commit 2b2ad532ec4454c762a881fbad5b9d1d1d42dd51 Author: teor teor2345@gmail.com Date: Tue Dec 26 18:38:03 2017 +1100
Add dir-list-spec.txt, a description of Tor's fallback directory list format
Incorporates changes based on atagar's review on #24742.
Documents the contents of the manually modified initial fallback version 2.0.0 list, and future generated lists.
Documents the format changes in the children of #22271. Closes #24742. --- dir-list-spec.txt | 451 ++++++++++++++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 451 insertions(+)
diff --git a/dir-list-spec.txt b/dir-list-spec.txt new file mode 100644 index 0000000..3087246 --- /dev/null +++ b/dir-list-spec.txt @@ -0,0 +1,451 @@ + Tor Directory List Format + Tim Wilson-Brown (teor) + +1. Scope and Preliminaries + + This document describes the format of Tor's directory lists, which are + compiled and hard-coded into the tor binary. There is currently one + list: the fallback directory mirrors. This list is also parsed by other + libraries, like stem and metrics-lib. Alternate Tor implementations can + use this list to bootstrap from the latest public Tor directory + information. + + The FallbackDir feature was introduced by proposal 210, and was first + supported by Tor in Tor version 0.2.4.7-alpha. The first hard-coded + list was shipped in 0.2.8.1-alpha. + + The hard-coded fallback directory list is located in the tor source + repository at: + + src/or/fallback_dirs.inc + + This document describes version 2.0.0 and later of the directory list + format. + + Legacy, semi-structured versions of the fallback list were released with + Tor 0.2.8.1-alpha through Tor 0.3.1.9. We call this format version 1. + Stem and Relay Search have parsers for this legacy format. + +1.1. Format Overview + + A directory list is a C code fragment containing an array of C string + constants. Each double-quoted C string constant is a valid torrc + FallbackDir entry. Each entry contains various data fields. + + Directory lists do not include the C array's declaration, or the array's + terminating NULL. Entries in directory lists do not include the + FallbackDir torrc option. These are handled by the including C code. + + Directlry lists also include C-style comments and whitespace. The + presence of whitespace may be significant, but the amount of whitespace + is never significant. The type of whitespace is not significant to the + C compiler or Tor C string parser. However, other parsers MAY rely on + the distinction between newlines and spaces. (And that the only + whitespace characters in the list are newlines and spaces.) + + The directory entry C string constants are split over multiple lines for + readability. Structured C-style comments are used to provide additional + data fields. This information is not used by Tor, but may be of interest + to other libraries. + + The order of directory entries and data fields is not significant, + except where noted below. + +1.2. Acknowledgements + + The original fallback directory script and format was created by + weasel. The current script uses code written by gsathya & karsten. + + This specification was revised after feedback from: + + Damian Johnson ("atagar") + Iain R. Learmonth ("irl") + +1.3. Format Versions + + 1.0.0 - The legacy fallback directory list format + + 2.0.0 - Adds name and extrainfo structured comments, and section separator + comments to make the list easier to parse. + +2. Format Details + + Directory lists contain the following sections: + - List Header (exactly once) + - List Generation (exactly once, may be empty) + - Directory Entry (zero or more times) + + Each section (or entry) ends with a separator. + +2.1. Nonterminals + + The following nonterminals are defined in the Onionoo details document + specification: + + dir_address + fingerprint + nickname + + See https://metrics.torproject.org/onionoo.html#details + + The following nonterminals are defined in the "Tor directory protocol" + specification in dir-spec.txt: + + Keyword + ArgumentChar + NL (newline) + SP (space) + bool (must not be confused with Onionoo's JSON "boolean") + + We derive the following nonterminals from Onionoo and dir-spec.txt: + + ipv4_or_port ::= port from an IPv4 or_addresses item + + The ipv4_or_port is the port part of an IPv4 address from the + Onionoo or_addresses list. + + ipv6_or_address ::= an IPv6 or_addresses item + + The ipv6_or_address is an IPv6 address and port from the Onionoo + or_addresses list. The address MAY be in the canonical RFC 5952 + IPv6 address format. + + A key-value pair: + + value ::= Zero or more ArgumentChar, excluding the following strings: + * a double quotation mark (DQUOTE), and + * the C comment terminators ("/*" and "*/"). + + Note that the C++ comment ("//") and equals sign ("=") are + not excluded, because they are reserved for future use in + base64 values. + + key_value ::= Keyword "=" value + + We also define these additional nonterminals: + + number ::= An optional negative sign ("-"), followed by one or more + numeric characters ([0-9]), with an optional decimal part + (".", followed by one or more numeric characters). + + separator ::= "/*" SP+ "=====" SP+ "*/" + +2.2. List Header + + The list header consists of a number of key-value