + 0.1.0.x series, and dir-spec.v2 for information on the protocol used by + the 0.1.1.x and 0.1.2.x series. + + Caches and authorities must still support older versions of the + directory protocols, until the versions of Tor that require them are + finally out of commission. See Section XXXX on backward compatibility. + + This document merges and supersedes the following proposals: + + 101 Voting on the Tor Directory System + 103 Splitting identity key from regularly used signing key + 104 Long and Short Router Descriptors + + AS OF 3 MAY 2007, THIS SPECIFICATION HAS NOT YET BEEN COMPLETELY + IMPLEMENTED. -0.1. Goals and motivation +0.1. History - There were several problems with the way Tor handles directory information - in version 0.1.0.x and earlier. Here are the problems we try to fix with - this new design, already implemented in 0.1.1.x: - 1. Directories were very large and use up a lot of bandwidth: clients - downloaded descriptors for all router several times an hour. - 2. Every directory authority was a trust bottleneck: if a single - directory authority lied, it could make clients believe for a time an - arbitrarily distorted view of the Tor network. - 3. Our current "verified server" system is kind of nonsensical. + The earliest versions of Onion Routing shipped with a list of known + routers and their keys. When the set of routers changed, users needed to + fetch a new list. - 4. Getting more directory authorities would add more points of failure - and worsen possible partitioning attacks. + The Version 1 Directory protocol + -------------------------------- - There are two problems that remain unaddressed by this design. - 5. Requiring every client to know about every router won't scale. - 6. Requiring every directory cache to know every router won't scale. + [XXX say which versions added what.] + + Early versions of Tor introduced "Directory authorities": servers that + served signed "directory" documents containing a list of signed "router + descriptors", along with short summary of the status of each router. + Thus, clients could get up-to-date information on the state of the + network automatically, and be certain that they list they were getting + was attested by a trusted directory authority. + + Later versions added directory caches, which download directories from + the authorities and serve them to clients. Non-caches fetch from the + caches in preference to fetching from the authorities, thus distributing + bandwidth requirements. + + Also added during the version 1 directory protocol were "router status" + documents: short documents that listed only the up/down status of the + routers on the network, rather than a complete list of all the + descriptors. Clients and caches would fetch these documents far more + frequently than they would fetch full directories. + + The Version 2 Directory Protocol + -------------------------------- + + During the Tor 0.1.1.x series, Tor revised its handling of directory + documents in order to address two major problems: + + * Directories had grown quite large (over 1MB), and most directory + downloads consisted mainly of router descriptors that clients + already had. + + * Every directory authorities was a trust bottleneck: if a single + directory authority lied, it could make clients believe for a time + an arbitrarily distorted view of the Tor network. (Clients + trusted the most recent signed document they downloaded.) Thus, + adding more authorities would make the system less secure, not + more. + + To address these, we extended the directory protocol so that + authorities now published signed "network status" documents. Each + network status listed, for every router in the network: a hash of its + identity key, a hash of its most recent descriptor, and a summary of + what the authority believed about its status. Clients would download + the authorities' network status documents in turn, and believe + statements about routers iff they were attested to by more than half of + the authorities. + + Instead of downloading all router descriptors at once, clients + downloaded only the descriptors that they did not have. Descriptors + were indexed by their digests, in order to prevent malicious caches + from giving different versions of a router descriptor to different + clients. + + Routers began working harder to upload new descriptors only when their + contents were substantially changed. + + +0.2. Goals of the version 3 protocol + + Version 3 of the Tor directory protocol tries to solve the following + issues: + + * A great deal of bandwidth used to transmit router descriptors was + used by two fields that are not actually used by Tor routers. We + save about 60% by moving them into a separate document that most + clients do not fetch or use. + + * It was possible under certain perverse circumstances for clients + to download an unusual set of network status documents, thus + partitioning themselves from clients who have a more recent and/or + typical set of documents. Even under the best of circumstances, + clients were sensitive to the ages of the network status documents + they downloaded. Therefore, instead of having the clients + correlate multiple network status documents, we have the + authorities collectively vote on a single consensus network status + document. + + * The most sensitive data in the entire network (the identity keys + of the directory authorities) needed to be stored unencrypted so + that the authorities . Now, the authorities' identity keys are + stored offline, and used to certify medium-term signing keys that + can be rotated. + +0.3. Some Remaining questions + + Things we could solve on a v3 timeframe: + + The SHA-1 hash is showing its age. We should do something about our + dependency on it. We could probably future-proof ourselves here in + this revision, at least so far as documents from the authorities are + concerned. + + Too many things about the authorities are hardcoded by IP. + + Perhaps we should start accepting longer identity keys for routers + too. + + Things to solve eventually: + + Requiring every client to know about every router won't scale forever. + + Requiring every directory cache to know every router won't scale + forever. - We attempt to fix 1-4 here, and to build a solution that will work when we - figure out an answer for 5. We haven't thought at all about what to do - about 6. 1. Outline - There is a small set (say, around 10) of semi-trusted directory + There is a small set (say, around 5-10) of semi-trusted directory authorities. A default list of authorities is shipped with the Tor - software. Users can change this list, but are encouraged not to do so, in - order to avoid partitioning attacks. - - Routers periodically upload signed "descriptors" to the directory - authorities describing their keys, capabilities, and other information. - Routers may act as directory mirrors (also called "caches"), to reduce - load on the directory authorities. They announce this in their - descriptors. - - Each directory authority periodically generates and signs a compact - "network status" document that lists that authority's view of the current - descriptors and status for known routers, but which does not include the - descriptors themselves. - - Directory mirrors download, cache, and re-serve network-status documents - to clients. - - Clients, directory mirrors, and directory authorities all use - network-status documents to find out when their list of routers is - out-of-date. If it is, they download any missing router descriptors. - Clients download missing descriptors from mirrors; mirrors and authorities - download from authorities. Descriptors are downloaded by the hash of the - descriptor, not by the server's identity key: this prevents servers from - attacking clients by giving them descriptors nobody else uses. + software. Users can change this list, but are encouraged not to do so, + in order to avoid partitioning attacks. + + Every authority has a very-secret, long-term "Authority Identity Key". + This is stored encrypted and/or offline, and is used to sign "key + certificate" documents. Every key certificate contains a medium-term + (3-12 months) "authority signing key", that is used by the authority to + sign other directory information. (Note that the authority identity + key is distinct from the router identity key that the authority uses + in its role as an ordinary router.) + + Routers periodically upload signed "routers descriptors" to the + directory authorities describing their keys, capabilities, and other + information. Routers may also upload signed "extra info documents" + containing information that is not required for the Tor protocol. + Directory authorities serve router descriptors indexed by router + identity, or by hash of the descriptor. + + Routers may act as directory caches to reduce load on the directory + authorities. They announce this in their descriptors. + + Periodically, each directory authority periodically generates a view of + the current descriptors and status for known routers. They send a + signed summary of this view (a "status vote") to the other + authorities. The authorities compute the result of this vote, and sign + a "consensus status" document containing the result of the vote. + + Directory caches download, cache, and re-serve consensus documents. + + Clients, directory caches, and directory authorities all use consensus + documents to find out when their list of routers is out-of-date. + (Directory authorities also use vote statuses.) If it is, they download + any missing router descriptors. Clients download missing descriptors + from mirrors; mirrors and authorities download from