pairs, embedded in + C-style comments. + +2.2.1 List Header Format + + "/*" SP+ "type=" Keyword SP+ "*/" SP* NL + + [At start, exactly once.] + + The type of directory entries in the list. Parsers SHOULD exit with + an error if this is not the first line of the list, or if the value + is anything other than "fallback". + + "/*" SP+ "version=" version_number SP+ "*/" SP* NL + + [In second position, exactly once.] + + The version of the directory list format. version_number uses + semantic versioning: https://semver.org + + In particular: + * major versions are used for incompatible changes, like + removing non-optional fields + * minor versions are used for compatible changes, like adding + fields + * patch versions are for bug fixes, like fixing an + incorrectly-formatted Summary item + + Version 1.0.0 represents the undocumented, legacy fallback list + format(s). Version 2.0.0 and later are documented by this + specification. + + "/*" SP+ "timestamp=" number SP+ "*/" SP* NL + + [Exactly once.] + + A positive integer that indicates when this directory list was + generated. This timestamp is guaranteed to increase for every + version 2.0.0 and later directory list. + + The current timestamp format is YYYYMMDDHHMMSS, as an integer. + + "/*" SP+ key_value SP+ "*/" SP* NL + + [Zero or more times.] + + Future releases may include additional header fields. Parsers MUST NOT + rely on the order of these additional fields. Additional header fields + will be accompanied by a minor version increment. + + separator SP* NL + + The list header ends with the section separator. + +2.3. List Generation + + The list generation information consists of human-readable prose + describing the content and origin of this directory list. It is contained + in zero or more C-style comments, and may contain multi-line comments and + uncommented C code. + + In particular, this section may contain C-style comments that contain + an equals ("=") character. It may also be entirely empty. + + Future releases may arbitrarily change the content of this section. + Parsers MUST NOT rely on a version increment when the format changes. + +2.3.1 List Generation Format + + In general, parsers MUST NOT rely on the format of this section. + + Parsers MAY rely on the following details: + + The list generation section MUST NOT be a valid directory entry. + + The list generation summary MUST end with a section separator: + + separator SP* NL + + There MUST NOT be any section separators in the list generation + section, other than the terminating section separator. + +2.4. Directory Entry + + A directory entry consists of a C string constant, and one or more + C-style comments. The C string constant is a valid argument to the + DirAuthority or FallbackDir torrc option. The section also contains + additional key-value fields in C-style comments. + + The list of fallback entries does not include the directory + authorities: they are in a separate list. (The Tor implementation combines + these lists after parsing them, and applies the DirAuthorityFallbackRate + to their weights.) + +2.4.1 Directory Entry Format + + If a directory entry does not conform to this format, the entry SHOULD + be ignored by parsers. + + DQUOTE dir_address SP+ "orport=" ipv4_or_port SP+ + "id=" fingerprint DQUOTE SP* NL + + [At start, exactly once, on a single line.] + + This line consists of the following fields: + + dir_address + + An IPv4 address and DirPort for this directory, as defined by + Onionoo. In this format version, all IPv4 addresses and DirPorts + are guaranteed to be non-zero. (For IPv4 addresses, this means + that they are not equal to "0.0.0.0".) + + ipv4_or_port + + An IPv4 ORPort for this directory, derived from Onionoo. In this + format version, all IPv4 ORPorts are guaranteed to be non-zero. + + fingerprint + + The relay fingerprint of this directory, as defined by Onionoo. + All relay fingerprints are guaranteed to have one or more non-zero + digits. + + Note: + + Each double-quoted C string line that occurs after the first line, + starts with space inside the quotes. This is a requirement of the + Tor implementation. + + DQUOTE SP+ "ipv6=" ipv6_or_address DQUOTE SP* NL + + [Zero or one time.] + + The IPv6 address and ORPort for this directory, as defined by + Onionoo. If present, IPv6 addresses and ORPorts are guaranteed to be + non-zero. (For IPv6 addresses, this means that they are not equal to + "[::]".) + + DQUOTE SP+ "weight=" number DQUOTE SP* NL + + [Zero or one time.] + + A non-negative, real-numbered weight for this directory. + The default fallback weight is 1.0, and the default + DirAuthorityFallbackRate is 1.0 in legacy Tor versions, and 0.1 in + recent Tor versions. + + weight was removed in version 2.0.0, but is documented because it + may be of interest to libraries implementing Tor's fallaback + behaviour. + + DQUOTE SP+ key_value DQUOTE SP* NL + + [Zero or more times.] + + Future releases may include additional data fields in double-quoted + C string constants. Parsers MUST NOT rely on the order of these + additional fields. Additional data fields will be accompanied by a + minor version increment. + + "/*" SP+ "nickname=" nickname* SP+ "*/" SP* NL + + [Exactly once.] + + The nickname for this directory, as defined by Onionoo. An + empty nickname indicates that the nickname is unknown. + + The first fallback list in the 2.0.0 format had nickname lines, but + they were all empty. + + "/*" SP+ "extrainfo=" bool SP+ "*/" SP* NL + + [Exactly once.] + + An integer flag that indicates whether this directory caches + extra-info documents. Set to 1 if the directory claimed that it + cached extra-info documents in its descriptor when the list was + created. 