authorities. + Descriptors are downloaded by the hash of the descriptor, not by the + server's identity key: this prevents servers from attacking clients by + giving them descriptors nobody else uses. All directory information is uploaded and downloaded with HTTP. - Coordination among directory authorities is done client-side: clients - compute a vote-like algorithm among the network-status documents they - have, and base their decisions on the result. + [Authorities also generate and caches also cache documents produced and + used by earlier versions of this protocol; see section XXX for notes.] -1.1. What's different from 0.1.0.x? +1.1. What's different from version 2? - Clients used to download a signed concatenated set of router descriptors - (called a "directory") from directory mirrors, regardless of which - descriptors had changed. + Clients used to download a multiple network status documents, + corresponding roughly to "status votes" above. They would compute the + result of the vote on the client side. - Between downloading directories, clients would download "network-status" - documents that would list which servers were supposed to running. + Authorities used sign documents using the same private keys they used + for their roles as routers. This forced them to keep these extremely + sensitive keys in memory unencrypted. - Clients would always believe the most recently published network-status - document they were served. + All of the information in extra-info documents used to be kept in the + main descriptors. - Routers used to upload fresh descriptors all the time, whether their keys - and other information had changed or not. 1.2. Document meta-format @@ -121,18 +237,68 @@ $Id$ Implementations before 0.1.2.5-alpha rejected any document with a KeywordLine that started with a keyword that they didn't recognize. - Implementations MUST prefix items not recognized by older versions of Tor - with an "opt" until those versions of Tor are obsolete. + When generating documents that need to be read by older versions of Tor, + implementations MUST prefix items not recognized by older versions of + Tor with an "opt" until those versions of Tor are obsolete. [Note that + key certificates, status vote documents, extra info documents, and + status consensus documents will never by read by older versions of Tor.] Other implementations that want to extend Tor's directory format MAY introduce their own items. The keywords for extension items SHOULD start with the characters "x-" or "X-", to guarantee that they will not conflict with keywords used by future versions of Tor. -2. Router operation + In our document descriptions below, we tag Items with a multiplicity in + brackets. Possible tags are: + + "At start, exactly once": These items MUST occur in every instance of + the document type, and MUST appear exactly once, and MUST be the + first item in their documents. + + "Exactly once": These items MUST occur exactly one time in every + instance of the document type. + + "At start, exactly once": These items MUST occur in every instance of + the document type, and MUST appear exactly once, and MUST be the + last item in their documents. + + "At most once": These items MAY occur zero or one times in any + instance of the document type, but MUST NOT occur more than once. + + "Any number": These items MAY occur zero, one, or more times in any + instance of the document type. + + "Once or more": These items MUST occur at least once in any instance + of the document type, and MAY occur more. + +1.3. Signing documents + + Every signable document below is signed in a similar manner, using a + given "Initial Item", a final "Signature Item", a digest algorithm, and + a signing key. + + The Initial Item must be the first item in the document. - ORs SHOULD generate a new router descriptor whenever any of the - following events have occurred: + The Signature Item has the following format: + + <signature item keyword> [arguments] NL SIGNATURE NL + + The "SIGNATURE" Object contains a signature (using the signing key) of + the PKCS1-padded digest of the entire document, taken from the + beginning of the Initial item, through the newline after the Signature + Item's keyword and its arguments. + + Unless otherwise, the digest algorithm is SHA-1. + + All documents are invalid unless signed with the correct signing key. + + The "Digest" of a document, unless stated otherwise, is its digest *as + signed by this signature scheme*. + +2. Router operation and formats + + ORs SHOULD generate a new router descriptor and a new extra-info + document whenever any of the following events have occurred: - A period of time (18 hrs by default) has passed since the last time a descriptor was generated. @@ -145,40 +311,36 @@ $Id$ - Its uptime has been reset (by restarting). - After generating a descriptor, ORs upload it to every directory - authority they know, by posting it to the URL + After generating a descriptor, ORs upload them to every directory + authority they know, by posting them (in order) to the URL http://<hostname:port>/tor/ 2.1. Router descriptor format - Every router descriptor MUST start with a "router" Item; MUST end with a - "router-signature" Item and an extra NL; and MUST contain exactly one - instance of each of the following Items: "published" "onion-key" - "signing-key" "bandwidth". + Router descriptors consist of the following items. For backward + compatibility, there should be an extra NL at the end of each router + descriptor. - A router descriptor MAY have zero or one of each of the following Items, - but MUST NOT have more than one: "contact", "uptime", "fingerprint", - "hibernating", "read-history", "write-history", "eventdns", "platform", - "family". + In lines that take multiple arguments, extra arguments SHOULD be + accepted and ignored. - Additionally, a router descriptor MAY contain any number of "accept", - "reject", and "opt" Items. Other than "router" and "router-signature", - the items may appear in any order. + "router" nickname address ORPort SOCKSPort DirPort NL - The items' formats are as follows: - "router" nickname address ORPort SocksPort DirPort + [At start, exactly once.] Indicates the beginning of a router descriptor. "address" must be an IPv4 address in dotted-quad format. The last three numbers indicate the TCP ports at which this OR exposes functionality. ORPort is a port at which this OR accepts TLS connections for the main OR protocol; - SocksPort is deprecated and should always be 0; and DirPort is the + SOCKSPort is deprecated and should always be 0; and DirPort is the port at which this OR accepts directory-related HTTP connections. If any port is not supported, the value 0 is given instead of a port number. - "bandwidth" bandwidth-avg bandwidth-burst bandwidth-observed + "bandwidth" bandwidth-avg bandwidth-burst bandwidth-observed NL + + [Exactly once] Estimated bandwidth for this router, in bytes per second. The "average" bandwidth is the volume per second that the OR is willing to @@ -189,17 +351,24 @@ $Id$ second period in the past day, and another sustained input. The "observed" value is the lesser of these two numbers. - "platform" string + "platform" string NL + + [At most once] A human-readable string describing the system on which this OR is running. This MAY include the operating system, and SHOULD include the name and version of the software implementing the Tor protocol. - "published" YYYY-MM-DD HH:MM:SS + "published" YYYY-MM-DD HH:MM:SS NL + + [Exactly once] + + The time, in GMT, when this descriptor (and its corresponding + extra-info document if any) was generated. - The time, in GMT, when this descriptor was generated. + "fingerprint" fingerprint NL - "fingerprint" + [At most once] A fingerprint (a HASH_LEN-byte of asn1 encoded public key, encoded in hex, with a single space after every 4 characters) for this router's @@ -209,7 +378,9 @@ $Id$ [We didn't start parsing this line until Tor 0.1.0.6-rc; it should be marked with "opt" until earlier versions of Tor are obsolete.] - "hibernating" 0|1 + "hibernating" bool NL + + [At most once] If the value is 1, then the Tor server was hibernating when the descriptor was published, and shouldn't be used to build circuits. @@ -217,22 +388,30 @@ $Id$ [We didn't start parsing this line until Tor 0.1.0.6-rc; it should be marked with "opt" until earlier versions of Tor are obsolete.] - "uptime" + "uptime" number NL + + [At most once] The number of seconds that this OR process has been running. "onion-key" NL a public key in PEM format + [Exactly once] + This key is used to encrypt EXTEND cells for this OR. The key MUST be accepted for at least 1 week after any new key is published in a - subsequent descriptor. + subsequent descriptor. It MUST be 1024 bits. "signing-key" NL a public key in PEM format - The OR's long-term identity key. + [Exactly once] - "accept" exitpattern - "reject" exitpattern + The OR's long-term identity key. It MUST be 1024 bits. + + "accept" exitpattern NL + "reject" exitpattern NL + + [Any number] These lines describe the rules that an OR follows when deciding whether to allow a new stream to a given address. The @@ -242,6 +421,8 @@ $Id$ "router-signature" NL Signature NL + [At end, exactly once] + The "SIGNATURE" object contains a signature of the PKCS1-padded hash of the entire router descriptor, taken from the beginning of the "router" line, through the newline after the "router-signature" line. @@ -250,11 +431,15 @@ $Id$ "contact" info NL - Describes a way to contact the server's administrator, preferably - including an email address and a PGP key fingerprint. + [At most once] + + Describes a way to contact the server's administrator, preferably + including an email address and a PGP key fingerprint. "family" names NL + [At most once] + 'Names' is a space-separated list of server nicknames or hexdigests. If two ORs list one another in their "family" entries, then OPs should treat them as a single OR for the purpose of path @@ -265,7 +450,9 @@ $Id$ be used on the same circuit. "read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL + [At most once] "write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL + [At most once] Declare how much bandwidth the OR has used recently. Usage is divided into intervals of NSEC seconds. The YYYY-MM-DD HH:MM:SS field @@ -276,8 +463,12 @@ $Id$ [We didn't start parsing these lines until Tor 0.1.0.6-rc; they should be marked with "opt" until earlier versions of Tor are obsolete.] + [See also migration notes in section 2.2.1.] + "eventdns" bool NL + [At most once] + Declare whether this version of Tor is using the newer enhanced dns logic. Versions of Tor without eventdns SHOULD NOT be used for reverse hostname lookups. @@ -289,9 +480,81 @@ $Id$ not generated, even when eventdns was in use. Versions of Tor before 0.1.2.1-alpha-dev did not parse this option, so it should be marked "opt". With some future version, the old 'dnsworker' logic - will be removed, rendering this option of historical interest only.] + will be removed, rendering this option of historical interest + only.] + + "caches-extra-info" 0|1 NL + + [At most once.] + + True if this router is a directory cache that provides extra-info + documents. If absent, the value should be treated as false. + + [Versions before 0.2.0.1-alpha don't recognize this, and versions + before 0.1.2.5-alpha will reject descriptors containing it unless + it is prefixed with "opt"; it should be so prefixed until these + versions are obsolete.] + + "extra-info-digest" digest NL + + [At most once] + + "Digest" is a hex-encoded digest (using upper-case characters) + of the router's extra-info document, as signed in the router's + extra-info. (If this field is absent, the router is not uploading + a corresponding extra-info document.) + + [Versions before 0.2.0.1-alpha don't recognize this, and versions + before 0.1.2.5-alpha will reject descriptors containing it unless + it is prefixed with "opt"; it should be so prefixed until these + versions are obsolete.] + +2.2. Extra-info documents + + Extra-info documents consist of the following items: + + "extra-info" Nickname Fingerprint NL + [At start, exactly once.] + + Identifies what router this is an extra info descriptor for. + Fingerprint is encoded in hex (using upper-case letters), with + no spaces. -2.2. Nonterminals in router descriptors + "published" + + [Exactly once.] + + The time, in GMT, when this document (and its corresponding router + descriptor if any) was generated. It MUST match the published time + in the corresponding router descriptor. + + "read-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL + [At most once.] + "write-history" YYYY-MM-DD HH:MM:SS (NSEC s) NUM,NUM,NUM,NUM,NUM... NL + [At most once.] + + As documented in 2.1 above. See migration notes in section 2.2.1. + + "router-signature" NL Signature NL + [At end, exactly once.] + + A document signature as documented in section 1.3, using the + initial item "extra-info" and the final item "router-signature", + signed with the router's identity key. + +2.2.1. Moving history fields to extra-info documents. + + Tools that want to use the read-history and write-history values SHOULD + download extra-info documents as well as router descriptors. Such + tools SHOULD accept history values from both sources; if they appear in + both documents, the values in the extra-info documents are authoritative. + + At some future time, to save space, new versions of Tor will no longer + generate router descriptors containing read-history or write-history. + Tools should continue to accept read-history and write-history values + in router descriptors produced by older versions of Tor. + +2.3. Nonterminals in router descriptors nickname ::= between 1 and 19 alphanumeric characters, case-insensitive. hexdigest ::= a '$', followed by 20 hexadecimal characters. @@ -300,6 +563,7 @@ $Id$ exitpattern ::= addrspec ":" portspec portspec ::= "*" | port | port "-" port port ::= an integer between 1 and 65535, inclusive. + [Some implementations incorrectly generate ports with value 0. Implementations SHOULD accept this, and SHOULD NOT generate it.] @@ -314,77 +578,231 @@ $Id$ bool ::= "0" | "1" - Ports are required; if they are not included in the router - line, they must appear in the "ports" lines. - -3. Network status format - - Directory authorities generate, sign, and compress network-status - documents. Directory servers SHOULD generate a fresh network-status - document when the contents of such a document would be different from the - last