0 indicates that it did not, or its descriptor was not + available. + + The first fallback list in the 2.0.0 format had extrainfo lines, but + they were all zero. + + "/*" SP+ key_value SP+ "*/" SP* NL + + [Zero or more times.] + + Future releases may include additional data fields in C-style + comments. Parsers MUST NOT rely on the order of these additional + fields. Additional data fields will be accompanied by a minor version + increment. + + separator SP* NL + + [Exactly once.] + + Each directory entry ends with the section separator. + + "," SP* NL + + [Exactly once.] + + The comma terminates the C string constant. (Multiple C string + constants separated by whitespace or comments are coalesced by + the C compiler.) + +3. Usage Considerations + + This section contains recommended library behaviours. It does not affect + the format of directory lists. + +3.1. Caching + + The fallback list typically changes once every 6-12 months. The data in + the list represents the state of the fallback directory entries when the + list was created. Fallbacks can and do change their details over time. + + Libraries SHOULD parse and cache the most recent version of these lists + during their build or release processes. Libraries MUST NOT retrieve the + lists by default every time they are deployed or executed. + + The latest fallback list can be retrieved from: + + https://gitweb.torproject.org/tor.git/plain/src/or/fallback_dirs.inc + + Libraries MUST NOT rely on the availability of the server that hosts + these lists. + + The list can also be retrieved using: + + git clone https://git.torproject.org/tor.git + + If you just want the latest list, you may wish to perform a shallow + clone. + +3.2. Retrieving Directory Information + + Some libraries retrieve directory documents directly from the Tor + Directory Authorities. The directory authorities are designed to support + Tor relay and client bootstrap, and MAY choose to rate-limit library + access. Libraries MAY provide a user-agent in their requests, if they + are not intended to support anonymous operation. (User agents are a + fingerprinting vector.) + + Libraries SHOULD consider the potential load on the authorities, and + whether other sources can meet their needs. + + Libraries that require high-uptime availablility of Tor directory + information should investigate the following options: + * OnionOO: https://metrics.torproject.org/onionoo.html + * Third-party OnionOO mirrors are also available + * CollecTor: https://collector.torproject.org/ + * Fallback Directory Mirrors + + Onionoo and CollecTor are typically updated every hour on a regular + schedule. Fallbacks update their own directory information at random + intervals, see dir-spec for details. + +3.3. Fallback Reliability + + The fallback list is typically regenerated when the fallback failure + rate exceeds 25%. Libraries SHOULD NOT rely on any particular fallback + being available, or some proportion of fallbacks being available. + + Libraries that use fallbacks MAY wish to query an authority after a + few fallback queries fail. For example, Tor clients try 3-4 fallbacks + before trying an authority. + +A.1. Sample Data + + A sample version 2.0.0 fallback list is available here: + + https://trac.torproject.org/projects/tor/raw-attachment/ticket/22759/fallbac... + + A sample transitional version 2.0.0 fallback list is available here: + + https://raw.githubusercontent.com/teor2345/tor/fallback-format-2-v4/src/or/f... + +A.1.1. Sample Fallback List Header + +/* type=fallback */ +/* version=2.0.0 */ +/* ===== */ + +A.1.2. Sample Fallback List Generation + +/* Whitelist & blacklist excluded 1326 of 1513 candidates. */ +/* Checked IPv4 DirPorts served a consensus within 15.0s. */ +/* +Final Count: 151 (Eligible 187, Target 392 (1963 * 0.20), Max 200) +Excluded: 36 (Same Operator 27, Failed/Skipped Download 9, Excess 0) +Bandwidth Range: 1.3 - 40.0 MByte/s +*/ +/* +Onionoo Source: details Date: 2017-05-16 07:00:00 Version: 4.0 +URL: https:onionoo.torproject.orgdetails?fields=fingerprint%2Cnickname%2Ccontact%2Clast_changed_address_or_port%2Cconsensus_weight%2Cadvertised_bandwidth%2Cor_addresses%2Cdir_address%2Crecommended_version%2Cflags%2Ceffective_family%2Cplatform&flag=V2Dir&type=relay&last_seen_days=-0&first_seen_days=30- +*/ +/* +Onionoo Source: uptime Date: 2017-05-16 07:00:00 Version: 4.0 +URL: https:onionoo.torproject.orguptime?first_seen_days=30-&flag=V2Dir&type=relay&last_seen_days=-0 +*/ +/* ===== */ + +A.1.3. Sample Fallback Entries + +"176.10.104.240:80 orport=443 id=0111BA9B604669E636FFD5B503F382A4B7AD6E80" +/* nickname=foo */ +/* extrainfo=1 */ +/* ===== */ +, +"5.9.110.236:9030 orport=9001 id=0756B7CD4DFC8182BE23143FAC0642F515182CEB" +" ipv6=[2a01:4f8:162:51e2::2]:9001" +/* nickname= */ +/* extrainfo=0 */ +/* ===== */ +,