one generated, and some time (at least one second, possibly longer) - has passed since the last one was generated. - - The network status document contains a preamble, a set of router status - entries, and a signature, in that order. - - We use the same meta-format as used for directories and router descriptors - in "tor-spec.txt". Implementations MAY insert blank lines - for clarity between sections; these blank lines are ignored. - Implementations MUST NOT depend on blank lines in any particular location. - - As used here, "whitespace" is a sequence of 1 or more tab or space - characters. - - The preamble contains: - - "network-status-version" -- A document format version. For this - specification, the version is "2". - "dir-source" -- The authority's hostname, current IP address, and - directory port, all separated by whitespace. - "fingerprint" -- A base16-encoded hash of the signing key's - fingerprint, with no additional spaces added. - "contact" -- An arbitrary string describing how to contact the - directory server's administrator. Administrators should include at - least an email address and a PGP fingerprint. - "dir-signing-key" -- The directory server's public signing key. - "client-versions" -- A comma-separated list of recommended client +3. Formats produced by directory authorities. + + Every authority has two keys used in this protocol: a signing key, and + an authority identity key. (Authorities also have a router identity + key used in their role as a router and by earlier versions of the + directory protocol.) The identity key is used from time to time to + sign new key certificates using new signing keys; it is very sensitive. + The signing key is used to sign key certificates and status documents. + + There are three kinds of documents generated by directory authorities: + + Key certificates + Status votes + Status consensuses + + Each is discussed below. + +3.1. Key certificates + + Key certificates consist of the following items: + + "dir-key-certificate-version" version NL + + [At start, exactly once.] + + Determines the version of the key certificate. MUST be "3" for + the protocol described in this document. Implementations MUST + reject formats they don't understand. + + "fingerprint" fingerprint NL + + [Exactly once.] + + Hexadecimal encoding without spaces based on the authority's + identity key. + + "dir-identity-key" NL a public key in PEM format + + [Exactly once.] + + The long-term authority identity key for this authority. This key + SHOULD be at least 2048 bits long; it MUST NOT be shorter than + 1024 bits. + + "dir-key-published" YYYY-MM-DD HH:MM:SS NL + + [Exactly once.] + + The time (in GMT) when this document and corresponding key were + last generated. + + "dir-key-expires" YYYY-MM-DD HH:MM:SS NL + + [Exactly once.] + + A time (in GMT) after which this key is no longer valid. + + "dir-signing-key" NL a key in PEM format + + [Exactly once.] + + The directory server's public signing key. This key MUST be at + least 1024 bits, and MAY be longer. + + "dir-key-certification" NL Signature NL + + [At end, exactly once.] + + A document signature as documented in section 1.3, using the + initial item "dir-key-certificate-version" and the final item + "dir-key-certification", signed with the authority identity key. + + Authorities MUST generate a new signing key and corresponding + certificate before the key expires. + +3.2. Vote and consensus status documents + + Votes and consensuses are more strictly formatted then other documents + in this specification, since different authorities must be able to + generate exactly the same consensus given the same set of votes. + + The procedure for deciding when to generate vote and consensus status + documents are described in section XXX below. + + Status documents contain a preamble, an authority section, a list of + router status entries, and one more footers signature, in that order. + + Unlike other formats described above, a SP in these documents must be a + single space character (hex 20). + + Some items appear only in votes, and some items appear only in + consensuses. Unless specified, items occur in both. + + The preamble contains the following items. They MUST occur in the + order given here: + + "network-status-version" SP version NL. + + [At start, exactly once.] + + A document format version. For this specification, the version is + "3". + + "vote-status" SP type NL + + [Exactly once.] + + The status MUST be "vote" or "consensus", depending on the type of + the document. + + "published" SP YYYY-MM-DD SP HH:MM:SS NL + + [Exactly once.] + + The publication time for this status document (if a vote), or the + start of the period for this vote (if a consensus). + + "valid-until" + + [Exactly once.] + + A time after which this vote or consensus will no longer be valid. + + "client-versions" SP VersionList NL + + [At most once.] + + A comma-separated list of recommended client versions, in + ascending order. If absent, no opinion is held about client versions. - "server-versions" -- A comma-separated list of recommended server + + "server-versions" SP VersionList NL + + [At most once.] + + A comma-separated list of recommended server versions, in + ascending order. If absent, no opinion is held about server versions. - "published" -- The publication time for this network-status object. - "dir-options" -- A set of flags, in any order, separated by whitespace: - "Names" if this directory authority performs name bindings. - "Versions" if this directory authority recommends software versions. - "BadExits" if the directory authority flags nodes that it believes - are performing incorrectly as exit nodes. - "BadDirectories" if the directory authority flags nodes that it - believes are performing incorrectly as directory caches. - - The dir-options entry is optional. The "-versions" entries are required if - the "Versions" flag is present. The other entries are required and must - appear exactly once. The "network-status-version" entry must appear first; - the others may appear in any order. Implementations MUST ignore - additional arguments to the items above, and MUST ignore unrecognized - flags. - - For each router, the router entry contains: (This format is designed for - conciseness.) - - "r" -- followed by the following elements, in order, separated by - whitespace: - - The OR's nickname, - - A hash of its identity key, encoded in base64, with trailing = - signs removed. - - A hash of its most recent descriptor, encoded in base64, with - trailing = signs removed. (The hash is calculated as for - computing the signature of a descriptor.) - - The publication time of its most recent descriptor, in the form - YYYY-MM-DD HH:MM:SS, in GMT. - - An IP address - - An OR port - - A directory port (or "0" for none") - "s" -- A series of whitespace-separated status flags, in any order: + + "known-flags" SP FlagList NL + + [Exactly once.] + + A space-separated list of all of the flags that this document + might contain. A flag is "known" either because the authority + knows about them and might set them (if in a vote), or because + enough votes were counted for the consensus for an authoritative + opinion to have been formed about their status. + + + The authority section of a vote contains the following items, followed + in turn by the authority's current key certificate: + + "dir-source" SP nickname SP identity SP address SP IP SP dirport NL + + [Exactly once, at start] + + Describes this authority. The nickname is a convenient identifier + for the authority. The identity is a hex fingerprint of the + authority's current identity key. The address is the server's + hostname. The IP is the server's current IP address, and dirport + is its current directory port. + + "contact" SP string NL + + [At most once.] + + An arbitrary string describing how to contact the directory + server's administrator. Administrators should include at least an + email address and a PGP fingerprint. + + The authority section of a consensus contains groups the following + items, in the order given, with one group for each authority that + contributed to the consensus: + + "dir-source" SP nickname SP address SP IP SP dirport NL + + [Exactly once, at start] + + As in the authority section of a vote. + + "contact" SP string NL + + [At most once.] + + As in the authority section of a vote. + + "fingerprint" SP fingerprint NL + + [Exactly once.] + + A hex fingerprint, without spaces, of the authority's current + identity key. + + "vote-digest" SP digest NL + + [Exactly once.] + + A digest of the vote from the authority that contributed to this + consensus. + + Each router status entry contains the following items. Router status + entries are sorted in ascending order by identity digest. + + "r" SP nickname SP identity SP digest SP publication SP IP SP ORPort + SP DirPort NL + + [At start, exactly once.] + + "Nickname" is the OR's nickname. "Identity" is a hash of its + identity key, encoded in base64, with trailing equals sign(s) + removed. "Digest" is a hash of its most recent descriptor (as + signed), encoded in base64 as "identity". "Publication" is the + publication time of its most recent descriptor, in the form + YYYY-MM-DD HH:MM:SS, in GMT. "IP" is its current IP address; + ORPort is its current OR port, "DirPort" is it's current directory + port, or "0" for "none". + + "s" SP Flags NL + + [At most once.] + + A series of space-separated status flags, in alphabetical order. + Currently documented flags are: + "Authority" if the router is a directory authority. "BadExit" if the router is believed to be useless as an exit node (because its ISP censors it, because it is behind a restrictive @@ -403,36 +821,38 @@ $Id$ "Running" if the router is currently usable. "Valid" if the router has been 'validated'. "V2Dir" if the router implements this protocol. - "v" -- The version of the Tor protocol that this server is running. If - the value begins with "Tor" SP, the rest of the string is a Tor - version number, and the protocol is "The Tor protocol as supported - by the given version of Tor." Otherwise, if the value begins with - some other string, Tor has upgraded to a more sophisticated - protocol versioning system, and the protocol is "a version of the - Tor protocol more recent than any we recognize." - The "r" entry for each router must appear first and is required. The - "s" entry is optional (see Section 3.1 below for how the flags are - decided). Unrecognized flags on the "s" line and extra elements - on the "r" line must be ignored. The "v" line is optional; it was not - supported until 0.1.2.5-alpha, and it must be preceded with an "opt" - until all earlier versions of Tor are obsolete. + "v" SP version NL - The signature section contains: + [At most once.] - "directory-signature" nickname-of-dirserver NL Signature + The version of the Tor protocol that this server is running. If + the value begins with "Tor" SP, the rest of the string is a Tor + version number, and the protocol is "The Tor protocol as supported + by the given version of Tor." Otherwise, if the value begins with + some other string, Tor has upgraded to a more sophisticated + protocol versioning system, and the protocol is "a version of the + Tor protocol more recent than any we recognize." - Signature is a signature of this network-status document - (the document up until the signature, including the line - "directory-signature <nick>\n"), using the directory authority's - signing key. + The signature section contains the following item, which appears + Exactly Once for a vote, and At Least Once for a consensus. - We compress the network status list with zlib before transmitting it. + "directory-signature" SP identity SP digest NL Signature -3.1. Establishing server status + This is a signature of the status document, with the initial item + "network-status-version", and the signature item + "directory-signature", using the signing key. (In this case, we + take the hash through the _space_ after directory-signature, not + the newline: this ensures that all authorities sign the same + thing.) "identity" is the hex-encoded digest of the authority + identity key of the signing authority, and "digest" is the + hex-encoded digest of the current authority signing key of the + signing authority. + +3.3. Deciding how to vote. (This section describes how directory authorities choose which status - flags to apply to routers, as of Tor 0.1.1.18-rc. Later directory + flags to apply to routers, as of Tor 0.2.0.0-alpha-dev. Later directory authorities MAY do things differently, so long as clients keep working well. Clients MUST NOT depend on the exact behaviors in this section.) @@ -484,6 +904,40 @@ $Id$ Thus, the network-status list includes all non-blacklisted, non-expired, non-superseded descriptors. +3.4. Computing a consensus from a set of votes + + Given a set of votes, authorities compute the contents of the consensus + document as follows: + + The "published" is the latest of all published times on the votes. + + The "valid-until" is the earliest of all valid-until times on the + votes. + + "client-versions" and "server-versions" are sorted in ascending + order; A version is recommended in the consensus if it is recommended + by more than half of the voting authorities that included a + client-versions or server-versions lines in their votes. + + The authority item groups (dir-source, contact, fignerprint, + vote-digest) are taken from the votes of the voting + authorities. These groups are sorted by the digests of the + authorities identity keys, in ascending order. + + A router status entry is included in the result if it is included by more + than half of the authorities (total authorities, not just those whose + votes we have). A router entry has a flag set if it is included by + more than half of the authorities who care about that flag. Two + router entries are "the same" if they have the same identity digest. + We use whatever descriptor digest is attested to by the most + authorities among the voters, breaking ties in favor of the one with + the most recent publication time. + + The signatures at the end of the document appear are sorted in + ascending order by identity digest. + +[CUTOFF HERE. STUFF BELOW THIS POINT HAS NOT YET BEEN UPDATED FROM V2.] + 4. Directory server operation All directory authorities and directory mirrors ("directory servers") @@ -886,3 +1340,5 @@ $Id$ XXX We should write down what return codes dirservers send in what situations. +8. Backward compatibility and migration plans + |